The influence of PO2, pH, and albumin on the in vitro contraction of vascular smooth muscle

A method by which gases can be added to a tissue bath containing proteins in solution is described and utilized in a study of the importance of O2, CO2 and albumin for the contraction of rings of rabbit pulmonary artery. In electrolyte solutions without protein, reduction of the oxygen tension from 700 to 150 mm Hg caused a shortening of the period during which contractions could be elicited by nerve specific electrical field stimulation before a significant decrease in the contractile response occurred. The addition of albumin (45 g/l) to the bath caused a significant increase in contractile response during the first hour and furthermore a prolongation of the period during which the following gradual decrease remained at an insignificant level. A reduction in oxygen tension in the albumin solution from 700 to 150 mm Hg caused a more abrupt and pronounced reduction in contractile response than the one seen in the protein free solution. The response increased when the pH in the saline solution was raised early during an experiment but not if the pH was raised later. Decreased responses were seen when the pH was reduced regardless of the length of the period prior to the pH change. It is emphasized that the method improves the possibilities for in vitro studies of the activity of protein bound drugs in the presence of dissolved proteins.