Effects of rilmenidine on bronchomotor responses in the guinea pig

This study compares the effects of 2 alpha 2-adrenergic agonists, rilmenidine (S 3341) and clonidine, on histamine-induced bronchoconstriction (HIB) in guinea pigs. Clonidine has previously been shown to potentiate HIB in guinea pigs. The study was conducted in anesthetized, paralyzed and ventilated guinea pigs. Six groups of at least 6 guinea pigs were pretreated with saline, rilmenidine (0.1, 0.3 and 1 mg/kg intravenously) or clonidine (0.01 and 0.03 mg/kg intravenously), respectively. Conductance, dynamic compliance and static compliance of the respiratory system were measured before and during histamine infusion (80 ng/kg/s) and expressed as percent variation. Clonidine potentiated HIB as previously reported. In contrast, rilmenidine potentiated HIB only at the dose of 1 mg/kg. As it is well known that HIB is influenced by adrenergic outflow, these results suggest that rilmenidine has less inhibitory effect than clonidine on adrenal secretion.