Circulating Testosterone Concentrations Research Articles

In-utero exposure to real-life environmental chemicals disrupts gene expression within the hypothalamo-pituitary-gonadal axis of prepubertal and adult rams

Environmental chemicals (ECs) have been associated with a broad range of disorders and diseases. Daily exposure to various ECs in the environment, or real-life exposure, has raised significant public health concerns. Utilizing the biosolids-treated pasture (BTP) sheep model, this study demonstrates that in-utero exposure to a real-life EC mixture disrupts hypothalamo-pituitary-gonadal (HPG) axis gene expression and reproductive traits in prepubertal (8-week-old, 8w) and adult (11-month-old) male sheep. Ewes were maintained on either BTP or pastures fertilized with inorganic fertilizer [control (C)] from approximately one month prior to insemination until around parturition. Thereafter, all animals were kept under control conditions. Effects on reproductive parameters including testosterone concentrations and the expression of key genes in the HPG axis were evaluated in eight-week-old and adult male offspring from both C and biosolids-exposed (B) groups. Results showed that, at 8w, relative to C (n = 11), B males (n = 11) had lower body weight, and altered testicular expression of HSD3B1, LHR and HSD17B3, BMP4, ABP, P27kip and CELF1. Principal component analysis (PCA) identified two 8w B subgroups, based on hypothalamic expression of GnRH, ESR1, and AR, and pituitary expression of KISSR. The two subgroups also exhibited different serum testosterone concentrations. The largest biosolids effects were observed in the hypothalamus of adult rams with NKB, ESR1, KISS1, AR, DLK1 and GNRH1 mRNA expression differing between B (n = 10) and C (n = 11) rams. Testicular steroidogenic enzymes CYP11A1 and HSD3B1 mRNA expression also differed between exposure groups. PCA identified two adult B subgroups, with BS1 (n = 6) displaying hypothalamic effects and BS2 (n = 4) both hypothalamic and testicular effects. The subgroups also differed in circulating testosterone concentrations. These findings demonstrate that exposure to a real-life EC mixture may predispose some males to infertility, by disrupting key functional HPG markers before puberty with consequent downstream effects on steroid hormones and spermatogenesis.

Testosterone and the risk of incident atrial fibrillation in older men: further analysis of the ASPREE study

A cardiovascular safety trial of testosterone in men with cardiovascular risk factors or disease found no difference in rates of major adverse cardiovascular events (MACE) or death but noted more atrial fibrillation (AF) events in testosterone-treated men. We investigated the relationship between endogenous testosterone concentrations with risk of developing AF in healthy older men. Post-hoc analysis of 4570 male participants in the ASPirin in Reducing Events in the Elderly (ASPREE) study. Men were aged ≥ 70 years, had no history of cardiovascular disease (including AF), thyroid disease, prostate cancer, dementia, or life-threatening illnesses. Risk of AF was modelled using Cox proportional hazards regression. Median (IQR) age was 73.7 (71.6-77.1) years and median (IQR) follow-up 4.4 (3.3-5.5) years, during which 286 men developed AF (15.3 per 1000 participant-years). Baseline testosterone was higher in men who developed incident AF compared men who did not [17.0 (12.4-21.2) vs 15.7 (12.2-20.0) nmol/L]. There was a non-linear association of baseline testosterone with incident AF. The risk for AF was higher in men with testosterone in quintiles (Q) 4&5 (Q4:Q3, HR=1.91; 95%CI=1.29-2.83 and Q5:Q3HR=1.98; 95%CI=1.33-2.94). Results were similar after excluding men who experienced MACE or heart failure during follow-up. Circulating testosterone concentrations within the high-normal range are independently associated with an increased risk of incident AF amongst healthy older men. This suggests that AF may be an adverse consequence of high-normal total testosterone concentrations. National Institute on Aging and National Cancer Institute at the National Institutes of Health; Australian Government (NHMRC, CSIRO); Monash University; and AlfredHealth.

Oral 3-hydroxybuturate ingestion acutely lowers circulating testosterone concentrations in healthy young males.

Ketone bodies, such as 3-hydroxybutyrate (3-OHB), have been frequently used by endurance athletes, such as cyclists, to enhance performance and recovery and are recognized for their health benefits and therapeutic effects for decades. Testosterone is a potent regulator of red blood cell production. Evidence suggests that ketone bodies can increase the production of erythropoietin, which stimulates red blood cell production. Therefore, we investigated whether an acute increase in 3-OHB levels affects testosterone levels in healthy young men. We studied six healthy, young male participants who fasted overnight and were tested twice: (i) after drinking 37.5 g of Na-D/L-3-OHB dissolved in 500 mL of distilled water (KET), and (ii) after drinking 500 mL of placebo saline water (0.9% NaCl) (CTR). During the KET trial, 3-OHB levels increased to approximately 2.5 mM. Testosterone levels decreased significantly by 20% during KET compared to 3% during CTR. A simultaneous increase in luteinizing hormone was observed in KET. We observed no changes in other adrenal androgens, such as androstenedione and 11-keto androgens. In conclusion, an acute increase in 3-OHB levels decreases testosterone levels. Concomitantly, an increase in luteinizing hormone was observed. This suggests that 3-OHB may counteract some of the beneficial effects of endurance training. Further studies, involving larger sample sizes and performance outcomes, are required to fully understand this phenomenon.

Scrotal insulation impairs spermatogenesis but not Sertoli cell endocrine function

Testicular thermal insult is detrimental to spermatogenesis and a common cause of testicular degeneration. Changes in semen quality after scrotal insulation are well understood but its effects on Sertoli cell function is still not fully characterized. Isoform-specific assays have provided opportunities for analysis of inhibin-A and B. Recent studies in stallions have shown inhibin-B decreases after treatment with a GnRH receptor antagonist but returns with spermatogenesis after treatment stops, suggesting it may be a useful biomarker for testicular damage and recovery (Ball.et.al. Theriogenology; 2019; 213:108-115). The hypothesis of the present study was that serum inhibin-B correlates positively with sperm parameters after scrotal insulation decreasing as sperm motility and production decline. Stallions were assigned to a untreated control (n=4) and treated group (n=5) that was submitted to scrotal insulation for 1 hour in the morning and 1 hour in the afternoon, for two consecutive days, using a thermal blanket surrounding the scrotum. The intratesticular temperature was measured immediately after the blanket was removed and increased ∼10°C during the insulation period. Semen was collected twice weekly, but semen and serum samples were evaluated weekly for 98 days after treatment. Testicular response was assessed by determination of the concentrations of testosterone and estrone sulphate (interstitial compartment) and inhibin-B (tubular compartment), respectively. Spermkinetics were analyzed by CASA (IVOS Version 12 Hamilton Thorne Research, MA, USA), sperm concentration by Neubauer hemocytometer (Optik Labor®, Lancing, England), serum concentrations of inhibin- B and estrone sulfate were determined by ELISA and testosterone by RIA. Data were analyzed by ANOVA for repeated measures. Sperm motility and total sperm number decreased from day 4 to 67 (P<0.05) and sperm abnormalities increased from day 17 and did not recover until the end of our evaluation (day 98). Testosterone concentrations declined acutely. A significantly reduction in circulating testosterone concentrations occurred at 4, 9 and 37 days after onset of scrotal insulation, which is probably the result of Leydig cell impairment. However, no changes in inhibin-B or estrone sulfate were seen in response to treatment (n.s.). In summary, thermal insult appears to affect germ cells, and Leydig cell but not Sertoli cell function and, consequently, does not disturb inhibin-B synthesis. It has to be concluded that inhibin-B is no reliable biomarker for testicular damage and recovery from thermal insults. Acknowledgements: Authors are grateful to São Paulo Research Foundation (FAPESP, grant #2019/01119-8 and #2022/03405-0), the John P. Hughes Endowment and the Clinical Endocrinology Laboratory, University of California-Davis.

Acute Performance, Daily Well-Being, and Hormone Responses to Water Immersion After Resistance Exercise in Junior International and Subelite Male Volleyball Athletes.

Horgan, BG, Tee, N, West, NP, Drinkwater, EJ, Halson, SL, Colomer, CME, Fonda, CJ, Tatham, J, Chapman, DW, and Haff, GG. Acute performance, daily well-being and hormone responses to water immersion after resistance exercise in junior international and subelite male volleyball athletes. J Strength Cond Res 37(8): 1643-1653, 2023-Athletes use postexercise hydrotherapy strategies to improve recovery and competition performance and to enhance adaptative responses to training. Using a randomized cross-over design, the acute effects of 3 postresistance exercise water immersion strategies on perceived recovery, neuromuscular performance, and hormone concentrations in junior international and subelite male volleyball athletes ( n = 18) were investigated. After resistance exercise, subjects randomly completed either 15-minute passive control (CON), contrast water therapy (CWT), cold (CWI), or hot water immersion (HWI) interventions. A treatment effect occurred after HWI; reducing perceptions of fatigue (HWI > CWT: p = 0.05, g = 0.43); improved sleep quality, compared with CON ( p < 0.001, g = 1.15), CWI ( p = 0.017, g = 0.70), and CWT ( p = 0.018, g = 0.51); as well as increasing testosterone concentration (HWI > CWT: p = 0.038, g = 0.24). There were trivial to small ( p < 0.001-0.039, g = 0.02-0.34) improvements (treatment effect) in jump performance (i.e., squat jump and countermovement jump) after all water immersion strategies, as compared with CON, with high variability in the individual responses. There were no significant differences (interaction effect, p > 0.05) observed between the water immersion intervention strategies and CON in performance ( p = 0.153-0.99), hormone ( p = 0.207-0.938), nor perceptual ( p = 0.368-0.955) measures. To optimize recovery and performance responses, e.g., during an in-season competition phase, postresistance exercise HWI may assist with providing small-to-large improvements for up to 38 hours in perceived recovery (i.e., increased sleep quality and reduced fatigue) and increases in circulating testosterone concentration. Practitioners should consider individual athlete neuromuscular performance responses when prescribing postexercise hydrotherapy. These findings apply to athletes who aim to improve their recovery status, where postresistance exercise HWI optimizes sleep quality and next-day perceptions of fatigue.

Sexually dimorphic pubertal development and adipose tissue kisspeptin dysregulation in the obese and preeclamptic-like BPH/5 mouse model offspring.

Preeclampsia (PE) is a devastating hypertensive disorder of pregnancy closely linked to obesity. Long-term adverse outcomes may occur in offspring from preeclamptic pregnancies. Accordingly, sex-specific changes in pubertal development have been described in children from preeclamptic women, but the underlying mechanisms remain vastly unexplored. Features of PE are spontaneously recapitulated by the blood pressure high subline 5 (BPH/5) mouse model, including obesity and dyslipidemia in females before and throughout pregnancy, superimposed hypertension from late gestation to parturition and fetal growth restriction. A sexually dimorphic cardiometabolic phenotype has been described in BPH/5 offspring: while females are hyperphagic, hyperleptinemic, and overweight, with increased reproductive white adipose tissue (rWAT), males have similar food intake, serum leptin concentration, body weight and rWAT mass as controls. Herein, pubertal development and adiposity were further investigated in BPH/5 progeny. Precocious onset of puberty occurs in BPH/5 females, but not in male offspring. When reaching adulthood, the obese BPH/5 females display hypoestrogenism and hyperandrogenism. Kisspeptins, a family of peptides closely linked to reproduction and metabolism, have been previously shown to induce lipolysis and inhibit adipogenesis. Interestingly, expression of kisspeptins (Kiss1) and their cognate receptor (Kiss1r) in the adipose tissue seem to be modulated by the sex steroid hormone milieu. To further understand the metabolic-reproductive crosstalk in the BPH/5 offspring, Kiss1/Kiss1r expression in male and female rWAT were investigated. Downregulation of Kiss1/Kiss1r occurs in BPH/5 females when compared to males. Interestingly, dietary weight loss attenuated circulating testosterone concentration and rWAT Kiss1 downregulation in BPH/5 females. Altogether, the studies demonstrate reproductive abnormalities in offspring gestated in a PE-like uterus, which appear to be closely associated to the sexually dimorphic metabolic phenotype of the BPH/5 mouse model.

Role of gonadotropin-releasing hormone-II and its receptor in swine reproduction.

The pig represents the only livestock mammal capable of producing a functional protein for the second mammalian form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II). To examine the role of GnRH-II and its receptor in pig reproduction, we produced a unique swine line with ubiquitous knockdown of endogenous GnRHR-II levels (GnRHR-II knockdown[KD]), which is largely the focus of this review. In mature GnRHR-II KD males, circulating testosterone concentrations were 82% lower than littermate control boars, despite similar luteinizing hormone (LH) levels. In addition, nine other gonadal steroids were reduced in the serum of GnRHR-II KD boars, whereas adrenal steroids (except 11-deoxycortisol) did not differ between lines. Interestingly, testes from GnRHR-II KD males had fewer, hypertrophic Leydig cells and fewer, enlarged seminiferous tubules than control testes. As expected, downstream reproductive traits such as androgen-dependent organ weights and semen characteristics were also significantly reduced in GnRHR-II KD versus control boars. Next, we explored the importance of this novel ligand/receptor complex in female reproduction. Transgenic gilts had fewer, but heavier, corpora lutea with smaller luteal cells than littermate control females. Although the number of antral follicles were similar between lines, the diameter of antral follicles tended to be larger in GnRHR-II KD females. In regard to steroidogenesis, circulating concentrations of progesterone and 17β-estradiol were lower in transgenic compared to control gilts, even though serum levels of follicle-stimulating hormone and LH were similar. Thus, GnRH-II and GnRHR-II represent a potential avenue to enhance fertility and promote the profitability of pork producers.

LBODP090 The Addition Of Anastrozole To Standard Testosterone Enanthate Treatment Significantly Improves Penile Size In Adolescent Boys With Micropenis

Abstract Background Micropenis is treated preferably in infancy (≤ 2 yrs) or at the onset οf puberty, usually with 3 (2-4) monthly testosterone enanthate I. M. injections at the dose of 100 mg/m2. This short-term therapy may temporarily advance bone maturation but with a concomitant increase in height velocity and no apparent change in predicted adult height. Bone maturation depends on locally produced estrogens by aromatization. Third generation aromatase inhibitors (AIs) are used as an off-label treatment to improve predicted adult height (PAH) in boys as well as in girls, either as monotherapy or in combination with growth hormone and/or puberty inhibition. They induce reverse binding inhibiting the activity of aromatase (a cytochrome P450 enzyme), which catalyzes the conversion of androstenedione and testosterone to estrone and estradiol, respectively, resulting in a substantial increase of the circulating testosterone concentrations. Aims To compare the traditional treatment of isolated - idiopathic - relative micropenis in boys with testosterone enanthate monotherapy to its combination with anastrozole 1 mg×1 p. o. Methods 164 boys with micropenis (stretched penile length ≤ -2 SD) received testosterone enanthate 100 mg/m2 I. M. /month either as monotherapy (n=63, mean age 10.8 yrs, group A) or in combination with anastrozole 1 mg/day (n=101, mean age 11 yrs, group B) for 3 months. Stretched penile length, bone maturation and auxological data were analyzed. All measurements were performed by the same examiner. The choice of therapeutic intervention was made randomly. Groups A and B did not differ in terms of age at intervention onset, bone age, target height or predicted adult height. They underwent a 6-month follow-up that included clinical examination, bone age X-ray evaluated by BoneXpert ver. 3.2. 0 (Visiana, Denmark), and laboratory tests at 8: 00hrs (LH, FSH, testosterone, estradiol, estrone), prior and under treatment. Results In both groups penile length normalized: for group A gain was +1.9 cm (+2. 08 SD) and for group B +2.24 cm (+2.3 SD), with group B attaining a greater length by +18% (p=0. 004) due to the higher testosterone concentrations attained by at least 50%. Group A presented a slight acceleration of height velocity with parallel advancement of their bone age maturation while group B with unchanged or lower estradiol and estrone concentrations maintained their height velocity with parallel movement of their bone age maturation. Conclusions Addition of anastrozole 1 mg/day p. o. in testosterone enanthate treatment for idiopathic-isolated-relative micropenis at the beginning of puberty significantly improves penile length by almost 20% while the tempo of height velocity and bone maturation continue their previous track. Presentation: No date and time listed

PMON257 Oral Ingestion of Macronutrients Selectively and Variably Decrease Circulating Testosterone Concentration in Healthy Men

Abstract We have previously reported acute suppression of testosterone in men after oral ingestion of dextrose. In the present study, we aimed to explore a potentially similar effect in response to other macronutrients. Eleven healthy men (age: 33-70 yrs, BMI 20.4-31.5 kg/m2) were studied in random order after an overnight fast on 4 separate days, involving oral ingestion of 300 ml of either water (control), dextrose, protein, or lipid solutions. Sessions were 6.5 h long, starting at 0800-0900 hrs. Test meals were isocaloric (400 kcal) and were ingested after the 4th blood draw (30 min point). Blood was collected at 10-min intervals for testosterone (ng/dL), and LH (IU/L) measurements. Means of the 1st 4 pre-intervention measures were used as the first value in all the time series. Mean delta-serum (macronutrients-water) testosterone and LH concentrations sampled at 10-minute intervals over 6 hour period were adjusted to the corresponding 1st value to correct for among the sessions inconsistent baseline testosterone and LH measures. Compared to the water day (control), mean (± SE) serum testosterone concentrations (ng/dL) in 11 subjects decreased from 415 ± 36 (control) to 370 ± 31 (dextrose: P=0.009), 340 ± 28 (protein: p=0.002), and 355 ± 30 (lipid: p=0.01). Corresponding LH (IU/L) values for dextrose (3.16 ± 0.29), protein (3.17 ± 0.39), and lipid (3.07 ± 0.29) were not significantly different from the control day (3.3 ± 0.29). Mean delta-testosterone time series revealed decreased testosterone of 63 ng/dL at 130 min after dextrose, 80 ng/dL at 200 min after protein, and 10 ng/dL at 70 min after lipid ingestion. Duration of suppression was variable among the 3 macronutrients, but most prolonged for protein lasting for 320 min. As oppose to testosterone, delta-LH concentrations were more positive rather than negative, suggestive of a potential testicular insult. In conclusion, oral ingestion of all macronutrients decrease circulating testosterone concentration, which appear to be independent of LH secretion. The effect is more intense and prolonged after protein intake, and minimal with lipid ingestion. Future studies are required to define the etiology, and the macronutrient effect on more prolonged basis. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

The Impacts of Female Access during Rearing on the Reproductive Behavior and Physiology of Pekin Drakes, and Flock Fertility.

Commercially housed Pekin ducks (Anas platyrhynchos) are typically reared in same sex groups to facilitate separate diet provisioning. Several female ducklings are sometimes mixed into the otherwise all-male pens. This practice is thought to increase flock reproductive success. To evaluate this hypothesis, we reared ducklings in alternating same-sex groups (150 hens or 30 drakes/pen; 8 groups/sex) and evaluated the impacts of rearing on drake mounting behavior, testosterone levels, and flock fertility. At 12 days, three females were placed into four of the male duckling pens. At 20-22 weeks of age, adjacent male and female pens were moved into pens within a breeder barn, and combined to form mixed-sex pens. The number of correctly aligned mounts performed by 10 focal drakes per pen was evaluated over 3 days (12 h/day) at 26, 32, and 45 weeks of age. Circulating testosterone concentrations were analyzed from blood plasma samples collected from the focal drakes at 15 (baseline), 22, 28, 34 and 45 weeks of age. Pen-level fertility was determined at 33-34 and 45-46 weeks of age. Mount and testosterone data were analyzed using a Generalized Linear Mixed Model and a Linear Mixed Model in R 4.0.5, with duck in pen as a random effect. A Linear Mixed Model was used to analyze fertility data, with pen as a random effect. None of the measured variables were impacted by rearing treatment, but all varied with flock age. Physical access to female ducklings during rearing did not enhance flock reproductive success.

Effects of whole-body vibration on reproductive physiology in a rat model of whole-body vibration

ABSTRACT Findings from epidemiological studies suggest that occupational exposure to whole-body vibration (WBV) may increase the risk of miscarriage and contribute to a reduction in fertility rates in both men and women. However, workers exposed to WBV may also be exposed to other risk factors that contribute to reproductive dysfunction. The goal of this experiment was to examine the effects of WBV on reproductive physiology in a rat model. Male and female rats were exposed to WBV at the resonant frequency of the torso (31.5 Hz, 0.3 g amplitude) for 4 hr/day for 10 days. WBV exposure resulted in a significant reduction in number of developing follicles, and decrease in circulating estradiol concentrations, ovarian luteinizing hormone receptor protein levels, and marked changes in transcript levels for several factors involved in follicular development, cell cycle, and steroidogenesis. In males, WBV resulted in a significant reduction in spermatids and circulating prolactin levels, elevation in number of males having higher circulating testosterone concentrations, and marked alterations in levels of transcripts associated with oxidative stress, inflammation, and factors involved in regulating the cell cycle. Based upon these findings data indicate that occupational exposure to WBV contributes to adverse alterations in reproductive physiology in both genders that may lead to reduction in fertility.

The function of the pituitary-testicular axis in dogs prior to and following surgical or chemical castration with the GnRH-agonist deslorelin.

Chemical castration, that is the reduction of circulating testosterone concentrations to castrate levels by administration of a GnRH-agonist implant, is a popular alternative to surgical castration in male dogs. Detailed information concerning the pituitary-testicular axis following administration of a GnRH-agonist implant is still scarce. Therefore, GnRH-stimulation tests were performed in male dogs, prior to and after surgical and chemical castration. This approach also allowed us to determine plasma concentrations of testosterone and oestradiol in intact male dogs for future reference and to directly compare the effects of surgical and chemical castration on the pituitary-testicular axis. In intact male dogs (n=42) of different breeds GnRH administration induced increased plasma LH, FSH, oestradiol and testosterone concentrations. After surgical castration basal and GnRH-induced plasma FSH and LH concentrations increased pronouncedly. Additionally, basal and GnRH-induced plasma oestradiol and testosterone concentrations decreased after surgical castration. After chemical castration, with a slow-release implant containing the GnRH-agonist deslorelin, plasma LH and FSH concentrations were lower than prior to castration and lower compared with the same interval after surgical castration. Consequently, plasma oestradiol and testosterone concentrations were lowered to values similar to those after surgical castration. GnRH administration to the chemically castrated male dogs induced a significant increase in the plasma concentrations of LH, but not of FSH. In conclusion, after administration of the deslorelin implant, the plasma concentrations of oestradiol and testosterone did not differ significantly from the surgically castrated animals. After GnRH-stimulation, none of the dogs went to pre-treatment testosterone levels. However, at the moment of assessment at 4,4 months (mean 133 days ± SEM 4 days), the pituitary gonadotrophs were responsive to GnRH in implanted dogs. The increase of LH, but not of FSH, following GnRH administration indicates a differential regulation of the release of these gonadotrophins, which needs to be considered when GnRH-stimulation tests are performed in implanted dogs.

Association of age, hormonal, and lifestyle factors with the Leydig cell biomarker INSL3 in aging men from the European Male Aging Study cohort.

BackgroundAging in men is accompanied by a broad range of symptoms, including sexual dysfunction, cognitive and musculoskeletal decline, obesity, type 2 diabetes, cardiovascular disease and hypertension, organ degeneration/failure, and increasing neoplasia, some of which are associated with declining levels of Leydig cell‐produced testosterone. High natural biological variance, together with multiple factors that can modulate circulating testosterone concentration, may influence its interpretation and clinical implications. Insulin‐like peptide 3 is a biomarker of Leydig cell function that might provide complementary information on testicular health and its downstream outcomes.ObjectivesTo characterize insulin‐like peptide 3 as a biomarker to assess gonadal status in aging men.Methods and materialsA large European multicenter (European Male Aging Study) cohort of community‐dwelling men was analyzed to determine how insulin‐like peptide 3 relates to a range of hormonal, anthropometric, and lifestyle parameters.Results and discussionInsulin‐like peptide 3 declines cross‐sectionally and longitudinally within individuals at approximately 15% per decade from age 40 years, unlike testosterone (1.9% per decade), which is partly compensated by increasing pituitary luteinizing hormone production. Importantly, lower insulin‐like peptide 3 in younger men appears to persist with aging. Multiple regression analysis shows that, unlike testosterone, insulin‐like peptide 3 is negatively dependent on luteinizing hormone and sex hormone‐binding globulin and positively dependent on follicle‐stimulating hormone, suggesting a different mechanism of gonadotropic regulation. Circulating insulin‐like peptide 3 is negatively associated with increased body mass index or waist circumference and with smoking, and unlike testosterone, it is not affected by weight loss in obese individuals. Geographic variation in mean insulin‐like peptide 3 within Europe appears to be largely explained by differences in these parameters. The results allowed the establishment of a European‐wide reference range for insulin‐like peptide 3 (95% confidence interval) adjusted for increasing age.ConclusionInsulin‐like peptide 3 is a constitutive biomarker of Leydig cell functional capacity and is a robust, reliably measurable peptide not subject to gonadotropin‐dependent short‐term regulation and within‐individual variation in testosterone.

Preliminary investigation of reproductive hormone profiles in the blacktip shark (

Accurate reproductive information is crucial for the effective management of sharks. Here, we used non-lethal methods to evaluate reproductive hormone profiles of blacktip sharks (Carcharhinus limbatus) off the coast of southern Florida (FL) as part of a preliminary investigation of this species’ reproductive patterns in the region. Circulating testosterone concentrations in males ranged from 0.04 to 320.7 ng mL−1, and concentrations peaked during months previously shown to represent peak spermatogenic activity. In females, circulating concentrations of oestradiol (E2) ranged from 12.5 to 941.4 pg mL−1, and progesterone (P4) ranged from 30.1 to 821.2 pg mL−1. E2 peaked during months with peak vitellogenic and ovulatory activity in previous studies; P4 displayed less variability among months. In general, changes in monthly hormone concentrations align well with the timing of reproductive events in C. limbatus in other regions. However, because of low monthly sample sizes and a lack of reproductive status confirmation, the female profiles raise interesting questions about this population’s reproductive cycle that could be explored in future studies. Additional studies should collect larger monthly samples and incorporate supplementary data to provide more insight into the reproductive cycle of this species in southern FL.

PSX-A-3 Late-Breaking: Analysis of serum chemistry for metabolic function in GnRH-II receptor knockdown and littermate control boars

Abstract Pigs are the only livestock species encoding functional proteins for both the second form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II), which are uniquely expressed in reproductive and non-reproductive tissues. To examine the physiological role of the GnRH-II/GnRHR-II system, we produced a swine line with reduced endogenous levels of GnRHR-II (GnRHR-II KD); males exhibit 70% diminished testicular GnRHR-II mRNA levels and 82% reduced circulating testosterone concentrations. Given that testosterone impacts metabolism, blood was collected from GnRHR-II KD (n = 5) and littermate control (n = 5) boars via indwelling jugular catheters, with serum isolated and subjected to veterinary diagnostic panels for metabolic analyte examination (PhysLab, Lincoln, NE). Statistical analyses utilized the MIXED procedure of SAS; the model included line as fixed and litter as random effects. Creatine kinase and blood urea nitrogen (BUN):creatinine ratios were elevated, creatinine was reduced (P &amp;lt; 0.01), and thyroxine tended to be decreased (P &amp;lt; 0.10) in GnRHR-II KD compared with control boars. Glucose, BUN, amylase, and lipase levels were not different. Liver products differed in transgenic versus control boars; levels of lactic dehydrogenase, aspartate and alanine aminotransferases (AST; ALT), and gamma-glutamyl transpeptidase were higher, whereas AST:ALT ratios, total protein, albumin, and globulin levels were lower (P &amp;lt; 0.05) in GnRHR-II KD boars. Albumin:globulin ratios and bilirubin (total and direct) did not differ. Additionally, serum cholesterol was decreased (P &amp;lt; 0.05), non-high density lipoproteins (HDLs) and low density lipoproteins (LDLs) tended to be decreased (P &amp;lt; 0.10), and triglycerides, HDLs, and cholesterol:HDL ratios did not differ between GnRHR-II KD and control males. These data suggest metabolic disruption in GnRHR-II KD boars, which may be due to suppressed gonadal steroidogenesis or ubiquitous knockdown of GnRHR-II expression. Supported by USDA/NIFA AFRI (2017-67015-26508) and Hatch Multistate (NEB-26–244) funds. USDA is an equal opportunity provider and employer.

Manipulation of Dietary Intake on Changes in Circulating Testosterone Concentrations.

Elevations in the circulating concentration of androgens are thought to have a positive effect on the anabolic processes leading to improved athletic performance. Anabolic-androgenic steroids have often been used by competitive athletes to augment this effect. Although there has been concerted effort on examining how manipulating training variables (e.g., intensity and volume of training) can influence the androgen response to exercise, there has been much less effort directed at understanding how changes in both macronutrient and micronutrient intake can impact the androgen response. Thus, the focus of this review is to examine the effect that manipulating energy and nutrient intake has on circulating concentrations of testosterone and what the potential mechanism is governing these changes.

Initiation of Gender-Affirming Testosterone Therapy in a Lactating Transgender Man.

Transgender and gender diverse individuals may choose to provide their infants with human milk. Lactating transgender men may experience gender dysphoria and desire to initiate or reinitiate gender-affirming testosterone therapy. However, there is limited safety data regarding use of testosterone during lactation. A 30-year-old G2P2 transgender man with gender dysphoria sought to initiate gender-affirming testosterone therapy while lactating. Subcutaneous testosterone was self-administered beginning at 13 months post-partum. We prospectively collected data on circulating testosterone concentrations in parent serum, milk, and infant serum over 5 months until the infant self-weaned. The infant was monitored for growth and development at routine pediatric outpatient appointments. Parent serum testosterone concentrations rose with the initiation of testosterone therapy, reaching therapeutic concentrations by Day 14. Milk testosterone concentrations also increased with a maximum concentration of 35.9 ng/dl when the lactating parent was on a dose of 80 mg subcutaneous testosterone cypionate weekly. The calculated milk/plasma ratio remained under 1.0 and the calculated relative infant dose remained under 1%. The infant had no observable side effects, and his serum testosterone concentrations remained undetectable throughout the study period. This is the first study with data regarding human milk and infant serum testosterone concentrations during the initiation of gender-affirming testosterone therapy in a lactating individual. This evidence can help families and clinicians with decisions regarding lactation and testosterone use.

Determining the Effects of Serial Injections of Pregnant Mare Serum Gonadotropin on Plasma Testosterone Concentrations, Testicular Dynamics, and Semen Production in Leopard Geckos (Eublepharis macularius).

Simple SummaryCurrent estimates have determined that one in five reptile species are already threatened with extinction. The aim of this study was to determine if pregnant mare serum gonadotropin could be used in leopard geckos (Eublepharis macularius) to stimulate the production of sperm and increase their testosterone concentrations. This information may aid in the development of breeding programs for endangered gecko species in the future that will be useful for conservation efforts. Our results demonstrated that this hormone did stimulate sperm production and increased testicular size in leopard geckos. However, it did not increase testosterone concentrations under the current conditions between October–December in the Northern hemisphere. Ultimately, future studies are needed to further characterize the annual reproductive cycle of leopard geckos.Reptiles are highly susceptible to anthropogenic activities as a result of their narrow geographical ranges and habitat specialization, making them a conservation concern. Geckos represent one of the mega-diverse reptile lineages under pressure; however, limited assisted reproductive technologies currently exist for these animals. Exogenous pregnant mare serum gonadotropin (PMSG) has been found to exhibit follicle stimulating hormone-like action and has been routinely used to alter reproductive hormones of vertebrates in assisted reproductive protocols. The purpose of this study was to determine the effects of serial injections of 20 IU and 50 IU PMSG on circulating testosterone concentrations, testicular dynamics, and semen production in a model species of gecko. Twenty-four captive-bred, adult, male leopard geckos (Eublepharis macularius) were divided into three treatment groups and administered a once-weekly injection of either PMSG or saline for a total of nine weeks. Ultrasonographic testicular measurements, electrostimulation for semen collection, and venipuncture were performed on days 0, 21, 42, and 63. Right unilateral orchidectomies and epididymectomies were performed in all animals on day 63; tissues were submitted for histopathology. PMSG treated geckos had significantly higher testicular volumes and weights, spermatozoa motility, and spermatozoa concentrations compared with controls. However, there were no significant differences in testosterone concentrations by treatment or time. Under the conditions outlined, PMSG is effective at stimulating spermatogenesis and increasing testicular size, but not effective at increasing testosterone concentrations in the leopard gecko between October–December in the Northern hemisphere.

Influence of circulating testosterone concentration on sperm cryoresistance: The ibex as an experimental model

Recent studies have noted that the circulating testosterone concentration may affect the ability of spermatozoa to survive cryopreservation. However, few attempts to confirm such a relationship have been made. Wild ruminant species have very marked seasonal changes in their reproductive function and strong annual changes in their plasma testosterone concentration. The present work examines the influence of induced changes in testosterone secretion on sperm variables following conventional slow freezing and ultra-rapid freezing, using the Iberian ibex as an experimental model. In a first experiment, testosterone levels were reduced in the middle of the rutting season (December) using the antiandrogen cyproterone acetate (CA). In a second experiment, testosterone levels were increased at the end of the rutting season (January) via the use of the androgen testosterone propionate (TP). During December, the testosterone concentration was found to be higher in the blood and seminal plasma of untreated males than in those of CA-treated males (p<0.001 and p<0.05, respectively). Compared with controls, the TP-treated animals had higher blood plasma testosterone concentrations but lower seminal plasma testosterone concentrations during January (p<0.01 and p<0.001, respectively). The seminal vesicles of the TP-treated males were larger than those of untreated males (p<0.05). When CA was administered, sperm viability improved compared with controls (p<0.05), irrespective of the freezing protocol followed. For the ultra-rapid freezing procedure, the cryoresistance ratio for motility decreased when TP was administered (p<0.05). The values for fresh sperm morphometric variables decreased during the 50days after the end of CA treatment (p<0.001) and increased over the same time after the end of TP treatment (p<0.001). The circulating testosterone concentration appears to influence sperm cryoresistance. This may explain the seasonal changes seen in sperm freezability in some species, independent of fresh sperm quality.

Neuroendocrine patterns underlying seasonal song and year-round territoriality in male black redstarts

BackgroundThe connection between testosterone and territoriality in free-living songbirds has been well studied in a reproductive context, but less so outside the breeding season. To assess the effects of seasonal androgenic action on territorial behavior, we analyzed vocal and non-vocal territorial behavior in response to simulated territorial intrusions (STIs) during three life-cycle stages in free-living male black redstarts: breeding, molt and nonbreeding. Concurrently, we measured changes in circulating testosterone levels, as well as the mRNA expression of androgen and estrogen receptors and aromatase in the preoptic, hypothalamic and song control brain areas that are associated with social and vocal behaviors.ResultsTerritorial behavior and estrogen receptor expression in hypothalamic areas did not differ between stages. But plasma testosterone was higher during breeding than during the other stages, similar to androgen receptor and aromatase expression in the preoptic area. The expression of androgen receptors in the song control nucleus HVC was lower during molt when birds do not sing or sing rarely, but similar between the breeding and the nonbreeding stage. Nevertheless, some song spectral features and the song repertoire differed between breeding and nonbreeding. Territorial behavior and song rate correlated with the expression of steroid receptors in hypothalamic areas, and in the song control nucleus lMAN.ConclusionsOur results demonstrate seasonal modulation of song, circulating testosterone levels, and brain sensitivity to androgens, but a year-round persistency of territorial behavior and estrogen receptor expression in all life-cycle stages. This suggests that seasonal variations in circulating testosterone concentrations and brain sensitivity to androgens is widely uncoupled from territorial behavior and song activity but might still affect song pattern. Our study contributes to the understanding of the complex comparative neuroendocrinology of song birds in the wild.