Effect of isotonic volume expansion on proximal tubular reabsorption of Na and fluid in the developing rat kidney.
Young rats (aged 22-24 days) and adult rats (aged 40-42 days) were studied during hydropenia (HP) and during volume expansion (VE) in order to clarify the role of the proximal tubule of the immature kidney in the blunted natriuretic response seen in young mammals during VE. The position of the last accessible site for micropuncture of the proximal tubular segment was determined. The disadvantages of using lissamine green as a marker of different tubular segments were investigated. Tubular function was ascertained by micropuncture of superficial proximal nephrons. Measurements of tubular length were made from latex casts of the proximal tubule. No side-effects of lissamine green were detected, when small quantities were used (20-30 microliter) and at least 20 min elapsed between the infusions of the dye and tubular samplings. The last accessible proximal tubule available for micropuncture was found to be similarly located in young and adult rats. Fractional reabsorption during HP remained constant during development. An equivalent degree of VE induced an increase in tubular load in both age groups, but it was more marked among younger rats. Absolute proximal reabsorption in both young and old rats in HP paralleled that of the tubular load. Fractional reabsorption, however, decreased slightly during VE but to the same extent in both age groups. This indicates a great flexibility in the immature proximal tubular under various tubular loads although it had been thought that this part of the nephron was in the later stages of development. The results simply that the proximal tubule does not create the blunted sodium response in the immature kidney during VE.
D000042:Absorption; D000818:Animals; D007668:Kidney / Q000254:growth & development* / Q000502:physiology; D007684:Kidney Tubules / Q000033:anatomy & histology / Q000502:physiology; D008086:Lissamine Green Dyes; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D008086:Lissamine Green Dyes; D012964:Sodium