Several studies have proposed that cyclooxygenase-2 (COX2) is involved in the regulation of nephrogenesis and that an impaired nephrogenesis may induce the development of hypertension. This study was designed to test the hypothesis that the decrease of COX2 activity leads to a reduction in nephron number, an increase in arterial pressure, and age-dependent renal alterations that are greater in male than in female rats. Arterial pressure was measured from the first to the 16th month of life in rats treated with vehicle or a COX2 inhibitor during the nephrogenic period. Stereological and histological evaluations and renal function studies were performed at different ages. Arterial pressure increased (14%; P<0.05) and nephron number decreased (17%; P<0.05) to similar levels in male and female COX2-treated rats. However, glomerular filtration rate (31%) and renal plasma flow (25%) decreased (P<0.05) in male but not in female COX2-treated rats. A greater (P<0.05) age-dependent elevation in glomerular hypertrophy was also found in male COX2-treated rats compared with their female littermates. Glomerulosclerosis and tubulointerstitial damage in renal cortex and medulla were also significantly enhanced in male but not in female aged COX2-treated rats. Our results demonstrate that the decrease in COX2 activity during renal development leads to a reduction in nephron number and to an elevation in arterial pressure that are similar in males and females. However, the consequent age-dependent deterioration of the renal structure and renal function is only significantly enhanced in male rats.