VASOACTIVE AGENTS AND BLOOD-PRESSURE REGULATION IN SEQUENTIAL ULTRAFILTRATION AND HEMODIALYSIS

Hypotension is a common and sometimes dangerous side effect of hemodia lysis. Its etiology is multifactorial and largely unknown. Earlier stu dies on the role of endogenous blood pressure regulating agents such a s catecholamines and renin have rendered conflicting results. We studi ed the influence of ultrafiltration and isovolemic hemodialysis separa tely on the plasma concentrations of the following blood pressure regu lating agents: adrenaline, noradrenaline, dopamine, neuropeptide Y, ca lcitonin gene-related peptide (CGRP), renin (PRA), angiotensin II, vas opressin, aldosterone and cortisol. During isolated ultrafiltration, p lasma levels of two strong vasoconstrictors (noradrenaline and angiote nsin II) and one strong vasodilator (calcitonin gene-related peptide, CORP) increased significantly (noradrenaline 3.24 +/- 0.60 nM to 4.31 +/- 0.55 nM; p = 0.032, angiotensin II 19.74 +/- 3.46 pmol/l to 28.49 +/- 7.24 pmol/l; p= 0.047) No symptomatic hypotension occurred. At the end of isovolemic hemodialysis, plasma levels of all the vasoconstric ting agents had decreased to pretreatment values, but those of CGRP ha d continued to rise (from 85.3 +/- 17.6 pmol/l to 114.5 +/- 25.3 pmol/ l, p=0.031). During isovolemic hemodialysis, blood pressure fell to sy mptomatic levels, but was restored at the end of treatment. The study shows that hemodialysis patients respond to fluid removal by ultrafilt ration with an increase in plasma levels of CORP, noradrenaline and an giotensin II. The net effect is an appropriate vasoconstriction and ad equate blood pressure is maintained during isolated ultrafiltration. D uring hemodialysis, the patients' blood volumes remained unchanged as evident by a stable hematocrit, the vasoconstrictor hormones returned to normal levels, but in several patients there was a continuous relea se of vasodilating CGRP. Hypotension, then occurred in these patients due to the imbalance between vasoconstricting and vasodilating factors .