Skeletal metabolism and body composition in acromegaly.

Abstract

The effect of hypersomatotropism on skeletal metabolism and body composition was investigated in ten acromegalic individuals. The techniques of whole body counting, total body neutron activation analysis, 47Ca tracer kinetics, quantitative microradiography and measurement of cortical and trabecular thickness of bone biopsy specimens were employed. The profound effect of growth hormone on protein metabolism was confirmed by the increase in mean 40K and total body N. Total body levels of Cl and P were also increased. Total body Na was increased as was the Na/K ratio indicating a relative increase in total body Na when related to lean body mass. There was no correlation between total body Na or Na/K and hypertension. 47Ca tracer kinetics revealed an increased exchangeable pool and increased bone turnover. Only 1 of 6 patients studied was definitely in positive Ca balance. Mean total body Ca was 9% higher than the predicted values calculated on the basis of height. However, normalization of total body Ca by relating it to lean body mass (Ca/K), revealed a reduced Ca/K ratio in 4 subjects. Although this may be the result of an increase in soft tissue mass that is greater than the increase in skeletal mass, two patients had total body Ca levels which were less than the values predicted on the basis of height. These two subjects must be considered to have osteopenia. Quantitative microradiography of bone biopsies obtained from the iliac crest showed normal bone formation levels and increased resorption levels as is seen in osteoporosis. However, the cortical thickness was normal in all patients studied and the trabecular width was normal or increased. It is likely that cortical thickness is maintained by increased periosteal apposition.