The interaction between renin-angiotensin system and sympathetic nervous system in the systemic circulation of conscious Sprague-Dawley rats

Experiments were carried out in conscious, unrestrained, male rats to evaluate possible interactions between the renin-angiotensin system and the sympathetic nervous system in the systemic circulation upon the intravenous administration of angiotensin II and a set of adrenergic agonists. Sixteen Sprague-Dawley rats with matched body weight received intraperitonial injection of reserpine (5mg/kg) one day before the rats were subjected to base line measurements of mean arterial blood pressure and heart rate before receiving bolus intravenous doses of noradrenaline, phenylephrine, methoxamine and angiotensin II that caused an immediate fall in the blood pressure of these rats. The animals were allowed to move freely during experiments. Dose-response carves were established for angiotensin II and adrenergic agonists-induced increase in mean arterial blood pressure. The results showed a significant (P<0.05) enhancement of the vascular responsiveness to noradrenaline, phenylephrine, methoxamine and Angiotensin II in the systemic vasculature of conscious rats. Reserpine enhanced the sensitivity of both vascular alpha(1)-adrenoceptors and AT(1) receptors to the vasoactive agents. The results obtained also demonstrate that angiotensin II-induced systemic vasoconstriction is contributed to by adrenergic actions, and that there is a possible interaction between Ang II receptors and adrenergic neurotransmission in conscious Sprague-Dawley rats.