Physiological and physiopathological modulations of the balance between alpha- and beta-adrenoreceptors

Adrenergic receptors exist as two subtypes, alpha, and beta, in various tissues. In rat liver, catecholamines exert the same effect on glycogenolysis and neoglucogenesis via either alpha or beta control. In this review we report on the modification in the balance between alpha- and beta-adrenoreceptors induced as the result of adrenalectomy and extrahepatic cholestasis. Following adrenalectomy, the number of beta-adrenergic receptors in rat liver, measured using specific radioligands, increases two-fold, with no change in the alpha-adrenoreceptors. In extrahepatic cholestasis we measured a fourfold increase in the number of beta-sites and a two- to threefold decrease in the number of alpha-sites. Moreover, this modification in the balance between alpha- and beta-adrenoreceptors was concomitant with the apparition of a mixed beta- and alpha-adrenergic regulation of glycogenolysis in cholestatic rats, whereas this process is purely or almost purely alpha-adrenergic in normal rats.