Intracellular free calcium and ionized plasma calcium during mineralocorticoid-induced blood pressure increase in man.

Intracellular free calcium is considered to play a key role in vascular smooth muscle contraction. Platelet-free intracellular and plasma total and ionized calcium were assessed during mineralocorticoid-induced blood pressure increase in eight normotensive subjects receiving 0.8 mg fludrocortisone per day for 6 weeks. Blood pressure rose within 1 week and showed a further increase up to the 6th week. Plasma noradrenaline and renin activity (PRA) showed a decrease after 1 week and remained suppressed throughout the study. Ionized plasma calcium fell during mineralocorticoid treatment without any significant changes in total plasma calcium. Intracellular free calcium markedly increased after 1 week and decreased towards control levels thereafter. Previous studies have shown that after 1 week of fludrocortisone administration total peripheral resistance is still normal or even subnormal, whereas it is increased after 6 weeks. Therefore, the initial increase in intracellular free calcium, if also present in arteriolar smooth muscle cells, does not appear to be directly related to the final elevation of total peripheral resistance.