Vasoactive properties of plasma protein fractions

¹ Department of Pathology, New York University Medical Center, New York City

The capacity of plasma to potentiate norepinephrine (NOR)-induced contractions of the rabbit aortic strip can be attributed to the plasma protein fractions, perhaps almost exclusively to their albumin content. Albumin, 0.2–2 mg/15 ml, potentiated a threshold test dose of NOR from minimal to maximal effect. In the presence of albumin 1–2 mg/15 ml, the threshold dose of NOR was decreased about five to ten times. Albumin, 500 mg/15 ml, did not have a greater potentiating effect. Albumin itself had no contracting ability. The blood of the anesthetized rabbit does not contain sufficient NOR to contract the aortic strip; such concentrations of NOR even in the presence of plasma proteins or albumin were ineffective. The data suggest that NOR does not contribute directly to the maintenance of normal vascular tone.

Key Words: norepinephrine potentiation • albumin potentiation of norepinephrine constrictor action • vascular-smooth-muscle-contracting substance • vascular tone and blood vasoactive substances

Submitted on July 19, 1963