dinoprost and acyline

In experiment 1, daily blood samples were available from Days 0 to 20 (Day 0 = ovulation) in mares with an interovulatory interval (IOI, n = 5) and in mares that developed idiopathic persistent corpus luteum (PCL, n = 5). The PCL was confirmed by maintenance of progesterone (P4) concentration until end of the experiment (Day 20). Significant interactions of group and day revealed the novel findings that luteinizing hormone (LH) was lower (P < 0.05) in the PCL group than that in the IOI group on Days 0 to 4, and prolactin was lower (P < 0.05) on Days 1, 4, 6, and 7. In experiment 2, treatment with a gonadotropin-releasing hormone antagonist (n = 6) significantly reduced LH on Days 1 to 6 compared with the controls (n = 6) but did not support the hypothesis that low LH during the postovulatory period increases the frequency of PCL. In experiment 3, P4, PGFM (a PGF2α metabolite), and prolactin concentrations on Days 12 to 20 from 2 reported experiments were combined to increase the number of mares with an IOI (n = 11) or a PCL (n = 11). An abrupt and complete decrease in P4 (luteolysis) began on Day 13 in the IOI group compared with a gradual and partial P4 decline after Day 12 in the PCL group. Concentrations of PGFM and prolactin were lower (P < 0.05) in the PCL group than those in the IOI group on the day at the end of the most pronounced decrease in P4. The PCL mares were subgrouped into those with an abrupt but incomplete P4 decrease (partial luteolysis; n = 5) at the expected time and those without partial luteolysis (n = 6). There were no significant differences between the 2 subgroups in concentrations of PGFM and prolactin, but on a tentative basis (P < 0.10), the concentration of PGFM seemed more focused on the day of the most pronounced decrease in P4 in the subgroup with partial luteolysis. Results for PCL compared with IOI indicated (1) postovulatory LH and prolactin were lower, (2) treatment to reduce postovulatory LH did not increase the incidence, and (3) both PGFM and prolactin were lower on the day of the most pronounced decrease in P4.

Topics: Animals; Corpus Luteum; Dinoprost; Female; Horse Diseases; Horses; Luteinizing Hormone; Luteolysis; Oligopeptides; Ovulation; Progesterone; Prolactin

On Day 16 (Day 0 = ovulation) or before the expected transition into the luteolytic period, heifers were not treated (control group, N = 7) or were treated with a single 0.1-mg dose of estradiol (E2) (E2 group, N = 6) or E2 combined with the GnRH antagonist acyline (E2/Ac group, N = 5). Hourly blood samples were collected from hour of treatment (Hour 0) to Hour 20. Estradiol induced a pulse of PGFM, but the peak of the pulse occurred 2 hours later (P < 0.05) and mean PGFM concentrations during the descending portion of the pulse were lower (P < 0.05) in the E2/Ac group than in the E2 group. In the E2 group, concentration of progesterone (P4) decreased (P < 0.05) during the ascending portion of the PGFM pulse, and increased (rebounded; P < 0.05) along with an LH increase during the descending portion. In the E2/Ac group, a rebound in P4 and an increase in LH were not detected during the descending portion of the PGFM pulse. The percentage of CL with color Doppler signals of blood flow increased (P < 0.04) concurrently with the PGFM increase during Hours 0 to 5 and during the ascending portion of the PGFM pulse. Blood flow and PGFM decreased concurrently. The following hypotheses were supported: (1) LH has a positive effect on PGFM pulses; (2) the rebound in P4 and the increase in LH during the descending portion of a PGFM pulse are functionally related; and (3) the increase in luteal blood flow in association with a PGFM pulse represents a direct effect of PGF2α rather than an effect of P4 or LH.

Topics: Animals; Cattle; Corpus Luteum; Dinoprost; Estradiol; Estrous Cycle; Female; Gonadotropin-Releasing Hormone; Luteinizing Hormone; Oligopeptides; Progesterone; Regional Blood Flow

A bolus treatment (e.g., 25 mg) of prostaglandin F(2alpha) (PGF) in the study of luteolysis in cattle results in dubious interpretations. Therefore, in experiment 1 of the present study, a 13,14-dihydro-15-keto-PGF (PGFM) pulse was simulated by incremental intrauterine (IU) infusion of PGF for 2.7 h on Day 14 postovulation. Concentrations of PGFM during the first hour of infusion and at the maximum were not different between simulated (n = 7) and spontaneous (n = 7) pulses. In experiment 2, four groups (n = 6 per group) were treated at Minute 0 (beginning of infusion) as follows: saline (infused IU), PGF (infused IU), acyline/saline, and acyline/PGF. Two hours before Minute 0, each heifer was given flunixin meglumine to inhibit endogenous PGF secretion, and heifers in the acyline/saline and acyline/PGF groups were given acyline to inhibit luteinizing hormone (LH). Plasma progesterone concentrations were similar among groups during Minutes 0 to 60, with no indication of an initial transient progesterone increase in the two PGF groups. Progesterone began to decrease in the PGF groups at Minute 60 and to rebound at Minute 135 after the PGFM peak at Minute 120. The rebound was complete in association with an increase in LH in the PGF group, but it was not complete when LH was inhibited in the acyline/PGF group. Luteal blood flow increased during PGF infusion in the two PGF groups and remained elevated for approximately 2 h after the PGFM peak in the PGF group but not in the acyline/PGF group. Novel findings were that an initial transient increase in progesterone did not occur with the simulated PGFM pulse and that LH stimulated a progesterone rebound and maintained the elevated luteal blood flow after the PGFM peak.

Topics: Animals; Cattle; Corpus Luteum; Dinoprost; Female; Luteinizing Hormone; Oligopeptides; Progesterone; Regional Blood Flow