Release of vasopressin, cortisol and β- endorphin in tetraplegic subjects in response to head-up tilt

Abstract

Plasma levels of f3-endorphin, vasopressin and cortisol during head-up tilt were measured in tetraplegic patients and in normal healthy subjects. In tetraplegic patients rapid tilt from the horizontal to 30° or 60° head-up induced orthostatic hypotension and increased plasma levels of cortisol, f-endorphin and vasopressin. In control subjects head-up tilt failed to alter plasma levels of these hormones. These data show that the head-up position in tetraplegics causes various endocrine reactions. The normal mechanism by which blood pressure is maintained on the assumption of an upright posture (the orthostatic reflex) is absent in tetraplegic patients. In normal individuals, the orthostatic reflex comprises an afferent system involving baroreceptor input through the ninth and tenth cranial nerves and an efferent effector system that is primarily the peripheral sympathetic system. This orthostatic reflex arc is broken by spinal cord transection, so that tetraplegic subjects show marked hypotension in response to the upright posture. In these subjects this orthostatic hypotension stimulates emergency endocrine reactions (Stephen, 1984). Tilting and standing of the tetraplegic subjects usually results in increased levels of vaspressin (Sved et al., 1985), cortisol (Vallbano et al., 1966), aldosteron and plasma renin activity (Johnson and Park, 1973; Mathias et al., 1975, 1980; Kamelhar et al., 1978; Kooner et al., 1988). In the present study we have demonstrated that the increases in plasma levels of cortisol and vasopressin are associated with increase in levels of plasma 13- endorphin during the head-up position of tetraplegic subjects. © 1990 International Medical Society of Paraplegia.