Abstract

The binding of H³-catecholamines was studied in uteri and hearts of immature rats pretreated with estradiol-17β. The uptake of circulating H³-epinephrine was much greater in the heart, but the rates of its disappearance from uterus and heart were similar. Reserpine released bound H³-catecholamines from uteri and hearts to the same extent, but tyramine had only a minor effect on the release, and cocaine no effect on the uptake of these neurohumors in the uterus. Estrogen treatment resulted in a marked increase in the binding of H³-epinephrine in the immature rat uterus. When uterine naturally occurring and administered catecholamines were studied by subcellular fractionation, there was no evidence of concentration of these substances in the "microsomal" fraction, containing granulated vesicles, as was found in the heart. Uterus contains only trace amounts of catechol-O-methyl transferase activity, but has large amounts of monoamine oxidase activity. Catechol-O-methyl transferase activity more than doubles during pregnancy.