Cyclic adenosine 3',5'-monophosphate-induced ovulation in the perfused rat ovary and its mediation by prostaglandins.

The role and mechanism of action of cyclic adenosine 3',5'-monophosphate (cAMP) in the ovulatory process was investigated by using the in vitro-perfused rat ovary model. Ovaries of pregnant mare's serum gonadotropin (PMSG, 20 IU)-primed rats were perfused for 21 h beginning in the morning of induced proestrus. In vitro stimulation with luteinizing hormone (LH; 0.1 micrograms/ml) resulted in 2.4 +/- 0.7 ovulations per treated ovary. Ovulations could also be induced by the addition of forskolin (30 microM) or dibutyryl cAMP (dbcAMP, 1 mM) with isobutylmethylxanthine (IBMX, 0.2 mM), with 11.8 +/- 1.9 and 18.6 +/- 4.4 ovulations per treated ovary, respectively. Indomethacin (5 micrograms/ml) significantly decreased the number of ovulations in the forskolin and dbcAMP + IBMX groups. The addition of prostaglandin E2 (PGE2; 1 micrograms/ml three times during the perfusion) to the forskolin + indomethacin group reversed the inhibition of ovulation (21.6 +/- 5.4 ovulations per treated ovary). Ovarian PGE tissue levels were significantly higher 10 h after stimulation with either LH, forskolin, or dbcAMP + IBMX compared to the unstimulated control group. Ovulated oocytes in the LH and forskolin groups resumed meiosis but oocytes in the dbcAMP + IBMX groups remained immature. This study shows that an increase in ovarian cAMP, even if not induced by LH, is sufficient to cause ovulation of preovulatory rat follicles, supporting the involvement of cAMP in the normal ovulatory process of the PMSG-treated rat. Furthermore, prostaglandin involvement in cAMP-induced ovulations is demonstrated.

Perfusion of the rat ovary in vitro: methodology, induction of ovulation, and pattern of steroidogenesis.

A method for perfusion of the rat ovary in vitro for the study of ovulation was developed and characterized. Immature rats (27-29 days old) were primed with 20 IU of pregnant mare's serum gonadotropin (PMSG). Two days later a laparotomy was performed, the aorta and vena cava were cannulated, the right ovary was isolated, and all vessels connecting with the aorta and vena cava except for the right ovarian artery and vein were ligated. The preparation was placed in the perfusion apparatus and perfused for up to 20 h with oxygenated Medium 199 containing 4% bovine serum albumin (37 degrees C, pH 7.4). The perfusion pressure was 70-90 mm Hg and the average flow was 1 ml . min . ovary. Ovulation was confirmed by oocyte recovery from the apparatus. Nine ovaries were perfused without further treatment (controls); only 1 ovulation occurred in this group. Nine ovaries received luteinizing hormone (LH; 0.1 microgram/ml) 1 h after the start of perfusion; 71 ovulations resulted (range, 3-13/ovary). Ovulations did not begin before 9 h after LH administration. Samples of medium were taken frequently for measurement of progesterone, estradiol and androstenedione. Levels of all three steroids rose rapidly and markedly in response to LH but increased only slightly in control perfusions. This study demonstrates that ovulation in the rat ovary can be induced in vitro and provides a basis for further studies on the mechanism of ovulation.

A gonadotrophin-releasing hormone (GnRH) antagonist inhibits GnRH- but not LH-induced meiosis in follicle-enclosed rat oocytes in vitro.

Previous studies have shown that gonadotrophin-releasing hormone (GnRH) can induce resumption of meiosis in follicle-enclosed rat oocytes. In the present study a GnRH antagonistic analogue ([D-pGlul,D-Phe2,-D-Trp3,6]LRF) was found to effectively abolish the stimulatory effect of a GnRH agonist upon resumption of meiosis and lactate accumulation in isolated pre-ovulatory rat follicles but the have no effect on LH stimulation of these parameters. It is concluded that although LH and GnRH can evoke a similar response they act through separate receptor sites and that it is unlikely that GnRH mediates the effect of LH on meiosis or glycolysis.