Somatosympathetic reflexes were studied in young hyperinsulinemic, insulin-resistant Zucker rats (ZFR) and related control strain (ZLR). Glucose metabolism was characterized by minimal model analysis of intravenous glucose tolerance test data. Eighteen 7-wk-old ZFR and seventeen ZLR, under pentobarbital anesthesia, were studied. The ZFR group showed significantly greater (p<0.05) mean body weight, plasma glucose and insulin concentration than ZLR, whereas no significant difference was found in basal values of mean arterial pressure (MAP) and heart rate (HR). Increments of mean pressure (MAP) and heart rate (HR) elicited by electrical stimulation of the sciatic nerve (5-s trains of 100 pulses, 0.5 ms pulse duration, 100-400 µA pulse intensity) were significantly higher (ANOVA, p<0.05) in the ZFR group 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 the ZFR compared with the ZLR group. Thus, this factor does not contribute to the enhancement in somatosympathetic reflexes observed in this strain. The ZFR group was characterized by having one fourth (p<0.05) the insulin sensitivity of the ZLR group. These results suggest that a stronger sympathetic nervous reactivity associates in the ZFR group with a severe insulin resistant state before the onset of hypertension and supports the hypothesis of the involvement of insulin-mediated stimulation of the sympathetic nervous system in the development of cardiovascular diseases related to alterations of glucose metabolism.