RESUMO
This study showed the effect of intravenous [iv] injection of melatonin in doses of 0.1, 0.5 and 1.0 mg/kg and serotonin in doses of 0.1, 0.3 and 0.5 mg/kg on the rate and depth of respiration in adult male rabbits. Intravenous injection of melatonin [1 mg/kg] caused a decrease in the frequency and an increase in the depth of respiration which resulted in a fall in PaCO2 and SaO2. Hypoventilation led also to an increase in PaCO2. The effect of melatonin on the rate and depth of respiration started immediately post-injection of melatonin and the maximum effect was recorded after 5 minutes and returned to the normal levels within 10 minutes of injection. Based on the results it can be concluded that melatonin as well as serotonin may have an important effect on the regulation of ventilation. Melatonin may affect respiration by acting directly on the muscle of respiration, while serotonin effect may be due to its direct action on chemoreceptors