SUBJECTS

The exact cause of the increased peripheral resistance in chronic arterial hypertension is un-known. It is not due to generalized overactivity of the vasomotor nerves for Prinzmetal and Wilson (1936), Pickering (1936a), and Stead and Kunkel (1940) showed that the vasoconstriction responsible for essential hypertension is not neurogenic. Search for abnormal pressor agents in the blood stream has generally been unsuccessful (Hilise, 1924: Aitken and Wilson, 1935; Pickering, 1936b). Likewise, with rare exceptions such as pheochromocytoma, no increase in the level of naturally occurring pressor hormones has been found (Engel and von Euler, 1950; Raab and Gigee, 1954). Organic narrowing of the arterioles cannot be responsible, for this occurs only in the later stages and in restricted portions of the vasculature (Moritz and Oldt, 1935). There remains, however, one further possibility of accounting for the generalized reduction of peripheral vascular calibre in hypertension: increased sensitivity of the terminal arterioles to normal constrictor stimuli. The present paper describes a method of selectively measuring the sensitivity of blood vessels and submits observations on groups of subjects with normal and raised blood pressures, respectively. SUBJECT