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V. V. PATWARDHAN and A. LANTHIER

Laboratoire d'Endocrinologie, Hópital-Notre-Dame et Département de Médecine, Université de Montréal, Montréal, Canada

(Received 8 June 1977)

In ovarian tissues, the synthesis of oestrogen from pregnenolone can proceed via progesterone and the 3-oxo-4-unsaturated steroid pathway or by way of dehydroisoandrosterone and the 5-unsaturated steroid pathway. In human ovaries, the follicle seems to prefer the 5-unsaturated pathway for formation of oestrogen (Ryan & Petro, 1966), whereas in the corpus luteum, the 4-unsaturated steroid pathway may be the only one that is operative (Ryan, 1963). The situation is not so clear in other species. In the rabbit, a reflex ovulator, ovarian follicles are known to secrete oestradiol (YoungLai, 1972). Furthermore, isolated follicles can form oestradiol, androgens and progesterone from endogenous (Mills, 1975) or exogenous (Mills & Savard, 1972) precursors in vitro. Mills & Savard (1972) incubated rabbit follicles with [1-14C]acetate and isolated labelled oestradiol and intermediates involved in the 4- and 5-unsaturated steroid

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V. V. PATWARDHAN and A. LANTHIER

Laboratoire d'Endocrinologie, Hôpital Notre-Dame et Département de Medicine, Université de Montréal, Montréal, Canada

(Received 28 June 1978)

Cyclic AMP has been implicated as an intermediate in some of the actions of luteinizing hormone (LH) on ovarian tissues, such as stimulation of steroidogenesis (LeMaire & Marsh, 1975). Both in vitro (Marsh, Butcher, Savard & Sutherland, 1966) and in vivo (Armstrong, Dorrington & Robinson, 1976), stimulation with LH results in a rapid increase in the amount of cyclic AMP in ovarian tissues, which precedes the LH-induced increase in steroidogenesis. Recently, studies on rat ovaries (Grinwich, Ham, Hichens & Behrman, 1976; Ratner, 1976; Ratner & Sanborn, 1976) have indicated that the ovarian tissue content of cyclic GMP may also be regulated by LH, but in a direction opposite to that of cyclic AMP. In the rabbit, Goff & Major (1975) have shown that administration of human chorionic gonadotrophin (HCG) causes a biphasic increase

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V. V. Patwardhan and A. Lanthier

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.

J. Endocr. (1985) 107, 77–81

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V. V. Patwardhan and A. Lanthier

ABSTRACT

The activities of guanylate cyclase and cyclic GMP (cGMP) phosphodiesterase, enzymes that are responsible for maintaining tissue levels of cGMP, were determined in the ovaries of rabbits killed without treatment or 4 h after administration of LH. Ovarian activities of the two enzymes were determined in the 100 000 g supernatant fraction (cytosol) and the resulting pellet (particulate fraction). Significant phosphodiesterase and cyclase activities were detected in both the cytosol and particulate fractions. Administration of LH had no significant effect on phosphodiesterase activity in either of the tissue fractions. On the other hand, LH caused a significant drop in guanylate cyclase activity in the cytosol and particulate fractions. This drop in the cyclase activity may be the cause of the decreased rabbit ovarian concentrations of cGMP that we have previously observed after LH stimulation.

J. Endocr. (1984) 101, 305–310