Presence of a serum vasoconstrictive factor following unilateral nephrectomy

Experimental hypertension is often associated with decreased renal mass and/or impediments to normal renal compensatory growth. This has led to the hypothesis that the renal growth factor (renotropin) is also a vasoconstrictor responsible for elevated blood pressure. Unilateral nephrectomy (uni) is the most popular mechanism to investigate compensatory renal growth. Accordingly, we examined the vasoconstrictive potential of rat sera following uni in order to compare it with serum renotropic activity. Compared to sham-operated (sham) rat sera, uni sera obtained at 24 hours after operation, a point in time when renotropic activity is highest, stimulated the constriction of isolated rat aortic rings significantly more than sham sera, and in a dose-dependent fashion. By paired analysis, the differences in constriction between uni and sham sera were significant at all doses examined. Unlike those obtained at 24 hours, uni sera did not show this response 48 hours, 1 week and 2 weeks after operation, simulating the temporal course of renotropin found in sera after uni. The uni serum factor was not influenced by dialysis suggesting that its molecular weight exceeds 6,000 daltons and that the vasoconstrictive response was not due to electrolyte differences between uni and sham sera. Vasoconstrictive activity was retained after serum passage through Affi-gel blue to remove albumin and after serum was heated in boiling water for 5 minutes. We conclude that a heat resistant serum vasoconstrictive factor with a molecular weight greater than 6,000 daltons arises shortly after uni but disappears once the remaining kidney begins to undergo a physiological compensatory growth response.