Hormonal Influences on Motility of Canine Uterine Horns

SUMMARY Motility of the uterine horn as determined by the sponge-tipped catheter technique was greater in dogs given (subcutaneously) a single dose of estrogen (0.3 mg./kg.) and a series of doses of progesterone (3 mg./ kg.) than that in dogs given only estrogen. Extremely weak and irregular activity was observed in untreated ovariectomized bitches, whereas in pregnant bitches, uterine contractions were regular and slow. The progesterone domination in the pregnant bitches did not appear to be the cause of weak uterine motility. The intravenous administration of norepinephrine (3 μg./kg.) produced a slight stimulatory uterine response followed by a period of relaxation in estrogen-treated and estrogen-plus-progesterone-treated bitches and in nontreated bitches in estrus. Nontreated metestral and pregnant bitches exhibited a relaxing response, and ovariectomized bitches responded by a complete arrest of uterine horn contractions after relaxation. The effect of norepinephrine on uterine motility appeared to be modified by the sensitivity of the uterus to estrogen and progesterone. Sectioning the hypogastric and the pelvic nerves did not alter the frequency and the amplitude of uterine contractions. The uterine nerves did not seem to influence the contractions of the uterine horns.