Granulosa cells from ovarian follicles (≥ 1 mm diameter) in Booroola ewes which are homozygous (FF) or heterozygous (F+) for the F gene have previously been shown to produce significantly more cAMP in response to FSH or LH than those from similar sized follicles in ewes without the F gene (++). The aim of these studies was to test whether these F gene-specific differences arose because of differences in cAMP-phosphodiesterase (cAMP-PDE) activity.
In the first study using 1 μmol cAMP/1 as substrate, no F gene-specific effects were noted in cAMP-PDE activity in granulosa cells from small (1–2·5 mm diameter, n = 4 per genotype) or large (≥ 3 mm diameter, n = 4 per genotype) follicles from FF, F+ or ++ ewes, despite F gene-specific effects in FSH (1 μg/ml)and LH (0·1 μg/ml)-induced cAMP accumulation in these same cell preparations. The overall mean levels of cAMP-PDE across all genotypes in cells from small and large follicles were 0·47± 0·04 (s.e.m., n = 12) and 0·28 ± 0·03 pmol cAMP/106 cells per min respectively; the mean PDE activity in cells from small follicles was significantly (P < 0·05) higher compared with that in cells from large follicles. In a second study, granulosa cells from each genotype were pooled over all follicle sizes (≥ 1 mm diameter, one pool per genotype) and the rates of cAMP hydrolysis tested over a range of substrate concentrations (0–16 μmol/l) but no genespecific differences with respect to the Michaelis constant and maximum velocity were noted. In a third study, the rates of FSH-induced cAMP accumulation by granulosa cells from small and large follicles of FF and ++ ewes were examined in the presence of a PDE inhibitor, 1-methyl-3-isobutylxanthine (0·2 mmol/l). In this study FSH (1 μg/ml) stimulated significantly more cAMP in cells from FF compared with ++ ewes in both small and large follicles. In cells from small follicles, the mean ± s.e.m. FSHstimulated cAMP levels were 4·7 ± 0·8 (n = 6) for FF ewes and 1·8 ± 0·4 (n = 8) pmol/106 cells per h for ++ ewes (P < 0·025). In large follicles, the cAMP levels were 17·0 ± 3·5 (n = 6) for FF ewes and 6·3 ± 0·5 pmol/106 cells per h for ++ ewes (P < 0·05).
Collectively, these data suggest that the F genespecific difference in cAMP synthesis is probably the result of an event(s) associated with its formation rather than its degradation.
Journal of Endocrinology (1989) 120, 287–293