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United States Department of Agriculture

Agricultural Research Service

Title: In Vivo Desensitization of a High Affinity Pgf2alpha Receptor in the Ovine Corpus Luteum

Authors
item Lamsa, J - WORCESTER FOUN EXP BIO MA
item Cushman, Robert
item Nay, M - WORCESTER FOUN EXP BIO MA
item Mccracken, J - WORCESTER FOUN EXP BIO MA

Submitted to: Prostaglandins Leukotrienes and Essential Fatty Acids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 24, 1991
Publication Date: February 19, 1992
Citation: Lamsa, J.C., Cushman, R.A., Nay, M.G., Mccracken, J.A. 1992. In vivo desensitization of a high affinity PGF2alpha receptor in the ovine corpus luteum. Prostaglandins. 43(2):165-179.

Interpretive Summary: Proper corpus luteum (CL) function is critical both for normal cyclicity and maintenance of pregnancy in mammals. The current study elucidates the mechanisms by which uterine prostaglandin F2alpha (PGF2alpha) work in concert with luteal oxytocin (OT) to control corpus luteum function. Low doses of PGF2alpha will stimulate luteal oxytocin secretion without inhibiting luteal progesterone secretion, pointing to the presence of both high and low affinity receptors for PGF2alpha. The role of the high affinity PGF2alpha receptor was assessed by monitoring the secretion rate of OT from the ovine CL in response to low doses of PGF2alpha. Within one hour of PGF2alpha infusion OT secretion was inhibited, and a minimum rest period of six hours was required before sensitivity to PGF2alpha was restored. The possibility that these findings could be explained by the depletion and resynthesis of OT was excluded by demonstrating an increase in OT secretion rate with supra-physiological levels of PGF2alpha two hours after desensitization. Collectively, these results indicate the presence of a high affinity receptor for PGF2alpha in the ovine CL which exhibits desensitization and recovery. The temporal nature of the desensitization and recovery of the high affinity PGF2alpha receptor controlling luteal OT secretion may contribute to the pulsatile nature of PGF2alpha release from the ovine uterus during luteal regression.

Technical Abstract: The corpus luteum (CL) of the sheep exhibits a differential sensitivity to PGF2alpha in vivo in terms of an increase in oxytocin (OT) secretion and a decrease in progesterone secretion, pointing to the presence in vivo of both high and low affinity receptors for PGF2alpha. The presence of the high affinity PGF2alpha receptor was assessed by monitoring the secretion rate of OT from the ovine CL in response to subluteolytic infusions of PGF2alpha. Rapid desensitization to PGF2alpha occurred after only one hour of infusion, while a minimum rest period of six hours was required to restore sensitivity. The possibility that these findings could be explained by the depletion and resynthesis of OT was excluded by demonstrating an increase in OT secretion rate with supra-physiological levels of PGF2alpha two hours after desensitization. Collectively, these results indicate the presence of a high affinity receptor for PGF2alpha in the ovine CL which exhibits desensitization and recovery in vivo. The temporal nature of the desensitization and recovery of the high affinity PGF2alpha receptor controlling luteal OT secretion may contribute to the pulsatile nature of PGF2alpha release from the ovine uterus.

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