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Gonadotropin Surge-Induced Up-Regulation of the Plasminogen Activators (Tissue Plasminogen Activator and Urokinase Plasminogen Activator) and the Urokinase Plasminogen Activator Receptor Within Bovine Periovulatory Follicular and Luteal Tissue¹

^a Departments of Animal Science ^b Physiology, Michigan State University, East Lansing, Michigan 48824-1225

This study examined the effect of the preovulatory gonadotropin surge on the temporal and spatial regulation of tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), and uPA receptor (uPAR) mRNA expression and tPA, uPA, and plasmin activity in bovine preovulatory follicles and new corpora lutea collected at approximately 0, 6, 12, 18, 24, and 48 h after a GnRH-induced gonadotropin surge. Messenger RNAs for tPA, uPA, and uPAR were increased in a temporally specific fashion within 24 h of the gonadotropin surge. Localization of tPA mRNA was primarily to the granulosal layer, whereas both uPA and uPAR mRNAs were detected in both the granulosal and thecal layers and adjacent ovarian stroma. Activity for tPA was increased in follicular fluid and the preovulatory follicle apex and base within 12 h after the gonadotropin surge. The increase in tPA activity in the follicle base was transient, whereas the increased activity in the apex was maintained through the 24 h time point. Activity for uPA increased in the follicle apex and base within 12 h of the gonadotropin surge and remained elevated. Plasmin activity in follicular fluid also increased within 12 h after the preovulatory gonadotropin surge and was greatest at 24 h. Our results indicate that mRNA expression and enzyme activity for both tPA and uPA are increased in a temporally and spatially specific manner in bovine preovulatory follicles after exposure to a gonadotropin surge. Increased plasminogen activator and plasmin activity may be a contributing factor in the mechanisms of follicular rupture in cattle.

First decision: 11 September 2001.

¹ Supported by USDA 98-35203-6226 (G.W.S.) and the Michigan Agricultural Experiment Station.

² Correspondence: George W. Smith, Michigan State University, Department of Animal Science, 1230D Anthony Hall, East Lansing, MI 48824-1225. FAX: 517 353 1699; smithge7{at}msu.edu

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