Hepatic steroid inactivating enzymes, hepatic portal blood flow, and corpus luteum blood perfusion in lactating dairy cattle

Abstract Text: In ruminants, a decrease in pregnancy rates may be due to decreased concentrations of progesterone (P4). It is important to note that both production from the corpus luteum and/or hepatic steroid inactivation impacts peripheral concentrations of P4. Cattle with an elevated dry matter intake have increased blood flow to the digestive tract and liver. This in turn leads to an increased delivery rate of steroids to the liver and thus increased metabolism of these substrates. Excessive hepatic steroid inactivation contributes to decreased peripheral concentrations, which can alter reproductive performance. The objective of this study was to examine the activity of hepatic steroid inactivating enzymes in pregnant versus non-pregnant lactating Holstein cows. Cows were synchronized using the Ovsynch plus CIDR protocol and bred via artificial insemination on d 0. At d 10 post-artificial insemination, hepatic portal blood flow was measured via transabdominal Doppler ultrasonography. Images of corpus luteum blood perfusion were collected using the power flow program of the Doppler ultrasound. Blood perfusion was analyzed by examining pixel density using ImageJ software. Liver biopsies were collected and frozen for later determination of cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A) and uridine diphosphate-glucuronosyltransferase (UGT) activities via luminogenic substrates. Aldo-keto reductase 1C (AKR1C) activity was measured using the specific substrate 1-acenapthenol. Pregnancy was determined at d 33 of gestation and treatment groups were retrospectively assigned as pregnant or non-pregnant. Data were analyzed using the mixed procedure of SAS. CYP1A, CYP2C, CYP3A, and AKR1C activity did not differ (P > 0.10) between pregnant and non-pregnant cows. Activity of UGT per kg of BW was increased (P < 0.05) in pregnant (60.1 ± 3.4 RLU/min/kg) vs. non-pregnant (50.6 ± 3.4 RLU/min/kg) cows. Blood perfusion of the corpus luteum did not differ (P > 0.30) between pregnant and non-pregnant cows. Absolute hepatic portal blood flow was increased (P < 0.05) in pregnant (997 ± 78 L/h) vs. non-pregnant cows (748 ± 78 L/h). Portal blood flow per kg of BW was increased (P < 0.05) in pregnant (1.65 ± 0.13 L/h/kg) vs. non-pregnant cows (1.27 ± 0.13 L/h/kg). The current study highlights the relevance of further investigation into steroid secretion and inactivation and their impact on the maintenance of pregnancy in dairy cattle. 

Keywords: blood flow, cattle, steroid