STIMULATORY EFFECT OF FSH IN VITRO ON THE EXTRACELLULARLY ACTIVE CYCLIC AMP PHOSPHODIESTERASE IN THE PREPUBERTAL RAT OVARY

Abstract

Intact prepubertal rat ovaries were incubated with radioactively labeled 3'',5''-cyclic (c) AMP 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. cAMP was degraded to AMP, which in turn was degraded to Pi and adenosine. An uptake of labeled products was also observed. NIH-FSH (National Institute of Health follicle stimulating hormone)-S9 (10 and 100 .mu.g/ml), but not NIH-LH (luteinizing hormone)-B8 (0.1-100 .mu.g/ml), increased the degradation of cAMP. Concomitantly, an increased accumulation of labeled adenosine and Pi and an increased uptake of labeled products were seen. Kinetic studies with low concentrations of cAMP (0.125-0.025 .mu.mol/l) revealed an apparent Km value of 0.12 .mu.mol/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 between LH and FSH on the cAMP system in the prepubertal rat ovary.