A HISTOCHEMICAL STUDY OF ENZYMES CONCERNED IN GLYCOGEN METABOLISM IN THE MYOMETRIUM OF PREGNANT AND PARTURIENT MICE

Abstract

SUMMARY Glycogen, and the activities of the enzymes phosphorylase, uridine diphosphate glucose-glycogen glucosyl transferase (UDPG-synthetase) and transglycosylase (branching enzyme) were investigated by histochemical techniques in the myometrium of intact and ovariectomized mice throughout the first pregnancy, during parturition induced by oxytocin, and on the first and second days post partum. In intact mice, glycogen remained near the limit detectable histochemically until the end of the second week, and phosphorylase activity was almost absent in muscle fibres of the inner (circular) layer but often strong in those of the outer (longitudinal) layer. During the third week there was a progressive increase in glycogen and UDPG-synthetase in both layers and of phosphorylase in the circular layer, culminating in heavy deposits of glycogen and very strong phosphorylase activity, particularly in the circular muscle, shortly before parturition. Colour reactions with iodine suggested that at some stages of pregnancy branching enzyme activity was deficient in the circular fibres. The distribution of UDPG-synthetase activity in late pregnancy appeared to be the same as that of phosphorylase and of native glycogen, but the amount was considerably less. During parturition, the most common pattern was of strong phosphorylase activity and heavy deposits of glycogen in the circular muscle fibres but absence or very patchy distribution of both in the longitudinal fibres. The possible mechanism for this differentiation is discussed. Tests to separate the activities of phosphorylase a and b were carried out. Activities of both forms appeared to increase during the last part of pregnancy but there was no evidence that at parturition phosphorylase existed mainly in the a form. Mice ovariectomized on day 14 or 15 of pregnancy were injected with a combination of progesterone, oestrogen and relaxin. Ovariectomized mice maintained on progesterone alone were resistant to oxytocin on day 19, but responsiveness could be restored by relaxin. Glycogen deposits were very small in mice given progesterone alone and appeared to be rather less than normal with all combinations of hormones. Data for phosphorylase were inconclusive.