RESUMO
Senescence and chronic kidney disease (CKD) reduce progressively glomerular filtration rate (GFR), which usually results in an increase in potassium renal secretion. To evaluate whether the transtubular potassium concentration gradient (TTKG) is more accurate parameter for evaluating the renal secretion of this cation than using fractional excretion of potassium as its urinary secretion marker, we studied 55 subjects, 43 of them were healthy elderly volunteers and 12 were CKD patients. Exclusion criteria were: abnormal plasma potassium level or presence of any disease or drug that could induce alteration of balance of this electrolyte levels. All the subjects were on a diet with a potassium content around 50 mmol/day. The curves, which demonstrate the relationship between creatinine clearance and TTKG and the grade of correlation between these two parameters were analyzed in both groups. We found that the transtubular potassium concentration gradient had a significant negative correlation with the creatinine clearance level in the healthy elderly group, while there was no correlation in the CKD group.
Assuntos
Creatinina/metabolismo , Falência Renal Crônica/sangue , Falência Renal Crônica/urina , Túbulos Renais/metabolismo , Potássio/metabolismo , Idoso , Idoso de 80 Anos ou mais , Taxa de Filtração Glomerular , Humanos , Pessoa de Meia-Idade , Concentração Osmolar , Índice de Gravidade de DoençaRESUMO
UNLABELLED: Transtubular potassium concentration gradient (TTKG) is an index of potassium secretory activity in the distal tubule. Since water reabsorption takes place in the distal tubule as well, urine potassium concentration is a less accurate index evaluating distal K+ secretion because the effect of water is not taken into account on urine potassium concentrations. Potassium secretion and water reabsorption are strongly related to age and renal function. As a consequence, TTKG would be altered in both elderly individuals, as well as in patients with chronic renal failure (CRF). The aim of this study was to assess and compare TTKG in these two groups. PATIENTS & METHODS: A total of 55 individuals were studied, 12 of them were patients with CRF and 43 healthy elderly subjects with normal renal function. Informed consent was obtained from all patients. Patients with diabetes mellitus, cardiac failure, cirrhosis, obstructive uropathy, hyperkalemia, hypokalemia, or taking any medication that could alter the potassium balance were excluded from the study. All subjects were on a diet containing 50 mmol of potassium intake daily (documented by a three-day dietary record). Plasma potassium, creatinine, urea, glucose and osmolality were measured in all as well. 24 h creatinine clearance (CrCl ) and TTKG were calculated. Statistical analysis was made using Student's t-test. RESULTS: TTKG was significantly lower in the elderly group (4.2+/-1.9 vs 6.2+/-1.8 , P 0.005)Both groups had a significantly lower TTKG when compared to healthy young people (8+/-2). Plasma and urine potassium levels, as well as plasma osmolality were similar in the two groups. Only urine osmolality was lower in the CRF group (382+/-141 vs. 514+/-180, P=0.01) CONCLUSION: Both old age and renal impairment lead to a reduced TTKG in comparison with young healthy people. Furthermore, TTKG is significantly lower in elderly healthy subjects compared to patients with CRF.