Effects of α1-Blockade on the Forearm Vascular Resistance Responses to Lower Body Negative Pressure in Young Borderline Hypertensives

To determine whether α1-blockade affects the forearm vascular resistance responses to lower body negative pressure (LBNP) in borderline hypertensives, six hypertensives (HTN; mean arterial pressure [MAP] = 109.9 ± 1.7 mm Hg, mean ± 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 α1-receptor blockade (BLK) and during placebo (PLA). Resting forearm vascular resistance (FVR) was greater in HTN than in NTN during PLA (34.8 ± 5.4 v 17.5 ± 3.1 units; P< .05), but not during BLK (28.1 ± 5.2 v 25.3 ± 9.9 units). When 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 throughout both trials; at −40 mm Hg of LBNP during BLK, the increase in FVR was 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 elevated 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 vasoconstrictor response to LBNP than do normotensives and α1-blockade does not appear to attenuate this response.