Acute Effects of Growth Hormone on Vascular Function in Human Subjects

GH is involved in the long-term regulation of peripheral vascular resistance and vascular reactivity. We determined whether GH plays a role in the acute regulation of vascular function in humans. The acute vascular effects of GH were studied in eight healthy subjects according to a double-blind, placebo-controlled design. Forearm blood flow (FBF), vascular resistance, and nitric oxide (NO) production were monitored during a 4-h infusion of GH into the brachial artery at a rate chosen to raise local GH to stress levels (approximately 40 ng/ml). During GH infusion, FBF rose 75% (P < 0.05), whereas forearm vascular resistance decreased comparably (P < 0.05). These changes were paralleled by augmented forearm release of NO (P < 0.02). GH heightened the response of FBF to the endothelium-dependent vasodilator acetylcholine (Ach; P < 0.02). With the highest Ach dose, FBF reached 30.4 +/- 4.2 and 16.9 +/- 3.1 ml/dl x min in the GH and placebo studies, respectively (P < 0.005). The slopes of the dose-response curves also differed markedly (0.45 +/- 0.07 and 0.25 +/- 0.05 ml/dl x min/ microg in the GH and placebo studies, respectively; P < 0.01). GH caused an upward shift of the FBF response to the endothelium-independent vasodilator sodium nitroprusside (P < 0.01), but did not affect the slope of the dose-response curve. GH infusion did not cause any appreciable increment in the venous IGF-I concentration in the test arm. In conclusion, GH acutely lowers peripheral vascular resistance and stimulates endothelial function. These effects are mediated by activation of the NO pathway and appear to be independent of IGF-I.