Gonadotropins and inhibins along the development of a luteinized rat ovarian tumor.

Luteinized intrasplenic ovarian tumors develop in response to high circulating gonadotropins. The relationship between tumor development, gonadotropins and inhibins was studied. Tumor-bearing animals were sacrificed weekly along the first 6 weeks of development. Inhibins were measured by enzyme-linked immunosorbent assay (ELISA), serum gonadotropins, GH and IGF-1 by RIA. Inhibin subunit mRNAs were determined by Northern blot. Tumor histology was examined. Ovarian grafts grew significantly along development. LH increased ten-fold on week 1; a further significant increment was observed on week 3. FSH peaked on weeks 1 and 2 and fell significantly thereafter. Serum inhibins markedly increased on weeks 3-5. Tumor inhibin A content and mRNA levels for alpha and beta A subunits also increased on week 3. Inverse correlations between inhibins and FSH and direct correlations between inhibins and LH were observed. Tumor inhibin A and IGF-1 contents correlated significantly. Increasing levels of luteinization were observed along tumor development. These luteinized tumors develop mainly in response to LH, since growth continues under FSH inhibition. The active inhibin secretion and the positive correlation between inhibins and LH suggests that LH may be the main driving force behind this production, while growth factors produced by the gonads may also participate in their regulation.

Correlation between inhibin secretion and damage of seminiferous tubules in a model of experimental autoimmune orchitis.

The aim of the present study was to evaluate inhibin secretion in rats with autoimmune orchitis. As we have previously described, experimental autoimmune orchitis (EAO) induced in rats by active immunization with testis homogenate and adjuvants is characterized by an interstitial mononuclear cell infiltrate and sloughing of the germinal epithelium. At 120 days after the first immunization 60% of the rats exhibited a severe orchitis with large areas of aspermatogenic seminiferous tubules in which only spermatogonia and Sertoli cells with cytoplasmic vacuolization remained attached to the tubular wall. None of the untreated (N) or control (C) rats revealed pathological alterations. Sixty percent decrease in testis weight was observed in rats with EAO compared with N or C groups. A 3-fold increase in serum FSH levels was observed in rats with EAO compared with N or C groups (19.8+/-3.7 vs 5.6+/-0.3 and 5.9+/-0.1 ng/ml respectively). A significant decrease in inhibin B levels was observed in rats with EAO when compared with N or C groups (40+/-4.6 vs 207+/-38.8 and 221.4+/-28.6 pg/ml respectively). An inverse correlation between inhibin B and FSH serum levels and a direct correlation between inhibin B and testis weight were found. Strong expression of the inhibin alpha-subunit in Sertoli cells of untreated and control rats was observed; this subunit was undetectable or poorly detectable in rats with orchitis. Positive staining for the inhibin alpha-subunit was also observed in Leydig cells of all groups studied. In conclusion, using a model of autoimmune orchitis our results show that circulating inhibin B levels and inhibin alpha-subunit expression in Sertoli cell cytoplasm closely correlate with the degree of damage of the germinal epithelium.

Dimeric inhibin A and B production are differentially regulated by hormones and local factors in rat granulosa cells.

In the present study, we have examined the role of hormones and growth factors in regulating dimeric inhibin production in immature rat granulosa cells. Purified granulosa cells from estrogen-primed immature rats were cultured under defined conditions. Inhibins A and B in the culture media were measured using a two-site enzyme-linked immunosorbent assay specific for each dimer. Under basal conditions, granulosa cells produced 14-fold more inhibin A than inhibin B (inhibin A, 2.0; inhibin B, 0.14 ng/ml, measured against human standards; average A/B apparent ratio, 14). Addition of increasing doses of FSH elicited dose-dependent increases in both inhibins, the effects being more pronounced on inhibin A than on inhibin B (9.4- and 4.1-fold increases, respectively; average A/B ratio, 34). Estradiol, when added alone, stimulated inhibin A production 3- to 6-fold, whereas minor changes were observed in inhibin B production. Insulin-like growth factor-I produced a similar stimulation of both inhibins (3-fold stimulation over control). This growth factor, however, induced a marked dissociation in the sensitivity of inhibins A and B to FSH stimulation, with maximal stimulation of inhibin B observed at comparatively lower concentrations of the gonadotropin. Transforming growth factor-beta (TGF-beta, 5 ng/ml) had a more marked stimulatory effect on inhibin B than on inhibin A production (7- to 14-fold vs. 2- to 5-fold for inhibin B and A, respectively). A more pronounced differential stimulation of inhibin B was also exerted by another member of the TGF-beta superfamily, activin A (A/B ratio, 0.66). This preferential stimulation of inhibin B by TGF-beta and activin A was amplified in the presence of FSH. Coculture of rat granulosa cells with freshly isolated bovine oocytes was also associated with a marked stimulation of inhibin B production (100-fold increase) and a comparatively lower stimulation of inhibin A (10-fold increase; A/B ratio, 1). The discrepancy between the proportion of inhibin dimers in serum (A/B ratio, 0.13) and those produced by untreated granulosa cells may suggest that intraovarian factors, such as TGF-beta, activin A, or oocyte-derived factor(s), are responsible for the shift of the ratio toward the predominance of inhibin B.