Although much is known about the factors involved in the control of blood flow, the cellular mechanisms of their action are poorly understood. This study investigated the mechanisms of norepinephrine, epinephrine, isoproterenol, and acetylcholine.
First, in a constant pressure/variable flow preparation we characterized the sheep brachial artery blood flow response to, and recovery from, 10-min infusions of each of these drugs. Then we used a computer model to simulate changes in blood flow in response to altered ion permeabilities or pump speeds (the mechanisms). We tried to produce responses like those to the drug infusions so that we could infer that the mechanisms invoked by the model were the ones involved in producing the experimental response.
Norepinephrine produces a rapid vasoconstriction and decrease in flow. There is a slight recovery during the infusion. The recovery takes several minutes and it is without overshoot. The response to epinephrine is diphasic. During the first minute there is a vasodilation and subsequent intense vasoconstriction which continues throughout the infusion. When the infusion is stopped there is a rapid recovery and an overshoot in flow. Isoproterenol results in an initial peak increase in flow during the first minute, hut recovers about one third of the increase and then steadily increases to the level of the original peak during the remainder of the infusion. There is a slow recovery. Acetylcholine also produces an extreme peak increase in flow, but about half of the increase is recovered in the first minute or two, and there is a slight decline during the remainder of the infusion. Flow recovers very rapidly when the infusion is stopped.
On the basis of our simulations our hypotheses are: (1) increased PNA is the major mechanism of norepinephrine action (alpha receptor); (2) stimulated Na-L ATPase is a major mechanism of isoproterenol (beta receptor), but not the only one' and (3) epinephrine involves a large stimulation of the Na pump and a small increase in PNA. We have no satisfactory hypothesis to offer for the mechanism of acetylcholine action.
Robert A. Brace
Gordon G. Power
Ramon R. Gonzalez
Master of Science (MS)
Year Degree Awarded
Date (Title Page)
Library of Congress/MESH Subject Headings
Blood Flow Velocity
Loma Linda University Libraries
This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.
Marks, Paul J., "Mechanisms of Control of Blood Flow in the Forelimb of Sheep" (1981). Loma Linda University Electronic Theses, Dissertations & Projects. 1024.
Loma Linda University Electronic Theses and Dissertations
Loma Linda University. Del E. Webb Memorial Library. University Archives