Hormonal and hemodynamic responses to halothane and enflurane in spontaneously hypertensive rats

Forty-two spontaneously hypertensive rats (SHR) and 42 normotensive Wistar-Kyoto rats (WKY) were anesthetized with either halothane or enflurane. Blood pressure, heart rate, cardiac output, distribution of blood flow, plasma renin activity, and plasma catecholamines were measured to determine in what manner the hypertensive animal responded to these two anesthetics. Major findings of the study were that plasma renin activity did not increase in the SHR despite a 25% reduction in MAP. The infusion of saralasin, an angiotensin II antagonist, resulted in a further decrease in blood pressure in SHR anesthetized with halothane but not with enflurane. Plasma catecholamine concentrations were elevated in the awake SHR and were decreased in SHR anesthetized with enflurane. Both halothane and enflurane anesthesia resulted in similar alterations in blood flow in the SHR. The normotensive WKY responded to halothane and enflurane in a different manner than the SHR. Plasma renin activity increased with the decrease in blood pressure with both agents. A further decrease in blood pressure occurred with saralasin infusion in WKY anesthetized with halothane or enflurane. Significant blood flow alterations occurred in the WKY anesthetized with both agents, but enflurane caused the greatest changes. The SHR may prove useful in examining the effects of anesthetic agents and other drugs so that we may have a better understanding of the perioperative management of the patients with essential hypertension.