Different types of smooth muscle hypertrophy.

Smooth muscles respond to changes in their working situation by rapid and pronounced adjustments of functional and structural properties. We have examined the effects of experimental portal hypertension on the smooth muscle of the rat portal vein in a series of studies that are summarized in this review. Within one week following partial ligation of the hepatic branches of the vein, the cross-sectional area of its muscle coat increased about twofold owing to increase in the size of the individual muscle cells. The hypertrophy was associated with membrane hyperpolarization, inhibition of spontaneous electrical and mechanical activity, and reduced sensitivity to exogenous norepinephrine. Active force per unit of cross-sectional area decreased, but metabolic studies indicated improved tension economy compared with normal portal veins. The literature on different types of hypertrophy in intestinal smooth muscle, urinary bladder, and uterus is briefly reviewed. The importance of mechanical distention and chemical trophic factors as stimuli for the growth processes is discussed.