Abstract
1 Pindolol is a β-adrenoceptor blocking drug with ISA (also called partial agonist activity). This means that in addition to blocking the effects of β-adrenoceptor agonists, it produces some stimulation of β-adrenoceptors.
2 In vitro studies with pindolol show that its maximum stimulant action is similar to that of isoprenaline in tissues possessing mainly β2-adrenoceptors, but is negligible in tissues possessing mainly β1-adrenoceptors. This suggests selective stimulation of β2-adrenoceptors.
3 In man the arteriodilator effects observed after intra-arterially infused pindolol at concentrations within the same range as those producing an antihypertensive effect also suggest a stimulant action on vascular β2-adrenoceptors.
4 The fact that pindolol prevents the reduction of resting heart rate and cardiac output observed after drugs lacking ISA at first sight suggests stimulation of cardiac β1-adrenoceptors. However, human atria possess not only β1- but also β2-adrenoceptors, stimulation of which would produce the same effect.
5 Although all β-adrenoceptor antagonists lower blood pressure, recent experiments have shown that those agents with combined β1-adrenoceptor blocking activity and ISA at those receptors are less effective. This observation lends weight to the thesis that pindolol does not stimulate β1-adrenoceptors since it lowers blood pressure as effectively as drugs lacking ISA.
6 The evidence available therefore suggests that although pindolol blocks both β1- and β2-subtypes, it selectively stimulates β2-adrenoceptors.
Keywords: pindolol, intrinsic sympathomimetic activity, β2-adrenoceptor
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