A histochemical study on the glycogen synthesizing enzyme in the myometrium of the pregnant and pseudopregnant rat.

Abstract

Summary. Glycogen and the activity of phosphorylase and glycogen synthetase were determined histochemically in the myometrium of the pseudopregnant (with and without deciduomata) and pregnant rat. In the pseudopregnant rat without deciduomata the activity of the two enzymes and the amount of glycogen present in the myometrium were greatest in the animals autopsied on the 11th to the 14th day. Phosphorylase activity was strong in both muscle layers while glycogen synthetase activity was present only in the outer longitudinal muscle layer. More glycogen granules were observed in the outer longitudinal than in the inner circular muscle layer. In the uteri with deciduomata the concentration of glycogen and the activity of phosphorylase and glycogen synthetase in the uterine muscle were highest in the rats killed on the 12th and 13th day of pseudopregnancy. The increase was noted primarily in the outer longitudinal muscle layer. The increase in phosphorylase activity was only slight in comparison with glycogen synthetase activity and there was no great reduction in phosphorylase activity after the 13th day as was observed for glycogen synthetase activity. An increase in the activity of the two enzymes and the amount of the polysaccharide was noted in the myometrium of rats autopsied on the 18th day of gestation which continued to the 21st day. A marked drop in the glycogen and glycogen synthetase activity of the myometrium was observed in the post-partum (1 to 5 days) rats while phosphorylase activity decreased slightly in the inner circular muscle layer. The in-vitro studies show that glycogen synthesized from glucose-1-phosphate and uridine diphosphate glucose can be observed in the myometrium of the pseudopregnant (with and without deciduomata) and pregnant rat. The glycogen content of the myometrium correlated more with glycogen synthetase activity than with phosphorylase activity. It is questionable whether the increase in glycogen and the activity of phosphorylase and glycogen synthetase can be explained by the action of oestrogen and progesterone. The possibility of relaxin playing a role in increasing enzymatic activity and the amount of glycogen in the myometrium is discussed.