Enhanced sympathetic reactivity associates with insulin resistance in the young Zucker rat

1 Department of Experimental Medicine, University of Genoa, Genoa; and 2 Department of Electromagnetics and Bioengineering, Polytechnic University of Marche, Ancona, Italy Submitted 2 September 2005 ; accepted in final form 7 March 2006 Somatosympathetic reflexes were studied in young hyperinsulinemic, insulin-resistant (Zucker fatty) rats (ZFR) and a related control (Zucker lean) strain (ZLR). Glucose metabolism was characterized by minimal model analysis of intravenous glucose tolerance test data. Seven-week-old ZFR ( n = 18) and ZLR ( n = 17) were studied under pentobarbital anesthesia. Mean body weight and plasma glucose and insulin concentration were significantly greater ( P < 0.05) in ZFR than in ZLR, whereas basal values of mean arterial pressure (MAP) and heart rate (HR) were not significantly different. Increments of MAP ( MAP) and HR ( HR) elicited by electrical stimulation of the sciatic nerve (5-s trains of 100 pulses, 0.5-ms pulse duration, 100- to 400-µA pulse intensity) were significantly higher (ANOVA, P < 0.05) in ZFR at each level of stimulus intensity. Regression analysis showed a linear increase in MAP and HR with increasing sciatic nerve stimulus intensity. Pressor responses to phenylephrine after ganglionic blockade demonstrated that vascular reactivity to adrenergic stimulation is not increased in ZFR compared with ZLR. Thus this factor does not contribute to enhancement of somatosympathetic reflexes observed in this strain. Insulin sensitivity in ZFR was one-fourth ( P < 0.05) that in ZLR. These results suggest that stronger sympathetic nervous reactivity in ZFR is associated with a severe insulin-resistant state before the onset of hypertension and support the hypothesis that insulin-mediated stimulation of the sympathetic nervous system is involved in the development of cardiovascular diseases related to alterations of glucose metabolism. sympathetic nervous activity; minimal model analysis; glucose kinetics; hypertension Address for reprint requests and other correspondence: P. Ruggeri, Section of Human Physiology, Dept. of Experimental Medicine, Viale Benedetto XV, 3, 16132 Genoa, Italy (e-mail: ruggeri{at}unige.it )