Receptor mediated gonadotropin action in the ovary

Abstract. The role of macromolecular synthesis in gonadotrophin, cholera enterotoxin and cAMP stimulated progesterone production by rat ovarian cells has been investigated. Both progesterone and cAMP accumulation were increased by cholera enterotoxin in a concentration dependent manner. Incubation of cells with cholera enterotoxin resulted in a 10–20-fold increase in cAMP levels. The effect was observed 15–20 min after addition of toxin. In contrast, stimulation of cAMP levels by hCG was immediate. Cyclic AMP production in response to trophic hormone reached a maximum at 60 min, while maximum stimulation in response to toxin was attained after 2–3 h of incubation. Activation of steroidogenesis in response to both cholera enterotoxin and gonadotrophin showed a lag period. hCG and cholera enterotoxin stimulated a maximum amount of progesterone production after 2 and 3 h of incubation, respectively. With the maximum effective concentration of hCG, addition of choleragen did not result in any further increase in steroidogenesis. Similarly 8 Br-cAMP and Bt2-cAMP also stimulated steroidogenesis. Progesterone response to cholera enterotoxin, hCG, LH, 8 Br-cAMP and Bt2-cAMP was completely blocked by incubation of cells with cordycepin, actinomycin D, emetine and cycloheximide. That the specific effect of these inhibitors was on macromolecular synthesis rather than a general non-specific toxic effect was demonstrated by inhibition of [3H]proline incorporation and the lack of effect of these inhibitors on cAMP production in response to hCG, LH and cholera enterotoxin. Emetine (10 μm) and cycloheximide (50 μm) inhibited cholera enterotoxin and hCG stimulated progesterone production when added at different time points during the incubation. Cordycepin (250 μm) also blocked toxin and hCG induced steroidogenesis in a similar manner. The concentrations of cordycepin, cycloheximide and emetine required to completely block hCG stimulated progesterone production were 250, 50, and 5 μm, respectively. Similar concentrations of these inhibitors also maximally inhibited 8 Br-cAMP and cholera enterotoxin stimulated steroidogenesis. No effect of these inhibitors on basal production of progesterone was observed. These results suggest that gonadotrophin induced progesterone synthesis is dependent upon the continued synthesis of short lived mRNA and protein(s).