Enhanced vasodilatation in essential hypertension by calcium channel blockade with verapamil.

The dependency of arteriolar tone on calcium influx was studied in 11 patients with essential hypertension (EH) and compared to 11 age-matched normotensive subjects (NT) by measuring the forearm blood flow response to intraarterial infusion of the calcium channel blocker verapamil (Verap) and the non-specific vasodilator sodium nitroprusside (Nip) using venous occlusion plethysmography. Verap in incremental dosages from 1 to 75 micrograms/100 ml forearm tissue induced a greater increase in forearm blood flow ( delta FAF) in EH then in NT, whereas there was no significant difference in delta FAF following Nip 1,2 micrograms/100 ml tissue. Delta FAF to Verap as adjusted for delta FAF to Nip was still greater in EH than in NT. Delta FAF to all dosages of Verap correlated positively with basal plasma epinephrine concentration in EH. At the two highest dosages of Verap, systemic blood pressure fell in EH, and the Verap-induced vasodilator (as adjusted for the response to Nip) correlated negatively to plasma renin activity or plasma angiotensin II concentration. These findings support the concept of an increased dependency of arteriolar tone on calcium influx in EH, which is related to the activity of the sympathetic nervous system. This association may be due to a common underlying derangement in transmembranous ionic fluxes in smooth muscle cells and sympathetic neurons in EH.