The aging Leydig cell: 2. Two distinct populations of Leydig cells and the possible site of defective steroidogenesis

Gonadotropin stimulation of cyclic adenosine monophosphate and testosterone production without detectable high-affinity binding sites in purified Leydig cells from rat testis

Rat testicular interstitial cells were separated by three different gradient-density procedures and, with each, two biochemically and morphologically distinct cell fractions were isolated. The lighter density cells in fraction-I bound iodine 125-labeled human chorionic gonadotropin (hCG) with high-affinity (apparent equilibrium dissociation constant, Kd, approximately 10(-10) M) without producing either cyclic adenosine monophosphate or testosterone in response to hormone action. The heavier-density cells displayed morphologic features typical of Leydig cells and produced cyclic adenosine monophosphate and testosterone in the presence of hCG without detectable 125I-labeled hCG high-affinity binding. These cell fractions were further characterized by studies using deglycosylated hCG, a known antagonist to hCG action. Cell concentration-dependent studies with purified Leydig cells revealed that maximal testosterone production was achieved when lower cell concentrations (0.5 x 10(6) cells/250 microliters) were used for in vitro hCG stimulation assays. Under these conditions, the 125I-labeled hCG binding was barely detectable (2.24 fmol; 2,698 sites/cell). Furthermore, these studies revealed that the hCG-specific binding in Leydig cells is overestimated by the classic method for nonspecific binding correction using excess unlabeled hormone. An alternate method is presented.

Delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity in two distinct density Leydig cells from immature rats. Differences in responsiveness to human chorionic gonadotropin or 8-bromoadenosine 3',5'-monophosphate

The present studies examined the responsiveness to human chorionic gonadotropin (hCG) or 8-bromoadenosine 3',5'-monophosphate (8-Br-cAMP) of delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity of cultured immature Band 2 (low density) or Band 3 (high density) Leydig cells isolated on Percoll gradients. Enzyme activity increased in relation to the dose of hCG or 8-Br-cAMP in both bands; however, activity in Band 2 cells increased about 200% above control, while activity in Band 3 cells increased only about 30-60% above control following 6 days of treatment. Maximal responses were observed 4-6 days following exposure to hCG or 8-Br-cAMP in both bands. Because elevated 5 alpha-reductase activity prevents testosterone accumulation in immature Leydig cells, Band 2 or Band 3 cells were cultured in the presence of 4-methyl-4-aza-3-oxo-pregnan-(20S)-carboxylate, a 5 alpha-reductase inhibitor, to assess the relationship between changes in delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity and testosterone formation. Although hCG or 8-Br-cAMP-stimulated delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity began to decline by day 8 or 10 of treatment, testosterone levels progressively increased for 10 days before declining in both bands. Thus, changes in enzyme activity did not strictly correlate with testosterone synthesizing capacity of cultured Leydig cells. Enzyme activity also was measured in cells cultured with the 5 alpha-reductase inhibitor to determine whether the responsiveness of delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity of Band 2 or Band 3 cells was due, in part, to low testosterone levels. delta 5-3 beta-Hydroxysteroid dehydrogenase-isomerase activity in Band 2 or Band 3 cells cultured without or with the inhibitor was similar, suggesting that testosterone does not inhibit the enzyme in immature Leydig cells. The greater responsiveness of delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity in Band 2 cells was not due to Leydig cell replication as neither total DNA or [3H]thymidine incorporation into DNA was altered by hCG or cAMP.

The questionable physiologic and epidemiologic basis for a male climacteric syndrome: preliminary results from the Massachusetts Male Aging Study

This paper examines the physiologic and epidemiologic evidence for a widely discussed syndrome termed either 'mid-life crisis', 'male menopause', 'male climacteric', or increasingly, 'andropause'. The paper is divided into 2 parts: (1) a review of evidence from physiologic studies conducted over the last decade that examine endocrine function in aging males; (2) a description of the salient features of an ongoing multidisciplinary epidemiologic study (the Massachusetts Male Aging Study) of a sample of approximately 1700 men aged 40-69 yr, randomly sampled from the general population. This study is markedly different in size and content from studies conducted to date. Preliminary findings suggest that age per se may be a relatively unimportant contributor to endocrine variability and that anthropometrics and life style phenomena may be at least as important.

Effects of aging on biologically active pituitary LH in rats

The effects of aging in the male rat on serum testosterone and LH and on the amounts of immunoreactive and biologically active pituitary LH were studied. Animals were killed at three, six, 12 and 24 months of age and serum and pituitary extracts prepared. Serum testosterone was significantly reduced by six months of age and remained at this low level throughout the study. The serum testosterone circadian rhythm was severely blunted in old animals. Serum LH was not effected by aging. Pituitary immunoreactive LH content was significantly decreased by 24 months of age, whereas the biological to immunological (B/I) ratio was not altered. However, the absolute amount of biologically active pituitary LH declined steadily with age from six months. These age-related effects were not caused by a gross redistribution of pituitary LH charge isohormones. These results suggest that the hypostimulated testis in the aging male rat may be related to a reduced amount of biologically active LH available for secretion.

Gonadotropin regulation of Leydig cell DNA synthesis

Adult male rats were injected s.c. with either saline, 100 IU hCG, 100 micrograms FSH, 50 micrograms LH, 100 micrograms PRL, 50 micrograms estradiol-17 beta, 500 micrograms or 10 mg testosterone; 50 micrograms estradiol-17 beta; animals were sacrificed at 12-120 h post-injection. Collagenase-dispersed interstitial cells (150-200 X 10(6) cells/2 ml) were incubated in vitro with 10 microCi [3H-methyl]thymidine for 1 h at 32 degrees C. Centrifugation of the cells on discontinuous 11-27% metrizamide gradients revealed thymidine incorporation in the regions of population I and II Leydig cells. A significant increase in thymidine incorporation into DNA after treatment with either hCG or LH was first detectable at 48 h, was equivalent to control values at 72 h and was again significantly increased at 96 h in population I and at 120 h in population II cells. [3H]Thymidine incorporation at 48 h, expressed as dpm/10(6) cells, was 2205 +/- 432 and 4119 +/- 929 vs. 16473 +/- 3795 and 11648 +/- 3427 for control and hCG-treated population I and II cells, respectively. Addition of 20 mM hydroxyurea suppressed [3H]thymidine incorporation, 97% and 96% in hCG-treated population I and II cells, respectively. Autoradiographic analyses revealed that nuclei from control and 48 h hCG-treated population I and II cells exhibited 1.2% and 2.3% vs. 7% and 6.8% silver grains, respectively. PRL had no influence on LH/hCG-enhanced DNA synthesis; however, estradiol-17 beta administration for 48 h dramatically suppressed thymidine incorporation. Population I Leydig cells exhibited a higher level of LH/hCG-stimulated DNA synthesis compared to population II cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal effects of diethylstilbestrol administration in vivo on testosterone production in Leydig cells

The temporal nature of estrogenic suppression of Leydig cell testosterone production was investigated. Adult rats were injected SC with 50 micrograms/100 g BW of DES or vehicle. Animals were sacrificed at 4, 8, or 12 h following a single injection or at 12 h following the latter of two daily injections for 1 or 2 days. Collagenase-dispersed interstitial cells were obtained, and population I and II Leydig cells were subsequently isolated on metrizamide gradients. Population I and II Leydig cells produced in vitro testosterone levels of 7.19 +/- 0.86 and 12.84 +/- 1.86 ng/10(6) cells/3 h, respectively. These levels were increased to 10- to 13-fold in the presence of hCG of dbcAMP. No significant difference was noted in the responsiveness of these two populations to the in vitro additions. DES administration in vivo for 8-48 h resulted in dramatic and significant decreases in basal and stimulated testosterone production in vitro in both populations. However, DES treatment for 4 h was relatively ineffective in blocking testosterone production in vitro. The inhibitory patterns exhibited by the two populations differed considerably. Population I displayed a uniform degree of inhibition throughout the treatment, whereas population II exhibited a more transient suppression by estrogen. Thus, population II appeared to be less sensitive to the estrogenic effects than population I at 48, 24, and 12 h of treatment. These data indicate that both population I and population II Leydig cells become sensitive to the inhibitory effects of estrogens between 4 and 8 h of in vivo treatment and suggest that certain differences exist between the two populations with respect to the temporal action of estrogens.

Ethanol directly increases dihydrotestosterone conversion to 5 alpha-androstan-3 beta,17 beta-diol and 5 alpha-androstan-3 alpha,17 beta-diol in rat Leydig cells

The direct effect of ethanol on dihydrotestosterone (DHT) conversion to 5 alpha-androstan-3 beta,17 beta-diol (3 beta-diol) and 5 alpha-androstan-3 alpha,17 beta-diol (3 alpha-diol) by adult rat Leydig cells was examined. Concentrations of ethanol comparable to blood levels of alcoholic men (2.2 - 65 mM) increased DHT conversion to 3 beta - and 3 alpha-diol, in direct relation to the dose of ethanol added; a 2-fold or greater stimulation was observed. Because this effect was blocked by 4-methylpyrazole or a saturating NADH concentration, these results suggest that this action is mediated by Leydig cell alcohol dehydrogenase activity. These results may have significant impact in the testis and/or other DHT sensitive tissues because ethanol may decrease the availability of the proposed active androgen.

Stimulation of ornithine decarboxylase activity by luteinizing hormone in rat testicular interstitial cells in vitro is age dependent

The developmental pattern of ornithine decarboxylase (ODC) responsiveness to luteinizing hormone (LH) in isolated rat testicular interstitial cells in vitro was examined and correlated with testosterone production by the same cells. LH caused a 60-100% stimulation of ODC activity in cells from 60-day-old rats but produced no response in cells from 30, 37, 41, 50 and 55-day-old animals. Interstitial cells from 25-day-old rats responded with a moderate (40%) but statistically significant enhancement of ODC activity to the highest LH dose (100.0 ng/ml) only. Testosterone production by control cells was low until day 41 (0.15-0.30 ng/10(6) cells per 4 h), and then markedly increased to adult levels (2.12 +/- 0.03 10(6) cells per 4 h). LH in all concentrations (0.1 - 100.0 ng/ml) employed caused a consistent 4 to 7-fold stimulation of testosterone production in interstitial cells at all ages studied. This study shows age-dependent stimulation by LH of ODC activity in rat testicular interstitial cells in vitro and no apparent correlation with testosterone production by the same cells.

Estradiol receptors of two distinct populations of Leydig cells

The optimal concentrations of molybdate (Mo) to prevent thermal inactivation of estrogen receptor (ER) were found to be 5-20 mM. Using metrizamide density centrifugation, interstitial cells of adult Sprague-Dawley rat testes (2-3 months of age) can be separated into 5 distinct bands. Band 2 (B2) and 3 (B3) cells represented functionally different Leydig cells. For measurement of cytosolic ER, purified Leydig cells (B2 and B3 cells) were homogenized in 10 mM Tris-EDTA buffer with 5 mM of Mo (pH 7.4) and centrifuged at 105,000xg for 60 min. Cytosols were used immediately for ER determination. ER of B2 cells was 24.0 +/- 3.1 fmol/mg protein (mean +/- SE, n = 7), which was significantly higher than that of B3 cells, 18.6 +/- 3.2 fmol/mg protein (n = 7), p less than 0.005. The association constants of these two populations of Leydig cells for E2 receptor were comparable, 5.1 X 10(10)M-1 for B2 cells and 4.2 x 10(10)M-1 for B3 cells. In response to hCG 100 IU s.c., ER of B2 cells was reduced to 2.0 +/- 0.38 fmol/mg protein (n = 5), which was 8.4% of the control B2 cells. ER of B3 cells was almost completely depleted by the same dose of hCG, to 0.70 +/- 0.38 fmol/mg protein, 3.7% of the control B3 cells.

IN CONCLUSION

B2 cells contained higher amounts of ER under basal conditions than B3 cells, and hCG-induced desensitization caused depletion of ER of both B2 and B3 cells.

The aging Leydig cell: VII. Cytoplasmic estradiol receptors

Plasma estradiol and cytosolic estradiol receptor levels of testes were determined in a group of young (2-3 months) and old (24 months) Sprague-Dawley rats. Estradiol binding sites for the young rats averaged 5.6 +/- 0.3 fmol/mg protein (x +/- SE, n=12), which was comparable to that of the old rats, 5.7 +/- 0.3 fmol/mg protein (n=12). Using Scatchard analyses, the association constants at equilibrium of estradiol receptor binding of the old and young rats were the same, 6.1 x 10 10 M-1. Plasma estradiol levels were also similar in both groups-19.6 +/- 2.8 pg/ml (n=14) for the young and 19.2 +/- 2.6 pg/ml (n=10) for the old rats. Our results suggest that impaired testosterone biosynthesis in old rats was not due to elevated plasma estradiol levels or to differences in testicular estradiol receptor content.