Inhibition of Oxytocin Induced Contractions in the Rat Uterus by Sialic Acid (in Vitro) 1

The sensitivity of the uterus is known to be regulated by estrogen and progesterone, but the nature of the involvement has not been clearly defined. It has been demonstrated in the rat that an inverse relationship exists between progesterone and uterine sialic acid (1) and that a direct relationship exists between estrogen and uterine sialic acid (1, 2). Preliminary work by author (unpublished data) and by Warren and Spicer (3) conflicts with the previous findings (1, 2). The membrane potentials of rat uterine cells were slightly increased with estrogen and greatly increased with progesterone (4). It has been postulated that rat uterine receptors for serotonin contains glycoproteins (5). The importance of glycoproteins in membrane structures has been neglected (6). Since sialic acid is an essential part of membrane glycoproteins and uterine sialic acid can be altered by the ovarian hormones, this experiment was conducted to determine the role glycoproteins might play in controlling the sensitivity of the uterus.

Materials and Methods. Charles River female rats weighing between 150-200 g were given 1 μg/kg of estradiol cypionate² 24 hr prior to the experiment. The rats were stunned by a blow on the head and one complete uterine horn was immediately removed. The uterine segment was placed in an isolated tissue bath³ at 30°. DeJalons (7) solution⁴ bubbled with 95% O₂ and 5% CO₂ was used to bathe the tissue.

Oxytocin⁵ was diluted from a stock concentration of 20 U/ml to a concentration of 0.2 U/ml. At the required time, increments of either 0.1 ml (0.02 U), 0.2 ml (0.04 U) or 0.3 ml (0.06 U) were diluted to 0.5 ml with DeJalons solution and injected into the tissue bath containing the uterine segment.