Stimulatory effect of FSH in vitro on the extracellularly active cyclic AMP phosphodiesterase in the prepubertal rat ovary.

Intact prepubertal rat ovaries were incubated with radioactively labelled adenosine 3',5'-cyclic monophosphate (cAMP) in Krebs bicarbonate buffer containing glucose. The rate of degradation of cAMP was determined by measuring the radioactivity in the medium after precipitation with Ba(OH)2 and ZnSO4. The fate of the nucleotide was followed by measuring the products in the incubation medium. Paper chromatography was used for the separation and identification of these products. It was found that cAMP was degraded to AMP, which in turn was degraded to inorganic phosphate (Pi) and adenosine. An uptake of labelled products was also observed. NIH-FSH-S9 (10 and 100 mug/ml), but not NIH-LH-B8 (0.1-100 mug/ml), increased the degradation of cAMP. Concomitantly, an increased accumulation of labelled adenosine and Pi as well as an increased uptake of labelled products were seen. Kinetic studies with low concentrations of cAMP (0.125-0.025 mumol/l) revealed an apparent Km value of 0.12 mumol/l for the phosphodiesterase (PDE) activity. FSH significantly changed the slope of the curve in the Lineweaver-Burk plot by increasing the PDE activity. The increased PDE activity in the presence of FSH is discussed in relation to earlier findings of differences in action betweeh LH and FSH on the cAMP system in the prepubertal rat ovary.