We have previously shown that transplantation of kidneys from genetically hypertensive to normotensive rats result in hypertension in renal graft recipients. To investigate whether this posttransplantation hypertension may have been the result of damage to the renal graft by high perfusion pressure before transplantation, we normalized blood pressure throughout life in spontaneously hypertensive rat (SHR) kidney donors by continuous antihypertensive treatment with the angiotensin-converting enzyme inhibitor ramipril (1 mg.kg-1.day-1 in drinking fluid). When kidneys from these rats were transplanted at age 20 wk to age-matched bilaterally nephrectomized F1 hybrids bred from SHR and Wistar-Kyoto (WKY) parents, posttransplantation hypertension still developed. In contrast, blood pressure did not change significantly in recipients of kidneys from ramipril-treated WKY rats. In the initial phase, recipients of SHR kidneys had a lower body weight and higher plasma urea concentrations than recipients of WKY kidneys. However, in the chronic phase, there were no significant differences between the two groups with respect to daily water intake, plasma urea concentration, glomerular filtration rate, renal blood flow, and weight of transplanted kidneys; no histological differences were observed between renal grafts from WKY and SHR donors, except for structural vascular hypertrophy in the latter group. We conclude that posttransplantation hypertension in recipients of SHR kidney grafts also develops, when the grafts have not been subjected to high renal perfusion pressure before transplantation. Our data support the hypothesis that SHR kidneys carry a primary defect, which can induce hypertension in renal graft recipients.

We determined whether transplantations of kidneys from stroke-prone spontaneously hypertensive rats (SPSHR) and from normotensive Wistar-Kyoto rats (WKY) alter blood pressure in renal graft recipients. Kidneys taken from seven male SPSHR and seven male WKY rats (blood pressure 186 +/- 4.8 and 111 +/- 3.7 mmHg, respectively) at the age of 20 wk were transplanted, using microsurgical techniques, to bilaterally nephrectomized age-matched male F1 hybrids (blood pressure 136 +/- 2.6 and 138 +/- 6.3 mmHg, respectively) bred from SPSHR and WKY parents. After renal transplantation, blood pressure in recipients of SPSHR kidneys rose to 146 +/- 11.8 (week 2), 163 +/- 16.4 (week 3), 192 +/- 17.1 (week 4), 222 +/- 17.7 (week 5), 221 +/- 12.6 (week 6), 218 +/- 20.3 (week 7), and 239 +/- 9.2 mmHg (week 8). There was no significant change in blood pressure in recipients of WKY kidneys. All rats recovered rapidly from surgery. After renal transplantation, there was a significant increase in daily water intake, a decrease in plasma renin activity, and a slight rise in plasma urea concentration. Our data show that transplantation of kidneys from adult SPSHR causes hypertension in normotensive recipients, indicating a major function for the kidney in SPSHR hypertension.

Renal transplantations were performed, using microsurgical techniques, with adult male two-kidney, one clip hypertensive rats (n=9) and sham-operated normotensive Wistar-Kyoto rats (ra=8) as kidney donors and with Fl hybrids, bred from Wistar-Kyoto and stroke-prone spontaneously hypertensive rat parents, as recipients. Systolic blood pressure before surgery was 200±2.7 mm Hg in hypertensive and 115±1.7 mm Hg in normotensive donors and 144±7.1 and 138 ±3.5 mm Hg in the two groups of recipients. Renal hypertension in donors was maintained for 14 weeks before surgery was performed and the nonischemic kidneys were transplanted. Bilaterally nephrectomized recipients of renal grafts from hypertensive donors developed sustained hypertension (185±3.9 mm Hg). In contrast, in recipients of renal grafts from normotensive donors, blood pressure decreased significantly to the level of the donors (111+3.7 mm Hg). Posttransplantation hypertension in recipients of renal grafts from hypertensive donors was associated with intrarenal vascular hypertrophy, smaller kidneys, a decreased glomerular filtration rate, an increased plasma urea concentration, and polydipsia as compared with normotensive transplanted controls. Renal pyelograms revealed no gross anatomic alterations of transplanted kidneys. Our data indicate that secondary damage to the renal grafts caused by high perfusion pressure before transplantation can induce hypertension in recipients of these kidneys. Furthermore, our data suggest that renal mechanisms may be necessary to maintain borderline hypertension in Fl hybrids. (Hypertension 1990; 15:429-435)

Primary hypertension in animals and humans probably represents several different pathophysiological states rather than being a uniform nosological entity. Among other factors, renal mechanisms may be primarily and secondarily involved. The availability of genetically homologous animal models for hypertension has greatly promoted studies on the etiology and pathogenesis of high blood pressure disease. In particular, renal transplantation studies between genetically hypertensive and normotensive rats from three different models have provided strong evidence for a primary role of the kidney in genetic hypertension. Other factors, such as vascular, neural, and humoral mechanisms have also been shown to be involved and may be particularly effective in increasing blood pressure, when they act through the kidney. Several functional and biochemical differences have been identified between kidneys from genetically hypertensive and normotensive animals. However, the relative contribution of each of these factors to the development of primary hypertension remains to be determined. Evidence from studies on human renal graft recipients also indicates that, among other factors, the kidney plays an important role in the development of primary hypertension in humans.