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PubMedDate not supplied

FSH immunoneutralization acutely impairs spermatogonial development in normal adult rats.

Follicle-stimulating hormone (FSH) plays an important part in testicular development. Its role in the regulation of spermatogenesis in the adult, however, remains controversial. This study aimed to explore the role of FSH in the maintenance of adult rat spermatogenesis by using immunoneutralization to selectively withdraw FSH action for periods of up to 8.5 days and then assessing the outcome by quantification of germ cell number. Adult rats received either an ovine polyclonal rat FSH antibody (FSHAb, 2 mg/kg subcutaneous daily-a dosage known to neutralize >90% of FSH in serum) for 2, 4, 7, or 8.5 days or a control sheep immunoglobulin (ConAb, 2 mg/kg) for 8.5 days. Testes were perfusion fixed, and germ cell numbers per testis were quantified using the optical disector (sic) stereological method. The percentage of seminiferous tubules displaying apoptotic cells was determined by the in situ end labeling method (TUNEL). FSHAb treatment for 4, 7, or 8.5 days significantly reduced the number of type A/intermediate spermatogonia (approximately 74% of control values) associated with stages I-IV. Similar reductions were seen in type B spermatogonial and preleptotene spermatocyte numbers after 8.5 days of FSHAb treatment (approximately 69% of control values; P < 0.05). Decreases (P < 0.05) in the numbers of pachytene spermatocytes in stages I-III and VIII, round spermatids in stages I-III, VII, and VIII (approximately 70% of control values), and step 19 elongated spermatids in stage VII (51% of control values) were achieved after 8.5 days of FSHAb treatment. Compared with control, FSHAb treatment increased the percentage of stage XIV-III tubules containing TUNEL-positive cells by about twofold after 7 days of FSHAb treatment (P < 0.05). This study supports a role for FSH in the maintenance of quantitatively normal adult rat spermatogenesis, specifically by regulating A3 and A4 spermatogonial subtypes. FSH may act on these spermatogonia by enhancing the stage-dependent survival of type A spermatogonia. Effects at other sites in spermatogenesis are suggested by the changes in spermatocyte and spermatid populations. However, to clarify these effects, selective FSH withdrawal would need to be prolonged until steady state had been achieved.

Animals↗
PubMed2002

Role of low circulating FSH concentrations in controlling the interval to emergence of the subsequent follicular wave in cattle.

The intervals between emergence of follicular waves 1 (first wave of an oestrous cycle) and 2, and between the associated FSH surges (surges 1 and 2), were studied in control (n = 7) and recombinant bovine (rb)FSH-treated (n = 7) heifers. The expected start of the deviation in follicle diameter between the two largest follicles of wave 1 was defined as the day on which the largest follicle reached 8.5 mm (day 0). In the control heifers, circulating concentrations of FSH decreased and oestradiol increased between day 0 and day 1.5 or day 2.0 in a reciprocal relationship. The opposite reciprocal relationship between an FSH increase and an oestradiol decrease occurred during the next 3 days. This temporal result is consistent with a negative systemic effect of oestradiol on FSH at this time. rbFSH was administered in a dosage regimen that was expected to result in a similarity between FSH surge 2 in the rbFSH-treated group and surge 2 in the control group. On average, surge 2 and wave 2 occurred approximately 2 days earlier in the rbFSH-treated group than in the control group, and characteristics of the FSH surge and follicular wave were similar (no significant differences) between groups. These results support the hypothesis that low circulating FSH concentrations after the deviation in follicle diameter control the interval to emergence of the subsequent follicular wave. However, in one of seven rbFSH-treated heifers, the largest follicle from the apparent stimulation of rbFSH reached only 5.7 mm; therefore, the possibility of involvement of additional mechanisms cannot be dismissed.

Animals↗
PubMed2002

[Continuous measurement of urine beta-FSH excretion in men with hypogonadism].

OBJECTIVES: To measure continuously the urine beta-FSH excretion in the patients with male hypogonadism, and to evaluate the significance of urine beta-FSH when used in the clinical practice and pathophysiological study on male hypogonadism. METHODS: Four health male volunteers (aged 19, 22, 27 and 33 years), four patients with the hypogonadotropic hypogonadism (aged 17, 17, 19 and 24 years) and five patients with idiopathy hypogonadism (hypergonadotropic, aged 16, 16, 17, 20 and 22 years) were asked to collect their morning-first urine samples for 30 to 32 days. One normal men collected his urine samples for 63 days. The urine beta-FSH was assayed with the method of EIA, then corrected by creatinine (Cr) concentration. RESULTS: The urine beta-FSH level of normal men was (1.16 +/- 0.20) micrograms/mg Cr, with the peak variation in their curves, peak level at 2.76 micrograms/mg Cr. The levels of urine beta-FSH of 4 patients with the hypogonadotropic hypogonadism were lower significantly than those of normal men [(0.58 +/- 0.31) (0.93 +/- 0.47) (0.47 +/- 0.33) and (0.60 +/- 0.40) micrograms/mg Cr], without fluctuation in their curves. beta-FSH levels of 5 patients with idiopathy hypogonadism were higher significantly [(3.02 +/- 0.93), (4.36 +/- 1.12), (4.79 +/- 0.78), (4.64 +/- 1.42) and (3.88 +/- 1.42) micrograms/mg Cr], with irregular fluctuation, the highest peak level at 6.83 micrograms/mg Cr. The second sexual characteristics of hypogonadal patients were poor and serum testosterone levels low. CONCLUSIONS: The urine beta-FSH level raised with irregular fluctuation in patients with idiopathy hypogonadism, while lowed without any fluctuation in patients with the hypogonadism. These findings suggested that the urine beta-FSH excretion was useful for the clinically classified diagnoses and pathophysiological study on male hypogonadism, and for observing the treatment reaction of androgen replacement.

Adolescent↗
PubMed2004

[Detection and potential function of anti-FSH antibodies in patients with spermatogenesis dysfunction].

OBJECTIVE: To detect the anti-FSH antibody using ELISA, and further probe into the role of anti-FSH in infertile patients. METHODS: The anti-FSH antibody was detected using ELISA in the serum of patients with spermatogenesis dysfunction, of infertile patients with normal sperm density and motility, and of normal fertile males. RESULTS: The positive rate of anti-FSH antibody in the patients with oligospermia and/or asthenospermia [22.4% (22/98)] was significantly higher than that in the normal fertile [4% (2/50)] (P < 0.05) and that in the infertile patients with normal sperm density and motility [6.7% (2/30)] (P < 0.05). The positive rate of anti-FSH antibody in the patients with oligospermia and/or asthenospermia was lower than that in the patients with azoospermia [54.5% (12/22)] (P < 0.05). There was no significant difference in the positive rate between the normal control and the sterile males with normal sperm density and motility. CONCLUSION: The anti-FSH antibody may be an important factor to cause spermatogenesis dysfunction by combining FSH to form immune compound and depress the activation of FSH.

Antibodies↗
PubMedDate not supplied

Cellular regulation of follicle-stimulating hormone (FSH) binding in rat seminiferous tubules.

Stage-specific binding of follicle-stimulating hormone (FSH) was measured in rat seminiferous tubules. The binding in single-point assays was over 3-fold higher (P less than 0.05) in stages XIII to I than in stages VI to VII of the epithelial cycle. No difference was found between the equilibrium association constants (Ka) of FSH binding in stages XIV to IV (10 +/- 1.9 X 10(9) 1/mol) and VII to VIII (9.2 +/- 0.6 X 10(9) 1/mol, mean +/- SEM, n = 5). In another experiment, the testes were dosed locally with 3 Gy of 4 MV x-irradiation to selectively lower the number of spermatogonia. After irradiation, FSH binding in staged seminiferous tubule segments was measured when the desired types of spermatogenic cells were reduced in number. Seven days after irradiation when differentiating spermatogonia and preleptotene spermatocytes were reduced in number, FSH binding was decreased in all stages of the cycle, but the cyclic variation remained. Seventeen days after irradiation when intermediate and type B spermatogonia and spermatocytes up to diplotene of stage XIII showed low numbers, FSH binding was decreased in all stages of the cycle and the stage-dependent variation disappeared. At 38 days when pachytene spermatocytes and early spermatids were reduced in number, similar results were found. But at 52 days postirradiation when all spermatids were low in number, FSH binding was slightly elevated compared with days 17 and 38. There were no significant differences in serum FSH or LH levels between irradiated and non-irradiated animals. These findings suggest that all spermatogenic cell types may stimulate FSH binding in the Sertoli cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Plasma concentrations of FSH and testosterone in male infertile patients.

We studied the statistical distribution of the plasma concentrations of FSH and testosterone in patients with oligoazoospermia as compared with normospermic subjects. The plasma concentration of FSH was determined in 429 patients with oligoazoospermia and 282 normospermic subjects ("controls"). In 118 out of these 429 patients and in 47 of the 282 controls, the plasma concentration of testosterone was also measured. The plasma concentrations of FSH differed significantly depending on the patients' values of spermatic concentration. The most significant difference was observed between azoospermic patients and controls, whereas the difference between patients with mild oligospermia and controls was not significant. Conversely, the plasma concentrations of testosterone did not correlate with the values of spermatic concentration and even the difference between azoospermic patients and controls did not reach the significance level. In addition, testosterone plasma concentrations did not differ between two sub-groups of patients who were defined depending on whether the plasma concentration of FSH was normal or high. Our findings confirm the inverse relation between plasma FSH levels and spermatic concentration which had already been observed in previous studies. However, a considerable overlap in the plasma concentrations of FSH has been found between sub-groups of patients with different spermatic concentrations. This overlap limits the clinical usefulness of the measurement of FSH concentration inasmuch as normal FSH plasma levels may often be associated with any value of spermatic concentration. Also, our data confirm that the measurement of testosterone plasma levels provides little clinical usefulness in male infertile patients.

Adult↗
PubMed1980

Effects of steroids on basal and GnRH-induced LH and FSH secretion by dispersed pituitary cells of immature female lambs.

The effects of 17 beta-estradiol (E2), progesterone (P) and their combination on the basal and GnRH-induced LH and FSH release were studied in immature female lamb pituitary cells. Lambs born in February (slaughtered at 12--13 weeks of age) (Y) or older (O) out of season born in the previous year and carried over to January and April (hoggets) were used as pituitary donors. The cells were preincubated for 24 h in the presence or absence of steroids, then washed and incubated for 2 h with or without GnRH. E2 (100 pg ml-1) depressed the basal and GnRH-induced LH and FSH release and P at the highest dose used (10 ng ml-1) decreased significantly the basal and GnRH-induced LH release, whereas it did not affect these parameters of FSH release from pituitary cells of Y. In contrast to these effects of steroids, E2 (10--1000 pg ml-1) stimulated the basal and GnRH-induced LH and FSH release from pituitary cells of O. P (0.1--10 ng ml-1), in a way inversely related to the concentration, stimulated the basal LH and FSH release; the higher P concentration did not affect the GnRH-induced FSH, while it permitted a small but significant increase of the GnRH-induce LH release in O (43% above the GnRH-treated level). Taking in account the basal release, the sensitivity of LH and FSH response to GnRH was increased by E2. In E2 + P treated cells, P did not modify the E2 effect on the LH responsiveness to GnRH in pituitaries of Y or O. On the other hand, P at the higher dose (10 ng ml-1) potentiated the stimulatory effect of E2 on basal and GnRH-induced FSH release in O. The results suggest that E2 and P can exert negative or positive effects on gonadotropin release from pituitary cells of immature female lambs depending on the developmental stage of the pituitary donors and the steroid concentration. P depressed the sensitivity of response to GnRH induced by E2.

Animals↗
PubMed1996

The effect of hormonal superovulatory preparation FSH on the levels of catecholamines in the blood plasma of sheep.

The effect of hormonal stimulation with FSH injection in the doses of 18 mg (360 IU) and 24 mg (480 IU FSH) on the levels of plasma catecholamines (dopamine, norepinephrine and epinephrine) was studied by radioenzymatic methods during synchronized oestrous cycles of the sheep. Catecholamines were determined in the blood plasma before and 24, 48, 96 and 120 hours after application of FSH. It follows from the results that the levels of plasma dopamine increased significantly (p<0.001) 24 and 48 hours after FSH application. Furthermore, the levels of dopamine (DA) during the other time intervals observed, compared with those of controls before hormonal stimulation, remained at a higher level. A lower dose of the hormone (18 mg) had a more pronounced effect on changes in the levels of plasma dopamine. Norepinephrine (NE) did not exhibit any significant changes in comparison with the plasma levels of dopamine in the sheep after hormonal stimulation with FSH. A statistically significant increase in plasma norepinephrine was recorded 24 hours after administration of 18 or 24 mg FSH. During the other time intervals observed, its levels did not differ from the control values. Plasma epinephrine (E) showed a significant increase 24 and 48 hours after FSH application but not later. The effect of FSH on plasma catecholamine levels was not dose-dependent and their increase was pronounced especially in the period of ovulation.

Animals↗
PubMed1998

The effect of activin and FSH on the differentiation of rat granulosa cells.

The differentiation of granulosa cells is regulated by follicle-stimulating hormone (FSH) and local ovarian factors. To further analyze the role of FSH and activin in this process, we have examined the effect of FSH and activin on FSH and luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor induction in granulosa cells. Granulosa cells from diethylstilbestrol (DES)-primed immature rats produce activin and maintain FSH receptor without LH/hCG receptor expression in the absence of FSH. On the other hand, FSH induced granulosa cells to differentiate into more mature granulosa cells in which higher LH/hCG receptor expression and diminished activin production were observed.

Activins↗
PubMed1998

In vitro inhibition of the bioactivity of follicle-stimulating hormone by antisera against a peptide representing part of the FSH-receptor.

The aim of the present work was to define an FSH receptor (FSHR) peptide that can induce antibodies that will inhibit the bioactivity of FSH. Therefore, the hFSHR sequence was aligned with that of all other known G-protein coupled receptors. An area with increased sequence homology was identified between the FSH-, LH-, TSH receptors, the C5a receptor and the IL8 receptor. The similarity consists of a richness in acidic (D and E) and hydrophobic (Y and F) residues. In hFSHR the sequence is EDNESSYSRGFDMTYTEFDYDLCNEVVD (amino acid 299-326). Research on both the C5a- and IL8-receptor has indicated that this part is responsible for hormone binding but not for signal transduction. Protamine. an antagonist for both the C5a- and IL8 receptor also inhibited the bioactivities of FSH and LH when tested in a bioassay. This suggests that in the hFSHR this region might also be involved in hormone binding. Specificity of this region towards the diverse ligands all binding to the C5a or to the IL8 receptor might be attributed to differences in the profile of alternating basic and hydrophobic residues. Therefore, the hypothesis was tested as to whether antisera raised against peptides of this FSHR-domain would inhibit FSH-bioactivity but not LH-bioactivity. Indeed antisera were found (anti-hFSHR 309-322) that inhibited the biological activity of FSH in a bioassay. These antisera proved to be specific since they did not inhibit the bioactivity of LH. These data suggest that the core sequence (hFSHR 309-322) of the aligned domain of the hFSHR, in analogy to the IL8- and C5a receptors, is involved in hormone binding and ligand specificity. This domain therefore forms a valuable tool in FSH- and FSHR research for scientific and medical purposes.

Amino Acid Sequence↗
PubMed1997

Men homozygous for an inactivating mutation of the follicle-stimulating hormone (FSH) receptor gene present variable suppression of spermatogenesis and fertility.

Gonadal function is controlled by the two pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). While LH mainly regulates gonadal steroidogenesis, FSH is considered essential for folliculogenesis in the female and spermatogenesis in the male. We recently discovered that an inactivating point mutation in the FSH receptor (R) gene causes a recessively inherited form of hypergonadotropic ovarian failure in homozygous females. This 566C-->T mutation, predicting an alanine to valine substitution, is located in exon 7 of the FSHR gene, in the region encoding the extracellular domain of the receptor molecule. Functional testing showed a clear-cut reduction in ligand binding and signal transduction by the mutated receptor. Hence, lack of FSH function is incompatible with ovarian follicular maturation and female fertility. In the male, FSH is generally considered essential for the pubertal initiation of spermatogenesis and maintenance of quantitatively normal sperm production in adults. We report here the first characterization of males homozygous for an inactivating FSHR mutation. They have variable degrees of spermatogenic failure, but, surprisingly, do not show azoospermia or absolute infertility. These results question the essential role of FSH for the initiation of spermatogenesis, and demonstrate that FSH is more important for female than for male fertility.

Adult↗
PubMedDate not supplied

Studies on low molecular weight follicle stimulating hormone receptor binding inhibitor (FSH-RBI) from ovine testis.

Follicle stimulating hormone receptor binding inhibitor (FSH-RBI) has been isolated from the aqueous extracts of ovine testis using Sephadex column chromatography. Sephadex G-75 fraction IV was found to inhibit the binding of (125I) FSH to rat testis receptors. Further purification of Sephadex G-75 fraction on Sephadex G-25 column gave three fractions (I-III). The maximum inhibitory activity to inhibit (125I) FSH binding to rat testis receptor was associated with fraction III only. FSH-RBI exerted a greater inhibitory effect on the formation of the hormone-receptor complex rather than on the dissociation of the preformed complex. FSH-RBI did not inhibit the binding of (125I) LH to rat testis receptors. A significant decrease in the mouse ovarian weight was observed when FSH-RBI was injected to hCG-primed female mice. The molecular weight determination studies show that molecular weight of FSH-RBI is approximately 1400 Daltons.

Animals↗
PubMed1984

Identification of specific FSH binding sites in the testes of adult monkeys of different species.

The interaction of 125I-labelled hFSH with primate testicular tissue from 4 species of adult monkeys (Macaca mulatta, M. nemestrina, M. fascicularis and Papio cynocephalus) was investigated. 125I-labelled hFSH binding to a particulate fraction (P1, 40 000 g) of frozen testes was highly specific and saturable. Displacement curves generated using the P1 fraction of testes from the 4 species and 125I-labelled hFSH and unlabelled FSH were very similar. The binding of FSH to the monkey testicular receptor was not species specific because purified FSH from heterologous species such as horse, sheep, pig and rat were very effective in competing with 125I-labelled hFSH for binding. The equine FSH was about 10 times more active than hFSH in this respect. Similarly, 125I-labelled ovine FSH bound as well as labelled hFSH to the testes fractions of all 4 monkey species. In marked contrast to the high binding of 125I-labelled hFSH, binding of 125I-labelled hCG with rhesus monkey testis homogenates and P1 fractions was very low. The FSH receptor in the adult rhesus monkey testis was present in much larger quantity than the LH receptor and was more readily detectable. Our studies show that frozen primate testis can be utilized for investigating testicular-FSH interactions.

Animals↗
PubMed1991

Differences in properties of the sheep testicular LH and FSH receptors.

Differences in binding and structural properties of ovine testicular FSH and LH receptors were investigated. The ovine FSH receptor did not discriminate between FSH of different species, although equine FSH was more reactive. In the same tissue, however, the LH receptor showed marked preference for ovine and bovine LH, reacting very weakly with other preparations of pituitary LH. Human chorionic gonadotrophin also reacted partly with the ovine LH receptor at 25 degrees C. However, at 4 degrees C, the optimum temperature for binding of the LH receptor to its homologous hormone, the receptor displayed no recognition for chorionic gonadotrophin preparations. Affinity cross-linking studies with ovine testicular membrane suggested that the ovine FSH receptor has an Mr of 70,000, which is very similar to that observed in the porcine ovary. The Mr of the ovine LH receptor was estimated to be 150,000, which is different from those of other mammalian species, including those that have been cloned. The data suggest that the binding and structural properties of the ovine FSH receptor are similar to those of other mammalian FSH receptors, whereas the ovine LH receptor appears to differ from other mammalian LH receptors in having a different Mr and in being more stringent in its requirement for pituitary LH.

Animals↗
PubMed1987

A decrease in FSH receptors of granulosa cells during follicular maturation in the domestic hen.

The follicles of the ovary in the domestic hen are arranged in a hierarchy. Responsiveness of the adenylyl cyclase enzyme system of the granulosa cells to FSH decreases as follicles proceed towards ovulation. To test the hypothesis that this decline in FSH responsiveness could be the result of a decrease in FSH receptor numbers, an FSH receptor assay was characterized for chicken granulosa cells and used to measure receptor number and affinity of the largest (F1), third largest (F3) and fifth largest (F5) follicles removed 18 h before ovulation. The numbers of binding sites for F1, F3 and F5 follicles (n = 4) were 0.22 +/- 0.05, 0.5 +/- 0.14 and 1.22 +/- 0.27 pmol hormone bound/mg protein respectively, and were significantly (P less than 0.001) different among follicles. The apparent association constants for the F1, F3 and F5 follicles were not different and had a value of 23.4 +/- 4.9 litres/nmol (n = 12). Our results indicate that FSH receptor numbers decrease in granulosa cells without a change in affinity as follicles approach ovulation. The decrease in FSH receptor numbers is associated with the reported decline in FSH-stimulated steroidogenesis and adenylyl cyclase activity which occurs during follicular maturation.

Animals↗
PubMed2005

FSH, the neglected sibling: evidence for its role in regulation of spermatogenesis and Leydig cell function.

The role of follicle stimulating harmone(FSH) in male reproductive function remains a matter of debate although recent evidences strongly suggest a role despite the controversies that arose following the results obtained with FSH-beta null mice and observations from human FSH receptor mutations. This review summarizes the recent developments of our understanding on the role of FSH in male reproduction. Specifically the results obtained with FSH-beta and FORKO null mice are be discussed in light of our observations employing active and passive neutralization of endogenous FSH in rodents and primates along with other studies. On the basis of results obtained employing a variety of models it can be conclude unequivocally that FSH regulates Leydig cell function and is essential for normal quantitative spermatogenesis.

Animals↗
PubMedDate not supplied

Individual differences in LH and FSH responses to orchidectomy and testosterone replacement therapy in rams.

Profiles of LH and FSH levels and pituitary LH responses to exogenous luteinizing hormone releasing hormone (LHRH) have been characterized in rams, castrated rams (wethers), and wethers implanted with testosterone. Rams were castrated when adult, and, at the time of castration, two groups of wethers were implanted with either four or eight testosterone capsules. Rams showed random pulses of LH and testosterone which were temporally related. The number of LH and testosterone pulses per 24 hours differed among rams, giving rise to large differences in the mean levels of these hormones. Mean FSH levels and pituitary LH responses to LHRH also differed among rams and were positively correlated to differences in LH levels. All three nonimplanted wethers showed a rhythmic pulsatile pattern of LH secretion and had elevated mean LH and FSH levels. There were, however, appreciable differences between wethers with regard to mean LH and FSH levels and pituitary LH responses to LHRH. Both four and eight testosterone capsules were effective in suppressing pulsatile LH secretion and mean LH and FSH levels in two out of three wethers. In a third animal within each of these groups, however, LH and FSH profiles and LH responses to LHRH were characteristic of nonimplanted wethers. These data suggest that individual rams have different inherent capacities to secrete gonadotropins which influence LH and FSH responses to castration and testosterone replacement therapy.

Animals↗
PubMed1995

Proliferation of newt spermatogonia by mammalian FSH via Sertoli cells in vitro.

Our previous studies showed that mammalian follicle-stimulating hormone (FSH) stimulated the proliferation and differentiation of secondary spermatogonia into primary spermatocytes in organ culture of testes fragments from Cynops pyrrhogaster. To elucidate how FSH stimulates spermatogonial proliferation, we studied the interaction of spermatogonia with somatic cells in the presence or absence of FSH in cultures of aggregated cells derived from fractionated cell populations. When spermatogonia or those with somatic cells were cultured, they formed aggregates with themselves or with somatic cells, respectively. Most of the somatic cells in the aggregates were Sertoli cells, judged by the lipid droplets in their cytoplasm. [3H]thymidine incorporation into aggregates and autoradiography demonstrated spermatogonial proliferation that was enhanced in the presence of FSH and somatic cells (most probably Sertoli cells), but not in the absence of FSH or in the presence of luteinizing hormone (LH). To examine whether direct contact between spermatogonia and Sertoli cells is indispensable for the stimulation of spermatogonial proliferation by Sertoli cells, the two cell types were separated by a 0.4 micron pore filter in two compartments of a bicameral chamber. In this case, Sertoli cells did not stimulate spermatogonial proliferation in the presence of FSH, indicating that direct contact between spermatogonia and Sertoli cells is indispensable for the stimulation of spermatogonial proliferation by Sertoli cells. Finally, Sertoli cells isolated from the testes from the primary spermatocyte stage did not stimulate spermatogonial proliferation in the presence of FSH. This result indicated that the function of Sertoli cells with respect to their stimulation of proliferation was stage-specific.

Animals↗