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Dale in 1906 recognized the sympatholytic activity of crude extracts of ergot as well as their property of direct stimulation of smooth muscle, including that of the blood vessels (1). Despite their sympatholytic effects their direct vasoconstrictor action prevented significant lowering of arterial pressure.Later chemical purification of the crude drug resulted in the isolation of five alkaloids: ergotamine (2), ergobasine (3), ergokryptine, ergocornine and ergocristine (4). The basic chemical structure of these compounds was clarified by Jacobs and Craig (5) who demonstrated the presence of lysergic acid in all of the alkaloids (6). By hydrogenating the reducible double bond of the lysergic acid component of four of these alkaloids, Stoll and Hofmann (7) in 1943 produced a new series of compounds, dihydroergotamine, dihydroergocristine, dihydroergocornine (DHO-180) 5 and dihydroergokryptine (DHK-135).5 Pharmacological studies in animals (8) indicated that these modified compounds have enhanced sympatholytic and adrenolytic properties but little or no direct constrictor action on smooth muscle. In addition, they are hypotensive, this effect being mediated at least in part via the central nervous system (9). In man DHO and DHK in non-toxic doses have sympatholytic and hypotensive prop- erties (10-12). Because of their possible value in the treatment of essential hypertension and peripheral vascular disease a further clarification of their hemodynamic effects in man was undertaken. MATERIALS AND METHODSThe subjects were patients, mostly hypertensive, admitted to the wards of the Massachusetts Memorial Hospitals. The methods used in this investigation were essentially the same as those described in a previous communication (13). DHO was administered by intravenous injection in a solution of sterile water containing 0.5 mg. of active substance per cc. Unless otherwise indicated arterial pressure was measured continuously with a Hamilton manometer (13). RESULTS I. Sympatholytic Effects a. Sympathetic Vasopressor ResponsesCertain vasopressor responses usually abolished or diminished after surgical sympathectomy (14)

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