Effects of furosemide on medullary oxygenation in younger and older subjects

Renal medullary hypoxia is characteristic of mammalian kidneys and can be a ssessed noninvasively in animals and humans by blood oxygen level-dependent magnetic resonance imaging (BOLD MRI). Water diuresis has been shown to im prove medullary oxygenation in young human subjects but not in elderly subj ects, a difference attributed to a decline in renal prostaglandin productio n with age. Loop diuretics such as furosemide also increase medullary oxyge nation in experimental animals, by inhibiting active transport and oxygen c onsumption in the medullary thick ascending limb. We examined, using BOLD M RI, this response to furosemide in eight younger (23 to 34 years) and eight elderly (64 to 81 years) healthy women. We also attempted to assess the ro le of prostaglandins in age-related differences, using ibuprofen to inhibit prostaglandin E-2 synthesis. Renal medullary oxygenation, initially low, i ncreased during furosemide diuresis in younger subjects. In the older popul ation, however, furosemide usually elicited little or no change in oxygenat ion of the renal medulla, despite profuse diuresis. Ibuprofen did not inhib it the action of furosemide to improve medullary pO(2) in younger subjects. Conclusions. The action of loop diuretics to improve medullary oxygenation, apparent in younger subjects, is blunted by normal aging. Inhibition of pr ostaglandin synthesis did not counteract the effect of furosemide in younge r subjects, suggesting that a decline in prostaglandin E-2 production with age is not the central cause of this age-related defect.