- The elastin content of the aortic muscle and the elastase-like activity of the extracts of aortic muscle were studied in spontaneously diabetic BB rats and in rats made diabetic by a single bolus i.v. injection of alloxan. In both modes of diabetes, the total alkaline-insoluble aortic elastin content was significantly reduced in diabetic rats compared to that in the corresponding control rats. This reduction in aortic elastin was also accompanied by a consistent increase in the elastase-like activities of the aortic extracts prepared from the same tissues. Such a reciprocal relationship between aortic elastin content and elastase-like activity has previously been reported in rats with malignant hypertension. Since the rats used in this study were not hypertensive, the altered elastin metabolism observed in this work is likely to be a manifestation of diabetic disease and may in part account for the vascular changes associated with diabetes mellitus.