Abstract
The possible influence of a β-adrenergic agonist, Clenbuterol, on GH, IGF-1, LH and cortisol secretion was investigated in young female calves. Clenbuterol (5 μg/kg liveweight) was fed twice daily for 3 weeks. Blood samples were taken twice daily; on days -5, 1, 3 and 5 of treatment, series of frequent samplings (10 h, 30 min intervals) were conducted to evaluate GH, LH and cortisol secretion. IGF-1 plasma concentrations were measured in the daily samples throughout the experiment. To register metabolic changes, nonesterified fatty acid (NEFA) concentrations were also recorded. In contrast to cortisol and LH secretion, that were not affected by Clenbuterol treatment, GH secretion was suppressed during the first day of treatment. On days 3 and 7 the differences between control and treated animals diminished. In the Clenbuterol treated calves, the age related increase of IGF-1 plasma concentrations slowed down during days 6-15 of treatment. Then this divergence leveled off. Postprandial NEFA concentrations were increased in the treated calves (P≤0.05). These results do not support an indirect mode of action of Clenbuterol through the somatotropic axis since the observed changes were not persistent and rather related to direct metabolic changes induced by Clenbuterol.
