Failure of exogenous LH to prevent PGF2α-induced luteolysis in beef cows |
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Authors: | Francisco Gonzlez-Menci Bruce D Murphy Jack Manns |
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Institution: | Department of Veterinary Physiological Sciences and Biology, University of Saskatchewan Saskatoon, Saskatchewan, Canada S7N 0W0 |
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Abstract: | Henderson and McNatty (Prostaglandins 9:779, 1975) proposed that LH from the preovulatory LH surge attached to receptors on luteal cells and that this attachment might protect the early corpus luteum from PGF2α induced luteolysis. To test this hypothesis, experiments were performed on heifers at day 10–12 of the cycle. Both jugular veins were catheterized and infusions of either saline (0.64 ml/min) or LH-NIH-B9 (10 μg/min; 0.64 ml/min) were given. Saline infusions were from 0–12 h; LH infusions were for 10 h and were preceded by a 2 h saline infusion. All animals were given 25 mg PGF2α im at 6 h (6 h into the saline infusion and 4 h into the LH infusion). Blood samples were taken at 0.5 h, 1 h and 4 h intervals from 0–12, 13–18 h and 22–24 h respectively. Serum was assayed for LH and progesterone by radioimmunoassay methods. Two animals received saline and two received LH in each experiment. Eact treatment was replicated 6 times. LH infusion resulted in a mean serum LH of 57 ng/ml compared to 0.90 ng/ml in saline infused animals. This elevation of LH did not alter PGF2α induced luteolysis as indicated by decline in serum progesterone. This experiment does not support the hypothesis that the newly formed corpus luteum is resistant to PGF2α because of protection afforded by the protestrus LH surge. |
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