Effect of cold exposure and nutrient intake on sympathetic nervous system activity in rat kidney

Renal sympathetic nervous system (SNS) responses to environmental temperature and diet were evaluated using [³H]norepinephrine ([³H]NE) turnover as the index of sympathetic activity. Pharmacological studies first demonstrated that renal NE was localized principally within storage granules of renal sympathetic nerves and regulated by central sympathetic outflow. Acute exposure to cold (4°C), which increased cardiac SNS activity (P < 0.00005), had no effect on renal SNS. A 48-h fast suppressed renal [³H]NE turnover by 37% (P = 0.00024) and cardiac [³H]NE turnover by 48% (P = 0.00608). Dietary supplementation with sucrose did not affect [³H]NE turnover in kidney in either of two separate experiments, although it increased cardiac NE turnover in both. On the other hand, lard feeding significantly increased [³H]NE turnover in both kidney and heart, whereas dietary protein supplementation exerted no effect on either renal or cardiac [³H]NE turnover. These studies demonstrate a unique pattern of sympathetic regulation in kidney, one which is highly responsive to fasting and dietary fat, but not to cold exposure or dietary sucrose.