Cardiovascular effects of intravenous infusions of 5-hydroxytryptamine in man.

Intravenous infusions of 5-hydroxytryptamine creatinine sulphate in doses of 1,2, and 3 mg./min. of the salt into 42 normal subjects caused a dilator response of the forearm vessels, consisting of an initial transient increase in flow usually followed by a smaller but sustained increase. A fall in forearm flow was not seen. Heart rate was invariably increased and the increase preceded other changes by 10 to 20 sec. suggesting a direct effect on the heart. The sustained increase in flow probably represents a balance between the direct constrictor action of the drug and a secondary dilator effect. The blood pressure response was variable and it appeared unlikely that it was responsible for more than a small part of the forearm flow changes. Two subjects appeared to be abnormally sensitive to the drug.