EFFECT OF DIAZEPAM ON ENDOCRINE AND CARDIOVASCULAR-RESPONSES TO HEAD-UP TILT IN HUMANS

Effects of the GABAergic drug diazepam (0.15 mg kg-1, i.v.) on cardiov ascular and endocrine responses to 50-degrees head-up tilt were evalua ted in seven men. During the initial phase of tilt (normotensive phase ), increases in heart rate (HR) and total peripheral resistance (TPR) and decreases in cardiac output were unaffected by diazepam. Also the associated increase in plasma noradrenaline did not change, while resp onse in plasma ACTH was diminished and in plasma cortisol abolished by diazepam (F(1, 10) = 6.45; P < 0.03). After 42 +/- 4 min of sustained tilt with saline (control) and 47 +/- 6 min (n.s.) after diazepam, pr esyncopal symptoms appeared (hypotensive phase) associated with decrea ses in HR, MAP, and TPR (P < 0.01). This episode induced a 2-3-fold in crease in plasma ACTH, beta-endorphin, prolactin, cortisol ( < 0.01), and a moderate increase in plasma adrenaline (P < 0.05). Diazepam did not significantly change cardiovascular and endocrine responses to the hypotensive phase of tilt. Results indicate that diazepam attenuates the cortisol part of pituitary-adrenal responses to moderate, but not to severe, central hypovolaemia in humans with no effect on cardiovasc ular tolerance.