Adenosine 3',5'-monophosphate primes the secretion of follicle-stimulating hormone

We investigated whether cAMP acts as a mediator for LHRH in either its immediate FSH release action or its self-priming action. Pituitary pieces from cyclic female rats were superfused in vitro in the presence of Bu2cAMP, 8-bromo-cAMP, or forskolin or used as controls. For pituitary pieces from proestrous rats, the first significant increase in the baseline FSH secretion rate occurred after approximately 90 min of exposure to elevated cAMP resulting from forskolin treatment. By comparison, in the same system LHRH caused a 3-fold increase in FSH secretion during a 10-min exposure to the peptide. In contrast to its ineffectiveness as a secretagogue, cAMP elevation resulted in a several-fold augmentation of both LHRH- and elevated K+-stimulated FSH secretion from pituitary pieces from proestrous, but not estrous, rats; for these experiments, superfusion with a cAMP analog or forskolin for varying times preceded a 10-min pulse of either 8 nM LHRH or 47 mM K+. Augmentation of K+-stimulated secretion was evident after 30 min of cAMP elevation. Priming of LHRH-stimulated FSH secretion required 30-90 min of pretreatment with cAMP; longer exposures to cAMP analogs or forskolin were coincident with greater potentiation. Cycloheximide prevented Bu2cAMP augmentation of LHRH-stimulated FSH secretion. These data show that cAMP does not mimic the FSH release action of LHRH, but does augment LHRH- or K+-stimulated FSH secretion with characteristics that lead us to suggest that cAMP mediates, at least in part, the self-priming function of LHRH.