Cardiovascular effects in rats of alpha1 and alpha2 adrenergic agents injected into the nucleus tractus solitarii

Abstract

The cardiovascular effects of selective alpha 1 and alpha 2 agonists and antagonists injected into the nucleus tractus solitarii (NTS) were studied in urethane-anesthetized rats. Methoxamine (0.3-3 micrograms) injected bilaterally into the NTS caused a dose-dependent increase in blood pressure and heart rate. Phenylephrine (6 micrograms) and an imidazolidine derivative St 587 (3 micrograms) similarly injected also produced an increase in blood pressure, whereas alpha-methylnoradrenaline and an azepine derivative B-HT 920 (1 and 3 micrograms) caused a decrease in blood pressure and heart rate. The pressor response to methoxamine (1 microgram) was markedly inhibited by prazosin (0.3 microgram) injected into the same sites or hexamethionum (25 mg/kg, i.v.). Prazosin (0.3 microgram) alone injected bilaterally into the NTS did not affect the blood pressure, while yohimbine (0.1 microgram) similarly injected increased the pressure. These results suggest that in the rat NTS there exist alpha 1 adrenoceptors responsible for an increase in arterial pressure. The NTS alpha 2 adrenoceptors seem to be involved in the tonic regulation of arterial pressure.

Antagonistic Oxytocin/α2‐Adrenoreceptor Interactions in the Nucleus Tractus Solitarii: Relevance for Central Cardiovascular Control

“…In fact, a threshold dose of oxytocin effectively and significantly counteracted the vasodepressor and bradycardic actions of an ED50 dose of clonidine in the NTS. Central administration of α 2 antagonists elicits hypertension and tachycardia (34, 35) and the activation of α 2 −adrenoceptors reduces sympathetic tone (36), indicating that these receptors mediate sympatholytic responses. Thus, it could be suggested that oxytocin decreases the sympatholytic action of clonidine.…”

Neural mechanisms of swallowing: Neurophysiological and neurochemical studies on brain stem neurons in the solitary tract region

“…Catecholamines and their agonists have a predominantly depressant effect on brainstem respiratory neurons [114] and potentiate inputs to NTS from other regions [115]. Microinjection of catecholamines into the NTS produces changes in respiration [1141, gastric motility [116] and cardiovascular parameters [117,118]. In experiments on the effects of catecholamines on rhythmic swallowing elicited by stimulation of the SLN, an inhibitory effect was produced by microinjection into the NTS of norepinephrine and the 0c-adrencrgic agonist, clonidine, as well as by microinjection of dopamine and its agonist, apomorphine [110].…”

Alteration of response to neuropeptide Y in the nucleus tractus solitarius of spontaneously hypertensive rats.

“…Autoradiographic studies indicate that both ap and a 2 -adrenergic receptors are located within the NTS. 7 Kubo et al 8 reported that the a r adrenergic receptor agonist phenylephrine injected into the NTS elicited pressor responses, whereas the a 2 -adrenergic receptor agonist a-methylnorepinephrine elicited depressor responses. In an in vitro study, Tsuda et al 5 reported that NPY potentiated the inhibition of stimulation-evoked [ 3 H]norepinephrine release by an a r agonist in slices of the medulla oblongata.…”