Abstract
In vagotomized, pentobarbital-anesthetized rats, neurotensin (NT) (0.9 μg kg −1) evokes biphasic pressor-depressor responses, the depressor component being the most important in magnitude. To support our previous proposal on the participation of mast cell mediators such as histamine and 5-hydroxytryptamine to the depressor effect of NT in rats, we studied the influence of various antiallergic and/or antiinflammatory drugs on the changes of blood pressure induced by NT and control agonists. The results showed that mepyramine and methysergide, given separately, inhibit by 54% and 34% respectively, the hypotensive phase of the response to NT. When given concomitantly, the two drugs convert the hypotensive phase of the response to NT, into a slight pressor effect. Disodium cromoglycate, an inhibitor of mast cell secretion, reduces by 96%, and dexamethasone by 100%, the depressor phase of the response to NT. These results clearly suggest the participation of mast cell histamine and 5-hydroxytryptamine in the hypotensive effect of NT in rats. To further our understanding of the mechanism by which NT and its mediators produce hypotension in rats we administered pentolinium, a ganglion-blocking drug, to vagotomized, pentobarbital-anesthetized rats. The results showed that pentolinium markedly inhibits the depressor components of the cardiovascular responses to NT, 5-hydroxytryptamine and histamine, and leads to the appearance of pressor effects for the three substances. These results were taken as an indication that NT and/or its mediators histamine and 5-hydroxytryptamine produce part of their hypotensive effect in rats by reducing the activity of the sympathetic nervous system.
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