Ultrastructure of uterine smooth muscle following progesterone or progesterone-estrogen treatment.

Abstract

AbstractThe ultrastructural effect of progesterone, alone and in combination with estrogen, on smooth muscle cells of the rat uterus was studied. Adult, bilaterally ovariectomized rats were untreated (controls) or treated with either progesterone (1 mg), estrogen (1 μg) or both on three consecutive days.Uterine muscle cells appeared larger and myofilaments more abundant in the progesterone‐treated rats than in the other groups of animals. Many micropinocytotic vesicles and several dense bodies were present in muscle cells of control, progesterone and estrogen‐progesterone‐treated rats. In the progestrone‐treated group, smooth muscle cells contained little granular endoplasmic reticulum and few ribosomes and glycogen particles, similar to the controls. Mitochondria were more numerous than in the control animals but similar to those seen in the estrogen or estrogen‐progesterone‐treated rats. Although an accumulation of granular endoplasmic reticulum, free ribosomes, glycogen particles and extensive Golgi complexes occurred in both estrogen and estrogen‐progesterone‐treated rats, they were more extensive in the former group.The observations indicate that progesterone alters the ultrastructure of the smooth muscle cells but not to the degree observed following estrogen stimulation. It does not markedly inhibit the effect of estrogen on the fine structure of the uterine smooth muscle cells. These observations support previous biochemical studies on glycogen concentration, RNA and protein synthesis in the rat uterus.