Transvascular fluid shifts following single injections of catecholamines in the alert rat: comparison of the effects of adrenaline, noradrenaline and stimulated activity.

Single injections of noradenaline and adrenalineeeee were made into the v. cava of conscious rats during continuous registration of arterial blood pressure and conductivity (reciprocal hematocrit) in blood from different circulatory areas. The resulting hct and B.P. changes were compared with similar changes elicited by a 3-sec tactile stimulus. Two phases of hct response--the first due to local vascular reactions, the second due to a general vasodilatory reaction--can be distinguished. Whereas adrenalin and noradrenaline show differential effectivity in producing the local reactions (the former more potent as a precapillary vasoconstrictor, promoting hct drop due to fluid inflow in the portal and hepatic vein, the latter more so in the renal vein and the aorta), adrenalin is invariably more effective in producing the second phase dilatory reaction with fluid outflow (hct rise). In the v. cava close to the iliac bifurcation a greater hemoconcentrative potency of adrenalin can be demonstrated, but only by close injections into the aorta. Close injections into the portal vein make postcapillary hepatic reactions more sensitive to adrenalin manifest. The catecholamine dose equivalent to a 3-sec tactile stimulus in the rat is 80-120 ng.