A NEW MODEL TO EVALUATE THE HYPERTENSIVE RESPONSE TO NOXIOUS STIMULI IN THE ANESTHETIZED, SPONTANEOUSLY HYPERTENSIVE RAT

We have developed a method to evaluate the hypertensive response after noxious-stimuli in anesthetized rats. Anesthetic level, stimuli, and responses were standardized by using an etomidate infusion, a series o f stimuli of increasing intensity applied to the tail, and measuring m aximal changes in systolic blood pressure (DELTASBP) after each stimul us. Normotensive Sprague Dawley rats (SD) (n = 7) were studied using a n etomidate infusion of 4.2 mg-kg-1.h-1. This method was then applied to spontaneously hypertensive rats (SHR) anesthetized with three rates of etomidate infusion: Group 1 (n = 8),7.0 mg.kg-1.h-1; Group 2 (n = 8),5.6 mg.kg-1.h-1; and Group 3 (n = 11), 4.2 mg.kg-1.h-1. Under anest hesia, three types of noxious stimuli were applied to the tail at 1-mi n intervals (13 total): (a) Type 1: 11 2-s electrical stimuli of incre asing intensity (0.4-12 mA, to produce threshold to maximal responses) ; (b) Type 2: one intense, prolonged electrical stimulus (10 mA, 5 s); and (c) Type 3: tail-clamping. After each stimulus, DELTASBP was meas ured. In the SHR, comparing single DELTASBP responses to single noxiou s stimuli after each of the three most intense stimuli showed no stati stically significant differences among the three anesthetic groups. In contrast, comparison of dose-response curves of multiple DELTASBP res ponses to multiple Type 1 (2-s) stimuli demonstrated a significant dif ference among the three anesthetic groups of SHR. Evaluating a series of hypertensive responses to a series of brief electrical stimuli of i ncreasing intensity may allow greater discrimination of arterial blood pressure responses in different anesthetic groups of SHR, as compared to conventional methods of evaluating a single response to a single n oxious stimulus. This may allow a different approach to study anesthes ia in hypertensive subjects.