In vitro stimulationof 5 alpha-dihydrotestosterone and testosterone secretion from bullfrog testis by nonmammalian and mammalian gonadotropins.

In vitro androgen secretion by bullfrog (Rana catesbeiana) testis was studied using mammalian and nonmammalian gonadotropins, including those from the bullfrog. LH from bullfrog, salamander, turtle, alligator, and sheep increased secretion of 5α-dihydrotestosterone (DHT) and testosterone (T) into incubation medium; Rana and ovine FSH preparations were inactive except at relatively high concentrations. Rana FSH, ovine PRL, and bovine GH did not influence LH-induced steroid secretion. Rana LH was about 3–10 times more potent than other nonmammalian LH preparations, and 30–50 times more potent than NIH-ovine LH. Dose-response characteristics were dependent upon incubation time and temperature. More DHT than T was present in incubation medium at all times and temperatures studied, and during all seasons. Contents of DHT and T in incubation medium were highly correlated, and the ratio $\text{DHT}\text{T}$ increased with time and with dose of LH. These data support in vivo observations and indicate that DHT is a major testicular androgen in the bullfrog, stimulated specifically by LH. Control of testicular androgen secretion by LH may represent the ancestral tetrapod condition.     

The role of androgen in the development of sexual differences in pituitary responsiveness to gonadotropin releasing hormone (GnRH) agonist in the bullfrog, Rana catesbeiana

Sexual differences in pituitary responsiveness to acute injection of gonadotropin-releasing hormone (GnRH) agonist, as measured by increments in plasma FSH and LH, were examined throughout development in the bullfrog, Rana catesbeiana. Untreated tadpoles, in various stages of metamorphosis, were unresponsive to GnRH agonist. Postmetamorphic males showed a progressive increase in the magnitude of pituitary response with age, whereas females remained relatively insensitive until after sexual maturation; males were always more responsive than females. Chronic (1–2.5 week) Silastic implants containing 5α-dihydrotestosterone (DHT) significantly augmented the pituitary response (for both gonadotropins) in intact postmetamorphic females at all ages; a similar, though less pronounced, action of testosterone in subadult females may have been due to its conversion to DHT. (Silastic implants of comparable size always produced higher circulating levels of DHT in females than in males as was observed in previous studies with gonadectomized frogs.) DHT enhanced the responsiveness of intact tadpoles (sexes undetermined); only the treated tadpoles responded to the GnRH agonist. Supplemental DHT did not enhance pituitary response in intact males; in fact, it attentuated the response in FSH. GnRH responsiveness paralleled changes in pituitary gonadotropin content; pituitary content of FSH and LH was higher in males than females; it showed a marked increase with age from tadpole to adult; and it was increased by DHT treatment. The potentiating effect of DHT on GnRH responsiveness and the significantly higher levels of DHT observed in males of all ages suggest that the nonaromatizable androgen DHT may be responsible for the early establishment and maintenance of sexual dimorphism in pituitary GnRH responsiveness in the bullfrog.     

Immunochemical studies on the pituitary gonadotropins (FSH and LH) from the bullfrog, Rana catesbeiana.

Separate antisera against bullfrog (Rana catesbeiana) FSH (FSH $\text{a}\text{s}$) and LH (LH $\text{a}\text{s}$) were generated in rabbits with partially purified gonadotropins. Ouchterlony agar diffusion techniques indicated that each antiserum was relatively specific for the homologous antigen, and there was no detectable precipitin reaction with pituitary gonadotropins from a variety of other tetrapod species, including several mammals, birds, and reptiles. Radioligand studies were performed with iodinated preparations of highly purified Rana FSH and LH. Binding studies with these labeled hormones indicated some cross-reactivity with both antisera; i.e., each antiserum bound the heterologous label to some extent. However, this cross-reaction was abolished by adsorbing the antisera with the opposite antigen; this adsorption did not affect the binding of the homologous label. Thus, the apparent cross-reactivity is attributed to separate antibodies in each serum. Electrophoretic analyses on polyacrylamide disc gels at basic pH further demonstrated the distinctiveness of each gonadotropin and its antiserum.Radioimmunoassay with adsorbed and unadsorbed sera confirmed this specificity of each serum for its homologous antigen and showed that this technique could be used as a sensitive method for quantifying gonadotropins. The degree of cross-reaction between gonadotropins was estimated at about 1% or less. Comparison with crude pituitary extract from bullfrog showed that both gonadotropins were considerably purified. Little or no cross-reaction was seen with bullfrog growth hormone or with FSH, LH, or TSH from other nonamphibian species with either antiserum.Biological studies demonstrated that the LH $\text{a}\text{s}$ neutralized the activity of Rana LH in a specific bioassay (in vitro ovulation in Xenopus), whereas the FSH $\text{a}\text{s}$ had no effect on the LH. In tests for FSH activity in Anolis, the activity of Rana FSH was blocked by both antisera, but the FSH $\text{a}\text{s}$ did not affect the biological activity of Rana LH. Thus, the activity of both bullfrog hormones in Anolis is judged to be intrinsic to the molecules. These results demonstrate that the antisera cross-react with the biologically active gonadotropin molecules.     

Endocrine status of the testicular feminized male (TFM) rat

The plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T), androstenedione (A), dihydrotestosterone (DHT), corticosterone and corticosterone binding globulin (CBG) were determined in 160- and 350-day testicular feminized male (tfm) and normal littermate (NL) rats. In the younger group the concentrations of T, A, DHT and 5α-androstan-3α,17β-diol (Adiol) were also determined in testis tissue.Tfm rats showed a greatly elevated plasma LH indicating lack of androgen feedback. Plasma FSH, however, was normal in both age groups, suggesting that inhibin production from tfm testes was relatively unaffected.Intratesticular concentrations of A were greatly elevated in the tfm animals at both ages whilst the testicular levels of T were highly reduced when compared to NL rats. This indicates a gonadal deficiency of the 17β-hydroxy steroid dehydrogenase (17β-HSD). Furthermore, the relatively low T: DHT ratio and high concentrations of Adiol in the tfm testes confirmed previous reports that the high 5α-reductase typical for the immature rat testis is maintained into adulthood in rats with the tfm condition. A considerable degree of peripheral conversion (A → T) probably helps to maintain normal or supranormal plasma levels of T. Gonadectomy rendered all plasma androgens undetectable, indicating that the adrenal contribution was negligible.Increasing age (350 days) was associated with a marked increase in circulating androgens in tfm rats. This is probably the reason for the observed significant reduction in circulating LH in this age group when compared to the 160-day animals. The aging tfm rat is predisposed to testicular tumors which, on the basis of histology, specific [¹²⁵I]hLH binding and in vitro responsiveness to hCG, appear to be of Leydig cell origin.Microflow fluorometry (MFF) of tfm testis cell suspensions revealed the presence of haploid cells, suggesting that meiosis proceeds to a limited extent.Plasma corticosterone levels in the tfm rat were normal although plasma CBG levels were highly significantly elevated at both ages when compared to the levels in NL rats. We suggest that the adrenal hyperplasia observed in tfm rats is secondary to reduced corticosterone production and diminished free corticosterone in the circulation.     

In vitro stimulation of cyclic-AMP production in Rana catesbeiana ovaries by homologous gonadotropins.

In vitro effects of purified Rana LH and FSH on cyclic AMP accumulation were examined in ovaries of immature and mature bullfrog, Rana catesbeiana, at different states of the sexual cycle. Rana FSH was active with clear dose dependency only in immature ovaries but was less potent than Rana LH. Mature females did not respond to Rana FSH. Rana LH always increased the cAMP accumulation in mature females but the response was lowest with prespawning and postspawning females.     

5α-Reduced androgens and testicular function in the immature rat: Effects of 5α-androstan-1 7β-ol-3one (DHT) propionate and 5α-androstan-3α,17β-diol

Increasing doses of dihydrotestosterone propionate (DHTP) and 5α-androstan-3α,17β-diol (ADIOL) were given to 21-day-old rats for 10 days. Various parameters of reproductive function were assessed including testis weight, epididymal androgen binding protein (ABP) (Sertoli cell activity), plasma LH and FSH and the testicular levels of androstenedione (A), testosterone (T), dihydrotestosterone (DHT) and 5α-androstan-3α,17β-diol (ADIOL).In the control population, of the androgens measured, only the testicular concentration of DHT was highly correlated with epididymal ABP levels.After treatment with varying doses of DHTP, testis weight and epididymal ABP exhibited a biphasic response with maximum suppression occurring at the 100–250gmg/day dose level. Recovery of both of these parameters to control levels with 5,000–10,000 μg/day DHTP was associated with an increase in testicular DHT to normal or Supranormal levels. Plasma LH and FSH (pituitary function) and testicular A and T (Leydig cell function) were suppressed in a dose-dependent manner at doses including and higher than 50 μg DHTP/day. The testicular content of ADIOL was returned to control levels with 500 μg DHTP/day, when Sertoli cell function and spermatogenesis were still markedly suppressed. At DHTP doseshigher than 500 Jug/day, ADIOL was the predominant intratesticular androgen.Treatment with ADIOL also evoked a biphasic response from testis weight and epididymal ABP comparable to that observed with DHTP and testosterone propionate (TP) (Weddington et al., 1976). Doses from 20–500 μg/day resulted in a gradual, dose-dependent suppression of all the parameters studied. Administration of 1000 μg/day ADIOL returned the testicular ADIOL content to the control level. At the same dose, epididymal ABP, testis weight and the other intratesticular androgens were still maximally suppressed. Doses of 5000 and 10,000 μg/day ADIOL elevated the endogenous ADIOL in the testis to 4 and 25 times the normal level respectively. These higher doses also caused a dose-dependent increase in intratesticular DHT which was paralleled by an increase in epididymal ABP and testis weight. Even at the highest dose of ADIOL injected, DHT, epididymal ABP and testis weight did not completely return to normal levels.It is concluded that the previously observed stimulation of Sertoli cell function and spermatogenesis by androgens, in the rat, is mediated through DHT. Furthermore, the findings indicate that the apparent direct stimulation of Sertoli cell function by ADIOL is mediated through its conversion to DHT. The sensitivity of the testis to various androgens cannot be clearly interpreted on the basis of the administered doses, but only in relation to the levels of endogenous androgens in the testis achieved by the hormone treatment. In this regard, the study emphasizes the need for careful interpretation of data involving androgen treatment, especially ADIOL, and suggests that the relative potency of androgens in a bioassay system does not necessarily provide clear information about their relative potency at the target cell level.     

Specific gonadotrophin binding sites in the bullfrog testis

We demonstrated the presence of specific binding sites for bullfrog luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in a testicular crude plasma membrane fraction of the bullfrog, Rana catesbeiana. The equilibrium analysis of the binding showed that a straight line was fitted to the Scatchard plot of LH and a curvilinear line to that of FSH, suggesting the presence of single-type binding sites for LH and the presence of multiple-type binding sites or negative cooperactivity of the binding for FSH. Competition experiments showed that bullfrog LH could replace the specific binding of bullfrog FSH and vice versa. Binding affinity of bullfrog LH to radioiodinated bullfrog FSH binding sites was as high as that of intact bullfrog FSH to the same sites. In contrast, binding properties of bullfrog FSH to radioiodinated bullfrog LH binding sites were not simple: the competition curve obtained with FSH against the binding of bullfrog LH had an extremely low slope value and was not parallel to that obtained with LH. These results suggest that differentiation of LH and FSH receptors is not complete in this species, although it has been reported that these hormones have separate actions on the testis. Competition experiments further showed that bullfrog testicular LH and FSH receptors possessed higher affinities for gonadotrophins of homologous or closely related animal species compared with phylogenically distant groups. Species specificity of the hormone-receptor interaction may cause species specificity of the gonadotrophin action.     

Effect of bullfrog LH and FSH on newt testes under different temperatures

Environmental temperature plays important roles for amphibian gonadal function. In this study, we examined the responses of testicular tissue of adult male newts (Cynops pyrrhogaster) to amphibian gonadotropins both in vitro and in vivo under different temperatures. When minced testes were incubated in vitro at different temperatures (8-37 degrees C) under an atmosphere of 95% O(2)-5% CO(2) for 3h with bullfrog luteinizing hormone (LH) or follicle-stimulating hormone (FSH), LH stimulated testosterone production more than FSH. The testosterone production increased as the incubation temperature increased. Hypophysectomized newts were injected with bullfrog LH or FSH and maintained at 8 or 18 degrees C. In the 18 degrees C group, the testicular weight of the hypophysectomized control decreased when compared with that of with the intact control. The testicular weight of the LH-treated hypophysectomized group decreased more than that of the hypophysectomized control, indicating that LH induced the evacuation of mature spermatozoa from the testes of LH-treated hypophysectomized newts. In the FSH-treated newts, the testicular weight was greater than that in the hypophysectomized control, and was maintained at a value similar to that of the intact control. In the 8 degrees C group, there was no significant difference in testicular size among the intact control, hypophysectomized control, and FSH-treated newts. LH strongly induced spermiation as it did at 18 degrees C. The plasma testosterone level in the hypophysectomized newts decreased dramatically, but LH was effective in restoring it. Its effect was more potent at 8 degrees C than at 18 degrees C. On the other hand, FSH did not induce a significant increase in the plasma testosterone levels at either temperatures. The results indicate a temperature-dependent difference in responsiveness of the testis both in vitro and in vivo to LH and FSH.     

Origin and regulation of plasma dihydrotestosterone and testosterone in the rough-skinned newt, Taricha granulosa.

The testis of the urodele amphibian Taricha granulosa was studied with regard to localization of androgen production and stimulation of androgen secretion by mammalian LH. Plasma testosterone (T) and 5α-dihydrotestosterone (DHT) increased in proportion to the amount of ovine LH injected; this stimulatory effect of ovine LH was essentially abolished by bilateral castration. In vitro androgen secretion from testicular fragments of the mature zone far exceeded that from fragments of the immature zone. These data indicate that in urodeles plasma T and DHT are produced by cells predominantly localized in the mature zone of the testis, even before spermiation has occurred.     

Effects of gonadectomy and sex steroids on pituitary gonadotrophin release and response to gonadotrophin-releasing hormone (GnRH) agonist in the bullfrog, Rana catesbeiana

Gonadectomy of adult bullfrogs, Rana catesbeiana, elevated plasma levels of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Profiles of plasma gonadotrophins after gonadectomy were similar in the two sexes; however, FSH increased faster in females than males. Both gonadotrophins continued to rise for several months and remained elevated after 1 year, but there was some dissociation between the two hormones; FSH increased sooner (1 week vs 3 weeks), reached higher levels (FSH/LH much greater than 1), and did not show the secondary decline exhibited in LH. Similarly, in subadult males and females, gonadectomy increased plasma FSH by 1 week but LH levels were less affected. Postgonadectomy increases in both gonadotrophins were prevented by chronic (6-week) implantation of capsules containing estradiol-17 beta (E2) or 5 alpha-dihydrotestosterone (DHT), and treatment with DHT and E2 within physiological ranges starting 1 year after gonadectomy also suppressed chronically elevated levels of plasma gonadotrophins. Compared to untreated gonadectomized frogs, the rate of increase in both plasma gonadotrophins. Compared to untreated gonadectomized frogs, the rate of increase in both plasma gonadotrophins was accelerated after removal of DHT at 6 weeks. Acute pituitary responsiveness to a gonadotrophin-releasing hormone (GnRH) agonist was markedly reduced in short-term (3.5-8 weeks) gonadectomized subadult males (but not females) and in long-term (1 year) gonadectomized males and females. Treatment with E2 had no effect on GnRH responsiveness in these frogs, but DHT implants significantly enhanced the response to agonist in both sexes. Thus, the nonaromatizable androgen--DHT--may have both negative feedback effects (at the hypothalamic level) and positive effects at the level of the pituitary, whereas, estrogen exhibited only the former, negative feedback activity. Sex differences in circulating DHT, which are detectable even in juveniles, may account for the sexual dimorphism in pituitary responsiveness to GnRH in the bullfrog.     

Crystalline dihydrotestosterone implants in the lateral septum of male rats. A positive effect on LH and FSH.

Previous investigations in our laboratory have shown that testosterone implanted into the lateral septum in male rats increases LH and FSH secretion. However, it was unclear whether the effect of testosterone was direct via androgen receptor, or indirect via the estrogen receptor after conversion by aromatization to estradiol. To answer this question, we implanted either testosterone or the non-aromatizable androgen 5 alpha-dihydrotestosterone (DHT), into the lateral septum of adult male rats and measured plasma levels of LH and FSH by radioimmunoassay 2 days after implantation. Both testosterone and DHT significantly increased the plasma LH and FSH concentrations. Mean concentration of LH in control animals was 0.21 +/- 0.06 ng/ml, a figure that increased to 0.7 +/- 0.12 and 0.55 +/- 0.1 ng/ml after DHT or testosterone implantation respectively. Mean concentration of FSH in control animals was 1.5 +/- 0.3 ng/ml; this figure increased to 3 +/- 0.3 and 2.9 +/- 0.3 ng/ml after DHT or testosterone implantation. Neither plasma DHT (64.0 +/- 5.6 vs. 52 +/- 5 ng/100ml) nor plasma testosterone levels (4.1 +/- 0.38 vs. 3.3 +/- 0.18 ng/ml) were significantly affected by the implants. We conclude that androgens independently of conversion to estrogen acting in the lateral septum facilitates the release of LH and FSH.     

In vivo regulation of steroidogenesis by ovine gonadotropins in male and female mudpuppies,Necturus maculosus Rafinesque

Using steroid radioimmunoassay the in vivo steroidogenic responses of male and female mudpuppies (Necturus maculosus) to single injections of ovine FSH and LH were investigated. In males, the major effect of LH was to stimulate testosterone and 5α-dihydrotestosterone secretion within 2 hr of injection, with a lesser effect on estrogen (estrone and estradiol-17β) secretion. In contrast, FSH primarily stimulated secretion of estrogens. The effects of both FSH and LH on steroid secretion in males were dose related. Castration of males reduced plasma androgen, and estrogen to very low or nondetectable levels and abolished the steroidogenic response to LH. Interrenalectomy prevented a postcastration rise in the progesterone level. In females, FSH did not stimulate steroid secretion but LH increased plasma androgens. Homologous pituitary extracts also stimulated plasma levels of all gonadal steroids measured.     

Relation between biological potency and clearance rates of gonadotropins in the lizard Anolis carolinensis.

Clearance of exogenous gonadotropins was studied in the lizard Anolis carolinensis in relation to the problem of variations in potency ratios between LH and FSH of different species of hormone. Studies with unlabeled bullfrog (Rana catesbeiana) gonadotropins revealed that the FSH had a much longer persistence time in the lizard than did LH; this was confirmed by direct immunological measurements of circulating hormone and by temporal profiles in the stimulation of gonadal androgen production in the lizard. Bullfrog FSH and LH labeled with ¹²⁵I had similar clearance rates; the clearance of (¹²⁵I) Rana LH was slower than that of the unlabeled preparation. In contrast, similar studies with unlabeled sea turtle (Chelonia mydas) hormones indicated that the LH is cleared more slowly than is FSH. These differences between the pairs of frog and turtle gonadotropins are consistent with the difference in LH/FSH potency ratios observed for the two species of hormone in the in vivo Anolis lizard testes weight bioassay. Thus, these data provide additional insights into the variability in effects of different species of gonadotropins: the relatively high potency of some species of LH may be related in part to increased half-lives.     

Do androgens directly regulate gonadotropin secretion in the polycystic ovary syndrome?

This study was designed to investigate whether androgens directly, independent of their aromatization to estrogens, disrupt gonadotropin secretion in hyperandrogenic women with the polycystic ovary syndrome (PCO). Pulsatile gonadotropin release and gonadotroph sensitivity to GnRH were determined on consecutive study days basally and during a primed continuous infusion of testosterone (T; n = 4; 100 micrograms/h; twice the mean production rate of T in PCO) or dihydrotestosterone (DHT; n = 5; 50 micrograms/h). To determine if the gonadotropin secretory changes during T infusion were secondary to spontaneous variation, four patients had two consecutive basal studies, and all patients received DHT on the third study day. T infusion that increased mean plasma T levels from 76 +/- 12 (+/- SE) to 315 +/- 28 ng/dl produced no significant changes in the amount or pattern of LH release or in LH sensitivity to GnRH. Mean plasma FSH levels decreased slightly but significantly during T infusion (basal, 242 +/- 29 vs. T 226 +/- 30 ng/ml LER-907; P less than 0.05 by two-tailed paired t test), but the pulsatile pattern of FSH release and FSH sensitivity to GnRH did not change. DHT infusion increased plasma DHT levels from 17 +/- 3 to 244 +/- 31 ng/dl, but did not alter the mean levels, pulsatile patterns, or sensitivity to GnRH of LH or FSH. These data suggest that androgens do not directly alter gonadotropin release in PCO. Thus, regulation of the hypothalamic-pituitary axis in women with PCO is different from that in men despite chronic exposure to hyperandrogenemia.     

Sexual maturation of the male rat. Influence of androgens on the pituitary response to single or multiple injections of LH-RH.

In an attempt to mimic the events surrounding the natural onset of puberty in the male rat, animals were castrated and implanted with Silastic capsules filled with testosterone (T). Capsule size was adjusted to maintain serum-luteinizing hormone (LH) at sham-castrated values. To these animals implanted with T capsules, androstenedione (delta 4), 5 alpha-androstane-17 beta-ol-3-one (DHT), 5 alpha-androstane-3 alpha-17 beta-diol (3 alpha-OL) or T were administered by subcutaneous injections (40 micrograms/100 g body weight). 12 h later, the animals received an intravenous injection of 50 ng LH-RH. Pre- and post-LH-RH injection blood samples were assayed for serum content of LH and follicle-stimulating hormone (FSH) by radioimmunoassay. Compared to sham animals, prepubertal males showed a potentiation in the LH response with testosterone alone. This effect was not prevented by delta 4; DHT or 3 alpha-OL injection returned the LH response to that of sham-operated animals. No such effects of androgens were present in pubertal or postpubertal rats. There was no effect on the FSH response in any age group. Different groups of animals received 3 doses of 10 ng LH-RH or saline prior to a single 50 ng LH-RH injection. Pubertal and postpubertal males showed a self-priming effect of LH-RH on the LH response. This effect was not present in prepubertal rats nor in any group of animals that had been castrated, regardless of whether or not T replacement was performed. The results indicate that complex alterations in pituitary function take place during the sexual maturation of the male rat. These changes may be inherent in the pituitary and/or related to variation in testicular androgen secretion.     

Plasma testosterone levels in male turtles, Chrysemys picta, following single injections of mammalian, avian and teleostean gonadotropins.

The response of male turles (Chrysemys picta) to single injections of either mammalian (human, ovine), avian (domestic hen) or teleostean (salmon) gonadotropins was studied at different points of the testicular cycle (May, July, November) by measurement of plasma testosterone. Mammalian FSH's and avian FSH and LH were markedly stimulatory, and the responses were qualitatively and quantitatively similar. Further, the condition of the testis at the time of injection did not appear to affect the response, with the exception that it was quantitatively less in May. The response was characterized by: (a) Rapidity, reaching maximum or near maximum between 1 and 2 hr postinjection. (b) Magnitude, rising from 10 to 20 ng T/100 ml plasma to 1200 ng/100 ml plasma. (c) Duration, not returning to original plasma levels of T until between 96 and 192 hr postinjection. Injections of purified ovine and human FSH at levels calculated to be equivalent in hormone content to 50 μg of ovine FSH standard duplicated the response. The response was dose related, a 50 μg dose of ovine FSH evoking a response about 10-fold that of a 5 μg injection. Injections of up to 50 μg of NIH ovine LH standard, or 25 μg purified ovine LH only doubled plasma T levels and 100 μg of teleostean gonadotropin had no effect.     

Androgens and spermatogenesis

Male infertility contributes to 50% of all cases of infertility. The main cause is low quality and quantity of sperm. In humans, spermatogenesis starts at the beginning of puberty and lasts lifelong. It is under the control of FSH and testicular androgens, and mainly testosterone (T), and therefore requires a normal gonadotroph axis, intratesticular T production by Leydig cells and functional androgen receptors (ARs) within testicular Sertoli cells. Various clinical cases illustrate the roles of T in human spermatogenesis. Men with complete congenital hypogonadotropic hypogonadism (HH) are usually azoospermic. Treatment by exogenous testosterone injection and FSH is not able to produce sperm. However, combined treatment with FSH and hCG is effective. This example shows that intratesticular T plays a major role in spermatogenesis. Furthermore, testicular histology of men with LH receptor mutations shows Leydig cell hypoplasia/agenesis/dysplasia with conserved Sertoli cell count. The sperm count is reduced, as in males with partial inactivating mutation of the androgen receptor. Some protocols of hormonal male contraception or exogenous androgen abuse induce negative feedback in the hypothalamic pituitary axis, decreasing FSH, LH and T levels and inducing sperm defects and testicular atrophy. The time to recovery after cessation of drug abuse is around 14 months for sperm output and 38 months for sperm motility. In summary, abnormal androgen production and/or AR signaling impairs spermatogenesis in humans. The minimal level of intratesticular T for normal sperm production is a matter of debate. Interestingly, some animal models showed that completely T-independent spermatogenesis is possible, potentially through strong FSH activation. Finally, recent data suggest important roles of prenatal life and minipuberty in adult spermatogenesis.     

Annual cycles of gonadotropins and androgens in the hibernating golden-mantled ground squirrel

Ground squirrels, captured in the field, were housed at ambient temperatures of 23 degrees (photoperiod = 10L:14D) for 13 months. Plasma was sampled at 3 to 4-week intervals and measured for gonadotropin and androgen levels. Testis size was examined monthly by laparotomy. Male ground squirrels showed clear circannual cycles in body mass, testis size, and levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), and dihydrotestosterone (DHT). During summer and fall, FSH, LH and androgen levels were low, testes were undeveloped, and body mass was increasing. Testes began to rapidly enlarge in January and reached maximum size in February. A rise in FSH preceded gonadal growth but LH remained low until near the time of testis mass peak. LH remained elevated during spring while FSH levels fell and testes regressed. Plasma T and DHT levels generally paralleled LH concentrations; DHT levels were approximately one-fifth those of T levels. During winter animals lost weight but were only occasionally found in a slightly hypothermic condition. Females had elevated plasma LH levels (greater than 1 ng/ml) predominantly in the spring but displayed no cycle in plasma FSH levels. A second group of males held at 4 degrees for 8 months (photoperiod = stimulated natural for 47 degrees N) were regularly torpid during a hibernation season that lasted between November and May. Most (15/21) of these males did not show gonadal development by spring; these non-reproductive males had had restricted body mass gains the previous fall. Plasma FSH was low in both reproductive and non-reproductive males during fall and winter but increased in March while animals were still hibernating. FSH levels continued to increase in April only in reproductive males and reached maximal levels after hibernation was spontaneously terminated. LH titers were elevated in individual males in winter during torpor and were greater in reproductive than in non-reproductive males in May. Androgen levels were undetectable in torpid squirrels, elevated in animals sampled during periodic arousals, and elevated in most males within 3 weeks after terminating hibernation.     

Reproduction in the Mexican leaf frog, Pachymedusa dacnicolor. II. The male

The Mexican leaf frog, Pachymedusa dacnicolor, an inhabitant of the semiarid, subtropical Mexican lowlands, displays a well-defined seasonal testicular cycle. Testis weight seems to be a reliable index of the reproductive status of the animal and plasma levels of androgens (testosterone, T; 5 alpha-dihydrotestosterone, DHT; androstenedione, A) correlate not only with testicular growth, but with callosity development, reproductive behavior, and breeding. During the fall and winter, testis weight reaches its minimum as do plasma concentrations of T, DHT, A, and estradiol-17 beta (E). Plasma levels of progesterone (P) are maintained at a very low level throughout the year. During the fall and winter, spermatogenesis is almost entirely absent and the callosities are white and smooth. No signs of reproductive behavior (calling and amplexus) are evident. Late spring marks the initiation of spermatogenesis, testis weight increase, darkening of callosities, and increase in plasma levels of androgens. The magnitude of callosity development and the onset of calling and amplectant behavior are correlated with a great rise in plasma androgen levels. Although plasma T concentrations were higher than plasma levels of DHT and A, this androgen failed to stimulate the development of callosities and calling behavior in successfully castrated males.     

High dose testosterone therapy for reduction of final height in constitutionally tall boys: does it influence testicular function in adulthood?

OBJECTIVE We have studied the effect of treatment with high doses of androgens during puberty on testicular function In adult men with constitutionally tall stature, taking Into account confounding factors interfering with sperm quality, since existing published data do not include whether testicular function is impaired by such treatment. DESIGN Historical cohort study. PATIENTS Forty-three previously androgen treated tall men (cases) and 30 non-treated tall men (controls). MEASUREMENTS Physical examination, semen analysis and plasma levels of LH, FSH, testosterone (T), sex hormone binding globulin (SHBG) and Inhlbin. RESULTS Sperm quality and testis volume were comparable between cases and controls. Mean sperm concentration was 66.4 ± 10⁶/ml in cases and 66.2 ± 10⁶/ml in controls. A left-sided varicocele was found In 45% of the cases and 37% of the controls. In cases we observed a significant effect of the age at start of androgen therapy on sperm motility (regr. coeff. (SE): 4.92 (2.41)%, P= 0.048). In addition, testicular size at start of therapy had a significant effect on sperm concentration (regr. coeff. (SE): 5.57 (1.54) ± 10⁶/ml, P= 0.0012) and on total sperm count (regr. coeff. (SE): 43.1 (7.73) ± 10⁶, P= 0.0001). Plasma levels of T, SHBG and Inhibin were not statistically different between the groups. Cases had significantly higher FSH levels (mean (SD) 3.3 (2.2) vs 2.1 (0-8) IU/I, P= 0.004) and significantly lower LH levels (mean (SD) 2.3 (0.9) vs 3.1 (1.4) IU/I, P= 0.019). We found a significant effect of age at start of therapy on plasma FSH level In the treated men (regr. coeff. (SE): ?0.73 (0.18) IU/I, P= 0.0003). CONCLUSIONS Treatment with high doses of androgens for reduction of final height in constitutionally tall stature has no long-term side-effect on sperm quality, testicular volume or plasma testosterone levels. However, treated men had significantly higher plasma levels of FSH compared with controls. The meaning of this difference remains to be established. Varicocele was present in 42% of the adult tall men.