Cytochrome oxidase activity in the hypothalamus of SHR and normotensive rats before and after fasting.

The metabolic activity in the brains of adult spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY), and Wistar (W) rats was assessed before and after fasting using cytochrome oxidase (COX) histochemistry. Before fasting, metabolic activity in the paraventricular (PVH) and supraoptic (SON) nuclei of the hypothalamus in SHR was greater than in control rats. Fasting elicited a decrease in arterial pressure (AP) in SHR and WKY; in SHR the decrease in AP was accompanied by a decrease of metabolic activity in the PVH and SON. The findings of this study support the hypothesis that the PVH and SON are involved in the hypertension and in the increased levels of sympathetic nervous activity and vasopressin production known to occur in SHR. In addition, the PVH and possibly the SON may be involved in the suppression of sympathetic nervous system activity and the lowering of arterial pressure which are associated with fasting.