Mechanism of vomiting by apomorphine

Abstract

Investigations done on normal or mediocolicular decerebrized dogs without anesthesia gave the following result.

Vomiting was frequently begun by dilation of tbe glottis along with prolonged contractions the abdominal press. At other times the first contraction resulted in closing of the glottis. However, the contraction of the muscles of the larynx, that is the closing of the glottis, did not mechanically influence the increase of abdominal pressure. This result is evident in experiments with isolated glot­ tis and tracheal cannula. The maximum increase in the resistance of the glottis usually coincides with the expiratory phase.

The fundamental factor in the increase of abdominal pressure affecting the ex­pulsion of the gastric contents is the short synergic contraction of the diafragm and abdominal muscles.

Tests evaluating apomorphine show that a moderate gastric repletion does not influence significantly the central emetic action.

With higher intragastric pressure (up to 30 or 40 cm H2O) there is a decrease in the dose of apomorphine necessary to provoke vomiting.

Gastric distention always accelerates momentarily the respiratory frequency. The influence of central excitability in the response has been demonstrated in various experiments, principally by the increase in the average dose of apomorphine in decerebrized animal.