An analysis of the purinergic component of active muscle vasodilatation obtained by electrical stimulation of the hypothalamus in rabbits

Abstract

1 In anaesthetized rabbits, electrical stimulation of the hypothalamus in areas analogous to the defence area in cats produces the ‘defence reaction.’ This response includes signs of arousal and a large increase in blood flow to skeletal muscle in the hind limb caused by a vasodilatation in the skeletal muscle vasculature. 2 The vasodilatation is a sympathetic response, and it is not dependent upon muscle activity in the hind limb. 3 The muscle vasodilatation is insensitive to α-adrenoceptor, β-adrenoceptor, cholinoceptor and histamine receptor antagonists. 4 Intra-arterial injections of the purinoceptor agonists, adenosine triphosphate (ATP) and adenosine, mimic the vasodilatation produced by electrical stimulation. 5 The P₁-purinoceptor blocker, aminophylline, attenuates adenosine-induced vasodilatation, but it does not affect the vasodilatation produced by ATP or hypothalamic stimulation. 6 The P₂-purinoceptor blocker, antazoline, attenuates the vasodilatation produced by both ATP and hypothalamic stimulation. 7 Our results suggest that the muscle vasodilatation produced by hypothalamic stimulation is mediated by purinergic nerves which release ATP and act on P₂-purinoceptors.