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 F(2alpha) (PGF(2alpha); dinoprost), two injections of different analogues of PGF(2alpha) (aPGF(2alpha)), 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 E(2) (PGE(2), 10(-6)M) for 24 h in culture media. The progesterone (P(4)) and PGE(2) concentrations in the media were measured by enzyme immunoassay. In the control CL (spontaneous estrus; n=5), LH and PGE(2) stimulated P(4) and PGE(2) (P<0.001). The effects of both factors on P(4) 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 PGE(2) were higher compared with the CL synchronized by aPGF(2alpha) (P<0.05). Pharmacological manipulation of the estrous cycle using aPGF(2alpha) may cause lower P(4) 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.