The effect of growth hormone (GH) replacement therapy on sympathetic nerve hyperactivity in hypopituitary adults: a double-blind, placebo-controlled, crossover, short-term trial followed by long-term open GH replacement in hypopituitary adults.

OBJECTIVE: To test whether sympathetic nerve hyperactivity associated with adult hypopituitarism and untreated growth hormone (GH) deficiency is affected by GH treatment. DESIGN AND METHODS: Sympathetic nerve activity to the muscle vascular bed (MSA) expressed as burst frequency (bursts/min) and incidence (bursts/100 heartbeats) was recorded in 10 hypopituitary patients (aged 48-69 years), before and after acute (1 week) randomized, double-blind, crossover treatment with a 1-month washout period and chronic (1 year) GH replacement treatment. RESULTS: MSA burst frequency and incidence remained unchanged from baseline values after the short-term treatment, but exhibited decreases in median values [from 53 to 47 bursts/min (P = 0.02) and from 85 to 70 bursts/100 heartbeats (P = 0.03), respectively] after 12 months of replacement therapy. Twenty-four-hour urinary excretion of nitrate increased after the short-term cross-over treatment and the long-term treatment (P = 0.04). Diastolic blood pressure and waist circumference decreased after the 12-month treatment (P = 0.02 and P = 0.04, respectively). No correlation was found between the reduction in MSA and the increase in 24-h urinary nitrate excretion, the decrease in diastolic blood pressure and waist circumference. CONCLUSIONS: The sympathoexcitation in adult GH deficiency and the modest decline in MSA seen after long-term GH replacement treatment may suggest that the somatotropic axis is involved in the regulation of central sympathetic outflow.