title: The effects of adrenoceptor agonists and antagonists on plasma potassium concentration in anaesthetized guinea-pigs, rabbits and rats.
abstract: An intravenous K+-sensitive electrode has been used to monitor plasma [K+] changes induced by alpha- and beta-adrenoceptor agonists in anaesthetized guinea-pigs, rabbits and rats. The effects of phentolamine and propranolol on these responses were studied. In the guinea-pig both alpha- and beta-adrenoceptor agonists produced a biphasic response consisting of an initial rapid increase in [K+] which was followed, within 1 min, by a fall below baseline. The antagonist studies indicated that in this species both phases of the response could be elicited by either alpha- or beta-adrenoceptor activation. In the rabbit the responses were both slower and smaller than those seen in the guinea-pig and required larger agonist doses. In addition it was found that the increase in plasma [K+] was alpha-adrenoceptor-mediated while the subsequent fall was seen only with beta-adrenoceptor activation. In the rat triphasic changes in plasma [K+] were seen consisting of an initial decrease which was alpha-adrenoceptor-mediated, followed by an increase and then a second fall which was elicited by beta-adrenoceptor stimulation. The increase in plasma [K+] was only slightly reduced by either alpha- or beta-adrenoceptor antagonists. Apamin, a toxin from bee venom which blocks Ca2+-activated K+-channels, was found to block the hyperkalaemic phase of the response in the guinea-pig and rabbit but had no effect in the rat. It is concluded that there are marked species differences in the effects of adrenoceptor agonists on plasma [K+] in vivo.
mesh_terms: D000758:Anesthesia; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D004837:Epinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004983:Ethanolamines / Q000494:pharmacology; D006168:Guinea Pigs; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D010109:Oxymetazoline / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000097:blood*; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013565:Sympatholytics / Q000494:pharmacology*; D013566:Sympathomimetics / Q000494:pharmacology*
chemical_list: D004983:Ethanolamines; D013565:Sympatholytics; D013566:Sympathomimetics; D000804:Angiotensin II; D010656:Phenylephrine; D001030:Apamin; C016980:amidephrine; D010109:Oxymetazoline; D011433:Propranolol; D008729:Methoxamine; D007545:Isoproterenol; D011188:Potassium; D004837:Epinephrine; D010646:Phentolamine