PHYSIOLOGICAL-ROLE OF 20-ALPHA-DIHYDROPROGESTERONE DURING THE ESTROUS-CYCLE IN GOATS

The relationships between the effects of single or repeated subcutaneo us injections of 25 mg progesterone on luteal function during the estr ous cycle in goats as well as the secretion of 20 alpha-dihydroprogest erone or 15-keto-13,14-dihydro-prostaglandin F-2 alpha (PGFM), the maj or metabolite of PGF(2 alpha), were investigated. A single dose of pro gesterone given on Day 4, 10, or 18 of the estrous cycle increased the concentration of 20 alpha-dihydroprogesterone and did not affect the length of the cycle. Each dose of progesterone on Days 2 to 5 increase d the concentration of 20 alpha-dihydroprogesterone (with a later decr ease each day to a nadir which then increased daily) and shortened the cycle. The 20 alpha-dihydroprogesterone concentration remained high; when it decreased, the concentration of the luteolytic agent PGFM bega n to increase. Daily doses of 25 mg 20 alpha-dihydroprogesterone given on Days 2 to 5 had no effect on the length of the cycle. These result s indicate that during the estrous cycle in goats, progesterone is cat abolized to the biologically inactive steroid 20 alpha-dihydroprogeste rone, but much of the progesterone that is given early in the luteal p hase of the estrous cycle causes premature luteolysis by stimulating a n increase in the release of PGF(2 alpha). The secretion of 20 alpha-d ihydroprogesterone may help to regulate progesterone production during the estrous cycle in goats. (C) 1997 by Elsevier Science Inc.