Role of the renal medulla in the resistance of rats to salt hypertension.

The role of the renal medulla in the sensitivity of rats to the hypertensive stimulus of salt overload was investigated in a strain of rats shown to be resistant to salt hypertension. Rats were divided into four groups: I -2/3 nephrectomy (medulla left intact); II - unilateral nephrectomy plus dissection of the medulla of the remaining kidney (UNDRM);III - UNDRM plus renomedullary autotransplantation; IV - UNDRM plus renocortical autotransplantation. Two weeks after surgery all rats were given 1% NaCl solution instead of drinking water, and the blood pressure was measured every week for 6 weeks. The blood pressure, although increased, was significantly lower in groups I and III than in the other two groups throughout the period of salt loading. Renal excretory function was similarly altered in all rats, as indicated by similar plasma creatinine concentrations. The results indicate that antihypertensive activity of the renal medulla may account for the high resistance of the described rat substrain to salt hypertension.