Characteristics of contraction in glycerinated uterine smooth muscle

¹ Department of Pharmacology, University of Mississippi Medical Center, Jackson, Mississippi

Glycerinated guinea pig uterine fibers developed a maximal tension of 40 g/cm² in castrated animals and 100 g/cm² in animals pretreated with estrone or estrone-progesterone in the presence of both adenosine triphosphate (ATP), 5 mm, and Mg, 5 mm. In the absence of Mg, Ca had no effect on contraction induced by ATP (pH 6.5). However, following maximal contraction in ATP and Mg, 1 mm Ca induced a variable slight increase in tension in freshly extracted fibers (4 days-1 month) but not in fibers extracted for over 2 months. At a constant Mg level, 5 mm, the tension developed was a function of the ATP concentration from 0.1 mm to 5 mm (ADP and creatine phosphate had no effect). Above 5 mm, ATP resulted in relaxation which could be prevented by raising the Mg concentration. It was concluded that contraction in uterine muscle was basically similar to contraction in skeletal and cardiac muscle and that these uterine preparations may contain a labile relaxing factor(s) but did not contain ATP restituting systems.