[Influence of narcotic analgesics, droperidol, diazepam, and flunitrazepam on the smooth muscles of small arteries (author's transl)].

In isolated segments of the rat tail artery, the influence of narcotic analgesics, their antagonists, droperidol, diazepam, and flunitrazepam on the vascular smooth muscle was investigated. The wall of this vessel consists of about 75 per cent smooth muscle fibres. For all agents studied, pressure-diameter relations were determined before and after a virtually maximum constriction which was induced with noradrenaline. The results were compared with those obtained under control conditions, i.e. prior to the addition of the drugs to the bath solution. Tested in pure Tyrode's solution, none of the agents produced a noticeable constriction or relaxation. Among the analgesics and their antagonists, morphine was the most potent in inhibiting the noradrenaline-induced constriction of the vessel (mean increase in diameter 15%). Pentazocine and levallorphan were less effective (mean increase 8%), and the administration of pethidine and naloxone was followed by even less relaxation, resulting in mean diameter increases of 4%. Piritramide and fentanyl did not show any effect. Depending on the pressure level, droperidol caused the diameter to increase 2 to 10%. Flunitrazepam brought about a marked relaxation (mean increase in diameter 15%), diazepam, however, did not influence the vessel segments. The results obtained show that the haemodynamic effects of the drugs used in this study, in particular those on the peripheral resistance, may, at least partially, be due to their direct influences on the vascular smooth muscle. The real pharmacologic mechanisms by which these effects are initiated, in most cases still remain to be investigated.