EFFECTS OF CATECHOLAMINES ON PREGNANT RAT UTERUS

1 The effects of noradrenaline (NA), adrenaline (Adr) and isoprenaline (Iso) have been studied on pregnant rat uterus, at various stages of gestation ‐ on the 10th and 20th days of pregnancy and on the first day post‐partum. 2 The three catecholamines were inhibitory in all stages of gestation, with the same order of potency as observed in non‐pregnant uteri (ie Iso > Adr > NA). However, mean pD2 values for the catecholamines tended to decrease as gestation progressed. 3 In 20 day pregnant and 1 day post‐partum uteri, in the presence of propranolol, NA and Adr produced consistent α‐adrenoreceptor mediated motor responses. 4 It is concluded that in the rat uterus, a form of pregnancy reversal occurs, in that there is a decrease in β‐adrenoreceptor responsiveness, and an increase in α‐adrenoreceptor responsiveness towards the end of gestation, and immediately post‐partum.