Effect of lysergic acid diethylamide (LSD-25) on morphine induced bradycardia.

Several antagonistic interactions between morphine and LSD-25 (lysergic acid diethylamide) have been demonstrated. LSD-25 antagonizes morphine induced analgesia in rats (1) and emesis in dogs (2). It also blocks the miotic action of morphine (3). On the other hand morphine blocks LSD-25 induced pyre xia in rabbits (4) and the central hypotensive effect of LSD-25 in dogs (5). Morphine produces marked bradycardia in rabbits (6) and the present study was undertaken to see if LSD-25 antagonizes this effect of morphine as well. Twenty-four conscious albino rabbits of either sex weighing from 1.2 to 1.5 kg were used in this investi gation. At the time of the experiment the animal was placed on a table. The electrocardiographic tracings (Lead II) were obtained with Cardiopan (Phillips) at intervals of five minutes. When the heart rate was stabilized the test drug was administered intraperitoneally and its effect on heart rate was observed for one hour. The durgs employed in this study were morphine hydrochloride, lysergic acid diethylamide, chlor promazine hydrochloride and perphenazine hydrochloride. Solutions of the drugs were freshly prepared in distilled water at the time of administration.