Physiological role of 20α-dihydroprogesterone during the estrous cycle in goats

Abstract

The relationships between the effects of single or repeated subcutaneous injections of 25 mg progesterone on luteal function during the estrous cycle in goats as well as the secretion of 20α-dihydroprogesterone or 15-keto-13, 14-dihydro-prostaglandin F 2α (PGFM), the major metabolite of PGF 2α, were investigated. A single dose of progesterone given on Day 4, 10, or 18 of the estrous cycle increased the concentration of 20α-dihydroprogesterone and did not affect the length of the cycle. Each dose of progesterone on Days 2 to 5 increased the concentration of 20α-dihydroprogesterone (with a later decrease each day to a nadir which then increased daily) and shortened the cycle. The 20α-dihydroprogesterone concentration remained high; when it decreased, the concentration of the luteolytic agent PGFM began to increase. Daily doses of 25 mg 20α-dihydroprogesterone given on Days 2 to 5 had no effect on the length of the cycle. These results indicate that during the estrous cycle in goats, progesterone is catabolized to the biologically inactive steroid 20α-dihydroprogesterone, but much of the progesterone that is given early in the luteal phase of the estrous cycle causes premature luteolysis by stimulating an increase in the release of PGF 2α . The secretion of 20α-dihydroprogesterone may help to regulate progesterone production during the estrous cycle in goats.