Sequential changes in catecholamine plasma levels during isotonic volume expansion in dogs

Abstract

Anesthetized dogs underwent 9% body weight isotonic saline loading over a period of 30 min with urine losses replaced before being allowed to lose excess volume and revert to control conditions. The sequential changes in hematocrit (Hct), urine volume (V), central venous pressure (CVP) and plasma catecholamines (NE [norepinphrine] + Epi [epinephrine]) were monitored. A striking inverse correlation was observed between CVP and plasma NE + Epi: the highest value for CVP was reached at the end of the loading period when plasma NE + Epi reached the lowest level, an observation which could not be attributed to hemodilution. Urine volume changes followed a pattern comparable to that of CVP although slightly lagging. No changes were observed in the plasma levels of dopamine (DA) under these acute conditions, and it is suggested that DA is not responsible for the diuresis, since haloperidol, an antagonist of DA peripheral action, had no effect under the present experimental conditions. The catecholaminergic system quickly reacts to changes in intravascular volume by constantly readjusting its tonus. This system cannot be excluded as a trigger mechanism which initiates, directly or indirectly, the diuresis that follows isotonic saline volume expansion, which, in many respects, is comparable to that produced by acute renal denervation.