The effects of adrenoceptor agonists and antagonists on plasma potassium concentration in anaesthetized guinea‐pigs, rabbits and rats

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Abstract
1 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. 2 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 indicate that in this species both phases of the response could be elicited by either .alpha.- or .beta.-adrenoceptor activation. 3 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. 4 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. 5 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. 6 It is concluded that there are marked species differences in the effects of adrenoceptor agonists on plasma [K+] in vivo.