Probable involvement of vascular angiotensin II formation in the β2-adrenoceptor-mediated facilitation of the neurogenic vasopressor response in the pithed rat
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Basal diastolic blood pressure was decreased by captopril, ramiprilate (angiotensin converting enzyme inhibitors), saralasin (an angiotensin II receptor antagonist), pepstatin A (a protease inhibitor with renin antagonistic properties) and by functional nephrectomy (ligation of both renal hili), but was not affected by procaterol (a β2-adrenoceptor agonist), nebivolol (a β1-adrenoceptor antagonist) and ICI 118,551 (erythro-dl-1-(7-methylindan-4yloxy)-3-isopropylaminobutan-2-ol; a β2-adrenoceptor antagonist).
The vasopressor response induced by electrical stimulation of the preganglionic sympathetic nerve fibres was increased by procaterol, whereas the increase in blood pressure evoked by exogenous noradrenaline was not affected. The pressor response to both electrical stimulation and exogenous noradrenaline was decreased by captopril, ramiprilate, saralasin and nephrectomy but was not affected by nebivolol and TO 1I8,551.
The facilitatory effect of procaterol on the neurogenic, electrically induced pressor response, which was also obtained when basal blood pressure was decreased by nephrectomy and increased by Lys8-vasopressin, was abolished by ICI 118,551 but not affected by nebivolol. Under none of these experimental conditions did procaterol alter the vasopressor response to exogenous noradrenaline. electrically induced rise in blood pressure was abolished by captopril, ramiprilate, saralasin and pepstatin A. The facilitatory effect of procaterol on neurogenic pressor effect was also abolished by captopril and saralasin in nephrectomized rats and by captopril in rats in which basal blood pressure was restored to control values by Lys8-vasopressin. The pressor response to exogenous noradrenaline was not altered by procaterol under any of these experimental conditions.
The present results suggest that the β2-adrenoceptor-mediated facilitation of noradrenaline release in the resistance vessels may involve local formation (i. e. synthesis in the blood vessel wall) of angiotensin II which in turn seems to activate presynaptic facilitatory angiotensin II receptors on the sympathetic nerve fibres.
Key wordsPithed rat β2-Adrenoceptors Vascular renin-angiotensin system Presynaptic angiotensin II receptors Sympathetic nerves
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