Abstract
We studied the secretory function of the corpus luteum (CL) in cows following different estrus synchronization protocols. Estrus was synchronized using one (n=4) or two injections (n=5) of prostaglandin F2α (PGF2α; dinoprost), two injections of different analogues of PGF2α (aPGF2α), luprostiol (n=5) and cloprostenol (n=5), at eleven-day intervals, a gestagen implant (norgestomet, n=5, for 10 days) or norgestomet together with a subsequent dinoprost injection on the day of implant removal (n=5). CL samples were collected by ovariectomy on Day 7-8 of the estrous cycle. Luteal strips were stimulated with LH (100 ng/ml) or prostaglandin E2 (PGE2, 10-6M) for 24 h in culture media. The progesterone (P4) and PGE2 concentrations in the media were measured by enzyme immunoassay. In the control CL (spontaneous estrus; n=5), LH and PGE2 stimulated P4 and PGE2 (P<0.001). The effects of both factors on P4 were reduced in the CL following dinoprost- and cloprostenol-synchronized estrus (P<0.05) and were absent in the luprostiol-synchronized CL (P>0.05). In the norgestomet-synchronized CL, the stimulatory effects of LH and PGE2 were higher compared with the CL synchronized by aPGF2α (P<0.05). Pharmacological manipulation of the estrous cycle using aPGF2α may cause lower P4 secretion. Estrus synchronization inhibited CL sensitivity to luteotropic factors. Therefore, attention should be focused on the estrous synchronization method in both in vivo and in vitro studies of CL functions in cattle.
