Intravascular infusion of lipid into ewes stimulates production of progesterone and prostaglandin

Effects of infusion of a lipid emulsion into ewes during mid- to late diestrus on serum concentrations of total cholesterol (TC), progesterone (P-4), prostaglandin (PG) F-2 alpha metabolite (PGFM), and PGE(2), and on ovulation rate were examined. In experiment 1, ewes received infusions of either saline (S, n = 3) or soybean oil emulsion (SE, n = 3) for 5 h on each of Days 9-13 of the estrous cycle. In experiment 2, ewes received infusions of either S (n = 4), SE (n = 5), or olive oil emulsion (OO, n = 5) for 5 h on each of Days 9 through 15 of the estrous cycle. In both experiment 1 and experiment 2, infusion of lipid increased serum concentrations of TC and P-4, which declined with time after infusion was terminated (treatment x hour interaction, experiment 1: TC, p < 0.01, P-4, p < 0.01; experiment 2: TC, p < 0.01, P-4, p < 0.001). Serum PGFM and PGE(2) concentrations were greater in lipid-infused ewes than in controls on Days 13 through 15 (treatment x hour interaction; p < 0.03, p < 0.001, respectively). Duration of the estrous cycle was shortened in GO-infused ewes (16.2 +/- 0.4 days) compared with that of SB- and S-infused ewes (17.2 +/- 0.2 and 18.0 +/- 0.0 days, respectively; p < 0.01). Numbers of corpora lutea and follicles, and diameter of follicles > 4 mm did not differ among treatment groups on Day 14 of the succeeding cycle after infusion. These data indicate that lipid infusion stimulated increases in serum concentrations of TC, P-4, and prostaglandins and may shorten the estrous cycle.