Renal function and morphometry in the dwarf rat following a reduction in renal mass

Background. The compensatory increase in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) which follows a reduction in renal mass may be mediated by growth hormone, a renal vasodilator. Methods. GFR, ERPF and glomerular morphometry were assessed in the dwarf rat, selectively deficient in GH, and compared its Lewis base strain. Studies were performed 21-days after sham-operation, unilateral nephrectomy or subtotal nephrectomy in age-matched animals. GFR and ERPF were assessed from the renal clearance of inulin and p-aminohippurate measured under barbiturate anaesthesia. Results. The dwarf rat had a lower GFR and ERPF than the Lewis rat, in proportion to its lower body weight and lower kidney weight. Kidneys from the dwarf rat had a similar number of glomeruli to the Lewis, but smaller glomerular components in proportion to a lower kidney weight. Following unilateral nephrectomy, GFR (dwarf + 58%, Lewis + 53%) and ERPF (dwarf + 58%, Lewis + 52%) increased to a similar degree in both rat strains. Glomerular diameter, volume and capillary surface area increased in proportion to kidney growth, although compensatory renal growth (dwarf + 62%, Lewis + 78%) was somewhat lower in the dwarf. Following 5/6 subtotal nephrectomy, GFR (dwarf + 143%, Lewis + 171%) increased to a similar degree in both rat strains while ERPF (dwarf + 108%, Lewis + 48%) and compensatory renal growth (dwarf + 115%, Lewis 86%) were greater in the dwarf than the Lewis rat. Subtotal nephrectomy was also associated with an increase in the thickness of the glomerular basement membrane in both rat strains. Conclusions. The results do not support a role for GH in the compensatory increase in renal function or hypertrophy which follows a reduction in renal mass, excluding this as a potential mechanism for: GH-dependent renal scarring.