Selective distribution of alpha-1 and beta adrenoceptors in pregnant rat uterus visualized by autoradiography

Receptor autoradiography using (-)-3-[125I]cyanopindolol and [3H]prazosin was used to study the distribution of beta and alpha-1 adrenoceptors in the rat uterus at early and midpregnancy. The binding of [3H]prazosin to slide-mounted sections at 25 degrees C was time dependent (K1 = 3.01 x 10(7) M-1 min-1, K2 = -0.0116 min-1) and saturable (1 nM). Competition binding curves with the selective alpha-1 and alpha-2 antagonists (prazosin, yohimbine) or alpha-1 and alpha-2 agonists (phenylephrine, clonidine) showed the presence of alpha-1 adrenoceptors; autoradiographic studies revealed that this subtype is highly localized in the circular layer of the myometrium during pregnancy. (-)-3-[125I]Cyanopindolol binding to slide-mounted sections of the pregnant uterus at 25 degrees C was time dependent (K1 = 4.68 x 10(8) M-1 min-1, K2 = -0.0117 min-1) and saturable (200 pM). Competition binding curves with beta-1 or beta-2 selective agonists (dobutamine, metaproterenol) and antagonists (atenolol, ICI 118,551) revealed the presence of beta adrenoceptors in the proportion of 67% beta-2 to 33% beta-1. Hyperfilm exposed to sections of the whole pregnant uterus incubated with (-)-3-[125I]cyanopindolol with or without ICI 118,551 or atenolol showed a high density of beta-2 adrenoceptors in the longitudinal layer of the myometrium and in the placenta. A small density of beta-2 adrenoceptors was also located in the decidua basalis on day 8 of pregnancy.