Abstract
Isotonic contractile responses of helically cut canine vascular strips to vasopressin, angiotensin, l-epinephrine and histamine were determined. There was a specific caudal increase in the sensitivity of aortic strips to vasopressin between the thoracic aorta and the bifurcation. At the height of the maximum response of the aorta to vasopressin at any anatomic level, further vasoconstriction could be elicited by angiotensin or l-epinephrine.
Maximum responses of renal and main pulmonary artery strips to angiotensin and l-epinephrine, and of common mesenteric veins to histamine and l-epinephrine, were determined. The maximum response of main pulmonary artery and of renal artery to angiotensin, and of mesenteric vein to histamine, was significantly less than the maximum response of the same strips to l-epinephrine. The difference between the maximum response of main pulmonary and renal artery to angiotensin was highly significant. The presence of high concentrations of histamine or angiotensin had no significant effect upon maximum responses to l-epinephrine.
A simple model was introduced which describes the response of the aorta to vasopressin and the different response maxima of vascular strips to drugs acting on separate receptor systems. The model is based upon a pharmacologically heterogeneous population of smooth musele cells within a single vessel, and employs the proportion of cells sensitive to a given drug as a parameter for calculation of drug response.
Footnotes
- Accepted February 15, 1965.
- The Williams & Wilkins Comapny
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