Rat's uterine motility responses to calcitonin in vivo

ABSTRACT

The effect of systemic administration of calcitonin hormone on the uterine contractions is uncertain. This work was carried out to elucidate the in vivo effect of calcitonin hormone administration on the myometrial contractility under different ovarian hormonal influences. All the studied rats were bilaterally ovariectomized and were allocated in 3 categories; estrogen-dominated model, progesterone-dominated model and ovariectomized rat model without any hormonal replacement therapy. Calcitonin hormone was injected intramuscularly in a dose of 1 I.U./kg b.w. for 5 days. The uterine horn preparations isolated from calcitonin-treated rats and their matching controls, were studied in thermostatically adjusted 36 C, isolated organ bath, under basal condition and in response to oxytocin hormone. Systemic administration of calcitonin resulted in a significant prolongation of the average relaxation time, average duration of contraction and a decrease in the total serum calcium level, together with an increase in the basal uterine motility index in the different calcitonin-treated rat group compared to their matching controls. This increase in the basal uterine motility could be attributed to its hypocalcemic effect. The effect of calcitonin hormone treatment on the basal uterine motility was more obvious in progesterone-dominated medium and was nullified in the estrogendominated enviroment, demonstrating the potentiating effect of progesterone and the antagonizing effect of estrogen on the calcitonin actions on the myometrial contractility. Regarding the uterine responses to oxytocin, systemic administration of calcitonin hormone completely abolished the uterine motility responsiveness to oxytocin that was clearly observed in estrogen-dominated media, demonstrating its inhibitory effect on the uterine smooth muscles. The calcitonin- induced myometrial relaxation was clearly obvious in all the studied rat models and this may point to its great value, when induction of uterine quiescence is needed, such as in treatment of threatened abortion or in increasing the success rate of in vitro fertilization [IVF]