Measured Testosterone Concentrations Research Articles

Effect of cosmetic hair treatment and natural hair colour on hair testosterone concentrations.

Testosterone analysis in hair allows for retrospective evaluation of endogenous testosterone concentrations, but studies devoted to investigating confounders in hair testosterone analysis have hitherto been scarce. The current study examined the stability of testosterone concentrations between two hair samples collected three months apart and investigated two potential confounding factors: natural hair colour and cosmetic hair treatments. Testosterone was analysed with an in-house radioimmunoassay with a limit of detection adequate for the purpose. The testosterone concentrations from the two samplings, at baseline and three months later, had an intra-individual correlation of moderate strength (rho = 0.378, p<0.001, n = 146). Hair treatment, such as colouring or bleaching, seemed to increase testosterone concentrations (p = 0.051, n = 191, and in a paired analysis in a subset of the cohort p = 0.005, n = 24), while no effect of natural colour in untreated hair (p = 0.133) could be detected. The current results suggest that cosmetic hair treatments need to be considered in hair testosterone analyses and demonstrate the utility of a radioimmunoassay to reliably measure testosterone concentrations in small hair samples in women.

Application of endocrine biomarkers to update information on reproductive physiology in gray whale (Eschrichtius robustus).

Most of our knowledge on reproductive biology of gray whales dates back to scientific research conducted during commercial whaling in the late 1950s and 1960s. The goal of the present study was to provide updated insights on reproductive physiology of gray whales, using progesterone and testosterone as biomarkers. We measured hormone concentrations using enzyme immunoassay (EIA) techniques in blubber biopsies collected from 106 individual whales from March to November over a span of 12 years (2004–2016) between California and Alaska. We found testosterone concentrations in males to increase significantly with age (P = 0.03). Adult males showed significantly elevated testosterone concentrations when sampled in the fall compared to the summer (P = 0.01), likely indicating physiological preparation for mating. We measured testosterone concentrations in females of different age classes, but no statistical differences were found. We found significantly higher progesterone concentrations in pregnant females compared to non-pregnant females and adult males (P< 0.001), indicating progesterone is a valid biomarker for pregnancy in gray whales. Both female and male calves had elevated progesterone concentrations, suggesting maternal transfer via lactation. We fit a mixture of two normal distributions to progesterone data from all non-calf females to identify clusters of high and low progesterone and estimated the probability of being pregnant for whales of unknown reproductive status. With this approach we identified likely pregnant and non-pregnant animals. This study represents an important milestone on reproductive profiles in this population, that can be used to estimate more accurate and precise reproductive parameters to be used for better understanding population dynamics of gray whales.

Effects of pomegranate juice on the sexual behavior, fertility and protective activity against aluminum exposure in male mice

This experiment aimed to determine how pomegranate juice (PJ) responds to oxidative stress induced by aluminum in male mice. A total of thirty-six male mice were separated into six groups. The first group (control group) received tap water. Groups two and three were given 20% and 40% PJ, respectively. Group four received 400 mg Al/kg, while groups five and six were given Al + 20% PJ and Al + 40% PJ, respectively. After the oral administration period, the sexual behavior of the mice was recorded. Blood was collected from the heart to measure testosterone concentration. After the animals were sacrificed, the reproductive organs were weighed, and the epididymis and testis were used for further evaluations. Our findings showed that Al decreased the body and organs weights, sexual behavior, sperm count, normal sperm, total and progressive sperm motility, testosterone level, and epithelial diameters of the seminiferous tubes. In addition, the PJ reduced these effects and minimized the aluminum toxicity in male mice. In conclusion, PJ protects against aluminum exposure in male mice by ameliorating sexual behavior and fertility.

Self-assembly Synthesis of Molecularly Imprinted Polymers for the Ultrasensitive Electrochemical Determination of Testosterone

Molecularly imprinted polymers (MIPs) can often bind target molecules with high selectivity and specificity. When used as MIPs, conductive polymers may have unique binding capabilities; they often contain aromatic rings and functional groups, which can undergo π-π and hydrogen bonding interactions with similarly structured target (or template) molecules. In this work, an electrochemical method was used to optimize the synthetic self-assembly of poly(aniline-co-metanilic acid) and testosterone, forming testosterone-imprinted electronically conductive polymers (TIECPs) on sensing electrodes. The linear sensing range for testosterone was from 0.1 to 100 pg/mL, and the limit of detection was as low as ~pM. Random urine samples were collected and diluted 1000-fold to measure testosterone concentration using the above TIECP sensors; results were compared with a commercial ARCHITECT ci 8200 system. The testosterone concentrations in the tested samples were in the range of 0.33 ± 0.09 to 9.13 ± 1.33 ng/mL. The mean accuracy of the TIECP-coated sensors was 90.3 ± 7.0%.

Reestablishment of sperm quality after long-term deslorelin suppression in tomcats

The aim of the study was to determine the time after treatment with a 4.7 mg deslorelin implant until Tomcat spermatogenesis activity was restored, and seminal parameters reached pre-implant values. Tomcats (n = 6) were randomly assigned to one of two treatments. Three cats (n = 3) received a deslorelin implant (4.7 mG; Suprelorin®, Virbac, France) in the interscapular subcutaneous region whereas three (n = 3) received no implant and served as control group. Semen samples were collected by electroejaculation every 4 wk from 3 mo before treatment (pretreatment samples) until reestablishment of pre-treatment sperm quality, 32 mo post-implant insertion (PI). Each semen sample was assessed for motility, velocity, concentration, total sperm count, viability, acrosome integrity, plasma membrane integrity and sperm morphology. After semen collection, testicular volume and presence/absence of penile spines were recorded. Additionally, blood samples were taken to measure testosterone concentration. An increase in sperm concentration and total sperm count was present 1 mo PI despite of an abrupt decrease in serum testosterone concentrations after 2–4 weeks. This initial stimulatory effect was followed by a decrease in seminal parameters, reduction of testicular volume and disappearance of penile spines 2 mo PI. A single Suprelorin® 4.7 mg implant suppressed sperm production for 22–25 months. No clinically side effect was observed during the study period. All toms returned to their initial seminal quality 23–28 months after treatment. Therefore, we conclude that Suprelorin® 4.7 mg is a safe option for reversible reproduction control during long periods in tomcats.

EVALUATION OF RAT LEYDIG CELL CULTURE COLLECTED WITH NYCODENZ GRADIENT IN PRODUCING TESTOSTERONE IN VITRO

The aim of this study was to evaluate the ability of rat’s Leydig cells collected with Nycodenz gradient in producing testosterone in vitro. Leydig cells were collected using 5 column of Nycodenz gradient (4, 8, 10, 12, and 15%) and cells were evaluated regarding its concentration, viability, and purity of Leydig cells. Media used to cultured Leydig cells were Dulbecco’s Modified Eagle’s Medium (DMEM)+10% newborn calf serum (NBCS); DMEM+10% NBCS+2,5 IU/mL human chorionic gonadotrophin (hCG); DMEM+10% NBCS+ 5 µg/mL insulin, 10 µg/mL transferrin, and 5 µg/mL Se (ITS); DMEM+10% NBCS+hCG+ITS at 5% CO 2 incubator with temperature of 37.5° C for 3 days. Culture medium was collected every day for testosterone analysis with enzyme-linked immunosorbent assay (ELISA). By adding ITS to the medium, Leydig cells concentration was significantly increased (8.92x10 6 cells/mL) compared to medium with serum (7.74x10 6 cells/mL) or hCG (7.68x10 6 cells/mL) (P<0.05). ITS and hCG in medium significantly increased Leydig cells concentration (10.40x10 6 cells/mL) at day 3 of culture (P<0.05). The result of parallelism test showed that the assay obtained good validity to measure testosterone concentration in culture medium. Testosterone in medium was detected at 1.80-2.60 ng/mL at day 1 of culture. In conclusion, Leydig cells collected with Nycodenz gradient had no effect to testosterone secretion from Leydig cells in vitro.

Comparisons between commercial salivary testosterone enzyme-linked immunosorbent assay kits

Introduction: Measuring testosterone concentrations is of interest both in clinical situations and for research, the latter expanding rapidly during recent years. An increased demand for convenient methods has prompted a number of companies to develop enzyme-linked immunosorbent assay (ELISA) kits to measure testosterone concentrations in saliva. However, the inter-comparability of kits from different manufacturers have yet to be determined.Aim of study: The aim of this study was to compare commercially available ELISA kits from four different manufacturers (Salimetrics, IBL, DRG and Demeditec).Methods: Saliva was collected from 50 participants (25 men and 25 women). Each sample was analysed by the four ELISA kits.Results: The correlations between the ELISA kits from Demeditec, DRG and Salimetrics were moderate to high with r-values > .77; however, proportional errors between the methods calls for caution. The ELISA kit from IBL malfunctioned and no results from this kit was obtained.Conclusions: Results from studies using the ELISA kits from Demeditec, DRG and Salimetrics are generally comparable; however, translation using the formulae presented in the current study could increase the accuracy of these comparisons.

Hematopoiesis Shows Closer Correlation with Calculated Free Testosterone in Men than Total Testosterone.

Serum total testosterone (tT)9 includes both free testosterone (fT) (0.5%–3% of total and believed to be the biologically active form) and sex hormone–binding globulin (SHBG)- and albumin-bound forms (1). Guidelines for diagnosing and treating male hypogonadism that emphasize measurement of tT (2) may not address the major variations in SHBG and consequent testosterone bioavailability (testosterone bioavailability [BT] either calculated or assayed directly) that are associated with age, obesity, anticonvulsant therapy, and thyroid and liver disease. For these reasons, recent Endocrine Society of Australia guidelines (3) acknowledge the value of measuring SHBG as well as BT, but nevertheless state that, “There is no evidence that free or bioavailable testosterone levels, which are usually not directly measured but calculated…are a better measure of androgen status than total testosterone level. Moreover, reference intervals for these [BT levels] are even less well defined than those for measured testosterone concentrations. Therefore, they [BT levels] are not recommended for clinical decision-making.” Although commercially available direct fT assays are not always robust, calculated fT (c-fT) values from a mass-action …

Examining factors that may influence accurate measurement of testosterone in sea turtles.

Differences in reported testosterone concentrations in male sea turtle blood samples are common in the veterinary literature, but may be accounted for by differences in sample handling and processing prior to assay. Therefore, our study was performed to determine best practices for testosterone analysis in male sea turtles (Caretta caretta and Chelonia mydas). Blood samples were collected into 5 collection tube types, and assay validation and measured testosterone concentrations were compared across different sample storage (fresh, refrigerated 1 week, or frozen), extraction (unextracted or ether-extracted), and processing treatment (untreated, homogenized, or dissociation reagent) conditions. Ether-extracted and dissociation reagent-treated samples validated in all conditions tested and are recommended for use, as unextracted samples validated only if assayed fresh. Dissociation reagent treatment was simpler to perform than ether extraction and resulted in total testosterone concentrations ~2.7-3.5 times greater than free testosterone measured in ether-extracted samples. Sample homogenization did not affect measured testosterone concentrations, and could be used to increase volume in gelled samples. An annual seasonal testosterone increase was observed in both species when ether extraction or dissociation reagent treatment was used. Annual deslorelin implant treatments in a Chelonia mydas male resulted in suppression of seasonal testosterone following the fourth treatment. Seasonal testosterone patterns resumed following discontinuation of deslorelin. Comparison of in-house and commercially available enzyme immunoassay kits revealed similar patterns of seasonal testosterone increases and deslorelin-induced suppression. Our study highlights the importance of methodological validation and provides laboratorians with best practices for testosterone enzyme immunoassay in sea turtles.

Prenatal testosterone exposure is related to sexually dimorphic facial morphology in adulthood.

Prenatal testosterone may have a powerful masculinizing effect on postnatal physical characteristics. However, no study has directly tested this hypothesis. Here, we report a 20-year follow-up study that measured testosterone concentrations from the umbilical cord blood of 97 male and 86 female newborns, and procured three-dimensional facial images on these participants in adulthood (range: 21-24 years). Twenty-three Euclidean and geodesic distances were measured from the facial images and an algorithm identified a set of six distances that most effectively distinguished adult males from females. From these distances, a 'gender score' was calculated for each face, indicating the degree of masculinity or femininity. Higher cord testosterone levels were associated with masculinized facial features when males and females were analysed together (n = 183; r = -0.59), as well as when males (n = 86; r = -0.55) and females (n = 97; r = -0.48) were examined separately (p-values < 0.001). The relationships remained significant and substantial after adjusting for potentially confounding variables. Adult circulating testosterone concentrations were available for males but showed no statistically significant relationship with gendered facial morphology (n = 85, r = 0.01, p = 0.93). This study provides the first direct evidence of a link between prenatal testosterone exposure and human facial structure.

Validation of a radioimmunoassay for measuring testosterone concentrations in plasma samples of the subterranean rodent Ctenomys talarum: outstandingly elevated levels in the wild and the effect of captivity

We validated the Coat-a-Count radioimmunoassay (RIA) kit for measuring testosterone in plasma samples of the subterranean rodent Ctenomys talarum and evaluated testosterone levels in free-living and captive individuals. The performance of the assay was evaluated by the assessment of parallelism, accuracy and precision. Moreover, the high specificity of the assay antibody was confirmed by high-pressure liquid chromatography with ultraviolet detector, followed by electrospray ionization tandem mass spectrometry. Results indicated that plasma samples have to be treated with heat and diluted before the RIA for the optimization of the assay. Plasma testosterone concentrations in free-living animals were outstandingly elevated (up to 329 ng/mL), which are among the highest ever reported for mammals. On the other hand, captivity produced a 14-fold decrease in plasma testosterone concentrations, emphasizing that very significant changes in the endocrine milieu may occur in wild animals kept under laboratory conditions. Our results place tuco-tucos as an interesting model for the study of androgen regulation in mammals, suggesting that target tissues may have low sensitivity to the testosterone signal and agree with a scenario of elevated levels of sex hormone-binding globulin in plasma.

Testosterone, Plumage Colouration and Extra-Pair Paternity in Male North-American Barn Swallows

In most monogamous bird species, circulating testosterone concentration in males is elevated around the social female's fertile period. Variation in elevated testosterone concentrations among males may have a considerable impact on fitness. For example, testosterone implants enhance behaviours important for social and extra-pair mate choice. However, little is known about the relationship between natural male testosterone concentration and sexual selection. To investigate this relationship we measured testosterone concentration and sexual signals (ventral plumage colour and tail length), and determined within and extra-pair fertilization success in male North American barn swallows (Hirundo rustica erythrogaster). Dark rusty coloured males had higher testosterone concentrations than drab males. Extra-pair paternity was common (42% and 31% of young in 2009 and 2010, respectively), but neither within- nor extra-pair fertilization success was related to male testosterone concentration. Dark rusty males were less often cuckolded, but did not have higher extra-pair or total fertilization success than drab males. Tail length did not affect within- or extra-pair fertilization success. Our findings suggest that, in North American barn swallows, male testosterone concentration does not play a significant direct role in female mate choice and sexual selection. Possibly plumage colour co-varies with a male behavioural trait, such as aggressiveness, that reduces the chance of cuckoldry. This could also explain why dark males have higher testosterone concentrations than drab males.

Effects of in vivo testosterone manipulation on ovarian morphology, follicular development, and follicle yolk testosterone in the homing pigeon

To date, our understanding of the function of testosterone in female reproductive physiology is only marginal although there are indications that testosterone is involved in modulating follicular recruitment, growth, atresia, and ovulation. Studies elevating testosterone in breeding female birds have, in most instances, found detrimental effects, such as delayed clutch initiation or decreased clutch size. In our previous study, testosterone treatment of female homing pigeons delayed clutch initiation without diminishing fecundity. In this study, we explore whether the observed effect might have been caused by testosterone influencing follicle maturation or ovulation. We implanted mature female pigeons with testosterone prior to pairing, which resulted in constant elevation of circulating testosterone concentrations within the physiological range. We killed females after they had laid the first egg and measured ovarian and follicular development. Ovarian mass and pre-hierarchical yolky follicles were not affected by the treatment; however, testosterone females produced smaller and lighter preovulatory follicles. High plasma testosterone levels at oviposition or a strong temporal increase in testosterone were negatively related to mass and diameter of second follicles. We proposed that sustained elevation of testosterone delays follicular maturation, potentially via negative feedback on the hypothalamo-pituitary-gonadal axis. Furthermore, to gain better insight into the regulation of yolk hormone acquisition, we measured testosterone concentrations in the preovulatory follicles. We found no differences between treatment groups but follicle yolk contained much higher levels of testosterone than yolk of un-incubated eggs, suggesting that hormone measurements performed after oviposition do not correctly reflect maternal allocation.

Laboratory work-up of testosterone

Measuring testosterone concentration is a central component of routine andrological diagnostics. To avoid complicated and often imprecise direct measurement of bioavailable testosterone, calculation by SHBG and albumin concentration is possible. When interpreting a measured testosterone concentration, numerous influencing factors have to be kept in mind. One main factor is circadian rhythm; furthermore, concentration decreases with advancing age. Changes of testosterone concentration can be caused by illness or the intake of specific drugs. The increase in SHBG concentration with age is of particular importance. Since internationally accepted standard values are missing, especially for elderly patients, their symptoms should always be considered when making a decision on hormone substitution.

Dehydroepiandrosterone sulphate interferes with the Abbott Architect direct immunoassay for testosterone

There are known difficulties in measuring testosterone in women using 'direct' (non-extraction) immunoassays. The positive bias encountered in many of these assays has been attributed to an unidentified interfering substance. We have evaluated the potential for dehydroepiandrosterone sulphate (DHEA-S) to cross-react in the Abbott Architect testosterone assay. Samples (n = 81) from female patients who had DHEA-S, direct and extracted testosterone measured were examined retrospectively. Possible cross-reactivity was evaluated by spiking both testosterone free assay diluent and serum from a woman with exogenous DHEA-S. The retrospective patient analysis of the data demonstrated a relationship between interference and DHEA-S (r = 0.78, P < or = 0.0001). Spiking studies revealed a linear relationship between added DHEA-S and the measured testosterone concentration. Consistent with the retrospective study, for every 1 micromol/L increase in DHEA-S, 0.23 nmol/L of testosterone was measured in the diluent. Spiking DHEA-S into serum gave only a 0.12 nmol/L increase in measured testosterone for every 1 micromol/L rise in DHEA-S. DHEA-S cross-reacts in the Abbott Architect direct immunoassay for testosterone to a clinically significant effect. This cross-reactivity is likely to be responsible for much of the interference observed when measuring testosterone in women by this method.

Relationship of serum testosterone concentrations to mate preferences in rams.

This study examined systemic testosterone concentrations in rams that were classified according to their sexual behavior and partner preference as either female-oriented (FOR), male-oriented (MOR), or asexual (NOR). For this purpose, we measured testosterone concentrations under three separate conditions: in conscious rams during the nonbreeding season (June) and breeding season (November), and in anesthetized rams during the breeding season. Basal testosterone concentrations in conscious rams were not different among the three groups (P > 0.05) in either season. However, when rams were anesthetized, mean systemic concentrations of testosterone in FORs (mean +/- SEM, 13.9 +/- 7.4 ng/ml serum) were greater (P < 0.05) than in NORs (0.9 +/- 0.1 ng/ml), but not in MORs (2.2 +/- 6.2 ng/ml), whereas testosterone concentrations were not different between MORs and NORs (P > 0.05). Concentrations of testosterone in the spermatic vein of FORs (127 +/- 66 ng/ml) were greater (P < 0.05) than in MORs (41 +/- 10 ng/ml) and NORs (19 +/- 7 ng/ml). Serum LH concentrations were not different. Cortisol was higher (P < 0.05) in anesthetized MORs (25.1 +/- 4.2 ng/ml) and NORs (27.2 +/- 4.4 ng/ml) than in FORs (10.9 +/- 1.8 ng/ml). These results demonstrate that circulating testosterone concentrations are related to sexual behavior only when rams are bled under anesthesia. Thus, differences in basal androgen concentrations in adulthood cannot be responsible for expression of male-oriented preferences or low libido in sheep. Instead, functional differences must exist between the brains of rams that differ in sexual preference expression.

The heritability of testosterone: a study of Dutch adolescent twins and their parents.

The heritability of total plasma testosterone levels, determined from blood samples, was examined in 160 adolescent twin pairs and their parents. Subjects were tested as part of a larger study of cardiovascular risk factors, conducted in Amsterdam. Each subject provided a sample of blood which was assayed to measure testosterone concentrations. Correlations of testosterone in monozygotic twins were higher than in dizygotic twins. No resemblance was found between testosterone values in fathers and those in their children and a moderate correlation was seen between mothers and their daughters. The lack of resemblance between family members of opposite sex suggests that different genetic factors influence plasma testosterone concentrations in men and women. In adolescent men, approximately 60% of the variance in testosterone levels is heritable. The lack of father-son resemblance suggests that different genetic factors may be expressed in adolescence and adulthood. In women, 40% of the variance in testosterone levels is heritable, both in adolescence and in adulthood.

Pregnancy Determination in Uncaptured Feral Horses

The urinary excretion of estrone sulfate (ES) by 25 free-roaming feral horses (Equus caballus) was measured by radioimmunoassay applied to extracts of urine-soaked soil. Twelve of 15 mares having ES concentrations >1.0 Ag/mg creatinine (f = 2.64 + 1.02 [SD]) produced foals. All 10 mares with ES concentrations <1.0 gg/mg creatinine (t = 0.44 ? 0.26) did not foal. Extracting urine from soil and measuring ES and creatinine can be used to determine pregnancy in free-roaming feral horses without the stress of capture or immobilization. J. WILDL. MANAGE. 52(2):305-308 The ability to determine pregnancy in freeroaming animals is poorly developed. Birth rates are an inadequate index because they do not provide information about fetal losses, which are vital in understanding nutrition, general health, or stress. To accurately assess pregnancy in wild animals, individuals are usually trapped or immobilized, blood samples taken, and pregnancy determined by measuring estrogen or progestin concentrations or some other specific pregnancy test (Kirkpatrick 1980). These methods, though adequate for domestic animals, frequently are cumbersome, expensive, and disruptive or severely disturbing when applied to wild animals (Seal et al. 1985). The concentrations of urinary steroids or their conjugated metabolites that change during pregnancy have been measured in many species. Captive animals in which pregnancy has been determined by measuring urinary estrogen or progestin metabolites include the gorilla (Gorilla gorilla) (Hopper et al. 1968, Czekala et al. 1983), ruffed lemur (Lemur variegatus) (Shideler et al. 1983a), vervet monkey (Cercopithecus aethiops) (Setchell et al. 1980), lion-tailed macaque (Macaca silenus) (Shideler et al. 1983b), rhesus monkey (Macaca mulatta) (Liskowski et al. 1970, Liskowski and Wolfe 1972), baboon (Comopithecus hamadryas) (Hodges et al. 1986), Indian rhinoceros (Rhinoceros unicornis) (Kassam and Lasley 1981), and horse (Raeside and Liptrap 1975, Evans et al. 1984, Kasman et al. 1984). Poole et al. (1984) measured testosterone concentrations in elephant (Loxodonta africana) urine samples deposited on the ground; urine samples were collected by aspirating the pool of urine minutes after urination occurred. Steroid analysis of urine-soaked soil samples could be an easy, accurate, and inexpensive method to determine pregnancy in fre -roaming species with a minimum of disturbance to the population being studied. Ou objective was to develop a test of pregnancy in free-roaming feral horses that is accurate, inexpensive, does not require capture or handling, and does not disturb the population being studied. Specifically, we tested for pregnancy by measuring a urinary estrogen metabolite conjugate, estrone sulfate, in urine-soaked soil. We thank L. R. Taylor, Bureau of Land Management, Billings, Montana, for providing age data for the mares in this study, and S. M. Kruemmling for assistance in collecting urine samples.

Growth and sexual maturation of the male house musk shrew (Suncus murinus)

The sexual maturation in the male house musk shrew, Suncus murinus, was investigated by weighing gonads, accessory sexual organs and various other organs, and measuring testosterone concentrations in the plasma from birth to 50 days of age. The histological and histochemical studies of the testis were also carried out. Testicular weight increased markedly from 10 days of age. On 15 days of age, the activity of delta 5-3 beta-Hydroxysteroid dehydrogenase (HSD) was detected in Leydig cells. In accordance with an increase of HSD activity, the concentrations of plasma testosterone raised rapidly from 15 days of age and reached a peak on Day 30. Growth of prostate glands and seminal vesicles showed a sigmoidal pattern and their significant growth began from Day 25. Sperms were detected first in the seminiferous tubules on Day 28, and most tubules were filled with many sperms on Day 33. From these results, the beginning of sexual maturation, i.e. puberty, of the male shrew is considered to be around Day 25. The weight gain of testes, accessory sexual organs and the body became slower on Day 40. The male animal of Day 40 could mate and impregnate the female. Therefore, the male shrew seems to attain to the sexual maturity between days 35 and 40.

Characterization and physiological validation of a radioimmunoassay for plasma testosterone in the male rat

A radioimmunoassay (RIA) to measure testosterone concentration in the plasma of male rats was formalized, tested and physiologically validated. The procedure measured testosterone equally well, whether or not estimation of recovery and chromatographic purification preceded the RIA. The results were equivalent to those achieved by the method of competitive protein binding. No 17β-hydroxy-5α-androstan- 3-one was found in the plasma of male rats. Adrenalectomy did not significantly decrease plasma testosterone in either male or female rats. The simplified protocol met all requirements of precision, sensitivity, accuracy and specificity. A single investigator can analyze 1, 000 plasma samples for testosterone in one week if necessary.