The aim of the experiment was to determine the acute and chronic effects of the beta-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 (T4),
triiodothyronine (T3),
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 less than .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 less than .05)
NEFA,
glucose and
insulin concentrations (160 vs 276 +/- 22 mumol/l, 4.1 vs 6.2 +/- 0.15 mmol/l and 29.9 vs 179.7 +/- 13.9 microU/ml, respectively). Plasma
IGF-I, T3, T4 and
cortisol concentrations were not altered by treatment. On day 13,
cimaterol increased (P less than .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 less than .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.