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105
Effects of Biweekly Administration of Recombinant Bovine Somatotropin on Steroid Metabolizing Enzymes during Early Gestation

Sunday, July 9, 2017
Exhibit Hall (Baltimore Convention Center)
Megan P. T. Owen, Mississippi State University, Department of Animal and Dairy Sciences, Mississippi State, MS
Keelee J. McCarty, Mississippi State University, Department of Animal and Dairy Sciences, Mississippi State, MS
Melissa M. Steichen, Mississippi State University, Department of Animal and Dairy Sciences, Mississippi State, MS
Carla D. Sanford, University of Florida, North Florida Research and Education Center, Marianna, FL
Luara B. Canal, University of Florida, North Florida Research and Education Center, Marianna, FL
Pedro L. P. Fontes, University of Florida, North Florida Research and Education Center, Marianna, FL
Nicky Oosthuizen, University of Florida, North Florida Research and Education Center, Marianna, FL
Nicolas DiLorenzo, University of Florida, North Florida Research and Education Center, Marianna, FL
Kim Vonnahme, Department of Animal Sciences, North Dakota State University, Fargo, ND
G. Cliff Lamb, Texas A&M University, Department of Animal Science, College Station, TX
Caleb O. Lemley, Mississippi State University, Department of Animal and Dairy Sciences, Mississippi State, MS
Previous research has shown that cattle treated with recombinant bovine somatotropin (rBST) yielded greater circulating steroid hormone concentrations which led us to hypothesize that cattle treated with rBST would have decreased activity of steroid and eicosanoid metabolizing enzymes. Ninety-seven Angus heifers were assigned to receive either rBST (BST; 500 mg/14 d) or no rBST (CONT) immediately prior to fixed-timed AI (TAI) following the 7 d Co-Synch + CIDR ovulation control protocol. Administration of rBST (sometribove zinc, Posilac, Elanco Animal Health, Indianapolis, IN) was by a single s.c. neck injection on d 0, 15, 29, 43, and 57 of gestation. Pregnancy was diagnosed by transrectal ultrasonography on d 29 and verified 64 d after TAI. Subsequently, a subset of pregnant heifers (n = 7 bST and n = 5 CONT) were harvested on d 80 of pregnancy for collection of the maternal liver, fetal liver, and corpus luteum. Placentomes were separated into caruncle and cotyledon portions. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A), and uridine 5’-diphospho-glucuronosyltransferase (UGT) activities were determined via luminogenic substrates. Activities were expressed per mg of protein, and data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC), using the Wilcoxon rank sum test, with significance declared at P ≤ 0.05. Activity of CYP1A was not different between treatments within maternal liver (P = 0.19), fetal liver (P = 0.53), caruncle (P = 0.32), cotyledon (P = 0.63), or corpus luteum (P = 0.76). Activity of CYP2C was greater (P = 0.01) in the maternal liver of BST vs. CONT heifers; however, activity was not different between treatments in caruncle (P = 0.91) or corpus luteum (P = 0.97). Activity of CYP2C was not detected in the fetal liver or cotyledon. Activity of CYP3A was only observed in maternal liver and was not different between treatments (P = 0.82). Activity of UGT was greater (P = 0.02) in corpora lutea samples from BST compared to CONT; however, activity was not different between treatments in maternal liver (P = 0.49) or fetal liver (P = 0.95), and was not detected in the caruncle or cotyledon. In conclusion, administration of rBST during the first 60 d of pregnancy increased activity of CYP2C in maternal liver and UGT in corpora lutea tissues compared with CONT. Therefore, the previously observed increase in peripheral concentrations of steroids is not associated with a decrease in steroid metabolizing enzymes.
See more of: ASAS Graduate Student Poster Competition: PhD Division
See more of: ASAS Graduate Student Poster Competition: PhD Division
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