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LH SURGE-INDUCED UPREGULATION OF PLASMINOGEN ACTIVATOR AND PLASMIN ACTIVITIES WITHIN BOVINE PREOVULATORY FOLLICLES.
Dow, Mark1,2, Pursley, J. Richard1, Smith, George1,2, 1 2
ABSTRACT- Follicular rupture and subsequent oocyte release are prerequisites for pregnancy. The LH surge initiates the proteolytic degradation of the follicle wall apex that precedes ovulation. The plasminogen activators (PA), urokinase plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), are implicated in the ovulatory process via their ability to convert plasminogen to its active form plasmin. Plasmin both directly and indirectly promotes follicle wall degradation. We have previously shown that tPA and uPA mRNA expression is increased in bovine preovulatory follicles following the LH surge. Our objective here was to determine the effect of a GnRH-induced LH surge on tPA, uPA and plasmin activity in preovulatory follicular fluid (FF) and follicle homogenates. Ovaries containing the preovulatory follicle were collected at 0, 6, 12, 18, and 24 h after GnRH injection (n=5-6 each). FF was harvested and homogenates prepared from basal and apical regions of the preovulatory follicles. Enzyme activity for tPA, uPA and plasmin was detected in FF and homogenates (basal and apical) using casein zymography. Preliminary experiments using specific inhibitors and appropriate standards attributed activity detected to tPA, uPA, or plasmin. Both tPA and uPA enzyme activities increased in follicle homogenates (basal and apical) by 12 h following the LH surge (P < 0.05). Enzyme activity for uPA remained elevated in follicle homogenates (basal and apical) through the 24 h timepoint (P< 0.05). However, tPA activity was differentially regulated in the apical versus basal regions of preovulatory follicles at the later timepoints. Activity for tPA remained elevated in the follicle apex through 24 h, whereas in contrast, by 24 h, activity in the preovulatory follicle base decreased to 0 h (presurge) levels. In FF, tPA and plasmin activity increased by 12 h following the LH surge and remained elevated through 24 h (P < 0.05). Activity for uPA in FF was not altered by the preovulatory LH surge (P > 0.05). This study demonstrates that PA and plasmin activities are regulated in bovine preovulatory follicles following the LH surge in a temporal and regional specific manner. The PA may help modulate the morphological and biochemical changes associated with the ovulatory process. Supported by USDA 98-35203-6226.
KEY WORDS: plasminogen activators, plasmin, ovulation, bovine
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