Pathophysiological differences between obese and non-obese spontaneously hypertensive rats.

A genetic variant of the spontaneously hypertensive rat (SHR) has been produced which becomes markedly obese as well as hypertensive, i.e. Obese/SHR weigh 800 g as against 300 g for non-obese cohorts. Serum enzymes (CPK, SGOT, SGPT and LDH) are frequently abnormally elevated, concomitantly with a high incidence of myocardial necrosis. Obese/SHR are hyperlipidaemic with severe fatty infiltration of the liver; they are hyperglycaemic with enormous islets of Langerhans and extensive beta-cell degranulation; despite elevated blood urea nitrogen (BUN) levels, they manifest little or no renal damage. Measurement of corticosterone, deoxycorticosterone (DOC) and aldosterone in Obese/SHR demonstrate marked hyper-responsiveness to moderate stress. Circulating prolactin levels are lower in Obese and non-obese/SHR compared to SHR, but Obese/SHR manifest unusually high increases incirculating prolactin levels in response to stress. Obese/SHR are hyperinsulinaemic and have subnormal growth-hormone levels. Desite mild hypertension, hyperglycaemia and hyperlipidaemia, Obese/SHR show no evidence of atheromatous change but do develop early polyarteritis nodosa. It is believed that the genetically programmed hypertension and hyperglycaemia is mediated by increased DOC, aldosterone and corticosterone production respectively, and that the obesity, hypertension, and diabetes in Obese/SHR may be likened to human Cushing's disease.