Liver blood flow and metabolic clearance rate of progesterone in sheep

To study the effects of feeding on concentrations of peripheral plasma progesterone, ovariectomised ewes, given exogenous progesterone, were fed 750 g of chopped lucerne hay at either 09.00 (group A, n = 5) or at 15.00 (group B, n = 5) or were fed ad libitum regularly through the experimental period (group C, n = 5). Peripheral blood samples were taken from each ewe at 09.00, 11.00, 15.00, 17.00 and 23.00. In ewes of groups A and B, mean plasma progesterone concentrations declined significantly (P < 0.05) after feeding. Mean progesterone concentrations of group C ewes remained low and were significantly different (P < 0.05) from the pre-feeding values of group A and B ewes. These results showed that the metabolic clearance rate of progesterone changed with the act of feeding. In a second experiment, portal, hepatic and mesenteric vein cannulae were placed in ovariectomised ewes (n = 17). They were then fed a ration calculated to maintain liveweight for seven days (M ration). The ewes were then infused with progesterone into a jugular vein and with p-amino hippuric acid into a mesenteric vein. Ewes were then allotted to receive either half M or twice M rations for seven days after which the infusions and blood sampling procedures were repeated. The mean rate of blood flow in the portal vein was directly related to the level of feed offered when ewes received either 1/2M, M or 2M rations. The liver and gut region removed a mean of 96 per cent of the progesterone entering these tissues.(ABSTRACT TRUNCATED AT 250 WORDS)