Testosterone Levels In Response Research Articles

Preliminary data on increased reactivity towards children in distress after testosterone administration in women: A matter of protection?

Emotional reactivity to others’ distress is a vital prerequisite for a caring response. Testosterone, in contrast, is mostly associated with protection of personal dominance and decreased responsiveness to others’ needs. However, experimental work also indicates that rising testosterone levels in response to infant distress can potentially facilitate protection. We assessed the impact of testosterone administration on participants’ emotional reactivity to infants in distress, measuring their facial responses on the corrugator supercilii forehead muscle (‘frowning’) and the zygomaticus major (‘smiling’) as an index of emotional responses towards children. Moreover, we probed whether the effect of testosterone is moderated by participants’ self-reported nurturance and protective tendencies. Our preliminary results showed that testosterone not only increased emotional reactivity to empathy eliciting images of children, but that this increase was strongest in participants with strong protective tendencies. Our administration study is the first to link testosterone to infant protection.

Interactions between observer and stimuli fertility status: Endocrine and perceptual responses to intrasexual vocal fertility cues

Both men and women find female voices more attractive at higher fertility times in the menstrual cycle, suggesting the voice is a cue to fertility and/or hormonal status. Preference for fertile females' voices provides males with an obvious reproduction advantage, however the advantage for female listeners is less clear. One possibility is that attention to the fertility status of potential rivals may enable women to enhance their own reproductive strategies through intrasexual competition. If so, the response to having high fertility voices should include hormonal changes that promote competitive behavior. Furthermore, attention and response to such cues should vary as a function of the observer's own fertility, which influences her ability to compete for mates. The current study monitored variation in cortisol and testosterone levels in response to evaluating the attractiveness of voices of other women. All 33 participants completed this task once during ovulation then again during the luteal phase. The voice stimuli were recorded from naturally cycling women at both high and low fertility, and from women using hormonal birth control. We found that listeners rated high fertility voices as more attractive compared to low fertility, with the effect being stronger when listeners were ovulating. Testosterone was elevated following voice ratings suggesting threat detection or the anticipation of competition, but no stress response was found.

Relationship between salivary and serum testosterone levels in response to different exercise intensities.

The anabolic hormone testosterone (T) continues to be researched extensively in exercise studies, with blood serum or plasma samples collected routinely. This method is considered both valid and reliable; however, the collection process can be invasive and difficult during exercise. For this reason, non-invasive sampling, such as saliva collections, is increasing in popularity. To investigate the association between salivary and serum T before and after various intensities of exercise to assess the validity of saliva collection for T measurement. 12 endurance-trained males (Mean ± SD; VOVO2max 58.2 ± 6.4 ml/kg/min, 22 ± 4.6 years, BMI 21.6 ± 1.9) completed three 30-minute exercise (cycling) sessions at 40% (Low), 60% (Moderate), and 80% (High) of VO2max as well as a 30-minute resting Control session on four separate days. Salivary (s) and serum (S) samples were assessed for T prior to (Pre), immediately post (Post), and 30 minutes post (30 Min Post) each session. Low exercise caused a significant (p<0.05) increase in ST, but not sT, while Moderate and High exercise caused an increase (p<0.01) in both ST and sT. A strong positive correlation (Spearman [rs]) existed between sT and ST in the Moderate (rs = 0.912 [p<0.001; n=36; 12 subjects x 3 measurement times-samples]), and High (rs = 0.898 [p<0.001]) sessions, but not as strong for the Low (rs = 0.517 [p=0.001]) session. These results suggest that sT and ST levels are strongly associated to exercise. However, the exercise-related sT and ST responses-changes were more closely aligned at Moderate and High intensities, suggesting a greater validity between the saliva and serum responses to higher intensity exercise.

Relationship Between Salivary and Serum Testosterone Levels in Response to Different Exercise Intensities

Relationship Between Salivary and Serum Testosterone Levels in Response to Different Exercise Intensities

The number of life-history stages does not influence the androgen responsiveness to male–male interactions: Sedentary and migratory black redstarts (Phoenicurus ochruros) do not elevate testosterone in response to simulated territorial intrusions

High plasma levels of testosterone at the beginning of the breeding season adjust male physiology for mating and promote territorial behavior in birds. Conversely intra-sexual competition may elicit a temporary increase in circulating testosterone. Male black redstarts (Phoenicurus ochruros) from migratory populations show the expected increase in baseline testosterone during early breeding, but circulating testosterone levels do not change in response to male–male interactions. Because sedentary populations express fewer life-history stages they may be more flexible in timing of life-history stages and more responsive to environmental modulation of hormone concentrations. Therefore, we tested whether the androgen responsiveness to male–male interactions differs between migratory (6 life-history stages) and sedentary black redstarts (3 life-history stages) during early breeding, predicting that in contrast to migratory birds, sedentary birds would modulate testosterone in response to simulated territorial intrusions (STI). In contrast to our prediction, sedentary males did not modulate post-capture testosterone levels in response to simulated territorial intrusions. Males of both populations increased testosterone after an injection of gonadotropin releasing hormone (GnRH), demonstrating that they were capable of increasing testosterone. Interestingly, in sedentary males the GnRH injection elicited a higher testosterone response in STI males than in control males. The two populations did not differ in their behavioral response to the STIs, except that sedentary males spent less time close to the decoy. In combination with previous data from black redstarts and other socially monogamous and biparental birds our current study adds to the growing evidence that current theory regarding hormone-behavior relationship needs to be refined.

Do evolutionary life-history trade-offs influence prostate cancer risk? a review of population variation in testosterone levels and prostate cancer disparities.

An accumulation of evidence suggests that increased exposure to androgens is associated with prostate cancer risk. The unrestricted energy budget that is typical of Western diets represents a novel departure from the conditions in which men's steroid physiology evolved and is capable of supporting distinctly elevated testosterone levels. Although nutritional constraints likely underlie divergent patterns of testosterone secretion between Westernized and non-Western men, considerable variability exists in men's testosterone levels and prostate cancer rates within Westernized populations. Here, I use evolutionary life history theory as a framework to examine prostate cancer risk. Life history theory posits trade-offs between investment in early reproduction and long-term survival. One corollary of life history theory is the ‘challenge hypothesis’, which predicts that males augment testosterone levels in response to intrasexual competition occurring within reproductive contexts. Understanding men's evolved steroid physiology may contribute toward understanding susceptibility to prostate cancer. Among well-nourished populations of Westerners, men's testosterone levels already represent an outlier of cross-cultural variation. I hypothesize that Westernized men in aggressive social environments, characterized by intense male–male competition, will further augment testosterone production aggravating prostate cancer risk.

Optimization of spermatogenesis‐regulating hormones in patients with non‐obstructive azoospermia and its impact on sperm retrieval: a multicentre study

Study Type - Therapy (outcomes) Level of Evidence 2a What's known on the subject? and What does the study add? Clomiphene citrate, hCG and human menopausal gonadotropin (hMG) are widely used in treatment of oligospermia, because they increase FSH and testosterone which are essential for spermatogenesis. Finding a sperm in non-obstructive azoospermia for intracytoplasmic sperm injection is a challenge and much effort is required to reach the optimum method of sperm retrieval. The study shows that a new protocol of clomiphene citrate, hCG and hMG in the treatment of non-obstructive azoospermia achieves an increase in the levels of FSH, LH and total testosterone to the target levels that we set. Our target level of FSH was 1.5 times its initial level and for serum testosterone it was 600-800 ng/dL. Using our described medical treatment protocol in cases of non-obstructive azoospermia, sperm may be found in patients' ejaculate (~11%) and if they remain azoospermic they will have a greater likelihood of sperms being obtained in testicular sperm extraction. To evaluate the effect of optimizing serum level of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone on sperm retrieval for intracytoplasmic sperm injection. A total of 612 patients with non-obstructive azoospermia were evaluated with routine history, physical examination and hormonal assessment. Of these, 116 patients underwent microsurgical (micro)-testicular sperm extraction (TESE) without any medical treatment and formed the control group and the remaining 496 patients were administered clomiphene citrate in a titrated dose. Patients were classified into four groups according to their response to clomiphene citrate. Group 1: patients with an obvious increase in FSH and total testosterone (n = 372). Group 2: patients showing an increase in FSH with no or little increase in LH and total testosterone (n = 62). For these patients we continued with clomiphene citrate and added human chorionic gonadotrophin (hCG). Group 3: patients with no increase in the levels of the three hormones (n = 46). Group 4: included patients with continuously decreasing serum testosterone levels in response to the increasing dose of clomiphene citrate (n = 16). Accordingly, patients in groups 3 and 4 discontinued clomiphene citrate and started hCG and human menopausal gonadotropin (hMG). Semen analyses were performed periodically and, in patients who remained azoospermic, micro-TESE was performed. Sperm were noted in 54 patients (10.9%) in semen analysis after treatment in all groups (with no significant difference) at a mean (sd) concentration of 2.3 (4.1) million/mL. For the 442 patients who remained azoospermic after treatment, successful sperm retrieval was significantly higher (57%) compared with the control group (33.6%). For patients with non-obstructive azoospermia, clomiphene citrate, hCG and hMG administration, leading to an increased level of FSH and total testosterone, results in an increased rate of sperm in the ejaculate and increased likelihood of successful micro-TESE.

Gestational Protein Restriction Reduces Expression of Hsd17b2 in Rat Placental Labyrinth1

Accumulating evidence strongly supports the premise that testosterone may be a key player in fetal programming on hypertension. Studies have shown that gestational protein restriction doubles the plasma testosterone levels in pregnant rats. In this study, we hypothesized that elevated testosterone levels in response to gestational protein restriction were caused by enhanced expression of steroidogenic enzymes or impaired expression of Hsd17b2, a known testosterone inactivator that converts testosterone to androstenedione in placenta. Pregnant Sprague-Dawley rats were fed normal (20% protein, control; n = 10) or a low-protein diet (6% protein, PR; n = 10) from Day 1 of pregnancy until killed at Days 14, 18, or 21. Junctional (JZ) and labyrinth (LZ) zones of placenta were collected for expression assay on steroidogenic genes (Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b2, and Srd5a1) by real-time PCR. The main findings include the following: 1) expressions of Cyp11a1, Hsd3b1, and Cyp17a1 in JZ were not affected by diet but were affected by day of pregnancy; 2) expression of Hsd17b2 in both female and male JZs was remarkably increased by PR at Days 18 and 21 of pregnancy; 3) expressions of Hsd17b2 were reduced by PR in both female and male LZ at Day 18 of pregnancy and in female LZ at Day 21 of pregnancy; and 4) expression of Srd5a1in LZ was not affected by day of pregnancy, gender, or diet. These results indicate that in response to gestational protein restriction, Hsd17b2 may be a key regulator of testosterone levels and associated activities in placental zones, apparently in a paradoxical manner.

Salivary Testosterone Levels in Men at a U.S. Sex Club

Vertebrate males commonly experience elevations in testosterone levels in response to sexual stimuli, such as presentation of a novel mating partner. Some previous human studies have shown that watching erotic movies increases testosterone levels in males although studies measuring testosterone changes during actual sexual intercourse or masturbation have yielded mixed results. Small sample sizes, "unnatural" lab-based settings, and invasive techniques may help account for mixed human findings. Here, we investigated salivary testosterone levels in men watching (n=26) versus participating (n=18) in sexual activity at a large U.S. sex club. The present study entailed minimally invasive sample collection (measuring testosterone in saliva), a naturalistic setting, and a larger number of subjects than previous work to test three hypotheses related to men's testosterone responses to sexual stimuli. Subjects averaged 40years of age and participated between 11:00pm and 2:10 am. Consistent with expectations, results revealed that testosterone levels increased 36% among men during a visit to the sex club, with the magnitude of testosterone change significantly greater among participants (72%) compared with observers (11%). Contrary to expectation, men's testosterone changes were unrelated to their age. These findings were generally consistent with vertebrate studies indicating elevated male testosterone in response to sexual stimuli, but also point out the importance of study context since participation in sexual behavior had a stronger effect on testosterone increases in this study but unlike some previous human lab-based studies.

Prenatal Testosterone Excess Reduces Sperm Count and Motility

The reproductive system is extremely susceptible to insults from exposure to exogenous steroids during development. Excess prenatal testosterone exposure programs neuroendocrine, ovarian, and metabolic deficits in the female, features seen in women with polycystic ovary disease. The objective of this study was to determine whether prenatal testosterone excess also disrupts the male reproductive system, using sheep as a model system. The extent of reproductive disruption was tested by assessing sperm quantity and quality as well as Leydig cell responsiveness to human chorionic gonadotropin. Males born to mothers treated with 30 mg testosterone propionate twice weekly from d 30 to 90 and with 40 mg testosterone propionate from d 90 to 120 of pregnancy (T-males) showed a significant reduction (P < 0.05) in body weight, scrotal circumference, and sperm count compared with control males. Mean straight line velocity of sperms was also lower in T-males (P < 0.05). Circulating testosterone levels in response to the human chorionic gonadotropin did not differ between groups. These findings demonstrate that exposure to excess testosterone during fetal development has a negative impact on reproductive health of the male offspring, raising concerns relative to unintended human exposure to steroidal mimics in the environment.

Adaptive variation in testosterone levels in response to immune activation: Empirical and theoretical perspectives

High testosterone levels reflect investment in male reproductive effort through the ability to produce and maintain muscle tissue and thus augment mate attraction and competitive ability. However, high testosterone levels can also compromise survivorship by increasing risk of prostate cancer, production of oxygen radicals, risk of injury due to hormonally-augmented behaviors such as aggression, violence and risk taking, reduced tissue and organ maintenance, negative energy balance from adipose tissue catabolism, and suppression of immune functions. Here, I briefly discuss how inter- and intra-individual variation in human male testosterone levels is likely an adaptive mechanism that facilitates the allocation of metabolic resources, particularly in response to injury, illness or otherwise immune activation. Maintaining low testosterone levels in resource-limited and/or high pathogen-risk environments may avoid some immunosuppression and suspend energetically-expensive anabolic functions. Augmenting testosterone levels in the presence of fertile and receptive mates, areas of high food resource availability, and low disease risk habitats will function to maximize lifetime reproductive success.

Latitudinal variation in plasma testosterone levels in birds of the genus Zonotrichia

Birds breeding in northern latitudes generally have elevated plasma testosterone levels throughout the breeding season with a peak at the onset of the breeding season. In contrast, tropical birds tend to have extremely low plasma testosterone levels year round with only a slight increase during breeding. While these patterns have been consistent in the species investigated, closely related species have not been investigated across a range of latitudes. Birds of the genus Zonotrichia present an ideal opportunity to investigate latitudinal variation in plasma testosterone levels as breeding populations occur from northern Alaska to southern Argentina. We studied three taxa of Zonotrichia: (1) Gambel’s white-crowned sparrows, Zonotrichia leucophrys gambelii, breeding at high latitude in northern Alaska, (2) Puget Sound white-crowned sparrows, Z. l. pugetensis, breeding at mid-latitude in Washington state, and (3) an equatorial population of the rufous-collared sparrow, Z. capensis, in Ecuador. To compare both baseline breeding and maximal testosterone levels, males from the three taxa were either bled immediately upon capture during the breeding season or first challenged with gonadotropin-releasing hormone (GnRH) and then bled. As a control, another group of birds experienced a saline challenge. Two-way ANCOVA, with treatment and taxa as factors and testis volume as a covariate, showed a significant effect of treatment on plasma testosterone levels. There was also a significant interaction between taxa and treatment. Contrary to expectations, the equatorial species exhibited greater plasma testosterone levels in response to the GnRH challenge than the high latitude species. There were no differences between the mid- and high-latitude species. The equatorial species had the smallest average testis size and within each taxa there were no relationships between plasma testosterone and testis size. These data suggest that latitudinal clines in plasma testosterone levels in Zonotrichia do not follow previously described patterns and that tropical birds can have levels of testosterone similar to northern latitude species.

The presence of the 21-hydroxylase deficiency carrier status in hirsute women: phenotype-genotype correlations

Objective: To determine the role of heterozygosity for mutations in the 21-hydroxylase gene ( CYP21) in the pathogenesis of hyperandrogenism. Design: Controlled clinical study. Setting: Tertiary care institutional hospital. Patient(s): Forty hirsute women and 13 healthy control women. Intervention(s): The source of androgen excess was determined by the changes in serum testosterone levels in response to a single 3.75-mg IM dose of triptorelin. Main Outcome Measure(s): CYP21 molecular genetic analysis and serum 17-hydroxyprogesterone levels. Result(s): Eight patients and one control were heterozygous carriers of CYP21 mutations. Two patients with adrenal hyperandrogenism and one patient with ovarian hyperandrogenism, who carried the V281L mutation had an increased ACTH-stimulated 17-hydroxyprogesterone level (>4.1 ng/mL) that persisted during gonadal suppression. Another patient with adrenal hyperandrogenism carried the V281L mutation, and her ACTH-stimulated 17-hydroxyprogesterone level was elevated only during gonadal suppression. Four patients (three with idiopathic hirsutism, one with ovarian hyperandrogenism) and one control were carriers of CYP21 mutations typically associated with classic congenital adrenal hyperplasia but had normal basal and ACTH-stimulated 17-hydroxyprogesterone levels. Nine patients without CYP21 mutations had increased ACTH-stimulated 17-hydroxyprogesterone levels; these decreased to normal in six of the patients during gonadal suppression. Conclusion(s): The response of serum 17-hydroxyprogesterone to ACTH does not predict CYP21 carrier status. No clear concordance was found between the CYP21 genotype and the functional origin of androgen excess.

Physical work causes suppression of ovarian function in women.

The suppression of reproductive function is known to occur in women engaging in activities that require high energetic expenses, such as sport participation and subsistence work. It is still unclear, however, if reproductive suppression is a response to high levels of energy expenditure, or only to the resulting state of negative energy balance. To our knowledge, this study provides the first evidence that work-related energy expenditure alone, without associated negative energy balance, can lead to the suppression of reproductive function in women. We document suppression of ovarian function expressed as lowered salivary progesterone levels in women from an agricultural community who work hard, but remain in neutral energy balance. We propose two alternative evolutionary explanations (the 'pre-emptive ovarian suppression' hypothesis and the 'constrained down-regulation' hypothesis) for the observed results.

Testosterone and territorial behaviour in sedentary and migratory sparrows

Abstract. Free-living male song sparrows, Melospiza melodia morphna, showed marked aggressive behaviour in response to simulated territorial intrusions throughout most of the year. Only during the prebasic moult, and during inclement winter weather, was territorial aggression suppressed. In contrast, free-living male white-crowned sparrows, Zonotrichia leucophrys pugetensis , showed the highest behavioural responses to simulated territorial intrusions in spring when territories were established. Responses then declined as the breeding season progressed, reaching a minimum during the prebasic moult. The latter species migrates to wintering grounds and does not show territorial aggression until the following spring. Plasma levels of testosterone paralleled changes in territorial aggression in white-crowned sparrows, but not song sparrows. The resurgence of autumnal territoriality was independent of any increase in circulating testosterone levels. Males of both species showed increases in testosterone levels in response to simulated territorial intrusions, but this was only significant in white-crowned sparrows. However, male song sparrows had higher levels of testosterone in spring in areas with a high density of territories than males in areas with a low density of territories. These data suggest that although territorial behaviour in the non-breeding season was independent of testosterone in song sparrows, such behaviour in the breeding season may be influenced by this steroid hormone. Finally, it appears that young, first summer, song sparrows were also able to establish a territory in early autumn with no changes in testosterone or luteinizing hormone.

Exposure to bleached kraft pulp mill effluent disrupts the pituitary-gonadal axis of white sucker at multiple sites

Our recent studies have demonstrated reproductive problems in white sucker ( Catostomus commersoni) exposed to bleached kraft pulp mill effluent (BKME) at Jackfish Bay on Lake Superior. These fish exhibit delayed sexual maturity, reduced gonadal size, reduced secondary sexual characteristics, and circulating steroid levels depressed relative to those of reference populations. The present studies were designed to evaluate sites in the pituitary-gonadal axis of prespawning white sucker affected by BKME exposure. At the time of entry to the spawning stream, plasma levels of immunoreactive gonadotropin (GtH)-II (LH-type GtH) in male and female white sucker were 30- and 50-fold, lower, respectively, than the levels in fish from a reference site. A single intraperitoneal injection of D-Arg 6, Pro 9N-Et sGnRH (sGnRH-A, 0.1 mg/kg) increased plasma GtH levels in male and female fish at both sites, although the magnitude of the response was greatly reduced in BKME-exposed fish. Fish at the BKME site did not ovulate in response to sGnRH-A, while 10 of 10 fish from the reference site ovulated within 6 hr. Plasma 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) levels were depressed in BKME-exposed fish and unlike fish at the reference site, failed to increase in response to sGnRH-A. Testosterone levels in both sexes and 11-ketotestosterone levels in males were elevated in fish from the reference site but were not further increased by GnRH treatment. In contrast, BKME-exposed fish exhibit a transitory increase in testosterone levels in response to the GnRH analog. In vitro incubations of ovarian follicles obtained from fish at the BKME site revealed depressed basal secretion of testosterone and 17,20β-P and reduced responsiveness to the GtH analog human chorionic gonadotropin and to forskolin, a direct activator of adenylate cyclase. By comparison, ovarian follicles from fish collected at BKME and reference sites produced similar levels of prostaglandin E basally and in response to a phorbol ester and calcium ionophore A23187, suggesting that BKME effects on ovarian function are selective and do not reflect a general impairment of ovarian function. BKME-exposed fish had plasma levels of testosterone glucuronide proportionately lower than those of reference fish, suggesting that there are site differences in the peripheral metabolism of steroids. These studies demonstrate that BKME exposure affects reproduction by acting at multiple sites in the pituitary-gonadal axis.

Possible hypothalamic impotencemale counterpart to hypothalamic amenorrhea?

Twenty-one men with erectile complaints who were found to have a low level of serum testosterone without a reciprocal elevation of the serum levels of luteinizing hormone were evaluated to identify whether the defect was of hypothalamic or of pituitary origin. Patients underwent a luteinizing hormone (LH)-follicle-stimulating hormone (FSH)-releasing hormone stimulation test that showed a normal but sluggish increase in LH and FSH levels, thus ruling out a pituitary defect and suggesting a suprapituitary abnormality. This was confirmed when, in response to clomiphene, patients had a normal increase in gonadotropin and testosterone levels. Although the basal as well as clomiphene and gonadotropin releasing hormone-stimulated levels of total testosterone and gonadotropins were identical in men less than and more than fifty years old, the elevation of free testosterone levels in response to clomiphene was higher in patients younger than fifty. This suggested that although the primary abnormality found in these patients is altered secretion of gonadotropin hormone-releasing hormone from the hypothalamus, an age-related decline in the responsivity of Leydig cells to LH may make it more manifest in older patients. Elevation of testosterone levels from a subnormal to a normal range in response to clomiphene administered for seven days suggests that the defect is functional and reversible and that the drug may be useful in treatment of sexual dysfunction in this group of patients.

Differential Effects of the Destruction of Leydig Cells by Administration of Ethane Dimethane Suiphonate to Postnatal Rats1

Ethane dimethane sulphonate (EDS) is a cytotoxic drug that selectively destroys Leydig cells in adult testes. This study has examined the effect of a single injection of EDS on the Leydig cell populations present in the testes of rats aged 5, 10, or 20 days. Microscopic examination of the tissue demonstrated that the fetal Leydig cell population was destroyed at all ages, but that subsequent development of the adult population of Leydig cells was not affected. Whilst the destruction of the fetal Leydig cells in this acute phase of EDS on 5-day-old rats was accompanied by a decline in serum testosterone levels, there was no apparent effect on this hormone when EDS administered at 10 or 20 days of age, despite the destruction of fetal Leydig cells in these rats. The long-term effects of EDS on Day 5 of age resulted in proliferation of the intertubular tissue in which more Leydig cells were observed, but serum testosterone and testosterone levels in response to human chorionic gonadotropin stimulation in vitro were normal despite moderate or severe disruption of the seminiferous epithelium. These data show that the fetal Leydig cells of immature testes are sensitive to the cytotoxic effects of EDS in the adult, but the response of the testes differs depending on the age at which the drug is administered.

Chronic GnRH administration in prepubertal male pigs

The effect of chronic pulsatile low-dose GnRH treatment on the juvenile testis and associated structures was evaluated in relation to hormonal parameters in the peripheral blood in the pig. Starting at 8 weeks of age, male pigs (crossbreds of Dutch Landrace and Yorkshire breeds) were injected 6 times daily im with 0, 75 or 250 ng GnRH/kg body weight during 4 weeks. Immediately after the treatment period, a GnRH stimulation test with 750 ng GnRH/kg iv was carried out. Samples for plasma LH, FSH, testosterone and 5 alpha DHT measurement were obtained weekly (basal level) and after GnRH stimulation. The pigs were castrated at 12 weeks of age and the weights and lengths of the testis, epididymis and cremaster muscle were recorded. Intratesticular testosterone and 5 alpha DHT concentrations were determined, and the testis and epididymis were evaluated for histological changes. Basal plasma hormone concentrations, intratesticular androgen concentrations and the response of the pituitary gland to stimulation had not been affected by GnRH treatment. Pigs receiving the higher treatment dose of GnRH showed less increase in testosterone levels in response to the stimulation dose at 12 weeks of age than the other pigs. Morphologically, no changes were observed in the epididymis and cremaster muscle after GnRH treatment and no signs of reactivation of structures that can provoke testicular descent could be seen. The development of the seminiferous epithelium was more advanced in the GnRH-treated groups, apparently in a dose-dependent manner.

Endocrine control of antler growth in red deer stags.

Observations of body weight, testis size, antler status, plasma testosterone and prolactin were made on 12 red deer stags during their first 2 years of life. Six of the stags were fed to appetite throughout the study (Group A) and 6 were fed a 70% restricted diet during each winter (Group B). In addition 6 of the stags , 3 from each group, were studied in more detail; LH and testosterone were measured either after a single injection of LH-RH or in samples taken at frequent intervals over a period of 8 or 24 h. During the study the stags became sexually mature, developed first their pedicles and then antlers and showed at least one complete cycle of casting and regrowth of the antlers . The stags in Group A developed their testes and pedicles about 2 months earlier than did those in Group B. Pedicle initiation was associated with increasing plasma testosterone levels in response to changes in LH secretion, and antler development occurred when testosterone levels were low or decreasing. Cleaning of the velvet was associated with high levels of plasma testosterone. Antler casting occurred when plasma testosterone concentrations were low or undetectable and prolactin levels were high or increasing. The relationship between LH and testosterone varied during the study; in spring when the testes and antlers were growing, relatively high levels of LH were associated with only small peaks of testosterone, yet in summer, when antler growth was complete and the antlers were clean of velvet, low LH concentrations were associated with large peaks of testosterone.