Relation of growth hormone and myocardial collagen accumulation in experimental diabetes

A pathogenic role of growth hormone in the tissue complications of diabetes has been postulated. Because collagen has been found to accumulate in myocardial interstitium in diabetes, we have undertaken a study of the relationship of plasma growth hormone levels to collagen accumulation in a canine model of chronic diabetes. Sedentary normal animals and diabetic animals were compared respectively with physically conditioned animals in which the collagen increment associated with diabetes was minimized. Basal growth hormone levels as well as increments induced by hormone release after clonidine have been related to the myocardial alteration. Myocardial collagen concentration was increased to 2.94 +/- 0.11 micrograms/mg dry weight in the sedentary diabetic animals vs. 1.97 +/- 0.07 micrograms/mg dry weight in sedentary normals (P less than 0.01), but was normal in the exercised diabetic animals after 1 year. However, levels of growth hormone in the basal state were similar in all four groups. After provocative stimulation with clonidine in the normals there was a progressive rise of growth hormone levels that was similar in the sedentary and physically conditioned animals. The diabetic groups exhibited a rise of plasma growth hormone that was not significantly higher in the nonexercised animals. Moreover the peak levels of growth hormone after clonidine were comparable. The data suggest that collagen accumulation in diabetic myocardium does not appear to be dependent on increased plasma levels of growth hormone, but a role for enhanced sensitivity to hormonal action is not excluded.