Plasma Androgen Concentrations Research Articles

Reciprocal relationships between pulsatile androgen secretion and the expression of mating behavior in adult male ferrets

The pulsatile secretion of androgen was similar over a 12-hr period in breeding male ferrets implanted with jugular catheters which either achieved an intromission with an estrous female or received no socio-sexual contact. This negative result contrasts with the previous demonstration ( Carroll, Erskine, and Baum, 1987, Endocrinology 121, 1349–1359) of a significant, delayed rise in mean plasma androgen concentrations in breeding male ferrets 5–12 hr after mating. Males used in that previous study had lower initial mean plasma levels of androgen and smaller testis diameters than the present males. We therefore asked whether differences in circulating androgen levels, characteristic of males in different phases of the seasonal breeding cycle, might affect the expression of mating behavior. Castrated males given 0, 0.2, 2.0, or 5.0 mg/kg of testosterone propionate (TP) showed dose-related increases in the expression of different components of sexual behavior, including neck gripping, mounting, and intromitting. Surprisingly, intromissive performance was significantly better in intact breeding males than in castrates given even the highest dosage of TP. These results suggest that ferrets' mating performance may vary with seasonal variations in androgen availability, and that the ability of males to exhibit a postcoital increase in the testicular secretion of androgen may be limited to the beginning or end of the breeding season, when circulating levels of androgen are relatively low. Mating-induced increments in androgen secretion at these times may enhance subsequent reproductive success by facilitating males' intromissive capacity, which is required for the induction of ovulation and optimal sperm transport in female partners.

Sex steroid profile and plasma vitellogenin during the annual reproductive cycle of the crested newt ( Triturus carnifex laur.)

The annual reproductive cycle of the crested newt, Triturus carnifex, has been studied in the field. Temperatures, rainfall, humidity, and photoperiod were recorded throughout the year. Adult male and female newts were sampled monthly; snout vent lengths, crest heights of males, and body ovarian, oviducal, testicular, and abdominal gland weights were recorded. Plasma samples were assayed for androgen, estradiol-17β, and progesterone by radioimmunoassay and for vitellogenin by enzyme-linked immunosorbent assay. Air, deep water, water surface, and soil temperatures were low from October to March, but increased in April and May without consistent summer variations. Ovarian and oviducal weights increased in October to reach maximum values between January and March (reproductive period). Crest height and abdominal gland weight in males mirrored the ovarian and oviducal pattern, while testicular weights were maximal in October and November. In females, plasma androgens were high during the reproductive period, and plasma estradiol peaked sharply in March, while plasma progesterone changed little. In the males plasma androgen and estradiol concentrations were similar to those of females, while plasma progesterone was significantly correlated with the cycle in testicular weight. In both sexes androgens showed a significantly negative correlation with air and water surface temperature. Plasma vitellogenin peaked in March but it did not correlate with either ovarian weight or plasma estradiol concentrations. These data support and confirm those previously reported for newts under laboratory conditions. The negative correlation between androgens and temperature suggests that this hormone may trigger the reproductive process. Moreover the correlations between plasma progesterone and testicular weight may indicate that this hormone is involved in male newts reproduction. The data for plasma vitellogenin do not concur with those previously described in other amphibians; this however is the first description of plasma vitellogenin in the crested newt and further studies are required to elucidate mechanisms of vitellogenin synthesis in T. carnifex.

Observations on activity, display behavior, coloration and androgen levels in the keeled earless lizard, Holbrookia propinqua

AbstractWe observed the distance moved, number of movements, and frequency of displays in ten minute intervals for two male color morphs, coral and yellow, and for brightly colored females, of Holbrookia propinqua. We also measured body sizes and, for males, plasma androgen concentrations. Distance moved, number of movements, and number of social displays were positively correlated in males. Females exhibited similar correlations, but the relationship between distance moved and number of displays was not significant. Males moved more often and greater distances than females. Females performed displays as frequently as did males, perhaps because we selected large, dominant females for observation. Distance moved, number of movements, and number of displays increased with body size in males. That these relationships did not hold in females may indicate a sex difference or reflect the small sample size and body size range of females. Plasma androgen concentrations increased with male body size, suggesting a possible androgenic mechanism of sexual selection for large size. Androgen level did not affect display frequency or distance moved. Distance moved increased with plasma androgen concentration, but when effects of body size were held constant, this relationship vanished. Coral and yellow males did not differ in androgen concentration, size, or in the observed behaviors.

Plasma androgen concentrations in initial samples from spotted hyaenas immobilized with Zoletil (CI-744) reflect hormonal status estimated by GnRH challenge and immobilization stress response

The use of single samples to assess the androgen status of animals can be problematic owing to extensive short-term fluctuations in the concentrations of these hormones. Thus, this study evaluated a number of estimates for both testosterone and androstenedione status in the spotted hyaena (Crocuta crocuta), namely, initial samples, the immobilization stress response and the response to exogenous GnRH administration, for their mutual consistency. This study found that in animals immobilized with Zoletil and maintained on halothane, all three estimates show a good consistency. Moreover, the large variance in androgen status reported here within the sexes explains earlier contradictory results, and implies that the debate concerning the sex-specific differences in plasma androgens is confounded by other variables such as the reproductive and social status of the individuals included in the analysis.

Androgenic deficiency in male rats treated with perfluorodecanoic acid

Effects of perfluorodecanoic acid (PFDA, 20–80 mg/kg, ip) on the androgenic status of sexually mature male rats were investigated 7 days after treatment. PFDA decreased plasma androgen concentrations in a dose-dependent fashion with an ED50 of approximately 30 mg/kg. The highest dose of PFDA decreased plasma testosterone and 5α-dihydrotestosterone concentrations to 12 and 18%, respectively, of ad libitum-fed control (ALC) values. Secondary to the decreased plasma androgen concentrations were dose-related decreases in the weights and epithelial heights of accessory sex organs. Results from pair-fed control (PFC) rats show that hypophagia in PFDA-treated rats was not a major cause of the low plasma androgen concentrations. When rats were castrated and implanted with testosterone-containing capsules, PFDA-treated and ALC rats had similar plasma testosterone concentrations and secondary sex organ weights. Therefore, the androgenic deficiency in intact PFDA-treated rats does not result from increased plasma clearance of androgens. Rather, PFDA must cause the androgenic deficiency by decreasing the secretion of testosterone from the testis. The decrease in testosterone secretion does not appear to result from a decrease in plasma luteinizing hormone (LH) concentrations, because plasma LH concentrations were not significantly altered by PFDA treatment. This finding suggests that PFDA treatment decreases testicular responsiveness to LH stimulation. The observation that PFDA treatment reduced the secretion of testosterone by testes stimulated in vitro with the LH analog human chorionic gonadotropin demonstrates that this is the case. In addition, since plasma LH concentrations did not increase in response to the low plasma androgen concentrations in PFDA-treated rats, we suggest that PFDA disrupts the normal feedback relationship which exists between plasma androgen and LH concentrations.

2,3,7,8-Tetrachlorodibenzo- p-dioxin increases the potency of androgens and estrogens as feedback inhibitors of luteinizing hormone secretion in male rats

2,3,7,8-Tetrachlorodibenzo- p-dioxin (TCDD) decreases plasma androgen concentrations in male rats, without increasing plasma luteinizing hormone (LH) concentrations. If plasma LH concentrations had increased appropriately, plasma androgen concentrations in these animals would have returned to normal. The mechanism by which TCDD prevents the compensatory increase in plasma LH concentrations was therefore investigated. TCDD was found to have no effect on the plasma disappearance of iv administered LH. Therefore, the failure of plasma LH concentrations to rise was not due to increased clearance of LH from the circulation, but rather to an effect of TCDD on LH synthesis and/or secretion by the pituitary. In the absence of gonadal steroids (i.e., in castrated rats) TCDD did not prevent the compensatory increase in plasma LH concentrations from occurring. This was shown by 20-fold increases in plasma LH concentrations in both control and TCDD-treated rats 1 week after castration. Thus, (1) the presence of gonadal steroids is required for TCDD to prevent the compensatory increase in plasma LH concentrations, and (2) TCDD does not impair LH secretion by acting, itself, as an androgen or estrogen. TCDD treatment also did not affect pituitary LH content in castrated, testosterone-implanted rats. The above findings demonstrate that TCDD does not decrease the maximum rate at which the pituitary can synthesize and secrete LH. Rather, TCDD alters the feedback regulation of LH secretion when gonadal steroids are present. To determine if TCDD affects the potency of testosterone and its metabolites 5α-dihydrotestosterone and 17β-estradiol as feedback inhibitors of LH secretion, rats were dosed with TCDD, castrated, and implanted with sustained-release capsules containing graded amounts of each steroid. Seven days later, the potencies of all three hormones as feedback inhibitors of LH secretion were increased by TCDD, with little effect on their plasma concentrations. The TCDD dose dependence for the increased effectiveness of testosterone as a feedback inhibitor of LH secretion (ED50 10 μg/kg) was similar to that reported for the imbalance between plasma LH and androgen concentrations (ED50 15 μg/kg). Also, time courses for both responses were similar; each was detected within 1 day of TCDD dosing and each was fully developed after 7 days. We conclude that the mechanism by which TCDD prevents the compensatory increase in plasma LH concentrations in male rats is by increasing the potencies of androgens (and estrogens) as feedback inhibitors of LH secretion.

Neuroendocrine, behavioral, and morphological changes associated with the termination of the reproductive period in a natural population of male rough-skinned newts ( Taricha granulosa)

Male rough-skinned newts ( Taricha granulosa) were collected from the same natural population every second week from early April to mid-June. They were either field-tested for their sexual responsiveness or used to measure the plasma concentrations of androgens and corticosterone, the brain concentrations of immunoreactive (ir) gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT), and morphological parameters. During the experimental period, the percentage of sexually responsive males gradually declined from 100 to 4%, concurrent with a decrease of plasma concentrations of androgens, but not corticosterone. Concentrations of irGnRH in two brain regions (medial septum; ventral telencephalon containing the nervus terminalis) did not change significantly during this time. In the infundibulum, irGnRH concentrations increased from the end of May to mid-June, which coincided with an increase in plasma androgen concentrations, a marked increase in testis weights, and a decrease of the proportion of males with spermatozoa in their vas deferens. During this period, no changes in irAVT concentrations in four brain regions (infundibulum; pars distalis of the pituitary; interpeduncular nucleus; cerebrospinal fluid) were detected, but significant changes were observed for irAVT in the dorsal preoptic area that were not correlated with the seasonal changes in behavior. Also, during this period, there were decreases in mean body weight and tail height, and in the proportion of males with smooth skin and dark nuptial pads. These results are discussed in view of our current knowledge of the endocrine mechanisms that regulate sexual behaviors and secondary sex characteristics in male amphibians.

The Influence of Age, Sex, and Rank on Yawning Behavior in Two Species of Macaques (Macaca fascicularis and M. fuscata)

AbstractYawning behavior was studied in two species of macaques: the long‐tailed macaque (Macaca fascicularis) and the Japanese macaque (M. fuscata). Japanese macaques yawned much more than long‐tailed macaques. Age, sex, and dominance rank exerted different effects on yawning in the two species. In the long‐tailed macaques, sex differences in frequency of yawning emerged only after sexual maturity; yawning rates increased significantly in both males and females as they reached sexual maturity; and, among males, dominance rank was positively correlated with frequency of yawning. Differently, in the Japanese macaques, males, both mature and immature, yawned more than same‐aged females; sexual maturity was associated with an increase in yawning in males only; and male rank did not correlate with the frequency of yawning. Regardless of interspecific differences, the overall results supported only in part the finding that, in Old World monkeys, yawning is largely influenced by plasma concentrations of androgens. There was evidence that social factors were also important in influencing the age‐sex class distribution of yawning.

Effects of intratesticular injections of estradiol and gonadotropin-releasing hormone (GnRHA, HOE 766) on plasma androgen levels in intact and hypophysectomized Torpedo marmorata and Torpedo ocellata

The effect of a gonadotropin-releasing hormone analog (GnRHA, HOE766) was studied in hypophysectomized elasmobranch fish Torpedo marmorata and T. ocellata. In addition, estradiol (E 2) effects were studied in intact and hypophysectomized (HPX) animals. Plasma androgen concentrations were measured 2 or 6 hr after GnRHA (100 ng or 10 μg) or 6 hr after E 2 (10 −9 or 10 −6 M) intratesticular injections. Both GnRHA and E 2 induced the increase of plasma androgen levels in HPX fish. E 2 also enhanced androgen levels in intact animals. It is concluded that GnRH-like substances and E 2 may modulate testicular activity in elasmobranch fish.

Increase In H-Y Antigen-Positive Lymphocytes in Hirsute Women: Effects of Cyproterone Acetate and Estradiol Treatment*

To investigate a possible relationship between lymphocyte H-Y antigen expression and plasma androgen concentrations in hirsute women, 27 hirsute women were studied. A significant increase in the percentage of H-Y-positive lymphocytes was found in both hirsute women with idiopathic hirsutism [13.4 +/- 2.9% (+/- SD); n = 15] and hirsute women with the polycystic ovary syndrome (13.0 +/- 2.8%; n = 12) compared to that in normal women (10.0 +/- 1.9%; n = 30; P less than 0.0005). Plasma testosterone and androstenedione concentrations, % H-Y+ lymphocytes, and hirsutism scores diminished during oral cyproterone acetate (50 mg/day) and percutaneous estradiol (3 mg/day) treatment. Significant correlations between % H-Y+ lymphocytes and hirsutism scores (P less than 0.001), % H-Y+ lymphocytes and plasma T concentrations (P less than 0.01) were found. We conclude that 1) women can produce H-Y antigen in the same way as men; 2) hirsutism is associated with an increase in H-Y antigen; and 3) the antiandrogen cyproterone acetate reduces H-Y antigen expression on lymphocytes.

Environmental and hormonal factors in seasonal breeding in free-living male Indian rose-ringed parakeets ( Psittacula krameri)

Seasonal changes in testicular activity, plasma luteinizing hormone (LH), estradiol (E 2), testosterone (T), and 5 α-dihydrotestosterone (5 α-DHT) were related to pair bond formation, nest building, nest defense, and parental behavior in freeliving Indian rose-ringed parakeets ( Psittacula krameri) in northwest India. Spermatozoa production occurred between January and March when daylengths were short (10–12 hr) and ambient temperature was seasonally low (8–20 °C). At other times of the year the testes were regressed. Plasma LH levels increased during the prebreeding period (September–December) when the birds were forming pairs and selecting or defending nest sites. Plasma LH levels increased further between January and March and decreased to seasonal low values during the post breeding period between April and June when the birds were caring for young. Concentrations of plasma androgens and estrogens were similar during the prebreeding and postbreeding phases of the breeding cycle. During the breeding period, the ratios between plasma 5 α-DHT and testosterone and between plasma estradiol and testosterone increased. It is proposed that the absence of marked seasonal changes in plasma steroid levels is related to nest defense behavior which occurs during the prebreeding, breeding, and postbreeding phases of the breeding cycle. Winter breeding makes it possible for the parakeets to avoid competition with other birds for nesting sites, to avoid fledging young during the monsoon period, and to take advantage of the winter pea crop which provides the female with extra nutrients for egg production.

Plasma steroid concentrations change in response to sexual behavior in Bufo marinus

Steroid hormone concentrations change in response to social or environmental stimuli in many vertebrates. To test this phenomenon in an amphibian, we examined plasma androgen (A) and corticosterone (B) concentrations in male marine toads ( Bufo marinus), a tropical species exhibiting intermale competition, amplectic clasping of females, and bouts of breeding behavior following rains. When males clasped females for 0, 1, 2, or 3 hr, plasma A concentrations were significantly and positively correlated with hours spent in amplexus. In field-sampled males, plasma A concentrations were higher in amplexing males than in single males. Among single males those found closer to breeding ponds had higher A concentrations than those more distant. These data support the hypothesis that sexual stimuli enhance plasma A concentrations in this amphibian. In 3-hr experimental tests and field-sampled males, B concentrations were higher in amplexing than in single males. Unlike some amphibians, short-term elevations of B apparently are not associated with decreased reproductive function. However, as in other amphibians in which high B concentrations are associated with stress-induced inhibition of reproduction, after 48–72 hr in captivity male toads showed high B concentrations and low plasma androgen concentrations. The bursts of sexual activities exhibited by B. Marinus following heavy rains were associated with no changes in A concentration and with increased B concentration.

Nicotine and cotinine effects on 3 alpha hydroxysteroid dehydrogenase in canine prostate

We have recently observed that cigarette smoking affects plasma androgen concentrations. The effects of nicotine and cotinine, two products of cigarette smoking, on testosterone metabolism were determined. The activity of delta 4 steroid 5 alpha-reductase, which converts testosterone to 5 alpha-dihydrotestosterone (DHT) was measured in isolated dog prostate nuclei using testosterone (0-200 nM) as substrate and NADPH as cofactor. Activity of 3 alpha-hydroxysteroid dehydrogenase (HSD), which converts DHT to 3 alpha-androstanediol (3 alpha-diol) and is a reversible enzyme, was measured in isolated dog prostate microsomes with DHT (0-20 microM) as substrate and NADPH as cofactor. When microsomal fractions were incubated for 1 hour with and without nicotine (0-50 microM) and cotinine (0-100 microM), enzyme activity of HSD was significantly suppressed (p less than 0.001). The Vmax was not affected significantly (p greater than 0.60) and Km increased with increasing concentrations of nicotine and cotinine (p less than 0.05). Both nicotine and cotinine are competitive inhibitors of HSD in dog prostate microsomes with Ki's of 61 and 89 microM, respectively. The apparent 5 alpha-reductase activity was unaffected by nicotine and cotinine. The inhibitors produced a marked effect on activity of HSD when used in concentrations achieved in humans who smoke cigarettes. The results suggest that nicotine and cotinine are competitive inhibitors of the HSD, an important enzyme involved in the metabolism of DHT and produce an accumulation of DHT. These products of cigarette smoking could alter androgen action in tissue such as skin and prostate.

Seasonal changes in testicular contents and plasma concentrations of androgens in the desert gerbil (Gerbillus gerbillus).

Gerbils were caught in the Béni-Abbès area (Algeria). Testicular endocrine activity was highest in spring (testicular wt 298 +/- 10 mg; seminal vesicle wt 603 +/- 62 mg; testicular testosterone and androstenedione content 9.2 +/- 1.7 and 0.5 +/- 0.1 ng/testis; plasma testosterone 832 +/- 200 pg/ml). Values decreased in summer, were lowest in late summer and in autumn (84 +/- 17 mg; 40 +/- 14 mg; 0.20 +/- 0.06 and 0.02 +/- 0.01 ng/testis; 228 +/- 54 pg/ml, respectively) and increased again in winter (December-January). The onset of testicular endocrine activity was concomitant with the lowest temperatures and the shortest photoperiod; it increased when temperatures and daylength were increasing and began to decline when temperatures and photoperiod were still maximal. These seasonal changes in the endocrine activity of the testis of the gerbil differ from those of the sand rat inhabiting the same area.

Effect of photoperiod on the diurnal rhythm of plasma testosterone, dihydrotestosterone and androstenedione in mature male chickens

1. 1. The effects of different photoperiods on the concentrations of plasma androgens, testes weight and on the diurnal rhythm of plasma testosterone (T), dihydrotestosterone (DHT) and androstenedione (A) in mature, single comb White Leghorn male chickens were studied. 2. 2. Birds were exposed to either 14 hr of light (lights on at 0600–2000 hr) or to 24 hr of light per day. 3. 3. Blood samples were collected from birds in both groups at 3-hr intervals and plasma levels of T, DHT and A were measured using radioimmunoassays. Following blood collection, birds were weighed, killed and testis weights were recorded. 4. 4. Under 14 hr of light, there was a diurnal rhythm of T and DHT with hormone concentrations peaking at the end of the dark period. There was no obvious rhythm for A. Exposure to 24 hr of light abolished the diurnal rhythm found under 14 hr of light. 5. 5. There was an increase not only in testis weights but also in body weight and hormone concentrations under 24 hr of light. 6. 6. It was concluded that photoperiod plays an important role in controlling the concentration and rhythm of androgens in mature male chickens.

PLASMA CONCENTRATIONS OF TESTOSTERONE, ANDROSTENEDIONE, DIHYDROTESTOSTERONE, 5α-ANDROSTANE-3α, 17β-DIOL, 5α-ANDROSTANE-3β, 17β-DIOL, AND ANDROSTERONE IN BULL CALVES: RESPONSE TO hCG

Plasma androgen concentrations were measured in bull calves sampled weekly from birth to 30 wk of age and in calves sampled every 30 min for 8 h at 6, 14, 22 and 30 wk of age, before and after administration of hCG (5 IU kg−1, i.v.). Mean plasma concentrations of testosterone rose to 20 wk of age and then fell, but were variable. Mean plasma concentrations of androstenedione rose to 14 wk of age and then declined. Mean plasma concentrations of 5α-androstane-3α, 17β-diol and 5α-androstane-3β,17β-diol did not change with age, but dihydrotestosterone and androsterone were elevated at 14 and 22 wk of age, respectively. The overall means were 0.9 ± 0.08 ng mL−1 for testosterone, and 0.6 ± 0.07 ng mL−1 for dihydrotestosterone. Other androgens were present at concentrations of < 0.3 ng mL−1. However, the total concentration of the 5α-reduced androgens exceeded that of testosterone in bull calves from birth to 28 wk of age. Changes in mean androgen concentration with age and in response to hCG appeared to be reflected primarily in changes in the amplitude of pulses in plasma androgen concentration. Significant increases in pulse amplitude for testosterone and androstenedione occurred in response to hCG in 14-, 22- and 30-wk-old bull calves and for 5α-androstane-3α,17β-diol in 30-wk-old calves. The developing bull calf differs from laboratory rodents in that there is no period of time during reproductive development when individual 5α-reduced androgens circulate in concentrations greater than testosterone. Key words: Bull calf, sexual maturation, androgens

Effects of passive immunization against oestradiol-17 beta on some endocrine values of the male lamb.

Passive immunization of male lambs against oestradiol-17 beta from 2 to 16 weeks of age significantly elevated androgen concentrations in plasma and depressed the median eminence content of dopamine. Removal of endogenous oestrogens had no significant effects on plasma FSH, LH or prolactin concentrations or on testicular growth and hypothalamic content of GnRH. These results suggest that endogenous oestrogens may indirectly suppress testicular androgen secretion by exerting a stimulatory influence on hypothalamic dopaminergic neurones, which in turn may inhibit GnRH secretion by the median eminence.

Seasonal variations of LH, prolactin, androstenedione, testosterone and testicular FSH binding in the male blue fox (Alopex lagopus).

The seasonal changes in testicular weight in the blue fox were associated with considerable variations in plasma concentrations of LH, prolactin, androstenedione and testosterone and in FSH-binding capacity of the testis. An increase in LH secretion and a 5-fold increase in FSH-binding capacity were observed during December and January, as testis weight increased rapidly. LH levels fell during March when testicular weight was maximal. Plasma androgen concentrations reached their peak values in the second half of March (androstenedione: 0.9 +/- 0.1 ng/ml: testosterone: 3.6 +/- 0.6 ng/ml). A small temporary increase in LH was seen in May and June after the breeding season as testicular weight declined rapidly before levels returned to the basal state (0.5-7 ng/ml) that lasted until December. There were clear seasonal variations in the androgenic response of the testis to LH challenge. Plasma prolactin concentrations (2-3 ng/ml) were basal from August until the end of March when levels rose steadily to reach peak values (up to 13 ng/ml) in May and June just before maximum daylength and temperature. The circannual variations in plasma prolactin after castration were indistinguishable from those in intact animals, but LH concentrations were higher than normal for at least 1 year after castration.

Androgènes et 17β-estradiol plasmatiques de l'Urodèle pyrénéen Euproctus asper durant la période de reproduction

The concentration of plasma androgens (A) and 17β-estradiol (E) in both males and females of Euproctus asper from June to November was determined by radioimmunoassay. The levels of androgens in males varied from a maximum of 980 ng/100 ml in June to a minimum of 172.5 ng/100 ml in July. A small increase was observed in September and a decrease in October–November. The concentration of androgens in females was comparable to that of males at the end of the cycle: 320 ng/100 ml; the values were high (470 ng/100 ml) in July and decreased to a minimum (80 ng) in September. The values of 17β-estradiol in females showed a different pattern during the reproductive cycle. The concentration was at a maximum in September, at the same time of the low concentration of androgens. In the males, the concentration of estradiol was very low (less than 17 ng/100 ml). Measurements of adenohypophysial volume and gonadotrophic cell diameter are discussed with respect to levels of circulating steroids.

Androgenic deficiency in male rats treated with 2,3,7,8-tetrachlorodibenzo- p-dioxin

Effects of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) on the male reproductive system were investigated. Sexually mature (290 g) Sprague-Dawley rats were given single oral doses of TCDD sufficient to cause varying degrees of hypophagia and impaired body weight gain. The largest doses decreased plasma testosterone and dihydrotestosterone concentrations by 90 and 75%, respectively, from ad libitum-fed control values, while decreasing seminal vesicle and ventral prostate weights by 68 and 48%. On Day 7, the approximate ED50 for these responses was 15 μg TCDD/kg, a nonlethal dose. Reductions in caput epididymis and testis weights were also observed. The androgenic deficiency was seen as early as 2 days after dosing and persisted for at least 12 days. Based on data from pair-fed control rats, only about half the decreases in accessory sex organ weights and in plasma androgen concentrations could be accounted for by TCDD-induced hypophagia or body weight loss. These signs of androgenic deficiency were not the result of stress (based in part on plasma corticosterone assays), nor could they be accounted for by the known effects of TCDD on steroid metabolism. While the TCDD-induced depression in plasma testosterone concentrations appears to be the primary event observed, the mechanism by which testosterone concentrations were decreased remains unknown. The androgenic deficiency may account for the male reproductive pathology and dysfunction in animals treated with overtly toxic doses of TCDD.