Journal of cardiovascular pharmacology vol:40 issue:3 pages:448-455
Neutral antagonists and inverse agonists can produce different cellular responses in some systems. The effects of chronic (14-day) infusion of three ligands, ICI-118,551, carvedilol, and alprenolol were examined in cardiac tissue from wild-type and transgenic mice with cardiac-specific overexpression of the human beta(2)-adrenoceptor. These ligands vary in their negative efficacy at the human beta(2)-adrenoceptor, with two (ICI-118,551 and carvedilol) behaving as inverse agonists and one (alprenolol) behaving as a neutral antagonist. Cardiac tissue from the transgenic mice exhibited elevated levels of protein kinase A activity and G protein receptor kinase-2. Fourteen-day infusions of the three ligands lowered the elevated levels of protein kinase A activity of the transgenic hearts to control levels. Alprenolol and carvedilol also decreased G protein receptor kinase-2 amounts to control levels. The left atria from transgenic mice exhibited an impaired inotropic response to histamine relative to responses of wild-type mice atria. Infusions of the inverse agonists and a neutral antagonist at the beta(2)-adrenoceptor significantly restored the impaired histamine response. Restoration of protein kinase A activity and the impaired histamine responses in the atria from transgenic mice can be observed following 14-day infusions of both a neutral antagonist and inverse agonists. The reversal of the effects of the transgene by both inverse agonists and a neutral antagonist suggests that agonist occupancy, and not spontaneous activity, of the beta(2)-adrenoceptor is producing the elevated protein kinase A activity and the impaired histamine response.