Necessity of Sequential Pulses of Prostaglandin F2alpha for Complete Physiologic Luteolysis in Cattle1

Abstract

The luteolytic effects of exogenous prostaglandin F2alpha (PGF) that did and did not simulate natural 13,14-dihydro-15-keto-PGF (PGFM) pulses were studied during mid-diestrus in 42 Holstein heifers. Plasma concentrations of PGF were assessed by assay of PGFM. In experiment 1, a single intrauterine injection of 4.0 mg of PGF into the uterine horn ipsilateral to the corpus luteum resulted in a precipitous progesterone decline, whereas sequential injections of 0.25 or 1.0 mg every 12 h resulted in a stepwise decrease (P < 0.05) following each injection. A progesterone increase occurred during the first 5 min before the luteolytic decrease but only for the 4.0-mg dose. From the results of experiment 2, a 2-h intrauterine infusion of a total of 0.5 mg of PGF was judged to best simulate a natural PGFM pulse. In experiment 3, simulation of sequential pulses at 12-h intervals resulted in a continuous precipitous decrease in progesterone to <1 ng/ml by the beginning of the fourth simulated pulse. In contrast, a single simulated pulse resulted in a 6-h progesterone decrease to a constant concentration for 3 days after treatment, followed by a return to control concentrations. The mean +/- SEM interval between the pretreatment and posttreatment ovulations was shorter (P < 0.05) in the group with sequential simulated pulses (14 +/- 1 day) than in the group with a single pulse (21 +/- 1 day). Results indicated that excessive PGF doses may stimulate nonphysiologic progesterone responses and supported the hypothesis that sequential PGF pulses are required to stimulate natural luteolysis in cattle.

63 Effect of Endometrial Biopsy on Uterine Health of Tropically Adapted Beef Cattle

“…The pro-oestrus (Day 17-21) starts with the regression of the CL and the subsequent decline of P4 concentration that allows the development of the ovulatory follicle for the subsequent oestrous cycle and results in a return to normal cyclicity (Ginther et al, 2009). In pro-oestrus, the circulating E2 stimulates a proliferative response at the endometrium, increasing both branching and size of the uterine glands and the proliferation of ciliated epithelial cells and glandular epithelium (Figure 1.1 a) (Ohtani et al, 1993, Wang et al, 2007.…”

“…The systemic level of P4 decreases, allowing the development of the ovulatory follicle from the subsequent oestrous cycle and the normal ciclicity returns. During luteolysis, the endometrial cells synthesize pulses of PGF2α that induces structural and functional regression of the CL decreasing the P4 levels, (Ginther et al, 2009). …”

“…In ruminants, a systemic P4 concentration threshold of above 1 ng/ml is suggestive of a functional CL, whilst concentrations below 1 ng/ml indicates a non-functional or a regressing CL (Chebel et al, 2006). The decrease in P4 is a consequence of structural and functional luteal regression of the CL, known as luteolysis, that is induced by the pulsatile release of prostaglandin F2-alpha (PGF2α) from the endometrium into the ovarian vein (Ginther et al 2009). …”

Effects of Cortisol on Pregnancy Rate and Corpus Luteum Function in Heifers: An <i>In Vivo</i> Study

“…PGF 2α released from the endometrium, especially the intercaruncular region of the surface epithelium of the uterus [55], in a pulsatile manner causes regression of the bovine CL [56,57]. Thus, for the initiation of bovine luteal regression, the pulsatile character of PGF 2α is much more important and plays a mandatory role rather than its absolute levels [56,57]. Furthermore, cortisol has been suggested to act in reducing the high levels of uterine PGF and to be one of the factors responsible for the generation of PGF 2α pulses in vivo in cattle [58].…”

“…At the end of the estrous cycle, cortisol can be involved in the luteolytic cascade by modulating uterine PGF 2α secretion and its action on the CL. PGF 2α released from the endometrium, especially the intercaruncular region of the surface epithelium of the uterus [55], in a pulsatile manner causes regression of the bovine CL [56,57]. Thus, for the initiation of bovine luteal regression, the pulsatile character of PGF 2α is much more important and plays a mandatory role rather than its absolute levels [56,57].…”