Development of fetal rat ovaries responsiveness to LH during organ culture

The responsiveness of fetal neonatal rat ovaries to LH was investigated in vitro using three complementary approaches. First, steroid production was assessed after culture. In control media, detectable levels of estrogens (estradiol and estrone) and progesterone were only observed from day 6 postpartum and during the second week of life respectively. In the presence of LH (100 ng/ml) ovaries produced both estrogens and progesterone from day 4 postpartum and the response to LH was enhanced with IBMX supplementation in the medium. Second, 3 beta-HSD activity was measured with either LH or (Bu)2 cAMP (1mM). Irrespective to the time-period studies (Bu)2 cAMP stimulated this enzyme whereas the stimulation with LH occurred only from day 5 postpartum Third, specific hCG binding was assessed and we found that it occurred only on days 7 and 10. However, when fetal ovaries were pretreated for 48 h with (Bu)2 cAMP, a specific hCG binding could be detected and progesterone production was enhanced in response to LH. An effect of the nucleotide via a stimulation of the neuraminidase activity did not seem to be involved. Lastly treatment of 18-day-old fetal ovaries with cholera toxin (10nM) or forskolin (1 microM) was found to stimulate progesterone production and VIP (0.1 to 1 microM) stimulated both the 3-HSD activity and the estradiol production. These data suggest that the absence of steroidogenic response to LH before day 4 postpartum could be explained by the absence of receptors, though the LH transmembrane signal-transduction system is functional in fetal ovaries.(ABSTRACT TRUNCATED AT 250 WORDS)