Exaggerated natriuresis in the conscious spontaneously hypertensive rat
Willis, L.R.; McCallum, P.W.; Higgins, J.T.
Journal of Laboratory and Clinical Medicine 87(2): 265-272
1976
ISSN/ISBN: 0022-2143 PMID: 1245791 Document Number: 101148
In response to acute saline loading many patients with essential hypertension exhibit exaggerated natriuresis relative to normotensive controls. The urinary responses of conscious, Okamoto-strain, spontaneously hypertensive rats (SHR), and Wistar-Kyoto normotensive rats (NTR) to acute saline loading were studied. Groups of 12 rats of each strain, 12 weeks old, were in metabolism cages for 1 week. Systolic blood pressures (tail cuff) were significantly different, 206 plus or minus 9 mmHg in SHR and 135 plus or minus 3 mmHg in NTR. After a 4-h control urine collection, 6 ml 0.9% NaCl was given by tube. Urine was collected again for 2 h. Control urinary excretions of Na, K and creatinine were 11.2 plus or minus 4.8 mu Eq/h, 50.1 plus or minus 7.6 mu Eq/h and 39.9 plus or minus 5.5 mg/h in SHR, and 13.8 plus or minus 2.4 mu Eq/ha, 34.9 plus or minus 5.5 mu Eq/h and 37.5 plus or minus 7.1 mg/h in NTR. The control values for Na, K and creatinine excretion in the 2 groups were not significantly different. After saline loading, Na and creatinine excretion rates increased in both groups but the increase in Na excretion in SHR, 60.8 plus or minus 7.2 mu Eq/h, was more than double and significantly different from that of the NTR, 26.6 plus or minus 3.7 mu Eq/h. The increments in creatinine excretion in the 2 groups were not different. In the NTR, urinary K excretion increased to 59.0 plus or minus 7.9 mu Eq/h whereas in SHR it was not altered, 12.0 plus or minus 8.8 mu Eq/h. The change in creatinine excretion as an index of change in glomerular filtration rate suggests that the greater increase in Na excretion by the SHR was the result of decreased fractional reabsorption of Na and not of a greater increase in glomerular filtration rate. The exaggerated natriuretic response to salt loading in SHR resembles that in hypertensive man except that in SHR a simultaneous kaliuretic response is absent.