EFFECTS OF ALPHA(1)-BLOCKADE ON THE FOREARM VASCULAR-RESISTANCE RESPONSES TO LOWER-BODY NEGATIVE-PRESSURE IN YOUNG BORDERLINE HYPERTENSIVES

To determine whether alpha(1)-blockade affects the forearm vascular re sistance responses to lower body negative pressure (LBNP) in borderlin e hypertensives, six hypertensives (HTN; mean arterial pressure [MAP] = 109.9 +/- 1.7 mm Hg, mean a SE) and seven normotensives (NTN; MAP = 81.5 +/- 1.4 mm Hg) underwent exposures of LBNP at pressures of -10, - 20, and -40 mm Hg during systemic alpha(1)-receptor blockade (BLK) and during placebo (PLA). Resting forearm vascular resistance (FVR) was g reater in HTN than in NTN during PLA (34.8 +/- 5.4 v 17.5 +/- 3.1 unit s; P < .05), but not during BLK (28.1 +/- 5.2 v 25.3 +/- 9.9 units). W hen expressed as a percentage of resting FVR, LBNP evoked an increased FVR (P < .001) that did not differ significantly between BLK and PLA in either group. FVR was higher (P < .001) in HTN than in NTN througho ut both trials; at -40 mm Hg of LBNP during BLK, the increase in FVR w as greater (P < .05) in HTN than in NTN (131 +/- 42 v 48 +/- 15%). MAP (relative to resting) was maintained throughout LBNP during PLA but, at -40 mm Hg, was lower (P < .01) during BLK for both groups. HR was e levated in BLK and was increased at -40 mm Hg (P < .01) for each group in each trial. This increase was greater during BLK (P < .05). These data suggest that borderline hypertensives have a greater vasoconstric tor response to LBNP than do normotensives and cu,blockade does not ap pear to attenuate this response. (C) 1997 American Journal of Hyperten sion, Ltd.