The nature of the adrenoceptors in the post-partum rat uterus.

1. Uteri were removed from rats 0.5 h to 8 days after parturition and were suspended in Locke solution at 37 degrees C.2. The agonists isoprenaline, adrenaline, noradrenaline and phenylephrine produced an inhibition of the post-partum rat uterus.3. In the presence of propranolol, the agonists noradrenaline, adrenaline, and phenylephrine had an excitatory effect on the post-partum rat uterus. This excitatory effect was blocked by phenoxybenzamine indicating that it is mediated through alpha-adrenoceptors.4. These excitatory alpha-adrenoceptors could be demonstrated for 5-6 days after parturition. By the 7th-8th days their existence was no longer apparent.5. Excitatory alpha-adrenoceptors were also demonstrated in the late pregnant rat uterus.