Measurement Of Plasma Testosterone Research Articles

Effects of Exogenous Human Chorionic Gonadotropin Administration on Plasma Testosterone and Semen Production in the Veiled Chameleon (Chamaeleo calyptratus)

Gamete collection, gamete preservation, hormone analysis, and artificial insemination have become integral parts of in situ and ex situ conservation programs for threatened and endangered species, and while these methods have been used to assist conservation in many different vertebrate groups, limited work has been done in reptiles. For example, semen collection in lizards has only recently been described and determined to be safe. The purpose of this study was to determine effective doses of human chorionic gonadotropin (hCG) for increasing plasma testosterone concentrations in the veiled chameleon (Chamaeleo calyptratus), as well as to determine whether the rise in testosterone impacts semen collection. A cross-over design was used. Chameleons were given injections of 100 IU, 200 IU, and 300 IU of hCG/animal and serial plasma testosterone measurements were collected over 24 hours. 100 IU/animal was determined to increase plasma testosterone concentrations similar to 200 IU, and 300 IU/animal. Following this, we determined weekly injections of hCG (100 IU/animal) would maintain elevated testosterone concentrations over 30 days. Additionally, we determined that elevated testosterone secondary to repeated injections of hCG decreased testicular size as determined by ultrasound. Repeated hCG injections and long-term elevation of plasma testosterone concentrations did not increase the likelihood to collect a semen sample with electroejaculation or improve ejaculate quality. Further research is needed to exogenously stimulate spermatogenesis and increase ejaculate quality to perform timed semen collections in male reptile species.

Sex-specific differences in atherosclerosis, thrombospondin-1, and smooth muscle cell differentiation in metabolic syndrome versus non-metabolic syndrome mice.

Metabolic syndrome (MetS) amplifies the risks of atherosclerosis. Despite well-known sexual dimorphism in atherosclerosis, underlying mechanisms are poorly understood. Our previous findings highlight a proatherogenic protein, thrombospondin-1 (TSP-1), in hyperglycemia- or hyperleptinemia (mimicking obesity)-induced atherosclerosis. However, the role of TSP-1 in the development of atherosclerosis prompted by co-existing hyperglycemia and obesity, characteristic of MetS, is unknown. The goal of this study was to examine sex-specific differences in lesion progression in a model of combined MetS and atherosclerosis (KKAyApoE) and interrogate how these differences relate to TSP-1 expression. Male and female KKAy+/-ApoE-/- (with ectopic agouti gene expression) and age-matched non-agouti KKAy-/-ApoE-/- littermates were placed on a standard laboratory diet from 4 to 24 weeks age followed by blood and tissue harvests for biochemical, molecular, and aortic root morphometric studies. Metabolic profiling confirmed MetS phenotype of KKAy+/-ApoE-/-; however, only male genotypes were glucose intolerant with elevated VLDL-cholesterol and VLDL-triglyceride levels. Aortic root morphometry demonstrated profound lipid-filled lesions, increased plaque area, and augmented inflammatory and SMC abundance in MetS vs non-MetS males. This increase in lesion burden was accompanied with elevated TSP-1 and attenuated LMOD-1 (SM contractile marker) and SRF (transcriptional activator of SM differentiation) expression in male MetS aortic vessels. In contrast, while lipid burden, plaque area, and TSP-1 expression increased in MetS and non-MetS female mice, there was no significant difference between these genotypes. Increased collagen content was noted in MetS and non-MetS genotypes, specific to female mice. Measurement of plasma testosterone revealed a link between the atherogenic phenotype and abnormally high or low testosterone levels. To interrogate whether TSP-1 plays a direct role in SMC de-differentiation in MetS, we generated KKAy+/- mice with and without global TSP-1 deletion. Immunoblotting showed increased SM contractile markers in male KKAy+/-TSP-1-/- aortic vessels vs male KKAy+/-TSP-1+/ +. In contrast, TSP-1 deletion had no effect on SM contractile marker expression in female genotypes. Together, the current study implicates a role of plasma testosterone in sex-specific differences in atherosclerosis and TSP-1 expression in MetS vs non-MetS mice. Our data suggest a sex-dependent differential role of TSP-1 on SMC de-differentiation in MetS. Collectively, these findings underscore a fundamental link between TSP-1 and VSMC phenotypic transformation in MetS.

Endogenous Testosterone Levels Are Associated with Risk of Type 2 Diabetes in Women without Established Comorbidity.

PurposeThe impact of endogenous androgen levels on the risk of type 2 diabetes in women remains uncertain. The objective was to investigate associations between endogenous androgen levels and risk of type 2 diabetes in young women without established comorbidity.MethodsIn this retrospective cohort study, women aged 18 to 50 years who underwent measurement of plasma testosterone, dehydroepiandrosterone-sulfate (DHEA-S), dihydrotestosterone (DHT), and sex hormone-binding globulin (SHBG) for the first time from January 2007 to December 2015 were included. Androgens were analyzed using tandem liquid chromatography mass spectrometry. Women with established comorbidity were excluded, using Danish healthcare registries. We calculated incidence rate ratios (IRRs, 95% confidence intervals) of type 2 diabetes according to quartiles of plasma androgens using multivariate Poisson regression models.ResultsA total of 8876 women, with a mean ± SD age of 38.5 ± 4.6 years and a median (interquartile range [IQR]) follow-up duration of 8.1 (6.6-9.4) years, were eligible for analyses. During 69 728 person-years, 69 women were diagnosed with type 2 diabetes. Women in the highest quartile of plasma total testosterone and calculated free testosterone displayed increased risk of type 2 diabetes compared with the lowest quartile: IRR 1.97 (1.01; 3.85), P = .048 and IRR 7.32 (2.84; 18.83), P < .001. SHBG was inversely associated with type 2 diabetes, Q4 versus Q1; IRR 0.06 (0.02; 0.21), P < .001. Plasma DHEA-S and DHT were not associated with incident type 2 diabetes.ConclusionsHigher levels of plasma total and free testosterone were associated with increased risk of type 2 diabetes among women.

Testosterone trajectories and reference ranges in a large longitudinal sample of male adolescents.

PurposePubertal dynamics plays an important role in physical and psychological development of children and adolescents. We aim to provide reference ranges of plasma testosterone in a large longitudinal sample. Furthermore, we describe a measure of testosterone trajectories during adolescence that can be used in future investigations of development.MethodsWe carried out longitudinal measurements of plasma testosterone in 2,216 samples obtained from 513 males (9 to 17 years of age) from the Avon Longitudinal Study of Parents and Children. We used integration of a model fitted to each participant’s testosterone trajectory to calculate a measure of average exposure to testosterone over adolescence. We pooled these data with corresponding values reported in the literature to provide a reference range of testosterone levels in males between the ages of 6 and 19 years.ResultsThe average values of total testosterone in the ALSPAC sample range from 0.82 nmol/L (Standard Deviation [SD]: 0.09) at 9 years of age to 16.5 (SD: 2.65) nmol/L at 17 years of age; these values are congruent with other reports in the literature. The average exposure to testosterone is associated with different features of testosterone trajectories such as Peak Testosterone Change, Age at Peak Testosterone Change, and Testosterone at 17 years of age as well as the timing of the growth spurt during puberty.ConclusionsThe average exposure to testosterone is a useful measure for future investigations using testosterone trajectories to examine pubertal dynamics.

E-4. 血漿Testosteroneの測定とその臨床応用

E-4. 血漿Testosteroneの測定とその臨床応用

Adverse Effects of a Clinically Relevant Dose of Hydroxyurea Used for the Treatment of Sickle Cell Disease on Male Fertility Endpoints

Two experiments were conducted to determine: 1) whether the adult male transgenic sickle cell mouse (Tg58 × Tg98; TSCM), exhibits the patterns of reproductive endpoints (hypogonadism) characteristic of men with sickle cell disease (SCD) and 2) whether hydroxyurea (HU) exacerbates this condition. In Experiment 1, blood samples were collected from adult age-matched TSCM and ICR mice (ICRM) (N = 10/group) for plasma testosterone measurements. Subsequently, mice were sacrificed, testes excised and weighed and stored spermatozoa recovered for the determination of sperm density, progressive motility and percentage of spermatozoa with normal morphology. In experiment 2, adult male TSCM were orally treated with 25 mg HU/kg body weight/day for 28 or 56 days. Control mice received the vehicle for HU (saline) as described above. At the end of the treatment periods, blood samples were collected for quantification of circulating testosterone. Subsequently, mice were sacrificed, testes and epididymides were recovered and weighed and one testis per mouse was subjected to histopathology. Stored spermatozoa were recovered for the determination of indices of sperm quality mentioned in Experiment 1. Testis weight, stored sperm density, progressive motility, percentage of spermatozoa with normal morphology and plasma testosterone concentrations of TSCM were significantly lower by 40, 65, 40, 69 and 66%, respectively than those of ICRM. These data indicate that adult TSCM used in this study suffered from hypogonadism, characteristically observed among adult male SCD patients. In Experiment 2, HU treatment significantly decreased testis weight on day 28, (0.09 ± 0.004g) that was further decreased on day 56 (0.06 ± 0.003g; treatment x time interaction) compared with controls (day 28, 0.15 ± 0.01g; day 56, 2, 0.16 ± 0.01g). Concomitant with a 52% shrinkage (P<0.001) in area of testes in 56 days of HU treatment, testes from HU-treated TSCM exhibited significant atrophic degeneration in the seminiferous tubules compared with controls. Furthermore, treated TSCM had only Sertoli cells and cell debris remaining in most of the seminiferous tubules in comparison with controls. Leydig cell prominence and hyperplasia were more evident (P<0.05) in the steroidogenic compartments of testes of HU-treated TSCM compared with controls. However, plasma testosterone concentrations were reduced by HU treatment (P<0.05; treatment x time interaction) compared with controls on the two time periods studied. Epididymides from HU-treated TSCM sustained a 25% shrinkage (P<0.05), along with 69 (P<0.005) and 95% reduction (P<0.005), in stored sperm density and sperm progressive motility (treatment x time interaction P<0.05), respectively on day 56 of treatment compared with controls. These data demonstrate that TSCM used in this study exhibited SCD-induced hypogonadism, thus authenticating their use for studying the effect of HU on male reproductive endpoints observed in SCD patients. Secondarily, our data show that HU treatment exacerbated the already SCD-induced hypogonadism to gonadal failure.

Effect of testosterone on neointimal proliferation and blood lipids after balloon-induced aorta injury in rabbits

To investigate the effect of testosterone on neointimal proliferation and blood lipids after balloon-induced aorta injury in male rabbits. Twenty-five male white rabbits were randomly divided into five groups with 5 in each. G1 underwent sham castration served as control group, rabbits in remaining 4 groups were castrated. One week after the castration, rabbits in G3, G4, G5 groups received 3 mg/kg, 6 mg/kg, 12 mg/kg testosterone undecanoate i.m, respectively, G2 was not received. Two weeks after the castration, deendothelializing balloon-induced injury in right iliac artery was performed in all animals. Two weeks after the injury, blood samples were drawn for measurement of plasma testosterone and lipids, and the right iliac arteries were excised for computer imagining analysis. Compared with G1, plasma levels of total cholesterol(TC), triglycerides(TG), low density lipoprotein(LDL) in G3, G4 and G5, gradually decreased, plasma levels of high density lipoprotein(HDL)gradually increased. There were most significant differences of plasma TC, TG and LDL(P<0.05) between G2 and G1. There were not significant differences of plasma TC, TG, HDL and LDL among all groups before endothelial denudation and 2 weeks after endothelial denudation (P>0.05). In G3, G4 and G5 the intimal area and radio of intima/media gradually decreased, there were significant differences between G2, G3, G4 and G1(P<0.05), the differences between G1 and G2 were most significant, and those of G5 were close to G1. Endothelial cell repair was observed with electron microscope. Endothelial cells from G2 to G5 became smoother gradually, which in G5 were very close to G1. Testosterone inhibits the intima proliferation induced by balloon-induced injury and improves blood lipids levels. The effects are enhanced by the dose increasing.

How to optimise treatment of erectile dysfunction above and beyond the beneficial effects of a phosphodiesterase type 5 inhibitor

The introduction in 1998 of the phosphodiesterase type 5 (PDE-5) inhibitors has changed the landscape of diagnosis and, in particular, the treatment of erectile dysfunction (ED). It has paved the road for a more profound insight into ED. ED and other ailments of elderly men, such as atherosclerosis, hypertension, diabetes mellitus and lower urinary tract symptoms were usually regarded as distinct diagnostic/therapeutic entities, but there is growing evidence that they are interrelated and are factors in ED. To optimise the treatment of ED, an integral approach to the health of the ageing male is required. There is an interdependence between the metabolic syndrome, ED and patterns of testosterone in ageing men. The main features of the metabolic syndrome are abdominal obesity, insulin resistance, hypertension and dyslipidaemia, significant factors in the aetiology of erectile function. The metabolic syndrome is associated with lower-than-normal testosterone levels. Testosterone is a determinant of glucose homeostasis and lipid metabolism. Testosterone is not only a factor in libido but also exerts essential effects on the anatomical and physiological substrate of penile erection. With these recent insights, the health problems of elderly men must be placed in a context that allows an integral approach. While PDE-5 inhibitors are the mainstay of treatment of men with ED, treatment of testosterone deficiency is becoming part and parcel of a new approach to both ED and the metabolic syndrome. The diagnostic work-up of ED should comprise measurement of plasma testosterone. If proven deficient, treatment with testosterone is indicated.

Fertilization-promoting peptide in reproductive tissues and semen of the male marmoset (Callithrix jacchus).

Fertilization-promoting peptide (FPP) is present in the prostate gland and semen of some mammals, and has been shown to enhance the fertilizing ability of both epididymal mouse and ejaculated human spermatozoa. The novel peptide may prove of importance for the treatment of some cases of male infertility, and a suitable animal model would be useful to test this hypothesis. To this end, we examined reproductive tissues and semen of the male marmoset for the presence of FPP. Peptides were extracted from seminal plasma, testes, prostate, and bulbourethral glands of intact and castrated male marmosets. The peptides were identified by ion-exchange chromatography followed by radioimmunoassay. The mean concentration of FPP immunoreactivity in semen from intact males was 58.7 nM (SE +/- 9.9 nM, n = 10), and anion-exchange chromatography revealed FPP as the only immunoreactive peptide present. Analysis of tissues revealed that FPP in semen was likely to be derived from the prostate gland, which contained this peptide as the major source of immunoreactivity (10.86 pmol/gland; SE +/- 4.39 pmol/gland, n = 4). Only low concentrations of FPP were detectable in the bulbourethral glands, and the peptide was undetectable in the testis. Surprisingly, FPP was readily detectable in the seminal plasma from one castrated marmoset and was present in the prostate gland from 3 castrates at levels which did not differ significantly from those in intact animals (5.47 pmol/gland, SE +/- 1.64 pmol/gland, n = 3). Plasma testosterone measurements indicated that residual circulatory androgens remained after castration, which may be consistent both with the maintenance of mating behavior and the presence of prostatic FPP. We conclude that FPP is present within the prostate gland and seminal plasma of the marmoset at concentrations consistent with a role in male fertility in this species.

Proposed definitive methods for measurement of plasma testosterone and 17α-hydroxyprogesterone

Objectives: This report provides the results of the development and evaluation of definitive isotope dilution/mass spectrometry (ID/MS) methods for the determination of testosterone and 17α-hydroxyprogesterone in human plasma at concentrations ranging from 1.4 to 37.9 nmol/L and 1.5 to 45.4 nmol/L, respectively. The internal standards were 16,16,17- 2H-testosterone and 21,21,21,- 2H-17α-hydroxyprogesterone. The development of optimum extraction and derivatization procedures, and studies of storage time, temperature effects, accuracy, and precision are presented. Results: The results indicate that the methods employing the TBDMS derivative of testosterone and MO-TMS derivative of 117α-hydroxyprogesterone are capable of generating accurate and precise data at the inherently low concentrations given, with recovery greater than 95%. Accuracy of testosterone in the fortified steroid-free and pooled plasma by ID/MS measurement was good because the relative error ranged from +3.1% to −0.7, with a mean of 0.9% over the concentration levels of 1.4 to 37.9 nmol/L testosterone, and the imprecision ranged from 4.2% to 0.7% CV, with a mean of 1.9%. Accuracy of 17α-hydroxyprogesterone in the fortified steroid-free and pooled plasma was also good, considering the inherently low concentrations. The relative error ranged from −2.1% to +1.5%, with a mean of 1.1%, and the imprecision ranged from 3.8% to 0.8% CV with a mean of 1.3% over concentration levels of 1.5 to 15.1 nmol/L. The high precision and accuracy and absence of statistically significant bias qualifies these methods as candidate definitive methods for plasma testosterone and 17α-hydroxyprogesterone.

Measurement of plasma testosterone by gas chromatography-negative-ion mass spectrometry using pentafluoropropionic derivatives.

Plasma testosterone was measured by gas chromatography-negative-ion chemical ionisation mass spectrometry (GC-MS). The testosterone was extracted from plasma using home-made Extrelut columns and diethyl ether elution. It was quantified as the pentafluoropropionate (PFP) derivative by selected-ion monitoring at m/z 560 (testosterone) and 563 (d3-testosterone), accounting for about 34% of the total ion. The characteristics of the method were: extraction recovery about 95%; linearity over the range 1.7-71.5 nmol l-1 with linear regression equation y = 1.41x + 0.0217, r = 0.999; detection limit 3.5 fmol injected with a signal-to-noise ratio of 7.4; within-day variation, 3% for GC-MS, and 5.8% for the whole process; day-to-day coefficient of variation, 6.6-11%, depending on the concentrations. There was a good correlation between the results obtained by GC-MS and RIA (r = 0.994), but the GC-MS values were significantly lower (p < 0.05) than those obtained by RIA.

A sensitive enzyme-linked immunosorbent assay (ELISA) for testosterone: use of a novel heterologous hapten conjugated to penicillinase

A microplate enzyme-linked immunosorbent assay (ELISA) has been developed for the measurement of testosterone in plasma. The assay uses a heterologous system consisting of a novel hapten 4-(17β-hydroxy-3-oxoestra-4,9-dien-11β-yl)butanoicacid (1) conjugated to penicillinase (β-lactamase). The key reaction in the synthesis of the hapten was the cuprate-mediated 1,4-conjugate addition on 3,3,17,17-bis-ethylenedioxy-5α, 10α-oxido-estr-9(11)-ene by the Grignard reagent derived from trimethyl 4-bro-moorthobutyrate; this regiospecifically introduces the 11β-butanoate function. The hapten-penicillinase conjugate was used in the assay in conjunction with the immuno globulin G (IgG) fraction derived from a previously characterized, highly specific, antitestosterone serum raised against a testosterone-19-O-carboxymethyl ether-bovine serum albumin (T-19-O-CME-BSA) conjugate. This unique system represents one incorporating three elements of structural heterology: bridge, site, and ring heterology between the antigen hapten and enzyme-linked hapten. The limit of detection was 10 pg of testosterone with a sensitivity range between 15 and 1,000 pg. A low level of cross-reactivity with 5α-dihydrotestosterone (6.17%) and 11β-hydroxytestosterone (1.03%) was noted. No interference was noted with other common androgens, estradiol, or progesterone. The sensitivity and selectivity observed in the assay may be attributable to the selection of penicillinase as the enzyme marker and the elements of conformational heterology between the antigen-linked and enzyme-conjugated steroid haptens.

Loss of Therapeutic Control in Congenital Adrenal Hyperplasia due to Interaction between Dexamethasone and Primidone

A 14-year-old girl with congenital adrenal hyperplasia showed rapid conversion from undertreatment to overtreatment when primidone, used to treat coexistent epilepsy, was withdrawn while on a constant steroid dose. In addition to signs of hypercortisolism and a decrease in random measurements of plasma testosterone and 170H-progesterone concentrations, the deterioration in control was also illustrated by changes in the pattern of blood spot steroid profiles. Adequate control was achieved only after a 3-fold reduction in steroid dose. The decrease in dose requirement was probably the result of a reversal of liver enzyme induction consequent upon the withdrawal of primidone.

Seasonal cycles in testicular activity in the frog, Rana perezi

Studies of seasonal testicular cycle based on spermatogenetic activity and direct measurement of plasma testosterone were made in male frog Rana perezi obtained from its natural biotope in the Iberian Peninsula. Testosterone plasma level was determined by radioimmunoassay and exhibited notable differences according to season: plasma testosterone was lowest (<0.5 ng/ml) in summer and then increased progressively to reach a peak in spring (3–4 ng/ml), coincident with mating. After spermiation, when an increase in temperature and photoperiod in the natural habitat occurs, levels decline, Fat bodies also show a pronounced seasonal cycle with total regression following breeding and maximal development in winter. However, testicular weight was independent of seasons, and no significant change was observed throughout the year. Histological evidence indicates that although cell nests of different types are present every month of the year, the most important spermatogenetic activity is initiated in summer. The possible relationship between spermatogenetic activity and testosterone production and the importance of environmental factors as synchronizers of seasonal reproduction are discussed.

Androstenedione rhythms in saliva in congenital adrenal hyperplasia.

Serial samples of saliva were collected at home by 17 patients being treated for congenital adrenal hyperplasia to determine the circadian rhythm of androstenedione as an index of therapeutic control. Single samples of blood for measurement of plasma testosterone, 170H-progesterone, and androstenedione concentrations were collected from these and a further seven patients for comparison. Plasma androstenedione concentrations showed a close correlation with plasma concentrations of 170H-progesterone and testosterone. There was a strong correlation between the salivary androstenedione profiles and plasma testosterone concentrations in pubertal girls. Concentrations of androstenedione in saliva decreased during the day but remained raised at each sampling time in relation to plasma testosterone concentrations. Salivary androstenedione profiles are shown as nomograms to distinguish the degree of therapeutic control. The concentration of androstenedione, measured in plasma or saliva, is an alternative marker to monitor control of treatment in congenital adrenal hyperplasia. The measurement in saliva is a useful index of androgen production when blood sampling is difficult.

Testosterone, testis size, seasonality, and behavior in group-living stumptail macaques ( Macaca arctoides)

During a 28-month period, data were collected on physiological parameters and sociosexual behavior of 13 adult male members of a large mixed-sex group of stumptail macaques living in an outdoor cage. Monthly measurements of plasma testosterone, testis size, and body weight revealed no systematic seasonally. Seasonal variations did occur in branch shaking and grooming (both with low rates in winter), but not in other behaviors studied (copulation, masturbation, aggression). Dominance ranks were stable throughout the study period and were not significantly correlated with mean testosterone levels. Temporal fluctuations in behavioral frequencies did not parallel testosterone fluctuations. Interindividual differences in behavioral frequencies were often correlated with dominance rank, but not with testosterone levels.

Plasma Testosterone Concentrations during Postnatal Development in the Male Common Marmoset

Repeated measurements of plasma testosterone (T) were made in 56 male marmosets from the day of birth until 300 days of age and in 44 adults (greater than 3 years). The resulting profile of plasma T during postnatal development shows higher levels during infancy (1-90 days) followed by a nadir between 100 and 170 days and then a progressive rise in T during puberty. Although T levels of up to 21 ng/ml were measured in infant males, mean levels (+/- SEM) were 5.4 +/- 0.6 ng/ml (days 1-10), declining gradually to 1.7 +/- 0.1 ng/ml (days 100-110). No increase in mean T levels between 15 and 100 days was identified, and the onset of puberty was earlier in some males than measured previously in this species.

Gestagens in the management of prostatic carcinoma.

Two different hormonal gestagens, cyproterone acetate and norethisterone, were studied in prostatic carcinoma, for the greatest part in advanced cases. Cyproterone acetate was administered to 80, norethisterone to 38 unselected patients. The period of study extended over 2 years or more. The mechanism of action of gestagens and the role of the hormone receptors are discussed. The significance of serial measurements of plasma testosterone by providing a monitor of hormonal therapy is emphasized. The relevant literature is reviewed. The value of gestagens as an alternative to the traditional hormone therapy of prostatic carcinoma is pointed out.

A novel pseudohomogeneous radioimmunoassay for the measurement of plasma testosterone

A description is given of a novel liquid phase immunoassay for the measurement of testosterone in peripheral venous plasma from men and women. The procedure involves: (i) competitive binding of the analyte and tritiated antigen to specific antibodies; (ii) enzymatic conjugation of the free ligand with glucuronic acid; and (iii) separation of the antibody-bound and free ligand by partition of the reactants into an organic and aqueous phase. The technique has been called ligand differentiation immunoassay (LIDIA). The mean sensitivity was 5 pg/tube (equivalent to 0.35 nmol/l female plasma; 0.87 nmol/l male plasma). The mean reagent blank (±SD) was 0.24 (0.12) nmol/l female plasma; 0.61 (0.30) nmol/l male plasma. A precision profile gave values < 5.0%; the within batch variation was <8.3% and the between batch variation over three months was 12.3%. An accuracy profile between the second and penultimate points on the calibration curve gave values between 77 and 103%. The correlation coefficient ‘ r’ between LIDIA and a heterogeneous radioimmunoassay was 0.92 when applied to plasma from men and 0.95 to samples from women.

Identification and measurement of testosterone in plasma and follicular fluid of the mare, using gas chromatography-mass spectrometry associated with isotope dilution.

Testosterone has been identified by mass spectrometry in blood and follicular fluid aspirated from mature Graafian follicles of mares. Quantitative measurements made by gas chromatography-mass spectrometry have validated the determination of plasma testosterone made by radioimmunoassay. However, because of high levels of epitestosterone (17 alpha-hydroxyandrost-4-en-3-one) in the follicular fluid, radioimmunoassay overestimates the true concentrations of testosterone. The occurrence of testosterone in mare follicular fluid at a concentration which is two orders of magnitude higher than that in peripheral plasma suggests that the follicle may contribute to the production of circulating testosterone. A biosynthetic pathway for oestradiol-17 beta which involves testosterone is therefore likely to occur in the mare ovary as in many other mammalian species.