Cardiovascular and Respiratory Actions of 5‐hydroxytryptamine in the Cat

Abstract

The respiratory and cardiovascular effects of 5-hydroxytryptamine (HT) in the cat have been described by several authors, but it is still not clear to what extent its effects are due to reflex or to direct actions.HT causes a temporary arrest of breathing in the cat (Reid and Rand, 1951). Ginzel and Kottegoda (1954) observed that, when small doses (2-6 ,ug.) were injected into the carotid sinus region of the cat, there was a brief apnoea followed by stimulation of breathing; these changes were accompanied by -a fall of blood pressure. Since denervation of the carotid sinus region abolished these effects they concluded that HT acts on either baro-or chemo-receptors. They also found 1954) reported that HT stimulates pulmonary stretch receptors, but admitted that some other type of sensory vagal nerve fibres might also be excited. Mott and Paintal (1953), in a small series of experiments, showed that the reflex apnoea caused by HT in the cat arose from sensory receptors lying between the great veins and the left atrium, and that it was abolished by cutting the vagi but not by cooling them to 2-3°C. Mott and Paintal (1953) and Paintal (1954) were unable to find any evidence that this substance stimulates or sensitizes pulmonary stretch, right or left atrial, or depressor, nerve endings. They concluded that the reflex apnoea caused by HT in the cat resembled that for the amidine compounds, and differed from that caused by veratridine; the latter has been shown to stimulate pulmonary stretch fibres (Meier, Bein, and Helmich, 1949;Dawes, Mott, and Widdicombe, 1951;Paintal, 1953). Hence there exists a difference of opinion regarding the site and mode of action of HT in causing reflex apnoea. The present investigation was undertaken in the hope of elucidating this question, and also with a view to analysing further reflex actions of HT in the cat. METHODSThe respiratory and cardiovascular changes produced by intravenous injections of HT were studied in 13 cats (1.5-3.2 kg.). The animals were anaesthetized with chloralose (60 mg./kg.) and the respiratory movements recorded by the body plethysmograph (Dawes, Mott, and Widdicombe, 1951). Carotid blood pressure was recorded by a mercury manometer and injections were made into the jugular vein. The cervical vagi were cooled by the method described by Dawes et al. (1951). Both vagi were cooled simultaneously to the same temperature.The effect of intravenous injections of HT on the blood flow in the hind legs was investigated in four cats (2.3-3.4 kg.). These animals were anaesthetized with pentobarbitone (30 mg./kg. intraperitoneally) and heparinized. The aorta was divided in the lower abdomen, a pump unit was introduced between the

The Effects of 5‐hydroxytryptamine and Its Antagonists on Tidal Air

“…This was explained as mainly a direct constriction of the bronchial muscle, but it also appeared to be partly reflex in origin. Kottegoda and Mott (1955) noted that 5HT increased intratracheal pressure in the vagotomized cat and attributed this to direct bronchoconstriction. A direct effect of 5HT on bronchial muscle, independent of reflexes, has been observed in the perfused lungs of the rabbit (Freyburger, Graham, Rapport, Seay, Govier, Swoap, and Van der Brook, 1952), cat (Gaddum, Hebb, Silver, and Swan, 1953) and guinea-pig (Bhattacharya, 1955).…”

Role of Atropine in Antagonizing the Effect of 5-Hydroxytryptamine (5-HT) on Bronchial and Pulmonary Vascular Systems

“…Figures 1 and 5 show the data from two groups of dogs receiving 5-HT through two different pathways in which the increase in dynamic pulmonary elasticity is of almost equal magnitude in both groups. Very little information is available on the effect of aerosol ized 5-HT on the bronchial system and most of the previous studies were carried out by direct administration of 5-HT into the pulmonary artery [10,24] or into the bronchial artery [9] in animals. There are few reports that inhalation of aerosolized 5-HT does not induce bronchospasm in normal subjects, but can elicit severe attack in asthmatic patients [18].…”

Peripheral Circulation

“…Page has discussed in a review serotonin and its cardiovascular actions (329), and further evidence that this substance can stimulate cardiopul monary receptors has been presented (265). In the kidney serotonin seems to exert no specific effects on circulation besides its action On the vasomotor nerves (92).…”