Is the somatotropic axis related to sympathetic nerve activity in healthy ageing men?

Objective The mechanisms underlying the age-related increase in blood press ure and sympathetic nerve activity remain largely unknown. The decline in g rowth hormone (GH) secretion and insulin-like growth factor-I (IGF-I) with age has been related to several cardiovascular risk factors. Low serum IGF- I levels in severe adult GH deficiency is associated with markedly increase d sympathetic nerve activity. This study evaluates whether a relationship b etween serum IGF-l and sympathetic nerve traffic exists in healthy aging me n. Design and methods Sympathetic nerve activity to the muscle vascular bed (M SA) was recorded in 56 healthy normotensive males, and related to age (rang e 21-71 years), body mass index (BMI, range 18.4-32.2), serum IGF-I and pla sma nitrate levels. Blood pressure, BMI and MSA increased with age, whereas IGF-I and plasma nitrate decreased. In a forward stepwise multiple regress ion analysis, age explained 40% of the variability in MSA and excluded othe r variables. Omitting age, IGF-I became the strongest independent predictor , explaining 23% of the variability in MSA. MSA was an independent predicto r of diastolic blood pressure, but its influence (10%) was less than that o f BMI (28%). BMI was not related to MSA or IGF-I. Conclusions Decreased serum IGF-I levels are coupled to increased MSA durin g ageing, an effect independent from the impact of increased body weight Al though MSA is a weak predictor of rising blood pressure with age, it consti tutes one possible pathway for the somatotropic axis to affect cardiovascul ar function in ageing. (C) 2001 Lippincott Williams & Wilkins.