AJP - Heart and Circulatory Physiology, Vol 246, Issue 5 683-H689, Copyright © 1984 by American Physiological Society
Pressor effects of brief and prolonged infusions of epinephrine in the conscious rat
J. Zabludowski, S. Clark, S. G. Ball, A. J. Brown, G. C. Inglis, A. F. Lever and G. Murray
Plasma epinephrine may be increased in some patients with essential
hypertension, and prolonged infusion of this catecholamine has been claimed
to raise blood pressure. The objectives of our experiments were to
determine whether continuous intravenous infusion of epinephrine raised
blood pressure in a rat preparation known to respond in this way to
angiotensin II in low dose and, if so, the plasma concentration of
epinephrine required to raise pressure in comparison to the physiological
range of plasma catecholamine concentration in the rat. Intravenous
infusion of epinephrine at a rate of 400 ng X kg-1. min-1 or less for 30
min into Wistar rats did not increase mean arterial pressure (MAP);
pressure did rise when the rate was increased to 800 ng X kg-1. min-1.
However, when rats were given epinephrine at 400 ng X kg-1. min-1 for 4
days with continuous blood pressure recording, average MAP showed a
progressive rise on successive days of infusion, reaching a maximum
increase of 12 mmHg on the 4th and final day of infusion (P less than
0.02). Blood pressure did not change significantly during epinephrine
infusion at 10 and 70 ng X kg-1. min-1. Plasma epinephrine was raised more
than 13 times basal at the highest rate of infusion. In comparison, blood
pressure and catecholamine concentrations increased only slightly although
significantly during a period of restraint. We confirm the existence of a
slowly developing pressor effect of epinephrine, but it is small and
requires a large sustained increase of plasma epinephrine for its
development.
