Increased cardiovascular beta-adrenoceptor responsiveness in underweight subjects

A comparison of cardiovascular responses to increasing bolus doses of the beta-agonist, Isoproterenol, was made between 11 normal weight (body mass index 19-22.5) and 9 underweight (body mass index 15.5-19) healthy, euthyroid male subjects from the same socio-economic background and on similar energy intakes. The positive chronotropic response and the fall in diastolic pressure observed during the dose response to Isoproterenol was significantly greater (P less than 0.05) in the underweights suggesting an enhanced beta-adrenoceptor responsiveness in this group. The cardiovascular responses to head-up tilt of underweight subjects were similar to those of the normal weight group. The study suggests that lean, underweight individuals may have a generalized increase in beta-adrenoceptor responsiveness.