Alpha-2 adrenergic agonists inhibit basal and stimulated osmotic water permeability in toad skin

The effect of selective alpha adrenergic agonists and antagonists on osmotic water permeability (Posm) across isolated skins of Bufo arenarum toads was investigated. Clonidine, an alpha-2 agonist, inhibited basal Posm and oxytocin, isoproterenol and theophylline stimulated Posm, but did not alter the hydrosmotic effect of exogenous cAMP. Blockade of the effect of clonidine on basal and stimulated Posm by the selective alpha-2 antagonist yohimbine supports the hypothesis that the inhibitory effect is mediated by the stimulation of alpha-2 adrenergic receptors.