Evaluation of hemodynamics, vascular reactivity and baroreceptor compensation in the insulin resistant Zucker obese rats

Incidence of essential hypertension has been reported to be significantly higher in the population afflicted with non-insulin dependent diabetes mellitus (NIDDM). The present studies were undertaken in the insulin resistant, Zucker obese rats to evaluate various factors that could lead to the development of high blood pressure. Direct blood pressure measurements in the conscious obese rats indicated that they were not consistently hypertensive although the blood pressures of the obese rats tended to be higher than that of the control lean rats. However, after Inactin® anesthesia blood pressures of the obese rats were significantly elevated which can be related to an increase in sympathetic tone since autonomic ganglionic blockade eliminated the differences between the pressures of the two groups. Under anesthesia, cardiac output per 100 gm body weight was significantly lower indicating inadequate tissue perfusion in the obese rats. In a separate series of studies carried out in conscious rats, reflexly mediated alterations in the heart rate to intravenous phenylephrine and sodium nitroprusside were significantly blunted in the obese rats. These observations which include enhanced central sympathetic discharge, inadequate systemic hemodynamics and attenuation of baroreceptor compensation collectively suggest that the insulin resistant obese rats are in a pre-hypertensive state and could develop sustained hypertension if they are exposed to other risk factors.