Central action of apomorphine and potentiation of its emetic effects

Abstract

The different aspects of the vomit have been studied in experimental investigations on dogs.

The effect of apomorphine during the phase of excitation in the EMG of the diaphragm is caracterized by an increa­se in the activity which corresponds to the greater inspiratory depth, with a discreet increase in the activity in the abdo­minal EMG (fig. 1).

When apomorphine is injected in ani­mals with a midprotuberantial section and after the bilateral vagotomy, provokes of prolongs apneustic breathing (fi­gure 2).

The phase of the expulsion of the vo­mit is caracterized by violent synergic contraction of both the diaphragm and abdominal expiratory muscles (figs. 4, 5, 6, 9, 10). In the prevomitive phase the simultaneous contraction of anthagonist muscles already appears (figs. 3 and 4) although not yet with the sufficient muscular tension to obtain a gastric emptying. During the vomit by apomorphine a change is registrated in the gastric motility which is defined by the preferential contraction of the pyloric antrum, with relaxation of the rest of the sto­ mach.

The increase of gastric pression, caused by the distensión of the stomach, produces in all animals the acceleration of the respiratory frequency and the diminution of the tidal volume (fig. 7). When the increase in the gastric pres­sion is due to the contraction of the sto­mach, it is always accompanied by the diminution of activity in the diaphragmatic and abdominal EMG, with the di­minution of the tidal volume, without an apreciable change in the frequency (fig. 8).

The increase of pression in the duodenum and antrum separated from the rest of the stomach, slows down the res­ piratory frequency. The increase of pres­sion in the gallbladder produces a dimi­nution in the tidal volume (fig. 8).

The midcollicular or midprotuberan­ tial decerebration determines an increase in the ED50 of apomorphine which passes from 12.1 mcrg/Kg in an intact ani­mal to 31.4 mcrg/Kg in the decerebrated animal. The administration of dosis of prectamide of 30 mg/Kg determines a significative increase in the number of responses to the ED50 of apomorphine. When in animal the response is not obtained with a dosis habitually emetic of apomorphine, we have always obtained the vomit by the administration of prec­tamide 10 minutes after that of apomor­ phine.

The bilateral vagotomy increase the threshold for the apomorphine, having obtained only three vomits in the serie of vaguectomized dogs (fig. 10), which shows that the threshold of the emetic center to the central emetics is dependent on the vagale afferent discharges.