Studies were carried out to determine the effect of uninephrectomy (UNX) on single nephron hemodynamics and proteinuria in the spontaneously hypertensive rat (SHR). Four groups were studied: two-kidney SHR and normotensive WKY controls; SHR + UNX and WKY + UNX. UNX was performed at age 8 to 10 weeks. Blood pressure and protein excretion were measured periodically, and micropuncture experiments of cortical nephrons were carried out at age 32 to 40 weeks. Systolic blood pressure was not significantly different between SHR and SHR + UNX. Protein excretion increased markedly in the SHR + UNX 6 months after UNX, as compared with the other three groups. In cortical nephrons, single nephron glomerular filtration rate (SNGFR) and plasma flow entering the glomeruli (SNPF) was lower in SHR + UNX than in WKY + UNX. Glomerular hydraulic pressure (PG) during stopped flow was closely comparable in all groups, rising only 2 mm Hg after UNX. SNGFR was measured in juxtamedullary (JM) nephrons 2 months after UNX, a stage before heavy proteinuria developed. We found that JM SNGFR was approximately 50% higher in SHR + UNX than in WKY + UNX. The observations suggest that following ablation of renal mass, superficial cortical glomeruli are not exposed to excessively high pressure or flow rates in the SHR. In contrast, JM glomeruli undergo a disproportionate rise in SNGFR, presumably associated with excessively high PG and/or blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)