Biomedical subjects
Publications and source records attributed to David M Robertson.
Targeted mutational screening of the inhibin-binding domain of betaglycan (exons 11 and 12) demonstrated an increased occurrence of the exon 12 194969T-->C variant in POF patients (27/54; 50%) compared to controls (8/41; 19.5%; P=.002); however, no gene variations were identified in exon 11.
CONTEXT: Male hormonal contraception via gonadotropin and intratesticular androgen withdrawal disrupts spermatogenesis at two principal sites: 1) spermatogonial maturation, and 2) spermiation. OBJECTIVE: The objective of this study was to explore the relative dependence of each stage of germ cell development on FSH and LH/intratesticular androgen action. DESIGN, SETTING, AND PARTICIPANTS: Eighteen men enrolled in this prospective, randomized 14-wk study at Prince Henry's Institute. INTERVENTIONS: Subjects (n = 6/group) were assigned to 6 wk of 1) testosterone (T) implant (4 x 200 mg sc once)+depot medroxy progesterone acetate (DMPA; 150 mg im once); 2) T implant+DMPA+FSH (300 IU sc twice weekly); and 3) T implant+DMPA+human chorionic gonadotropin (hCG; 1000 IU sc twice weekly as an LH substitute). Men then underwent a vasectomy and testicular biopsy with previously reported control data used for comparison. MAIN OUTCOME MEASURES: Germ cell number (assessed by the optical disector stereological approach) and intratesticular androgen levels were determined. RESULTS: T+DMPA alone significantly suppressed type B spermatogonia, preleptotene through to pachytene spermatocytes, and round spermatids from control (P < 0.05). All germ cell subtypes were maintained at control levels by either FSH or LH activity, except pachytene spermatocytes, which were found to be lower in the hCG vs. FSH (P < 0.01) and control groups (P < 0.05). CONCLUSIONS: FSH and LH maintained spermatogenesis independently in this gonadotropin-suppressed model. Compared with LH, FSH showed better maintenance of pachytene spermatocyte number, whereas improved conversion to round spermatids was suggested with hCG treatment. Future contraceptive treatment strategies must consider independent regulation of spermatogenesis by both FSH and LH/intratesticular androgens for maximum efficacy.
Follistatin is a potent extracellular antagonist of members of the TGFbeta superfamily that use activin type II receptors (ActRII/IIB) as part of their signaling complex. A recent crystallographic study indicates that follistatin contacts activin-A residues at both the type I (ALK4) and type II receptor binding interfaces. However, the relative contribution of these two sites on human activin-A to follistatin binding has not been determined. Residues at these sites were mutated to alanine and mutants were screened for their ability to bind follistatin and ActRII and induce FSH secretion from a gonadotrope cell line. Despite extensive mutagenesis across the type I receptor interface, activin-A affinity for follistatin was not significantly diminished. In contrast, mutagenesis of residues at the type II binding interface had pronounced effects on activin's interaction with follistatin. In particular, residues Leu92, Tyr94, Ile100, and Lys102 were critical for high-affinity follistatin binding. Interestingly, mutation of another primary determinant of ActRII/IIB binding, Ser90, did not affect follistatin affinity, suggesting that the interaction surfaces for type II receptors and follistatin were overlapping but not identical. In support, mutation of Asp95, on the opposite edge of the common ActRII/follistatin interface, was disruptive for follistatin binding without affecting ActRII/IIB interactions. Activin-S90A was able to compete with wild-type activin for follistatin binding, whereas activin-D95A, due to its 8-fold lower affinity for follistatin, is a potent activin agonist. These reagents could be used to modulate follistatin antagonism of activin and related ligands in processes such as cancer, wound healing, and reproduction.
Inhibins are expressed in the adrenal cortex, but little is known of their binding or role in the adrenal. The aims of the present study were, first, to establish whether a mouse adrenocortical (AC) cell line expresses inhibins/activins and bone morphogenetic proteins (BMP), along with proteins required for inhibin to antagonise activin and BMP actions and, secondly, to characterise and compare inhibin binding sites and proteins in the rat adrenal gland and AC cells. AC cells were found to: (1) express mRNA for multiple BMPs (BMP-2, -3, -4, -6, -8a), growth/differentiation factors (GDF-1, -3, -5, -9), Lefty A and B, and the inhibin alpha, beta(A) and beta(B) subunits (2) secrete inhibin A and inhibin B and (3) express mRNA encoding the inhibin co-receptor, betaglycan, along with activin and BMP type I (ALK2-7) and type II (ActRII, ActRIIB, BMPRII) receptors, and binding proteins (follistatin, BAMBI, gremlin). When applied to sections of rat adrenal glands, [(125)I]inhibin A specifically bound to cells of the adrenal cortex, mainly in the zona reticularis. Scatchard analyses of in vitro [(125)I]inhibin A binding to dispersed rat adrenal cells and AC cells revealed sites of high affinity (K(d)(1) of 0.18 and 0.15 nM, respectively) and low affinity (K(d)(2) of 2.6 and 1.3 nM, respectively. Competition for [(125)I]inhibin A binding by activin A or B (30 nM) was negligible, whereas BMP-2, -6 and -7 competed for between 21 and 33% of specific inhibin A binding (IC(50) between 0.2 and 0.3 nM). Inhibin B crossreaction with inhibin A binding sites was < 8%. Multiple binding protein complexes (molecular weight ranging from 35 to > 220 kDa) were affinity labelled by [(125)I]inhibin A on both the primary rat adrenal and AC cells. The species of > 220 kDa were shown by immunoprecipitation to include betaglycan, the species of 105 kDa is consistent in size with type II receptors for activin/BMP, and that of 62 kDa co-migrates with the inhibin-follistatin complex. In summary, the results show that inhibin A binds selectively and with both high and low affinity to AC cells via multiple binding proteins, including a single betaglycan-like species. The results support the role of glycosylated betaglycan in the high affinity binding of inhibin A, but provide consistent evidence from two independent sources of adrenal cells that inhibin A interacts with several membrane proteins in addition to those currently understood to mediate the anti-activin/BMP actions of inhibin.
Spermiation is the final step of spermatogenesis and culminates in the disengagement (release) of elongated spermatids from Sertoli cells into the seminiferous tubule lumen. Spermiation failure, wherein spermatids are retained by Sertoli cells instead of releasing, occurs after hormone suppression. The mechanisms involved in spermatid disengagement and retention are not well understood. We previously showed that beta(1)-integrin is associated with spermatids until the point of disengagement, but the ectoplasmic specialisation junction (ES) is not. The aims of this paper are to further characterise the complex that is present immediately prior to spermatid disengagement by identifying the alpha-integrin form dimerised with beta(1)-integrin, localising focal adhesion kinase (FAK) and determining if microtubules are involved. Adult Sprague-Dawley rats received testosterone and oestradiol implants and an FSH antibody for 7 days to suppress testicular testosterone and FSH and induce spermiation failure. Control rats were treated with saline. Immunohistochemical analysis showed that alpha(6)-integrin and a phosphorylated form of FAK (FAK-Tyr(397)) are present between late spermatids and Sertoli cells after ES removal, until the point of disengagement, and both proteins remain associated with retained spermatids after spermiation failure induced by hormone suppression. Using dual-label immunofluorescence, tubulins (and thus microtubules) were observed to co-localise with ES, but were neither associated with elongated spermatids just prior to release nor with retained spermatids following hormone suppression. These results suggest that microtubules are not involved in the final release of spermatids from Sertoli cells. We conclude that spermatid release during spermiation is mediated by a 'disengagement complex' containing alpha(6)beta(1)-integrin and phospho-FAK, the function of which can be affected by gonadotrophin suppression.
Embryo implantation and trophoblast invasion are tightly regulated processes, involving sophisticated communication between maternal decidual and fetal trophoblast cells. Decidualization is a prerequisite for successful implantation and is promoted by a number of paracrine agents, including activin A. To understand the downstream mechanisms of activin-promoted decidualization, the effects of activin on matrix metalloproteinases (MMPs) (important mediators of decidualization) were investigated. Activin A stimulated endometrial production of proMMPs-2, -3, -7, -9, and active MMP-2. In contrast, inhibin A was a potent inhibitor of proMMP-2, and antagonized the effect of activin on MMPs. Activin is up-regulated with decidualization, and MMPs-2, -3, and -9 increase in parallel. Furthermore, proMMP-2 production is stimulated when decidualization is accelerated with activin, and suppressed when activin is neutralized, attenuating decidualization. These data support that activin A promotes decidualization through up-regulating MMPs. Previous in vitro evidence proposes further roles for activin and MMPs in promoting trophoblast invasion; therefore, we examined their interrelationships in early human implantation sites. MMPs-7 and -9 were produced by static cytotrophoblast subpopulations, whereas MMP-2 was strikingly up-regulated in invasive extravillous cytotrophoblasts (EVT). Maternal decidua is the primary source of activin, where a role in stimulating MMP-2 in iEVTs can be envisaged. Inhibin was absent from cytotrophoblast populations, except for a dramatic up-regulation in endovascular EVT plugs, coinciding with a down-regulation of MMP-2. This suggests that inhibin may have a role in the cessation of vascular invasion. These data support that activin, via effects on MMPs, is an important factor in the maternal-fetal dialog regulating implantation.
Activins are members of the transforming growth factor-beta (TGF-beta) superfamily that control many physiological processes such as cell proliferation and differentiation, immune responses, wound repair and various endocrine activities. Activins elicit these diverse biological responses by signaling via type I and type II receptor serine kinases. Recent studies have revealed details of the roles of inhibin, betaglycan, follistatin and its related protein follistatin-related gene (FLRG), Cripto and BAMBI in antagonizing activin action, and exogenous antagonists against the activin type I (SB-431542 and SB-505124) and type II (activin-M108A) receptors have been developed. Understanding how activin signaling is controlled extracellularly is the first step in providing treatment for wound healing and for disorders such as cachexia and cancer, which result from a deregulated activin pathway.
Oestrogen is a metabolite of testosterone, but its role in spermatogenesis is ill-defined. Oestrogen may exert its effects on spermatogenesis, as oestrogen receptor (ER)-beta has been localised to both germ and somatic cells. This study sought to establish whether the restoration of early germ cell numbers in spermatogenesis by high-dose exogenous testosterone was influenced by its metabolite, oestrogen. The ER antagonist (ICI 182780) was administered, at a dose known to impair oestrogen action in the male reproductive tract, during testosterone treatment of gonadotrophin-releasing hormone (GnRH)-immunised rats, and germ cell numbers were determined. GnRH-immunised adult Sprague-Dawley rats (n=7-8 per group) received two doses of testosterone, either as a Silastic implant (24 cm (T24 cm)) or an injectable ester for 10 days alone or in combination with ICI 182780 (2 mg/kg, s.c. injection daily). Control rats received vehicle alone. Testes were perfusion-fixed and germ cells were quantified by the optical disector technique. GnRH-immunisation reduced (P<0.001) both type A/ intermediate spermatogonial and type B spermatogonial/ preleptotene spermatocyte number (56% of control) and leptotene/zygotene spermatocyte number (63% of control). Pachytene spermatocyte and round spermatids were reduced to 12% and l% (P<0.01) of control respectively. Testosterone treatment did not increase type A/intermediate spermatogonial number compared with GnRH-immunised controls over the 10-day study period. Treatment with testosterone-esters increased type B spermatogonial/preleptotene spermatocytes and leptotene/zygotene spermatocyte numbers (both being ~83% of control, P<0.05), while T24 cm treatment did not significantly increase their numbers (~73% of control) compared with GnRH-immunised controls. Both treatments increased pachytene spermatocyte and round spermatid numbers to 55% and 8% of control respectively. Co-administration of ICI 182780 had no effect on any of these germ cell numbers. We conclude that oestrogen action plays no role in the short-term restoration of spermatogenesis by testosterone in the GnRH-immunised rat.
The inhibins are produced and secreted by several ovarian cancers. Monitoring serum levels by immunoassay may be a useful diagnostic aid in the initial assessment of this disease and in monitoring its potential recurrence following surgery. The assays are applicable to women after menopause when the majority of ovarian cancers are detected, and when the normal ovarian production of inhibin is low to negligible. A new inhibin immunoassay (total inhibin ELISA) has been developed with the intention of widespread clinical application. The assay readily detects granulosa cell and mucinous tumours. CA125, a widely used ovarian cancer marker, detects the other main ovarian cancer types (serous, endometrioid, undifferentiated) with high sensitivity. The combination of the two tests detects the majority of ovarian cancers with high specificity (95%) and sensitivity (95%). Studies have been undertaken to assess its application to women in the perimenopausal stage and to younger women during normal reproductive life. These studies are providing a platform for the introduction of the test into clinical practice.
Inhibin is a dimeric (alpha and either betaA or betaB subunit) protein involved in the regulation of fertility. Inhibin A and B or its free alpha subunit monomer are elevated in various gonadal and prostate cancers and thus serve as useful diagnostic tools for certain ovarian tumors either as a serum marker or as an immunocytochemical marker for tissue sections. Serum inhibin levels are of value in the initial diagnosis and subsequent follow-up of sex cord stromal tumors, in particular granulosa cell tumors, and mucinous epithelial adenocarcinomas primarily after menopause. Immunocytochemistry using inhibin alpha subunit antisera can aid in the classification of sex cord stromal tumors and their differentiation from other cancers. Although serum inhibins are elevated in prostatic and testicular cancers, this is of little diagnostic value at the present time.
This study aimed to establish whether the degree of suppression of serum FSH and LH was related to sperm concentration in three testosterone (T) plus progestin contraceptive regimens. We measured serum FSH and LH using a modified, highly sensitive immunofluorometric assay in samples obtained from three published studies using T enanthate (TE; 100 and 200 mg weekly) plus daily oral doses of cyproterone acetate (CPA; 5-100 mg), levonogestrel (LNG; 150-500 micro g), or desogestrel (DSG; 150-300 micro g). Overall, men with sperm concentrations below 0.1 million/ml had significantly lower gonadotropin levels (serum FSH, approximately 0.12 IU/liter; serum LH, approximately 0.05 IU/liter) than oligospermic men (sperm concentrations, 0.1-5 million/ml; serum FSH, 0.23-0.5 IU/liter; serum LH, 0.05-0.56 IU/liter), but the relationship was weak, indicating the possible existence of other determinants. Multivariate logistic regression was used to identify the influence of candidate predictors of spermatogenic effects of the T plus progestin regimens. In the LNG and DSG studies, the marked suppression of serum LH to less than 5% of baseline values (<0.15 IU/liter) was a consistent and highly significant predictor of sperm concentration (reduced to 2-7% that seen at higher LH levels) and the likelihood of its suppression below 1 million/ml (a proposed threshold for contraceptive efficacy). Serum FSH was not a significant independent predictor. The use of DSG and CPA (but not LNG) was a significant independent predictor of sperm suppression, and regimens that contained 200 mg TE weekly caused less spermatogenic suppression than 100 mg TE weekly. These findings suggest that T-progestin contraceptive regimens suppress sperm concentration by gonadotropin-dependent and -independent mechanisms. The suppression of serum LH is a major predictor of the suppression of sperm concentration suppression in the LNG and DSG treatment studies. On the other hand, the greater spermatogenic suppression in regimens containing DSG or CPA suggests that these progestins have additional actions to suppress spermatogenesis via a gonadotropin-independent mechanism(s)
To examine the hormonal characteristics of menstrual cycles in healthy women approaching menopause, serum hormone profiles were investigated annually in this longitudinal study of 13 healthy women between 4 and 9 yr before menopause and the year of the menopause. Serum FSH, LH, estradiol, progesterone, total inhibin, inhibins A and B, and prolactin were determined in blood samples collected annually three times weekly for 4 wk beginning with the onset of menses. Menstrual bleeding diaries covering this 4- to 9-yr period were also collected allowing the prospective identification of the final menstrual period. A change in serum hormone patterns was observed in cycles approaching menopause, exemplified by an increasing number of cycles of prolonged length with a prolonged follicular phase resulting in a failure to detect a luteal phase rise in serum progesterone within the 4-wk collection period. These prolonged cycles (designated B cycles based on a previous work) were analyzed separately and compared with the remaining ovulatory (D) cycles. No B cycles were identified in any women earlier than 27 cycles from menopause. The proportion of B cycles increased as menopause approached, reaching 62% in the last 10 cycles. The proportion of D cycles decreased accordingly. The B cycles during the initial 4-wk collection period were characterized by elevated FSH, LH, FSH/inhibin A and FSH/inhibin B ratios, and longer duration, although cycle length/subject was not significantly different presumably due to the small number of B cycles. The D cycles showed no changes in hormonal profiles over the 4- to 9-yr time period. These data indicate that there is a time-related change in the character of menstrual cycles as menopause approaches, with an increasing proportion of cycles observed with prolonged follicular phases that may either be delayed ovulatory cycles or anovulatory cycles. The increase in the proportion of B cycles with elevated early follicular phase FSH levels and low inhibin/FSH ratios toward menopause provides a basis for the apparent early increase in serum FSH and decrease in serum inhibins observed previously in studies of the menopause transition based on sampling confined to the follicular phase only. The data amplify and clarify current concepts of the endocrine basis of the menopause transition.
BACKGROUND: Testicular regulation of inhibin B may be influenced by the germ cell complement. METHODS: We examined the effects of gonadotrophin stimulation on serum inhibin B and pro-alphaC in 25 normal men at (i) control (stimulation test 1), (ii) after spermatogenic suppression induced by testosterone plus progestin treatment (stimulation test 2), and (iii) during spermatogenic recovery induced by FSH and/or hCG treatment (stimulation test 3). For each test, subjects received a single injection of 1200 IU FSH or 5000 IU hCG or both. RESULTS: Inhibin B and pro-alphaC fell with spermatogenic suppression (75 and 51% of pre-treatment baseline respectively, P < 0.05). Inhibin B response to FSH (130-144%) was similar in controls and after germ cell suppression. Pro-alphaC response after germ cell suppression compared with control was significantly increased (P < 0.05) with both FSH (210-229% versus 140-185%) and hCG (254-261% versus 145%). All treatments partially restored spermatogenesis with no clear relationship apparent between inhibin B and sperm count. CONCLUSIONS: We conclude that: (i) serum inhibin B and pro-alphaC are only partially gonadotrophin dependent, (ii) spermatogenic suppression does not modify inhibin B response to FSH but enhances pro-alphaC response to both FSH and hCG, and (iii) inhibin B is a poor marker of spermatogenesis in this model of gonadotrophic manipulation in normal men.
Dizygotic twinning in humans is influenced by genetic factors suggesting inherited variation affects follicle development and predisposes to double ovulations. In a previous study, we conducted a detailed examination of follicle development and variation in hormone concentrations during the menstrual cycle in mothers of DZ twins (MODZT) compared with an age-matched control group of mothers of singletons. We did not detect differences in FSH concentrations between mothers of twins and mothers of singletons. Serum inhibin concentrations were measured by a radioimmunoassay that did not distinguish between dimeric inhibin A and B forms and free inhibin alpha subunit. We therefore analyzed the samples from this study with specific assays to determine whether concentrations of inhibin A and B were different between MODZT and controls and therefore contribute to the twinning phenotype. There were no significant differences between MODZT with single ovulations and control women in inhibin A and B concentrations during the cycle, including the critical period for the selection of the dominant follicle. These data suggest that the genetic cause of twinning is not associated with changes in FSH concentrations or recognised feedback mechanisms regulating FSH release.
The pubertal initiation of spermatogenesis is reliant on androgens, and during this time, 5alpha-reduced androgens such as dihydrotestosterone (DHT) are the predominant androgens in the testis. Two 5alpha-reductase (5alphaR) isoenzymes (5alphaR1 and 5alphaR2) have been identified, which catalyze the conversion of testosterone to the more potent androgen DHT. The present study aimed to investigate the developmental pattern of 5alphaR isoenzymes and their relationship to the production of 5alpha-reduced androgens in the postnatal rat testis. Both 5alphaR1 and 5alphaR2 isoenzyme mRNAs were measured by real-time polymerase chain reaction, isoenzyme activity levels by specific assays, and testicular androgens by radioimmunoassay after high-performance liquid chromatographic separation. Both 5alphaR1 and 5alphaR2 mRNAs and activity levels were low in the 10-day-old (prepubertal) testis, peaked between Days 20 and 40 during puberty, and then declined to low levels at 60-160 days of age. The developmental pattern of both 5alphaR isoenzyme activity levels was mirrored by the testicular production of 5alpha-reduced metabolites. Although 5alphaR1 was greater than 5alphaR2 at all ages, it is likely, given the substrate preferences of the two, that both isoenzymes contribute to the pubertal peak of 5alpha-reduced androgen biosynthesis. The peak in 5alphaR isoenzymes and 5alpha-reduced metabolite production coincided with the first wave of spermatogenesis in the rat, suggesting a role for 5alpha-reduced metabolites in the initiation of spermatogenesis. This was explored by acute administration of a 5alphaR inhibitor (L685,273) to immature rats. The L685,273 markedly suppressed testicular 5alphaR activity during puberty by 75%-86%. However, a marked increase was observed in testicular testosterone levels (in the absence of changes in LH), and no decrease was observed in the absolute levels of 5alpha-reduced metabolites. Therefore, whether the formation of DHT in the presence of low testosterone levels in the pubertal testis is required for the initiation of spermatogenesis cannot be tested using 5alphaR inhibitors. We conclude that both 5alphaR1 and 5alphaR2 isoenzymes are involved in the peak of 5alpha-reduced androgen biosynthesis in the testis during the pubertal initiation of spermatogenesis.
This review explores the pituitary-ovarian hormones involved with ageing and the onset of menopause. The serum patterns of pituitary-ovarian hormones throughout the menstrual cycle alter as menopause approaches. The increase in follicular phase FSH prior to menopause is attributed to an early decline in the ovarian hormone, inhibin B, which negatively regulates follicle-stimulating hormone (FSH) secretion. Serum inhibin B is believed to reflect the age-related decrease in ovarian follicle reserve, which is the primary source of serum inhibin B. The later rise in serum luteinizing hormone (LH) during the menopause transition is due to a cessation of ovarian follicle development. Hormonal patterns during the luteal phase of the menstrual cycle also show changes with age but these changes are poorly understood.
We report a 12-month-old infant who presented with a 4-month history of isosexual precocious puberty secondary to an estrogenizing Sertoli-Leydig cell tumor of the ovary. Total serum immunoreactive inhibin and subunits A and B were markedly elevated before surgical resection and subsequently decreased 7 wk later into the normal prepubertal range. Twenty weeks following surgical removal, the patient presented again with central precocious puberty; inhibin B levels were raised on this occasion, a luteinizing releasing hormone stimulation test confirmed central precocious puberty. This is the youngest reported occurrence of this rare sex cord stromal neoplasm. The prognosis of this extremely rare tumor presenting at this early juvenile stage is uncertain. This report illustrates the usefulness of serum inhibin as a tumor marker during therapeutic suppression with leuprorelin acetate for central precocious puberty. Analysis of genomic and tumor DNA revealed a normal nucleotide sequence for the LH receptor and the Galpha(s) gene. To understand the molecular pathogenesis of this tumor we analyzed mRNA levels for the inhibin A and B subunits, FSH receptor, LH receptor aromatase, steroidogenic factor-1 and the ER beta genes. Molecular characterization reveals the presence of genes specific for granulosa and Leydig cells; the relative expression of these genes, in addition to its histologic characteristics, suggests that this tumor may result from a dysdifferentiation of a primordial follicle.
Testosterone (T) treatment suppresses gonadotropin levels and sperm counts in normal men, but the addition of a progestin may improve the efficacy of hormonal contraception. This study aimed to investigate the speed and extent of suppression of testicular germ cell number induced by T plus or minus progestin treatment and correlate these changes with serum gonadotropins and inhibin B levels, testicular androgens, and sperm output. Thirty normal fertile men (31-46 yr) received either testosterone enanthate (TE, 200 mg im weekly) alone or TE plus depot medroxyprogesterone acetate (DMPA, 300 mg im once) for 2, 6, or 12 wk (n = 5 per group) before vasectomy and testis biopsy. Five men (controls) proceeded directly to surgery. The inclusion of DMPA led to a more rapid fall in serum FSH/LH levels (time to 10% baseline: FSH; 12.6 +/- 2.6 vs. 7.9 +/- 1.4 d; LH, 9.9 +/- 3.4 vs. 3.4 +/- 1.7 d, TE vs. TE+DMPA, respectively, mean +/- SD, both P < 0.0001), yet the mean time to reach a sperm count 10% of baseline was not different (23.7 +/- 7.3 vs. 25.3 +/- 13.9 d, NS). The maximum extent of FSH/LH suppression was identical at 12 wk (mean serum FSH 1.2 and 1.6%, and mean LH 0.3 and 0.2% of baseline: TE vs. TE+ DMPA, respectively) as was sperm count suppression (5 of 5 and 4 of 5 men, respectively, with sperm counts < or =0.1 x 10(6)/ml). Serum inhibin decreased to 55% control at 12 wk in the TE+DMPA group (P < 0.05) but was unchanged by TE treatment (86% control, NS). Testicular T levels declined to approximately 2% of control levels, but testicular dihydrotestosterone and 5alpha-androstane-3alpha,17beta-diol (Adiol) levels were not different to control. Germ cell numbers as determined by stereological methods did not differ between TE and TE+DMPA except at 2 wk when type B spermatogonia and early spermatocytes were significantly lower in the TE+DMPA group (P < 0.05). In all groups, a marked inhibition of Apale-->B spermatogonial maturation was seen along with a striking inhibition of spermiation. We conclude that: 1) the addition of DMPA hastens the onset of FSH/LH suppression, correlating with a more rapid impairment of spermatogonial development, but in the longer term, neither germ cell number nor sperm count differed; 2) testicular dihydrotestosterone and Adiol levels are maintained during FSH/LH suppression despite markedly reduced T levels suggesting up-regulation of testicular 5alpha-reductase activity; and 3) spermatogonial inhibition is a consistent feature, but spermiation inhibition is also striking and is an important determinant of sperm output.