Effects of cimaterol administration on plasma concentrations of various hormones and metabolites in friesian steers

Abstract

The aim of the experiment was to determine the acute and chronic effects of the β-agonist, cimaterol, on plasma hormone and metabolite concentrations in steers. Twelve Friesian steers (liveweight = 488 ± 3 kg) were randomly assigned to receive either 0 (control; n=6) or .09 mg cimaterol/kg body weight/day (treated; n=6). Steers were fed grass silage ad libitum. Cimaterol, dissolved in 140 ml of acidified distilled water (pH 4.2), was administered orally at 1400 hr each d. After 13 d of treatment with cimaterol or vehicle (days 1 to 13), all animals were treated with vehicle for a further 7 d (days 14 to 20). On days 1, 13 and 20, blood samples were collected at 20 min-intervals for 4 hr before and 8 hr after cimaterol or vehicle dosing. All samples were assayed for growth hormone (GH) and insulin, while samples taken at −4, −2, 0, +2, +4, +6 and +8 hr relative to dosing were assayed for thyroxine (T 4), triiodothyronine (T 3), cortisol, urea, glucose and non-esterified fatty acids (NEFA). Samples taken at −3 and +3 hr relative to dosing were assayed for IGF-I only. On day 1, cimaterol acutely reduced (P<.05) GH and urea concentrations (7.6 vs 2.9 ± 1.4 ng/ml; and 6.0 vs 4.9 ± 0.45 mmol/l, respectively; mean control vs mean treated ± pooled standard error of difference), and increased (P<.05) NEFA, glucose and insulin concentrations (160 vs 276 ± 22 μmol/l, 4.1 vs 6.2 ± 0.15 mmol/l and 29.9 vs 179.7 ± 13.9 μU/ml, respectively). Plasma IGF-I, T 3, T 4 and cortisol concentrations were not altered by treatment. On day 13, cimaterol increased (P<.05) GH and NEFA concentrations (7.7 vs 14.5 ± 1.4 ng/ml and 202 vs 310 ± 22 mEq/l, respectively) and reduced (P<.05) plasma IGF-I concentrations (1296 vs 776 ± 227 ng/ml). Seven-d withdrawal of cimaterol (day 20) returned hormone and metabolite concentrations to control values. It is concluded that : 1) cimaterol acutely increased insulin, glucose and NEFA and decreased GH and urea concentrations, 2) cimaterol chronically increased GH and NEFA and decreased IGF-I concentrations, and 3) there was no residual effect of cimaterol following a 7-d withdrawal period.