The effect of clenbuterol administration in utero and throughout lactation on pre- and post-natal muscle development in the rat.

The beta-adrenergic agonist, clenbuterol was fed to pregnant rats during gestation and throughout lactation. Changes in muscle morphology and composition were studied in foetal and weanling rats. Drug treatment did not affect mean foetal number, but mean foetal body weight was significantly reduced. Heart weights were increased and both muscle weight and secondary to primary fibre ratios were decreased in foetuses exposed to clenbuterol in utero. In animals exposed to clenbuterol throughout gestation and lactation, muscle weights, and protein, RNA and DNA content and total fibre numbers were reduced. In addition a drug induced anabolism was observed in the muscles of the dams. The data are discussed in terms of a direct drug effect on immature and differentiated muscle together with a possible indirect action through the repartitioning action of clenbuterol.