Postpartum changes in the mechanical responses of the circular muscle of rat uterus.

Abstract

The circular muscle strips were isolated from rat uterus 10-60 h after parturition, and the electrical and mechanical responses were investigated. The muscle strips exhibited a variety of contractile activity ranging from frequent spontaneous contractions generated on an elevated muscle tone to a sustained contracture, when incubated with Mg-free Krebs solution. The muscle tone was lowered, and phasic contractions were abolished when the external Ca was removed. Muscle tone was also lowered by addition of 1.2 mM Mg, 1 mM spermidine, or 1 mM tetracaine. The membrane potential was about -25 mV in a muscle which exhibited a contracture, and the membrane was hyperpolarized by 20-25 mV by the application of 1.2 mM Mg or 1 mM spermidine. Addition of indomethacin (1.5-4.5 x 10 -5 M) caused a gradual decrease in muscle tone, and the membrane was hyperpolarized. In view of the above results, it is hypothesized that Ca-influx was increased, for which prostaglandin(s) was probably responsible, in the circular muscle of postpartum rat uterus, thereby elevating the muscle tone in Mg-free solution.

The effect of co-administration of intravenous calcium chloride and oxytocin on maternal hemodynamics and uterine tone following cesarean delivery: a double-blinded, randomized, placebo-controlled trial

“…In the presence of spinal anesthesia, as in our patients, the response to pure alpha-adrenergic agonists, compared with mixed alpha-and beta-adrenergic agonists, is diminished owing to alterations in venous return. 22 We were unable to demonstrate further augmentation in the onset or strength of uterine contractions with the use of CaCl 2 , despite the demonstration of such an effect in in-vitro uterine muscle strips from pregnant animals [23][24][25][26] and humans. 27,28 The absence of clinical effect cannot be ascribed to the peripheral administration of CaCl 2 being extracellular, as extracellular (plasma) iCa 2+ levels have been shown to influence intracellular calcium levels and subsequent uterine contractility.…”