Differential stimulation of synaptosomal norepinephrine uptake by high salt diet in Dahl rats

We have studied the norepinephrine (NE) uptake processes directly in synaptosomes isolated from the hypothalamus of both Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats. Both DS and DR rats were divided into two dietary groups, one high salt diet group and one low salt diet group. NE uptake was highly sodium dependent (averaging 80%) and ouabain sensitive (averaging 55%). The initial 3H-NE uptake by the hypothalamic synaptosomal fraction of DR and DS rats on a low salt diet during the first 10-min incubation period averaged 1.19 +/- 0.083 and 1.50 +/- 0.138 pmol/mg protein respectively while those of DR and DS on a high salt diet were 1.69 +/- 0.124 and 1.64 +/- 0.092 pmol/mg protein respectively. Baseline values of NE uptake on low salt diet were relatively high in DS compared to that in DR controls. High salt diet had a stimulatory effect on the net uptake of 3H-NE by hypothalamic synaptosomes of both strains of rats, DS showed an overall enhancement of 9% as compared to DR (42% increase, P = 0.003). This differential enhancement by the high salt diet was apparently contributed to by the sodium-mediated and ouabain sensitive amine uptake process and possibly resulted from a defective inducibility of (Na+-K+)-ATPase in DS rats.