Similar Vasoconstrictor Responses to Calcium in Normotensive and Essential Hypertensive Men 1 2

Abstract

Summary

To study limb vascular responses in man to elevations in plasma calcium concentrations, we infused test isosmolar solutions of CaCl₂ (0.115, 0.230, and 0.460 meq calcium/min) and NaCl and control isosmolar solutions of NaCl into the brachial arteries of 10 normotensive men and eight men with essential hypertension of mild to moderate severity. Limb blood pressures were monitored, limb blood flow was measured by indicator-dilution, and limb vascular resistance was calculated as mm Hg/ml flow/min/100 cm³ limb volume. Measured concentration of calcium in limb venous plasma during infusion of 0.460 meq calcium/min was 11.5 ± 0.8 meq/liter (mean ± SEM) with individual values ranging up to 20 meq/liter. Changes in limb venous serum sodium, potassium, magnesium, and osmolality were similar during control and CaCl₂ infusions. Decreases in limb venous blood hematocrit during CaCl₂ infusions were the same or greater than those during control infusions. The infusions did not significantly change systemic blood calcium concentration or blood pressures. Limb blood flow decreased and resistance increased in response to CaCl₂. Increments averaging as little as 2.2 meq/liter elevated limb resistance by about 45%. Log dose-response curves were linear. Responses did not differ in normotensives and hypertensives (P > 0.8). We conclude that the vascular response to acute elevation of plasma calcium concentrations up to 20 meq/liter in the limb of man is an impressive vasoconstriction. We found no evidence for abnormal vascular responses to calcium in essential hypertensive men.

We appreciate the cooperation and assistance of the staff of the Veterans Administration Hospital, Saginaw, MI, especially Mrs. Mollie Wheatley, Dr. Kent Bradley, and the nursing staff of the medical wards. Dr. Francis J. Haddy aided us in preparation of the manuscript. Mr. Donald L. Anderson's technical assistance was invaluable.