GABAB receptor‐mediated inhibition of the neurogenic vasopressor response in the pithed rat1

Open Access
Publisher Website
Google Scholar
Abstract
1 The effects of γ-aminobutyric acid (GABA) and related drugs on the vasopressor response induced by electrical stimulation (single pulse of 30 V and 1 ms) of the preganglionic sympathetic nerve fibres or by injection of noradrenaline 0.3 nmol kg−1 were studied in the pithed rat. 2 The electrically-induced increase in diastolic blood pressure was inhibited by GABA and the GABAB-receptor agonist R-(−)−baclofen but was not affected by its S-(+)-enantiomer and by the GABAA-receptor agonists muscimol and 3-aminopropane sulphonic acid. 3 The dose-response curve of R-(−)−baclofen for its inhibitory effect on the electrically-induced vasopressor response was shifted to the right by the GABAB-receptor antagonist 2-hydroxysaclofen, but was not affected by the GABAA-receptor antagonist bicuculline. 2-Hydroxysaclofen and bicuculline by themselves did not affect the electrically-induced vasopressor response. 4 The increase in diastolic blood pressure induced by exogenous noradrenaline was not affected by the GABA-related drugs, which also had no (or very slight) effects on the basal diastolic blood pressure. 5 It is concluded that GABA inhibits catecholamine release in the resistance vessels of the rat via GABAB-receptors, probably located presynaptically on the postganglionic sympathetic nerve fibres.