Influence of Metabolic Alkalosis Induced by Intravenous Infusion of Bicarbonate Solution on Blood Pressure and Electrolytes in Hypertensive Subjects

It is a well known fact that the thiazide derivatives and their analogues produce more or less metabolic alkalosis in the subjects treated with them. Concerning the relationship of acidbase equilibrium to the regulation of blood pressure, however, we have had only a few reports. Since this prblem seems to be important to elucidate the hypotensive mechanism of the thiazide derivatives, the author attempted in the present study to determine the influence of metabolic alkalosis induced by intravenous in-fusion of sodium bicarbonate solution on blood pressure in the hypertensive subjects. Materials and Methods One hundred and fifty ml of 7 per cent sodium bicarbonate solution was infused intravenously in 10 hypertensive subjects. Blood pressure was estimated before and every 5 minutes after the infusion of bicarbonate solution, for I hour. Arterial blood pH, sodium, potassium, chloride and bicarbonate concentrations in plasrna, and sodium and potassium concentrations in the red blood cells were estimated before and 30 minutes and I hour after the infusion. Results Arterial blood pH markedly rose after the intravenous infusion of 7 per cent of sodium bicarbonate solution. Systolic and diastolic blood pressures progressively fell in all subjects. Both systolic and diastolic blood pressures showed minimum levels 30 minutes after the infusion and then gradually returned to near the pre-infusion levels. Only the decrease in diastolic pressure was significant statistically 30 and 35 minutes after the infusion. Sodium concentration in plasma slightly increased whereas potassium concentration showed a gradual decrease. These changes, however, were not significant. Bicarbonate concentration significantly increased and chloride concentration decreased but the latter change was not significant. Sodium concentration in the red blood cells slightly increased and the ratio of plasma sodium to sodium in the red blood cells decreased. But both changes were not significant. Potassium concentration in the red blood cells had no change. The ratio of potassium in the red blood cells to plasma potassium increased though its increase was not significant. Discussion DRIPPS and COMROE have reported that respiratory acidosis induced by the inhalation of C2 gas raise blood pressure in normal subjects. This finding is contrary to PAGE & OLMSTED'S observation that it lower blood pressure in normal dogs. On the other hand, WALDON and GOLDSTEIN and WELLER have noted a tendency of respiratory acidosis in the patients with essential hypertension. Because of these conflicting information, it is interesting to investigate the relationship of the alteration in acid-base equilibrium to blood pressure, especially with reference to the hypotensive mechanism of the thiazide derivatives which often disturb acid-base equilibrium to some extent. In the present study it was demonstrated that metabolic alkalosis induced by intravenous infusion of sodium bicarbonate solution lower systolic and diastolic blood pressures in the hypertensive subjects. It is, however, difficult to say whether the decrease of blood pressure following the infusion of bicarbonate solution is induced directly by metabolic alkalosis itself or indirectly through the alterations in electrolytes distribution accompanied by alkalosis. So far it would appear likely that metabolic alkalosis itself lowered blood pressure directly, since the alterations in electrolytes distribution induced by alkalosis were significant. Summary Intravenous infusion of sodium bicarbonate raised arterial blood pH and lowered gradually systolic and diastolic blood pressures in hypertensive subjects. Alterations of electrolytes distribution were not significant.