Cardiovascular actions of venom of the stonefish Synanceja horrida

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Abstract
Possible mechanisms of the hypotensive effect of small-to-moderate doses of stonefish venom in rabbits were investigated. Some decrease in blood pressure occurred in the absence of, or prior to, a decrease in force of contraction of the heart, suggesting that peripheral vasodilatation was at least in part responsible for the blood pressure fall after small doses of venom. A decreased force of contraction was associated with the greater decline in blood pressure produced by larger doses of venom. Vasodilatation did not occur in skeletal muscle after intra-arterial injection of venom, and possible effects on other vascular beds were not investigated. Adrenergic blockade was excluded as a mechanism of action of the venom, and evidence of a lack of effect on autonomic ganglionic transmission was obtained. The pressor responses to carotid artery occlusion and anoxia and the depressor responses to central stimulation of the cut right vagus and depressor nerves were unaffected by hypotensive doses of venom.