INSULIN INDUCES MEDIAL HYPERTROPHY OF MYOCARDIAL ARTERIOLES IN RATS

To investigate the effect of hyperinsulinemia on arteriolar hypertroph y, myocardial hypertrophy, and blood pressure, we administered insulin intraperitoneally to SHR and WKY rats for 3 consecutive weeks. To pre vent hypoglycemia, the drinking water contained 10% sugar, and to acce ntuate the blood pressure, their chow contained 8% table salt. Blood p ressure was measured by the tail-cuff method. Heart weights were facto red with body weights. Arterioles of similar to 100 mu m in diameter w ere examined at the end of the experiment and the vascular wall thickn ess was factored with the lumen diameter. At the end of 3 weeks, blood pressure rose in the SHR but not in the WKY rats. The heart weights i n the WKY normotensive rats did not increase, whereas in the SHR they did. Furthermore, there was a significant rise in vessel wall thicknes s in the rats that received insulin, whether there was a rise in blood pressure or not and whether they had an increase in heart weight or n ot. There was a similar rise in blood glucose in all the groups, with slightly more accentuated rise in the SHR that received insulin. Never theless the increase in vascular wall thickness occurred only in the g roups which received insulin. This seems to preclude the importance of hyperglycemia per se as the causative agent for the increase in vascu lar wall thickness in this study. The increase was in the form of medi al hypertrophy without any sign of atherosclerosis. It seems, therefor e, that hyperinsulinemia is associated with hypertrophy of the media o f arterioles regardless of the increase in heart weight or the rise in blood pressure.