Follicle-stimulating hormone and the regulation of testosterone secretion in rabbit testes.

Regulation of testosterone secretion is presumably mediated by interstitial cell-stimulating hormone (ICSH). However, there is little information on the actions of other chemical messengers in regulating testosterone secretion. We have shown that follicle-stimulating hormone augments testosterone secretion stimuated by ICSH in rabbit testes perfused in vitro with an artificial medium.

Tissue content of dihydrotestosterone in human prostatic hyperplasis is not supranormal.

The dihydrotestosterone content of normal peripheral and benign hyperplastic prostates was measured in tissue obtained at open surgical procedures on 29 men of ages 36 to 82 yr. The dihydrotestosterone content in normal prostates (mean +/- SE, 5.1 +/- 0.4 ng/g tissue) and in benign hyperplastic prostates (5.0 +/- 0.4) was similar. In 11 patients in whom both normal and hyperplastic prostatic tissue was harvested simultaneously at the same operation, there was no significant difference in the content of dihydrotestosterone in the two types of tissue. These findings fail to confirm the widespread belief that dihydrotestosterone content is elevated in benign hyperplastic prostates. Our data differ from the reported literature in one major respect: the dihydrotestosterone content of normal peripheral prostate in this study is three to four times higher than previously reported. This difference between the present and earlier studies was resolved by experiments performed on cadavers, which were the source of normal prostatic tissue used by other investigators. Dihydrotestosterone content was measured in seven cadavers ranging in age from 19 to 82 yr of age. The results of this experiment indicate that the dihydrotestosterone content of prostatic tissue removed at autopsy is factitiously low (0.7-1.0 ng/g tissue). This finding was confirmed by in vitro incubations of fresh prostatic tissue at 37 degrees C that demonstrated reduction of dihydrotestosterone content to low levels within 2 h. When taken together, these results indicate that when prostatic tissue is harvested appropriately, the dihydrotestosterone content of normal peripheral and hyperplastic tissues is the same. This finding should influence future research into the etiology of benign prostatic hyperplasia.

Comparison of spontaneous and experimentally induced canine prostatic hyperplasia.

Spontaneous prostatic hyperplasia in the beagle appears to progress with age from a glandular to a cystic histological appearance. Prostatic hyperplasia can be induced in young beagles with intact testes by treatment for 4 mo with either dihydrotestosterone or 5 alpha-androstane-3 alpha, 17 beta-diol, alone, or with either of these steroids in combination with 17 beta-estradiol. In contrast, the induction of prostatic hyperplasia in young castrated beagles, in which the gland had been allowed to involute for 1 mo, requires the administration of both 17 beta-estradiol and either 5 alpha-androstane-3 alpha, 17 beta-diol or dihydrotestosterone. Testosterone and 17 beta-estradiol, either singly or in combination, did not produce the hyperplastic condition in intact or castrated beagles. The experimentally induced prostatic hyperplasia is identical in pathology to the glandular hyperplasia that occurs naturally in the aging dog with intact testes. However, cystic hyperplasia was not produced by any of the treatments tested in young animals.

Spontaneous benign prostatic hyperplasia in the beagle. Age-associated changes in serum hormone levels, and the morphology and secretory function of the canine prostate.

This paper is a cross-sectional study of spontaneous benign prostatic hyperplasia (BPH) in a single canine species. The effects of aging and hormonal changes on the growth, histology, and glandular secretory function of the canine prostate were studied in 42 male beagles ranging in age from 8 mo to 9 yr. The beagle prostate enlarges for at least 6 yr, whether normal or hyperplastic. In contrast, prostatic secretory function, determined by ejaculate volume and total ejaculate protein, declines markedly after 4 yr of age. These reciprocal growth and functional changes in the prostate are closely associated with a progressive increase in the incidence of BPH, which is already apparent in some dogs by age two. With age there is a modest decrease in serum androgen levels with no apparent change in serum 17 beta-estradiol levels. This suggests that the growth and functional changes that are associated with the development of BPH and are initiated very early in life reflect an altered sensitivity of the prostate to serum androgens or a response to the relative decrease in the serum androgen to estrogen ratio.

Simultaneous determination of testosterone, 5alpha-androstan-17beta-ol-3-one, 5alpha-androstane-3alpha,17beta-diol and 5alpha-androstane-3beta,17beta-diol in plasma of adult male rabbits by radioimmunoassay(1).

A simultaneous radioimmunoassay procedure for plasma testosterone (T), 5alpha-androstan-17beta-ol-3-one (DHT), 5alpha-androstane-3alpha,17beta-diol (3alphaol), and 5alpha-androstan-3beta,17beta-diol (3betaol) is described in this report. Peripheral plasma concentrations of T, DHT, 3alphaol, and 3betaol were 1.16 +/- 0.26, 0.49 +/- 0.15, 0.17 +/- 0.03, and 0.24 +/- 0.04 ng/ml, respectively, in adult male rabbits. In contrast, T, DHT, 3alphaol, and 3betaol peripheral plasma concentrations in dexamethasone-treated castrate rabbits were 0.07 +/- 0.01, 0.02 +/- 0.01, 0.07 +/- 0.01, and 0.05 +/- 0.01 ng/ml, respectively. These results represent the first simultaneous measurement of T, DHT, 3alphaol, and 3betaol in peripheral plasma of any male vertebrate. Moreover, we suggest that DHT, 3alphaol, and 3betaol represent the unidentified immunoreactive material found in peripheral plasma of male rabbits by Falvo and Nalbandov (1).

Kinetic studies on the development of the adult population of Leydig cells in testes of the pubertal rat.

The objective of this study was to determine whether postnatal increases in rat Leydig cell number result from differentiation of precursor cells, division of existing Leydig cells, or both. Our approach was 1) to examine changes in the absolute number of Leydig cells and potential precursor cells (macrophages, pericytes, and mesenchymal, endothelial, and myoid cells) per testis on day 19 of gestation (day -2) and days 7, 14, 21, 28, and 56 postpartum; 2) to examine the frequency with which mesenchymal and Leydig cells divide during prenatal and postnatal development; and 3) to identify and examine the fate of the progeny of Leydig and mesenchymal cell divisions during prenatal and postnatal development. Stereological methods were used to show that mesenchymal cells comprised 44% of the total interstitial cell population and Leydig cells 16% on day -2, whereas by day 56 postpartum the relationship had reversed; mesenchymal cells comprised 3% and Leydig cells 49%. These results suggested a precursor-product relationship between mesenchymal and Leydig cells because no such reciprocal relationship was observed between Leydig cells and macrophages, pericytes, endothelial, or myoid cells. Autoradiographic analysis of [3H]thymidine incorporation into mesenchymal and Leydig cells was consistent with this interpretation. In a series of pulse-chase experiments, the percentage of labeled mesenchymal and Leydig cells was measured after a single injection of [3H]thymidine on days 2, 14, 28, and 56 postpartum, each followed by sampling at timed intervals (between 1 h and 14 days) thereafter. Starting on day 14, the percentage of labeled Leydig cells was approximately 1% immediately after injection of [3H]thymidine and increased significantly to approximately 6% by 6 days after injection. No such increase was observed when rats were similarly injected starting on days 2, 28, and 56 postpartum. The rise in Leydig cell labeling between days 14 and 28 postpartum did not result in a decline in the number of silver grains over labeled Leydig cell nuclei, indicating that the increase in the percentage of labeled cells was not caused by Leydig cell division. These observations led us to conclude that the increase in Leydig cell labeling from days 14 to 28 was the result of recruitment from a compartment of labeled mesenchymal cells. In contrast, our analysis indicated that from day 28 postpartum and thereafter until the mature number of Leydig cells is attained, Leydig cells are generated by division of morphologically recognizable Leydig cells.

Effects of luteinizing hormone withdrawal on Leydig cell smooth endoplasmic reticulum and steroidogenic reactions which convert pregnenolone to testosterone.

Depletion of endogenous LH with sc implants of testosterone-17 beta-estradiol (T-E) caused a reduction in the Leydig cell smooth endoplasmic reticulum (SER) over a 10-day treatment period. Decreases also occurred in some, but not all, of the testicular steroidogenic reactions responsible for the conversion of pregnenolone (PREG) to testosterone. The conversions of progesterone (PROG) to 17 alpha-hydroxyprogesterone, 17 alpha-hydroxyprogesterone to androstenedione, and androstenedione to testosterone were significantly correlated (P less than 0.05) with the loss of Leydig cell SER. In contrast, the testicular conversion of PREG to PROG in rats deprived of endogenous LH for up to 10 days was identical to that in intact controls. Similar results were obtained when rats were hypophysectomized for 10 days. These results indicate that the Leydig cell enzyme activities responsible for converting PREG to PROG are distributed in the Leydig cell SER fraction which remains in Leydig cell cytoplasm 10 days after LH withdrawal, and thus, the bulk of these enzyme activities are sequested in a SER compartment that is resistant to LH withdrawal.

Restoration effects of exogenous luteinizing hormone on the testicular steroidogenesis and Leydig cell ultrastructure.

In the present study, we explored the restoration effects of exogenous LH on Leydig cell ultrastructure and testicular steroidogenesis in rats that were deprived of endogenous LH via treatment with testosterone-17 beta-estradiol-filled Silastic implants for 10 days. Exogenous LH was supplied continuously via Alzet miniosmotic pumps at the rate of 1 microgram/h for 3, 6, 12, and 24 h or 1, 2, 4, 8, and 12 days. Testes were then perfused in vitro with medium containing 1) LH, 2) 20 alpha-hydroxycholesterol, or 3) pregnenolone substrate, which allowed us to assess LH-stimulated testosterone secretion, cholesterol side-chain cleavage activity, or the conversion of pregnenolone to testosterone, respectively. Other testes were perfusion fixed via the testicular artery for morphometric measurement of Leydig cell number and volume per testis and the surface area of Leydig cell cytoplasmic smooth endoplasmic reticulum (SER), inner mitochondrial membrane, and outer mitochondrial membrane. The results verified that Leydig cell smooth endoplasmic reticulum and inner and outer mitochondrial membrane surface areas are drastically diminished (P less than 0.05 vs. intact controls) by LH withdrawal. Also, the results verified that exogenous LH administered in situ restores Leydig cell ultrastructure and capacity to biosynthesize testosterone. However, the recovery of Leydig cell structure and steroidogenic reactions occurred at strikingly different rates upon restoration of LH after 10 days of the treatment with testosterone-17 beta-estradiol implants. For example, the restoration of testicular capacity to synthesize progesterone in response to LH stimulation or 20 alpha-hydroxycholesterol substrate was completed within 24 h. In contrast, the restoration of Leydig cell SER and testicular capacity to synthesize testosterone from pregnenolone was completed only after 8 days of continuous LH treatment (P greater than 0.05 vs. intact controls). Thus, our results show that LH rapidly restores Leydig cell post-LH receptor steroidogenic events up to and including cholesterol side-chain cleavage activity. Interestingly, there is no temporal association between the recovery of cholesterol side-chain cleavage activity and the surface area of inner mitochondrial membrane surface area. In contrast, 8 days are required to coincidentally restore SER surface area and the capacity of Leydig cells to synthesize testosterone from pregnenolone. We conclude that different cellular mechanisms are involved in the LH-dependent restoration of inner mitochondrial cholesterol side-chain cleavage activity and SER-associated conversion of pregnenolone to testosterone.

Maintenance of advanced spermatogenic cells in the adult rat testis: quantitative relationship to testosterone concentration within the testis.

The studies described herein were designed to examine whether there is a threshold concentration of testosterone (T) within the seminiferous tubules that is required to maintain spermatogenesis in the rat, or alternatively, whether there is a dose-response relationship between the intratesticular T concentration and the maintenance of spermatogenesis. T was administered to intact adult male rats via sustained release polydimethylsiloxane capsules in order to experimentally clamp T at well defined concentrations within the seminiferous tubules. Implantation of T-filled capsules of increasing sizes resulted in linear increases in T concentrations in serum, interstitial fluid, and seminiferous tubule fluid (STF). We examined the effect of step decreases in intratesticular T concentration on the numbers of advanced spermatogenic cells maintained by the testis over a 2-month period. Quantitatively complete spermatogenesis was maintained despite an 80% reduction in the STF T concentration (to approximately 13 ng/ml) from control values. The ability of the testis to maintain complete spermatogenesis was extremely sensitive to further decreases in STF T concentration. Thus, reduction of the STF T concentration from approximately 13 to 9 ng/ml resulted in a reduction in the number of advanced spermatids that were maintained in the testis by approximately 100 x 10(6). Reduction of the STF T concentration to approximately 4 ng/ml resulted in a further reduction in the number of advanced spermatids per testis by 100 x 10(6). Taken together, these data support the contention that there is far more T present within the seminiferous tubules of intact rat testes than is required to maintain quantitatively normal spermatogenesis and reveal for the first time that there is a dose-response relationship between the STF T concentration and the quantitative maintenance of advanced spermatogenic cells in the rat testis.

Testosterone secretion by rat, rabbit, guinea pig, dog, and hamster testes perfused in vitro: correlation with Leydig cell ultrastructure.

Stereological methods were employed to determine volume and surface densities of cytoplasmic organelles in Leydig cells of hamster, rat, rabbit, dog, and guinea pig testes. Contralateral testes were perfused in vitro with maximally stimulating gonadotropin concentrations to determine the capacity of these testes to secrete testosterone. Significantly different amounts of testosterone were secreted by in vitro perfused testes of the five species when maximally stimulated with ovine LH. Significant differences also were seen in the volume and surface densities of smooth endoplasmic reticulum, mitochondria, rough endoplasmic reticulum, and lipids in Leydig cell cytoplasm of the five species. Most interestingly, linear positive correlations were seen between testosterone secretion and smooth endoplasmic reticulum volume (r = 0.99) and surface (r = 0.99) densities. Thus, virtually all of the differences in testosterone secretion by maximally stimulated testes of five species could be accounted for by between-species differences in the amount of Leydig cell smooth endoplasmic reticulum.

Dihydrotestosterone concentration of beagle prostatic tissue: effect of age and hyperplasia.

Dihydrotestosterone (DHT) concentration was measured in prostatic tissue obtained from castrate or intact beagles treated with androgens and/or estradiol-17 beta. Also DHT concentration was measured in prostatic tissue of beagles ranging from 0.7-9.2 yr; some with and others without spontaneously occurring benign prostatic hyperplasia (BPH). Three major results were forthcoming. First, a linear, positive correlation was observed between prostatic weight and DHT concentration in castrated or intact beagles treated with 11 of 15 steroid hormone regimens. Four additional treatments including intact or castrated beagles treated with either DHT or 5 alpha-androstan-3 alpha,17 beta-diol alone resulted in high concentrations of prostatic DHT but not equally high prostatic weight. Thus, prostatic DHT concentration is not always tightly coupled with prostate weight in the beagle. Second, there was no significant (P greater than 0.25) difference in prostatic DHT concentration between dogs with histologically normal prostates and those with spontaneous BPH. Thus, contrary to earlier reports, the tissue concentration of DHT in dog prostatic hyperplasia is not supranormal. Third, there was a dramatic change in prostatic DHT concentration which peaked at 3.8 yr. We conclude that steroid hormone treatment regimens which caused elevated prostatic DHT concentrations did not always result in equally high prostatic weight in the beagle. Also, if androgens like DHT are related causally to BPH in the dog, they probably play a permissive rather than an inductive role in the disease process.

Effect of adrenocorticotropin and other proopiomelanocortin-derived peptides on testosterone secretion by the in vitro perfused testis.

Several lines of evidence have demonstrated the presence of POMC-derived peptides in testicular tissue. Consequently, this study was designed to determine the effects of ACTH and other POMC-derived peptides on testosterone secretion by the in vitro perfused testis. Infusion of synthetic human ACTH-(1-24) at a concentration of 500 ng/ml increased (P less than 0.01) testosterone secretion over that in nontreated controls by in vitro perfused rabbit and guinea pig testes, but not by rat, hamster, or dog testes. This increase in testosterone secretion after ACTH treatment, however, was less (P less than 0.01) than that after the infusion of a maximally stimulating concentration of ovine LH (100 ng/ml). Using rabbit testes, the testosterone response to ACTH was demonstrated to be dose dependent and specific, since similar responses were observed after the infusion of synthetic human ACTH-(1-39) and purified porcine ACTH-(1-39) and since no response was observed after the infusion of a variety of ACTH fragments. Infusion of alpha MSH, beta-endorphin, or naloxone had no effect (P greater than 0.10) on testosterone secretion by either rabbit or rat testes at the doses used. These data show that rabbit and guinea pig, but not rat, hamster, and dog, testes secrete testosterone in response to ACTH.

Restoration of spermatogenesis by exogenously administered testosterone in rats made azoospermic by hypophysectomy or withdrawal of luteinizing hormone alone.

The major objective of the studies presented herein was to compare the extent to which exogenously administered testosterone is able to restore spermatogenesis in adult rats made azoospermic by withdrawal of all pituitary hormones (hypophysectomy for 4 weeks) vs. withdrawal of LH alone [testosterone- and estradiol-filled (TE) polydimethylsiloxane implants of 2.5 and 0.1 cm, respectively, for 8 weeks]. In hypophysectornized (Hypox) rats, serum LH and FSH were both undetectable; in the rats that received TE implants, serum LH was undetectable, but FSH was unaffected compared to control values. Seminiferous tubule fluid testosterone concentrations were reduced significantly from their control values of 60-65 to 1.4-1.7 ng/ml in the azoospermic Hypox and TE rats. These rats then received testosterone-filled implants of 4, 12, 18, or 24 cm and were killed 2 months later. In both the Hypox and TE rats, seminiferous tubule fluid testosterone concentrations rose linearly with increasing capsule sizes, and with each of the implant sizes, these concentrations did not differ significantly between the Hypox and TE rats. This made it possible for the first time to examine the effects of comparable intratesticular testosterone concentrations on the numbers of advanced spermatids per testis that could be restored in the azoospermic testes of rats lacking all pituitary factors vs. those lacking only LH. The results that we present demonstrate that the numbers of restored advanced spermatids were consistently and significantly lower in Hypox than in TE rats despite equivalent seminiferous tubule fluid testosterone concentrations. These results provide quantitative conclusive evidence to support the contention that pituitary factors in addition to LH are required for the quantitative restoration of spermatogenesis in the adult rat testis.

Effect of luteinizing hormone on Leydig cell structure and testosterone secretion.

Hypophysectomy or sc implantation of testosterone-estradiol 17 beta (T-E) filled polydimethylsiloxane capsules for 5 days caused a dramatic reduction in testosterone secretion when testes subsequently were perfused in vitro. The diminution in testosterone-secreting capacity of testes from T-E treated rats was coupled closely with reductions in the membrane surface areas of Leydig cell cytoplasmic organelles, particularly those of the smooth endoplasmic reticulum. Simultaneous treatment of T-E implanted rats with LH (12 micrograms/day), but not with FSH, PRL, TSH, or GH, maintained both the Leydig-cell cytoplasmic membranes and the capacity of testes to secrete testosterone in vitro. Testosterone secretion by testes from hypophysectomized rats treated simultaneously with T-E plus LH was identical to that in control rats. Therefore, T-E did not inhibit directly the Leydig cell steroidogenic apparatus. Taken together these results suggest that one of the trophic effects of LH in the Leydig cell is to maintained the integrity of smooth endoplasmic reticulum and enzymes responsible for the conversion of pregnenolone to testosterone.

Differentiation of Leydig cell precursors in vitro: a role for androgen.

An enriched fraction of mesenchymal-like cells was isolated from the testes of 21 day old rats. Testosterone production (ng/10(6) cells.24 hours) by these cells when cultured in vitro was measured by radioimmunoassay of HPLC-purified extracts of culture medium. In the presence of LH + DHT there was a significant increase in testosterone secretion from 22 +/- 10 ng after day 1 of culture to 284 +/- 75 ng on day 3 (P less than 0.01). By contrast, LH or DHT alone were without significant effect. We conclude that LH alone is insufficient but that androgen and LH induce mesenchymal-like Leydig cell precursors from 21 day old rats to produce testosterone.

To what extent can spermatogenesis be maintained in the hypophysectomized adult rat testis with exogenously administered testosterone?

In a previous study it was demonstrated that spermatogenesis can be maintained quantitatively with exogenously administered testosterone in adult intact rats that lack LH. The studies described herein were designed to examine the extent to which spermatogenesis can be maintained quantitatively with exogenously administered testosterone in adult rats that lack all pituitary hormones. Adult male rats were hypophysectomized and testosterone was administered at the time of hypophysectomy via sustained release polydimethylsiloxane (PDS) capsules of increasing lengths. We used the PDS capsules to clamp testosterone at defined concentrations within the seminiferous tubule fluid over a 2- to 3-month treatment period. Mean testis weights and advanced spermatid numbers per testis stabilized by 8 weeks of testosterone treatment regardless of testosterone dose. Both testis weight and advanced spermatid number responded to testosterone dose, reaching plateaus of 1.2 g and 170 x 10(6) per testis, respectively. These values were 60% of, and significantly less than, the respective control values. This result was in striking contrast to the results of our previous study of LH-suppressed intact rats, in which exogenously administered testosterone resulted in testis weights and advanced spermatid numbers that plateaued at values not significantly different from those in controls. These different effects of testosterone in intact and hypophysectomized rats occurred despite the fact that the seminiferous tubule fluid testosterone concentrations achieved in the hypophysectomized rats (up to 25 ng/ml) were greater than the minimal testosterone concentration found previously to be required to maintain spermatogenesis quantitatively in LH-suppressed intact rats (13 ng/ml). Taken together, these results demonstrate clearly that intratesticular testosterone doses that are as high as or higher than those that maintain spermatogenesis quantitatively in intact rats lacking LH fail to maintain spermatogenesis quantitatively in rats lacking all pituitary hormones.

Restoration of advanced spermatogenic cells in the experimentally regressed rat testis: quantitative relationship to testosterone concentration within the testis.

We examined the effect of exogenously administered testosterone (T) on the quantitative restoration of advanced spermatogenic cells in adult rat testes rendered azoospermic by treating rats with polydimethylsiloxane (PDS) implants of T and estradiol (E). Experimental rats received PDS-TE implants for an initial 8-week period; control rats received empty implants. By 8 weeks of PDS-TE treatment, rats became severely oligospermic, and the T concentration within the seminiferous tubule fluid (STF) was reduced approximately 80% (from 57.8 ng/ml in controls to 9.6 ng/ml). After the initial 8-week PDS-TE treatment, PDS-TE implants were removed from one group of rats; a second group of PDS-TE-implanted rats received an additional PDS-T implant of 24 cm. Eight weeks after the removal of PDS-TE implants or the implantation of additional T, testis weight and numbers of advanced spermatogenic cells were restored to those of control rats. The STF T concentration 8 weeks after the removal of PDS-TE implants also was restored to that in control rats. In contrast, the STF T concentration increased to only 40% of control values in the rats that received an additional T implant. Despite this 60% reduction in T concentration compared to the control value, advanced spermatogenic cell number was restored to a value indistinguishable from that of intact controls. These observations indicate that spermatogenesis can be quantitatively restored in PDS-TE-implanted rats with exogenously administered T, and moreover, that this restoration does not require the high T concentration found in the STF of intact control rats.

Effect of long term deprivation of luteinizing hormone on Leydig cell volume, Leydig cell number, and steroidogenic capacity of the rat testis.

Leydig cells atrophy, losing cytoplasmic volume and the capacity for testosterone secretion, within 1-2 weeks of LH deprivation. We investigated the effects of long term (0-16 weeks) LH deprivation on the volume of an average Leydig cell, the volume of Leydig cells per testis, the number of Leydig cells per testis, and testosterone secretion by in vitro perfused testes. Endogenous LH was suppressed in adult rats by testosterone/estradiol-filled (TE) Silastic implants. The presence of Leydig cells in testes was verified by 1) morphological examination using light and electron microscopy, 2) histochemical localization of 3 beta-hydroxysteroid dehydrogenase activity (3 beta HSD), and 3) conversion of pregnenolone to progesterone by in vitro perfused testes. Marked quantitative differences existed in Leydig cell morphology among control and treated rats. The volume of an average Leydig cell and the total volume of Leydig cells per testis decreased (P less than 0.01) rapidly and progressively after TE implantation. At 16 weeks, the average Leydig cell lost 90% of its cytoplasmic volume and 65% of its nuclear volume. Analysis of variance failed to detect a significant decline in Leydig cell number per testis, despite a 16% reduction from the value in control rats (22.2 +/- 1.5 x 10(6)) in rats treated for 16 weeks (18.7 +/- 1.5 x 10(6)). After TE implantation, LH-stimulated testosterone secretion by in vitro perfused testes diminished (P less than 0.01) rapidly to 5% of the control values at 1 week and less than 0.3% of the control value from 4-16 weeks. In contrast, 25% of 3 beta HSD activity was retained (P less than 0.01 vs. controls) at 16 weeks, based on the rate of pregnenolone conversion to progesterone. Moreover, testes of treated rats secreted progesterone at a rate twice that of controls, when the steroid secretion rates were expressed per volume of Leydig cell cytoplasm. Loss of the testosterone-secreting capacity of testes after LH withdrawal was associated with a loss in the volume, but not a significant loss in the number, of Leydig cells. Thus, LH was required to maintain the differentiated structure and function of Leydig cells, but was not required to maintain the overwhelming majority of Leydig cells in the adult rat testis through 16 weeks. Moreover, at least one steroidogenic enzyme, 3 beta HSD, was retained by Leydig cells after long term LH deprivation.

Testosterone secretion by rat, rabbit, guinea pig, dog, and hamster testes perfused in vitro: correlation with Leydig cell mass.

Testes from guinea pigs, rabbits, dogs, rats, and hamsters perfused in vitro with maximally stimulating concentrations of ovine LH released 9.76 +/- 2.05, 12.80 +/- 3.15, 28.94 +/- 3.01, 3.18 +/- 0.41, and 0.70 +/- 0.12 microgram testosterone (T)/h, respectively. Adjusting for differences in testicular weight did not eliminate significant (P less than 0.01) species variation in testicular capacity for T secretion in response to ovine LH. Similarly, correction for Leydig cell mass, as determined by morphometric analysis, still left significant (P less than 0.01) differences in the testosterone secretion rates in response to ovine LH for guinea pigs (262.5 +/- 38.6 micrograms T/g Leydig cell), rabbits (205.5 +/- 50.7 micrograms T/g Leydig cell), dogs (116.4 +/- 14.8 micrograms T/g Leydig cell), rats (83.55 +/- 21.80 micrograms T/g Leydig cell), and hamsters (18.24 +/- 3.55 micrograms T/g Leydig cell). The data suggest that significant between-species variation of T production in response to ovine LH is not due to quantitative differences in the mass of Leydig cells.

Short term androgen production by rat ovarian follicles and long term steroidogenesis by thecal explants in culture.

To characterize the aromatizable and 5 alpha-reduced androgens produced by developing ovarian follicles, small antral (SA) and preovulatory (PO) follicles, theca and granulosa cells were incubated for 4 h with or without 8-bromo-cAMP and androstenedione. In addition, thecal explants were cultured for 10 days with or without ovine LH (oLH) to determine if the hormone-induced changes in androgen synthesis by developing follicles could be mimicked in vitro. Short term incubations of SA and PO follicles, theca and granulosa cells in medium alone resulted in limited accumulation of androgen [testosterone, 5 alpha-androstan-17 beta-ol-3-one (DHT), 5 alpha-androstan-3 alpha, 17 beta-diol (3 alpha diol), and androsterone], as determined by RIA. In the presence of 8-bromo-cAMP, PO follicles produced large quantities of testosterone (3 ng), DHT (1 ng), 3 alpha diol (15 ng), and androsterone (14 ng), while SA follicles accumulated much less androgen (0.69, 0.05, 1.23, and 1.3 ng, respectively). In the presence of androstenedione and 8-bromo-cAMP, both SA and PO follicles and theca produced large amounts of aromatizable and 5 alpha-reduced androgens. SA and PO granulosa cells required the presence of the substrate androstenedione to produce androgens, primarily testosterone and 3 alpha diol. Therefore, progesterone, androstenedione, and 5 alpha-reduced androgens were used to monitor LH action on thecal cell function in culture. Small antral theca cultured in basic culture medium alone (containing 10% fetal calf serum) displayed an increased ability to accumulate androstenedione by day 6, approximately 3 times that observed on day 2. However, a 5-fold further increase in androstenedione accumulation was observed by day 6 for SA theca cultured in the presence of oLH. Maintenance of progesterone accumulation by SA theca throughout the culture period also was dependent on the presence of LH. In contrast, androstenedione accumulation by PO theca required the presence of LH in the culture medium, while progesterone accumulation in these cultures did not. Little or no 5 alpha-reduced androgen accumulated in the media of SA and PO theca cultured in basic culture medium alone. However, SA and PO theca cultured with oLH accumulated approximately 1 ng androsterone by day 10. We conclude that 1) SA and PO follicles, theca and granulosa cells possess the enzymes required to produce large amounts of 3 alpha diol and androsterone; 2) low concentrations of oLH are required to stimulate SA thecal steroidogenesis and to maintain PO thecal androstenedione accumulation in culture.(ABSTRACT TRUNCATED AT 400 WORDS)