This study investigates the effects of angiotensin I converting enzyme inhibitor (ACEI) treatment on glomerular hypertension and injury in rats with reduced renal mass. Four groups of male Munich-Wistar rats underwent ⅓ renal ablation and segmental infarction of the left kidney. Groups 1 and 3 received no specific therapy, while Groups 2 and 4 were treated with enalapril in their drinking water. Micropuncture and morphological studies were conducted at 4 and 8 weeks post-ablation. Key findings include: - Untreated rats (Groups 1 and 3) developed systemic hypertension and progressive glomerular injury, characterized by elevated glomerular capillary hydraulic pressure and plasma flow rate. - Enalapril treatment (Groups 2 and 4) prevented systemic hypertension and maintained normal glomerular hemodynamics, without significantly compromising glomerular filtration rate. - At 8 weeks, enalapril-treated rats (Group 4) had significantly lower proteinuria and fewer glomerular lesions compared to untreated rats (Group 3). The study suggests that controlling glomerular hypertension effectively limits glomerular injury in rats with reduced renal mass, supporting the hypothesis that glomerular hemodynamic changes mediate progressive renal injury when nephron number is reduced.This study investigates the effects of angiotensin I converting enzyme inhibitor (ACEI) treatment on glomerular hypertension and injury in rats with reduced renal mass. Four groups of male Munich-Wistar rats underwent ⅓ renal ablation and segmental infarction of the left kidney. Groups 1 and 3 received no specific therapy, while Groups 2 and 4 were treated with enalapril in their drinking water. Micropuncture and morphological studies were conducted at 4 and 8 weeks post-ablation. Key findings include: - Untreated rats (Groups 1 and 3) developed systemic hypertension and progressive glomerular injury, characterized by elevated glomerular capillary hydraulic pressure and plasma flow rate. - Enalapril treatment (Groups 2 and 4) prevented systemic hypertension and maintained normal glomerular hemodynamics, without significantly compromising glomerular filtration rate. - At 8 weeks, enalapril-treated rats (Group 4) had significantly lower proteinuria and fewer glomerular lesions compared to untreated rats (Group 3). The study suggests that controlling glomerular hypertension effectively limits glomerular injury in rats with reduced renal mass, supporting the hypothesis that glomerular hemodynamic changes mediate progressive renal injury when nephron number is reduced.