Interactions between indices of calcium metabolism and blood pressure during calcium infusion in humans

Calcium plays a central role in maintaining vascular tone. Recent studies indicate that there are continuous relationships between systemic calcium metabolism and BP, as over the whole range of normal and raised BPs there is an inverse correlation between plasma ionised calcium concentration and BP. Twenty-two subjects with normal or moderately elevated BP participated in the present study, undertaken to investigate the interactions between systemic calcium metabolism and BP during a two-hour constant-rate calcium infusion in the absence and in the presence of concomitant verapamil infusion. During the infusion there was an increase in plasma ionised calcium by 0.40 mmol/l, SBP rose by 14 mmHg, and DBP by 9.7 mmHg. Higher basal plasma ionised calcium and lower basal serum parathyroid hormone concentrations were associated with a more pronounced diastolic pressor response to the calcium infusion. A greater DBP increase was also accompanied by more pronounced parathyroid hormone suppression, determined as cyclic adenosine monophosphate excretion, and greater tissue uptake of calcium during the infusion. Conversely, higher basal BPs were associated with greater tissue calcium uptake during the infusions. This relationship was abolished when verapamil was present. The present findings extend the previous observations of continuous relationships between indices of calcium metabolism and BP and indicate that both a direct effect of the calcium ion and indirect effects, as evidenced by cyclic adenosine monophosphate excretion, affect the BP response to acute hypercalcaemia.