Diet-induced alterations in hepatic progesterone (P4) catabolic enzyme activity and P4 clearance rate in lactating dairy cows

Elevated rates of steroid clearance may lead to lower reproductive success in several mammalian species. Cytochrome P450 (EC 1.14.14.1) and aldo-keto reductases (AKR; EC 1.1.1.145–151) are involved in the first phase of steroid inactivation, before second phase conjugation and excretion of the steroid metabolite. The current objectives were to determine liver blood flow (LBF), hepatic enzyme activity, and metabolic clearance rate (MCR) of progesterone (P4) in dairy cows consuming isoenergetic and isonitrogenous diets formulated to cause divergent insulin secretion. Insulin concentrations increased by 22% in cows fed the high cornstarch diet, and both cytochrome P450 2C and cytochrome P450 3A activities were decreased (P