Factors Affecting the Response of the Uterus to Serotonine

SUMMARY 1. The sensitivity of the rat uterus to serotonine (5-hydroxy-tryptamine) is high in oestrus, but appears to diminish in dioestrus. 2. The sensitivity of the rat uterus to serotonine is high in pregnancy, but diminishes in the immediate post-partum period. 3. Ovariectomy diminishes the sensitivity of the rat uterus to serotonine. Sensitivity can be restored by oestradiol and stilboestrol, but not by some other steroid hormones. 4. Some blocking agents so far described do not appear to be specific for serotonine. 5. An inhibiting effect of parachlorometacresol on the spontaneous activity and response of the uterus to serotonine is described.