Vasomotor function of smooth muscle in the main pulmonary artery

Abstract

Isotonic contractions were measured in helically cut strips of canine main pulmonary artery (MPA). Applied tension/unit area was of the order of magnitude of average tangential stress calculated for MPA wall in vivo. Angiotensin was found to be a highly effective vasoconstrictor in this preparation. Epinephrine, norepinephrine, phenylephrine, metaraminol, methoxamine, mephentermine and 5-hydroxytryptamine also produced significant vasoconstriction, while oxytocin and vasopressin were ineffective. Aeration with 100% CO₂ resulted in slight vasodilation, followed by progressive vasoconstriction after pH fell below 6.0. Maximum shortening (S_max) was elicited by l-epinephrine in preparations under tensile stress of 6.4 x 10⁴ to 16.5 x 10⁴ dynes/cm². S_max (average 20%) was directly related (r = 0.78, P < 0.01) to the amount of elongation which took place during equilibration of strips under tension. The results suggest the feasibility of active regulation of MPA geometry by smooth muscle.