Differential control of immunoreactive alpha-inhibin and progesterone production by marmoset luteal cells in vitro: evidence for a paracrine action of alpha-inhibin on basal and gonadotropin-stimulated progesterone production.

There is an increase in plasma concentrations of immunoreactive (ir) inhibin unaccompanied by a rise in plasma progesterone during early pregnancy in the marmoset monkey. We investigated the potential involvement of hCG and prostaglandin E 2 (PGE2 ) in stimulating a selective increase in inhibin concentrations by measuring the production of ir-a-inhibin and progesterone by dispersed luteal cells cultured under serum-free conditions. After one day, hCG had no effect on progesterone production by the cells but stimulated a significant increase (p < 0.05) in a-inhibin production. PGE 2 significantly increased progesterone production (p < 0.001) but inhibited the production of a-inhibin (p < 0.001). After three days of culture, output of a-inhibin fell to low levels and no significant effect of hCG or PGE2 was detected. Progesterone also fell with time in culture, but hCG maintained production resulting in a significant increase above control levels (p < 0.001). The addition of low density lipoproteins (LDL) to the culture medium increased progesterone production (p < 0.001) while decreasing a-inhibin production (p < 0.01). Immunoneutralization of endogenous a-inhibin resulted in a significant decrease in both basal (p < 0.05) and gonadotropin-stimulated (p < 0.05) progesterone concentrations. These results provide further evidence for differential control of progesterone and at-inhibin production by marmoset luteal cells and show that hCG can selectively stimulate a-inhibin production. In addition, oa-inhibin may have a local paracrine action in the marmoset CL, enhancing both basal and gonadotropinstimulated progesterone secretion.