SPECIES DIFFERENCES IN THE RESPIRATORY AND CARDIOVASCULAR RESPONSE TO SEROTONIX (5-HYDROXYTRYPTAMINE)

¹ The Research Department, Ciba Pharmaceutical Products, Inc., Summit, New Jersey

1. Single i.v. doses of serotonin caused qualitatively and quantitatively different respiratory and cardiovascular responses in dogs, cat. s and rabbits.

2. Isolated perfused dog, cat and rabbit hearts all showed a positive but quantitatively different inotropic and chronotropic response to serotonin.

3. Activation of pulmonary stretch receptors after i.v. injections of serotonin could be demonstrated in cats and dogs, but not in rabbits.

4. Experiments in animals of all three species after section of both vagi, the spinal cord at C₆ and after pretreatment with various automiomic blocking agents led to the conclusion, that the species differences in the cardiovascular and respiratory response to serotonin are largely due to reflexes originating in the heart and the lungs.

5. After section of both vagi and the spinal cord at C₆ serotonin caused a uniform blood pressure response and the respiratory stimulating effects were eliminated to a large extent in all three species. A direct stimulation of the carotid bodies or the brain by serotonin is therefore unlikely as a cause of the respiratory reactions described in this paper.