Comparable effect of isotonic infusions on blood pressure in the anephric rat.

Abstract

SUMMARYWhether and to what extent sodium chloride infusions elevate blood pressure acutely were examined in conscious, normotensive, and spontaneously hypertensive (SHR) anephric rats. All animals were bilaterally nephrectomized 18 hours before study.Normotensive Wistar rats, allowed no food or water post nephrectomy (Groups I-IV), received either no infusion (Group I, control) or intravenous infusion of isotonic solutions of either NaCI, mannitol, or dextrose at a rate of 0.018 ml/min for 2 hours. Mean arterial pressure (MAP) measurements were determined directly by arterial catheter for control (C), 1 hour, and 2 hours. Blood pressure was increased above control in all groups at 1 hour and 2 hours (p < 0.05). The increase in MAP with NaCI was similar to that with no infusion or infusion of mannitol or dextrose. Normotensive Wistar rats (Groups V-VI) and SHR (Group VII) were allowed free access to food and water post nephrectomy and received either no infusion (Group V, control) or infusion of isotonic saline at a rate of 0.037 ml/min for 2 hours. MAP was elevated above control in all groups (V-VII) at 1 and 2 hours (p < 0.05). The magnitude of the rise was similar among all groups. Food and water accessibility post nephrectomy did not alter results. In both sets of experiments when saline was infused we were unable to identify any increase in blood pressure greater than control at either infusion rate. In fact, we continued the saline infusion in Group VI, until 100 ml of saline was infused without any elevation in blood pressure above control. We conclude that during the 2 hours of observations neither sodium nor chloride ions exert an independent eifect on MAP in normotensive or hypertensive anephric rats when compared to no infusion or isotonic isovolemic infusions of mannitol or dextrose during the same time period. (Hypertension 5: 421-426, 1983) KEY WORDS • sodium chloride • mannitol • dextrose • Wistar Kyoto rats spontaneously hypertensive rats • acute infusions C HRONIC dietary administration of sodium chloride may elevate blood pressure under a variety of specific conditions.'" 3 It has been assumed that this action is mediated indirectly because of accompanying fluid retention and the resultant increase in intravascular volume. 4 Although the volume theory is widely accepted, other mechanisms such as release of a slow pressor substance have been suggested 5 '6 as an alternate means by which sodium chloride indirectly induces an elevation in blood pressure.Although there exists a large body of literature on chronic sodium administration and blood pressure, Received April 14, 1982; revision accepted December 8, 1982. there are few studies dealing with the effects of acute sodium administration on blood pressure. In 1980, Hatzinikolaou et al., 7 found higher blood pressures in normotensive anephric rats receiving acute infusions of hypertonic saline than in those receiving hypertonic mannitol. The pressor action of hypertonic saline was not completely inhibited by a vasopressin antagonist, and the...