Effect of Body Condition Score on Steroid and Eicosanoid Metabolizing Enzymes in Various Horse Tissues

Alterations in BCS have been shown to directly affect reproductive efficiency in mammalian species. This variation in nutritional status has been shown to alter production and metabolism of hormones within the body, which are vital throughout the estrous cycle and gestation. Our objective was to determine the activity of steroid and eicosanoid metabolizing enzymes in horses with varying BCS. In addition, we examined tissue distribution of steroid and eicosanoid metabolizing enzymes in horses. We hypothesized a concomitant increase in BCS and activity of steroidogenic enzymes. The BCS of twenty non-pregnant, anestrous mares were established by 2 trained individuals, recorded prior to euthanasia, and tissue samples were collected from the liver, kidney, adrenal gland, ovary, and endometrium for later analysis. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A), and uridine 5’-diphospho-glucuronosyltransferase (UGT) activities were determined using luminogenic substrates and expressed per mg of protein. The MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) was used to test effect of BCS within a given tissue with age and BW as covariates. Main effect of tissue was tested using the Wilcoxon rank sum test, and statistical significance was declared at P < 0.05. Activity of CYP1A was not different across BCS except in adrenal tissues (P = 0.03), where BCS 5 was greater than BCS 4 and 6, which were similar. Activity of CYP1A was 100-fold greater (P < 0.0001) in the liver than in the adrenal, ovary, and kidney; whereas activity of CYP1A was undetectable in the endometrium. Activity of CYP2C was 100-fold greater (P < 0.0001) in the liver than in the adrenal, ovary, and endometrium; whereas activity of CYP2C was undetectable in the kidney. Activity of CYP3A was only detectable in the liver. Activity of UGT was not different across BCS except in the kidney (P = 0.02), where BCS 4 was lesser than BCS 5 and 6, which were similar. Activity of UGT was 3-fold greater (P < 0.0001) in the liver vs. kidney; whereas activity of UGT was 9-fold greater (P < 0.0001) in the kidney vs. the ovary and endometrium. In general, BCS did not alter the activity of steroid and eicosanoid metabolizing enzymes in horses. However, tissue differences of these enzymes indicated abundant hepatic metabolism in horses. Based on these findings, further research is warranted to comprehend the relationship between BCS and hormone metabolizing enzymes in livestock.