Kinetics of splanchnic progesterone metabolism in ewes fed two levels of nutrition.

The objective of this study was to determine whether chronic nutritional treatment influences progesterone (P4) metabolism by splanchnic tissues and to develop a mathematical model of P4 metabolism in ewes. Five ovariectomized (ovx), multiparous ewes were assigned to a high feed intake and five multiparous ovx ewes were assigned to a low feed intake. The ewes with high feed intake received daily ME intakes of 99 kcal/BWkg.75, and the ewes with low intake received daily ME intakes of 63 kcal/BWkg.75. Catheters were placed surgically in the abdominal aorta, the portal vein, a branch of the hepatic vein, and a mesenteric vein. Blood and plasma flows across visceral organs were determined by marker dilution (p-aminohippuric acid), and P4 was determined with a RIA. The net splanchnic P4 flux and oxygen (O2) consumption were determined during five rates of P4 infusion into the jugular vein (112, 224, 449, 897, and 1,795 micrograms/h). Splanchnic O2 consumption was greater (P = .05) in the ewes with high feed intake. Net splanchnic P4 flux did not differ (P > .10) between nutritional treatments. The correlation between net splanchnic P4 flux and O2 consumption did not differ from zero (P = .69). Net splanchnic P4 flux was related linearly to plasma arterial P4 concentration. Splanchnic tissue clearance rate was 18% of the infusion rate. The behavior of the P4 model indicates that whole-body P4 metabolism is the sum of first-order kinetic reactions. The data indicate that splanchnic clearance of P4 is not affected by nutritional status.