CORRELATION BETWEEN ALPHA-1 BETA-ADRENOCEPTOR RATIO AND SPONTANEOUS UTERINE MOTOR-ACTIVITY IN THE POSTPARTUM RAT/

The spontaneous uterine motor activity of the post-partum rat was inve stigated in parallel with the in-vitro determination of the density of the alpha(1) and beta- adrenergic receptors of the myometrium. The in -vivo experiments were performed by an improved method, using a Millar catheter fitted with a latex microballoon. The spontaneous contractil ity of the post-partum rat uterus was found to be highest 24 h after d elivery, indicating that this time is the most suitable for pharmacolo gical examinations of tocolytic agents. A very close correlation was f ound between the results of the in-vivo experiments and the alpha(1)/b eta-adrenergic receptor ratio assessed by an in-vitro receptor assay, thus indicating that the state of the adrenergic receptor system funda mentally determines the contractility of the uterus. This conclusion i s supported by the fact that the pharmacological sensitivity of the ra t uterus to prazosin and fenoterol changed as a function of the postpa rtum time in accordance with the alpha(1)/beta-adrenoceptor ratio. The se results and the relevant data available reveal a crucially importan t role of an alpha(1)-adrenoceptor-mediated process. implicating alpha (1)-blockers as theoretically potent agents for inhibition of prematur e uterine contractions.