The Preovulatory Increase in Ovarian Collagenase Activity in the Rat Is Independent of Prostaglandin Production*

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Abstract
In the present study, we have examined the role of gonadotropins and prostaglandins in the preovulatory increase of ovarian collagenase activity in the rat. Whole ovaries of immature PMSG-primed rats (20 IU) were removed before and 8 h after the rats were treated with human (h) CG, Nembutal, and/or indomethacin. The ovaries were homogenized in a solution containing Triton X-100 (0.25%) and centrifuged. Collagenase was extracted by resuspending the pellets in buffer containing 100 mM CaCl2, heating to 60 C for 6 min, and centrifuging. The supernatants were treated with dithiothreitol (2 mM) and iodoacetamide (5 mM) to inactivate collagenase inhibitors. Collagenase activity was measured as the percent digestion of 3H-type I collagen/100 .mu.l aliquot of ovarian sample. At zero time (52 h after PMSG), ovarian collagenase activity was 4.2 .+-. 1.2% digestion (mean .+-. SEM, n = 3). In ovaries collected 8 h after the endogenous LH surge or 8 h after the administration of 10 IU hCG at time zero, collagenase activity rose to 19.6 .+-. 2.1 (n = 6) and 22.5 .+-. 1.7% digestion (n = 11), respectively. Indomethacin (1.5 mg/100 g BW) administered 30 min after hCG, produced no change in collagenase activity (24.8 .+-. 2.5% digestion, n = 7) although the expected increase in ovarian prostaglandin E after hCG treatment was blocked. When the endogenous LH surge was blocked with Nembutal (3 mg/100 g BW), collagenase activity in 8-h ovaries was 6.8 .+-. 1.1% digestion (n = 10). The Nembutal block of the preovulatory collagenase increase was overcome by administration of hCG (8-h ovarian enzyme activity = 22.7 .+-. 3.2% digestion, n = 8). These observations demonstrate that hCG stimulates ovarian collagenase activity and that this stimulation is not dependent on prostaglandin synthesis.