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Ovarian Function During the Estrous Cycle of the Cow: Ovarian Blood Flow and Progesterone Release Rate^1,2,

University of Florida, Gainesville 32611

⁷ To whom requests for reprints should be addressed.

Abstract

To study the function of the corpus luteum (CL) through its major secretory product, progesterone (P₄), catheters were inserted into the carotid artery (via the facial artery) and the ovarian vein (n=12), and electromagnetic flow transducers were placed around the ovarian artery cycling Angus and Hereford cows (n=6). Blood samples were taken four times daily (at 0600, 1200, 1800 and 2400 h) and ovarian blood flow (OBF) was monitored for 60 min immediately after each blood sampling. After chromatography, P₄ was measured by radioimmunoassay. The P₄ concentrations in the ovarian vein (OP₄) was correlated to OP₄ (r=.24; P<.05) and day of the cycle (r=.35; P<.05). The OBF changed among days (P<.35). The highest rates were noted during luteal maturation (23 ml/min; SE = .09) and the lowest were noted with the demise of the CL (SP₄<1 ng/ml) and approach of estrus (8 ml/min; SE = .07). The OBF was correlated with SP₄ (r= .24; P<.05), although no within-day trends were noted. Exogenous estrone (6 mg) administered via jugular vein decreased OBF within 30 to 45 min, but similar injections of P₄ (up to 100 mg) had no effect. Progesterone release (P₄R) from the ovary [(OP₄-SP₄) x OBF] was higher in the morning hours (P<.05). The P₄ concentration (OP₄, SP₄) and release (P₄R) exhibited wide variations among and within days. The changes in OP₄ and P₄R were both good indicators of CL development, maturation and regression, as associated with SP₄ changes. Oxygen (O₂) and carbon dioxide (CO₂) concentrations monitored in the carotid artery and ovarian vein indicated that the ovary with the CL was not limited in O₂ availability or CO₂ removal during periods of low blood flow or high secretion of P₄.

¹ Florida Agr. Exp. Sta. Journal Ser. No. 2641.

² This research was supported by a grant from NIH RO1-HD-05659.

³ Roman L. Hruska U. S. Meat Animal Research Center, Agr. Res. Ser., Clay Center, NE 68933.

⁴ Dept. of Anim. Sci.

⁵ Dept. of Obstet. and Gynecol.

⁶ Dept. of Dairy Sci.

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