Non-selectivity of yohimbine for adrenergic receptors in fish liver.

Here we report that in isolated catfish hepatocytes, yohimbine, usually thought to act as a specific antagonist for AR of the alpha-2 subtype, at high concentrations, increases AC activity and sinergistically enhances the forskolin-induced enzyme stimulation. Such effects are counteracted by the beta-AR antagonist propranolol, but not by the alpha-AR antagonist phentolamine. Together with previous evidence that yohimbine blocks the rise of intracellular calcium induced by epinephrine via alpha1-AR, the present results seem to indicate that this compound is not suitable for studying alpha2-AR in fish liver.