Luteal blood flow and concentrations of circulating progesterone and other hormones associated with a simulated pulse of 13,14-dihydro-15-keto-prostaglandin F2α in heifers

Abstract

Progesterone and luteal blood flow effects of an i.u. 2-h infusion of 0.25 mg/h of prostaglandin F 2a (PGF) that simulated a natural pulse of 13,14-dihydro-15-keto-PGF (PGFM) were compared to the effects of a single bolus i.u. injection of PGF (4 mg) that induced complete luteolysis in heifers. Blood sampling and an estimate of the percentage of luteal area with colour-Doppler signals of blood flow were performed every 2 min for 20 min and less frequently thereafter for 6 h. After the beginning of PGF infusion or a bolus injection, progesterone increased to a peak at 14 and 10 min respectively, and was accompanied by an increase in blood flow in the bolus group but not in the infusion group. Progesterone then decreased for 1 or 2 h and was accompanied by a continued elevation in blood flow in the PGF bolus group and by a slight increase in the PGF infusion group. Progesterone then rebounded in both groups, but the rebound was greater in the infusion group. Blood flow decreased during the descending arm of the progesterone rebound. Cortisol and prolactin began to increase 6 min after the bolus PGF injection but did not increase during or after PGF infusion. The increases in cortisol, prolactin and blood flow after a PGF bolus treatment but not during a simulated PGFM pulse indicated that the bolus treatment was pharmacologic, and its use may lead to faulty conclusions on the nature of physiologic luteolysis. The comparisons between progesterone and blood flow are novel.

Ultrasound monitoring of blood flow and echotexture of the corpus luteum and uterus during early pregnancy of beef heifers

“…Both P4 and CL blood flow appear to respond to this luteolytic dose of PGF [10,36]. Furthermore, in this study the overall trends in CL blood flow area and ratio appear to be in agreement with the expression of pro and antiangiogenic factors described throughout the lifecycle of the CL [37].…”

“…Color Doppler ultrasound of the CL is a relatively new method for analyzing CL physiology [1]. Using color flow as opposed to spectral Doppler, luteal blood flow has been studied extensively during spontaneous and induced luteolysis [8][9][10] and throughout the estrous cycle [11]. Relatively few studies have reported the vascular changes in the CL between pregnant and nonpregnant animals [11,12].…”

Dynamics of Circulating Progesterone Concentrations Before and During Luteolysis: A Comparison Between Cattle and Horses1

“…However, the 1.0-or 0.25-mg doses require sequential treatments (e.g., every 12 h) for complete luteolysis in a stepwise fashion, demonstrating the importance of natural PGF pulsatility. The nonphysiological increase did not occur when a PGFM pulse was simulated by intrauterine infusion of PGF in heifers [14,25] or by an intravenous infusion in mares [26]. Furthermore, an initial increase in progesterone was not detected in blood samples collected every 15 min from heifers in temporal association with the beginning nadir or ascending portion of a spontaneous PGFM pulse [28].…”

“…Recent studies have shown that the immediate progesterone response to PGF treatment is nonphysiological in both cattle [14,25] and horses [26,27]. In both species, the nonphysiological increase occurs when a PGF dose is much higher than the animal experiences with a natural PGF pulse.…”

“…An overdose of PGF that induces complete luteolysis also immediately increases the concentrations of pituitary and adrenocortical hormones in cattle [25,[29][30][31] and horses [26, GINTHER AND BEG 27,32]. The immediate increase in the pituitary hormones does not occur in association with a natural PGFM pulse or when a PGFM pulse is simulated by PGF infusion in either heifers [25] or mares [26].…”