Role of prostaglandin E 2 in basal and noradrenaline-induced progesterone secretion by the bovine corpus luteum

Abstract

The role of prostaglandin E 2 (PGE 2) in basal and noradrenaline (NA)-stimulated utilization of high density lipoprotein (HDL) as a source of cholesterol for progesterone synthesis was examined. In Experiment 1, a cannula was inserted into the aorta abdominalis through the coccygeal artery (cranial to the origin of the ovarian artery) in mature heifers, to facilitate infusion of NA (4 mg/30 min; n=3) on day 10 of the estrous cycle. Three other heifers were similarly cannulated to serve as control. Before, during, and after NA or saline infusion, blood samples from the vena cava were collected every 5–15 min for analysis of PGE 2, progesterone, and cholesterol. Each NA infusion stimulated ( P<0.01) secretion of both hormones in heifers. Short-duration increases ( P<0.05) in progesterone were observed due to the infusion of NA while cholesterol was not altered significantly. In addition, increases in PGE 2 concentrations ( P<0.05) compared to controls were seen after NA infusion. Therefore, we used an in vitro model to verify the effect of PGE 2 on HDL utilization by luteal cells from day 5 to 10 of the estrous cycle. In the preliminary experiment, 10 −6 M of PGE 2 out of four different doses examined was selected for further studies, since it evoked the highest release of progesterone. In the next experiment, it was found that HDL increases progesterone secretion by luteal cells and both PGE 2 and LH increased ( P<0.05) the response to HDL while NA did not. In the last in vitro experiment, progesterone stimulated PGE 2 secretion by luteal cells. In conclusion, PGE 2 may be directly involved in the utilization of cholesterol from HDL for progesterone synthesis. Furthermore, PGE 2 may influence NA-stimulated progesterone secretion by the corpus luteum (CL). It is concluded that there is a positive feedback loop between progesterone and luteal PGE 2 during days 5–10 of the estrous cycle.