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

Abstract

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 (PP4 tended (P0.75) versus the high fiber diet (40±6 l/h×BW^0.75). The half-life of P₄ was increased (P4 clearance without any changes in LBF. This dietary relationship with hepatic enzyme activity may explain some of the observed alterations in steroid profiles during the estrous cycle or gestation of the high producing dairy cow.