Uterine Motility of the Estrogenized Rabbit

A technique for isotonic and isometric recording of uterine contractions in vivo is described. No significant difference was found in the spontaneous contractions recorded simultaneously from the two horns by the two methods. On the other hand, differences were found in the responses to gradually increasing stimuli, such as increasing concentrations of noradrenaline or of increasing strength of stimulation of the hypogastric nerve. The isotonic response rapidly reached a maximum, whereas the isometric response increased more gradually. Since the isotonic response can be maximal in spite of submaximal activation, the isometric response is a more reliable quantitative measure, which is in agreement with previous findings with in vitro recording. However, for qualitative evaluation of responses near threshold stimulation, isotonic recording at low loads is preferable. Anesthetics administered i.v. in small doses to lightly anesthetized animals slightly enhanced uterine contractions, whereas deep anesthesia and local application of the anesthetics depressed the activity. Uterine motility is extremely sensitive to decrease in body temperature.