Resetting of tubulo-glomerular feedback sensitivity by dietary salt intake

Summary Tubulo-glomerular feedback participates in the regulation of superficial nephron filtration rate, SN-GFR [13,29,30,32]. In the present experiments we investigated the possibility that the feedback response is modulated by salt intake. Five groups of rats were pretreated with diets containing different intake. Five groups of rats were pretreated with diets containing different amounts of sodium chloride in either food or drinking water. Estimated NaCl intake ranged from about 0.5 to 12 mEq per day and rat. Feedback response was tested in individual nephrons by comparing SN-GFR's derived from either distal tubular segments (i.e. with the macula densa region being perfused at normal rates) or end-proximal segments (i.e. with the flow in the macula densa region being acutely reduced). In accordance with earlier observations [8, 28], proximal SN-GFR exceeded the distal value in salt-deprived and control animals by 8.7 nl/min±8.6 (P<0.05) and 7.6 nl/min±5.4 (P<0.001) respectively. In contrast, rats supplied with 6, 11, or 12 mEq Na/day showed a proximal-distal SN-GFR difference of 1.4 nl/min ±8.5 (P<0.05), 1.2 nl/min±6.7 (P>0.05), and 4.6 nl/min±8.8 (P<0.001). Thus, elevation of NaCl intake either abolishes or diminishes feedback sensitivity in the subnormal flow range. We conclude that tubulo-glomerular feedback sensitivity is reset when sodium chloride intake is altered.Work performed during tenure of an Alexander von Humboldt-Dozentenstipendium.