Relationship between luteal function and metabolic clearance and production rates of progesterone in the mare

The functional activity of the equine CL was measured by its ability to convert [4-14C]3beta-hydroxy-5-en-20-one to [4-14C]pregn-4-en-3,20-dione. The capacity of homogenates of CL of different ages followed the temporal pattern of plasma progestagen concentrations. In ten mares which ovulated twice at intervals of 0 to 9 days in the same cycle, the conversion capacity of the CL from the second ovulation was similar to that from the first ovulation. After adjusting for age, the CL from the first of two ovulations had a similar conversion capacity as that resulting from a single ovulation. Plasma metabolic clearance rates of progesterone were similar on the 8th day after ovulation in mares having one and two ovulations. Progesterone production rates were also similar in mares with one and two ovulations. A two-component disappearance curve was observed following cessation of the [3H]progesterone infusion in mares that ovulated once or twice in the same cycle.