Ovarian cyclic GMP concentration and guanylate cyclase activity in immature rats after treatment with pregnant mare serum gonadotrophin

Abstract

We have previously reported that the LH-induced decrease in the concentration of ovarian cyclic GMP (cGMP) in the rabbit was accompanied by a drop in ovarian guanylate cyclase activity. The present experiments were carried out to see if the increase in cGMP concentration that occurs in immature rat ovaries after stimulation with pregnant mare serum gonadotrophin (PMSG) is also accompanied by changes in guanylate cyclase activity. Total ovarian cGMP, along with ovarian weight, was found to be increased at 16 h after PMSG treatment. Ovarian concentrations of cGMP, however, increased only after that period (at 20, 24 and 48 h) and the increase was progressive. Guanylate cyclase activity was found in both the cytosol and 100 000 g particulate fractions of the immature rat ovaries. Forty-three hours after PMSG treatment, activity in the particulate fraction was found to be significantly increased. This increase in guanylate cyclase activity was also found at 20 h but not at 16 h. Thus, the increase in ovarian cGMP concentration in immature rats after PMSG treatment was accompanied by increased guanylate cyclase activity.

Gonadotropin-controlled mammal oocyte meiotic resumption

“…Recently, granulosa cells from porcine large follicle shew strong expression of ANP (153). In addition, pregnant mare's serum gonadotropin (PMSG) increased the production of ANP and cGMP in rat ovary (161,162), and LH results in decrease of cGMP by suppressing guanylate cyclase activity in rabbit ovary (161). Taken together, it can be hypothesized that accumulation of cGMP under FSH stimulation (during follicular growth) may serve to prevent untimely oocyte maturation until ovulation after the LH serge (Figure 2).…”

Review

“…Cyclic GMP can, in contrast to cAMP, be produced both by a membrane-bound guanylate cyclase (GC) and a soluble GC (Waldman and Murad, 1987), both existing in the rat ovary (Patwardhan and Lanthier, 1985). We used ANP and SNP selectively to stimulate the membrane bound and the soluble GC respectively (Leitman et al, 1987).…”