Review article

Abstract

Tocolysis means drug-induced Inhibition of premature or excessive uterine activity [38], Other terms, such äs "sedation of the irritated myometrium" or "relaxation of the uterus" have the same meaning; they are, however, not commonly applied [10,11,17,29]. At the beginning of the research for new substances with inhibitory effect on the uterus it was postulated that progesterone or newlydeveloped gestagen preparations could inhibit uterine activity. In vitro äs well äs in vivo experiments showed that progesterone, in concentrations present during pregnancy [37,56], exerts a synergistic effect on oxytocin and increases uterine activity. High concentrations which should be applied exclusively for experimental purposes showed the block inaugurated by CSAPO [18]. Together with estrogen, progesterone increases the metabolic activity of the uterus. Prolonged influence leads to relaxation of the tissue and increased uterine weight. The collagen content äs well äs that of nucleic acids, glycogen, and lipids is raised. The sensitivity to exogenous Irritation, e. g. uterine distension by the growing fetus, or to drugs, e. g. oxytocin, increases. Due to the low solubility in water, the considerable affinity to serum protein, and a half-life of 15 minutes, even the highest possible concentrations of progesterone cannot be expected to exert a sufficient effect on the myometrium [31,36,54]. et al. [35] published their findings concerning the relaxant effect on the isolated uterus of the ß-adrenergic substance isoxsuprine. First clinical experiences with isoxsuprine were reported by