BETA(2)-ADRENOCEPTORS AND CYCLIC-AMP IN L YMPHOCYTES AND THEIR RELATIONSHIP TO UTERINE CONTRACTILITY

It is especially in the long-term application where the pharmacodynami cs of the betamimetics determine their effectiveness. According to the time and dosis, there is a decrease in the density and function of th e beta(2)-adrenoceptors (desensitization). Clinically, this means a lo ss of effectiveness. This study investigated whether in the course of a normal pregnancy (n = 22) there is a change in the effectiveness of the betamimetics, as expressed by a change in the number of beta(2)-ad renoceptors or their function. The results show a 50% decrease in the number of beta(2)-adrenoceptors to the 36th gestational week and an in crease to initial values after delivery. A similar pattern is found fo r the function of the beta(2)-adrenoceptors (cyclic AMP). The implicat ions for the uterus might be that, with advancing pregnancy, it become s less prone to relaxation and that the betaadrenergic system, as a me chanism supporting prepare the way for delivery at term, becomes less significant. For tocolysis with betamimetics, the decrease of the beta (2)-adrenoceptor density means that, with increasing gestational age, the responsiveness of the uterus to betamimetics decreases.