Summary. The cAMP outputs by granulosa cells from 3–4·5 mm diameter (medium) follicles of Booroola FF ewes were similar to those by cells from ≥5 mm diameter (large) follicles of ++ ewes with respect to time or dose of FSH, cholera toxin or forskolin. Likewise, the cAMP outputs by cells from 1–2·5 mm diameter (small) FF follicles were similar to those by cells from small and medium ++ follicles with respect to time or dose of FSH, cholera toxin or forskolin. At FSH, cholera toxin or forskolin doses of 1 μg/ml, 0·5 μg/ml and 10 −4 m respectively, the granulosa cell cAMP outputs of medium FF or large ++ follicles were approximately 2-fold (P < 0·05) higher than in the respective small FF and medium ++ follicles. The effects of cholera toxin plus forskolin or FSH plus forskolin were additive irrespective of genotype or follicle size, with significant differences (P < 0·05) observed between follicle sizes but not genotype. No differences were noted between cholera toxin plus forskolin or FSH plus forskolin on granulosa cell cAMP output.
For the FSH and forskolin treatments, increased mean cAMP outputs were evident after 10 min, whereas after cholera toxin treatment they were not evident until after 20 min incubation. For all treatments the rate of cAMP production tended to slow down after 40–60 min.
Pre-incubation of granulosa cells with pertussis toxin subsequently resulted in a significantly greater (P < 0·05) FSH-induced output of cAMP relative to the untreated controls irrespective of follicle size. However, no gene-specific differences were noted when the cAMP outputs of cells from medium or small FF follicles were compared with cells from large or small–medium ++ follicles respectively.
These results indicate that the activity (or composition) of the regulatory and catalytic components of adenylate cyclase in the FF granulosa cells change in a manner similar to those observed in ++ cells with the only difference being that the increases in cyclase in FF ewes occurs as follicles enlarge from 1–2·5 to 3–4·5 mm in diameter, whereas in ++ ewes they occur as follicles enlarge from 3–4·5 to ≥ 5 mm in diameter. No evidence was found to link the F gene to the granulosa cell cAMP response independently of follicle size. It is suggested that the association between the F gene and the size-specific difference in follicle maturation may be unrelated to the FSH receptor/cAMP generating system.
Keywords: FSH; cholera toxin; pertussis toxin; forskolin; cAMP; granulosa cells; Booroola ewes; F gene