Effect of irradiated dib-cAMP on the tonic and phasic activity of human myometrium

Cyclic AMP, used as dibutyryl derivative for better permeability, has a relaxing effect on smooth muscle preparations from human uterine tissue (surgical material). The observed decrease of tonus and frequency depends on the concentration applied, shown in the range between 50 and 300 microM. cAMP looses its physiological activity by irradiation in vitro; in addition an inhibitory action of the irradiation products on uterine tissue could be proved. From the data of the Lineweaver-Burk plots, showing the competition between non-irradiated and irradiated cAMP, a ten-to twentyfold higher affinity of the irradiation products to the receptor compared to that of this transmitter could be calculated. The results show that preparations of human origin with beta-receptors behave similarly to animal tissues with beta-receptors. They are further discussed with respect to a better understanding of dose-response curves for chemical and physiological inactivation.