Atrial natriuretic peptide and renal adaptation to contralateral nephrectomy in healthy man

Tamm-Horsfall protein in urine after uninephrectomy/transplantation in kidney donors and their recipients

Tamm-Horsfall protein (THP) is a large glycoprotein with unknown physiological function synthesized in the thick ascending limb of the loop of Henle. Urinary THP has recently been suggested as being suitable for monitoring the functional state of transplanted kidneys. In the present study, the urinary excretion of THP after uninephrectomy and transplantation among relatives was determined in order to study the influence of the acute reduction in renal mass on the excretion of this peptide. Glomerular filtration rate (GFR), estimated by the plasma clearance of 51Cr-EDTA, and the excretion rate of THP were measured 2 days before nephrectomy and 5, 12, 26 and 54 days after nephrectomy/transplantation in 22 healthy living kidney donors and in 16 of their recipients. In the donors, THP excretion rate of the kidney to remain in the donor was 22.3 micrograms/min before and 33.7 micrograms/min at 5 days after uninephrectomy (p < 0.01) and remained increased by around 40% throughout the study period. GFR of the remaining kidney rose from 47 ml/min before to 61 ml/min at 5 days after uninephrectomy (p < 0.001). The THP excretion rate/GFR ratio remained unchanged in the donors. In the kidney to be transplanted, THP excretion rate was unchanged before and after transplantation. There was no significant increase in GFR in the recipients, which was significantly lower than GFR of the donors all the time. In matched pairs of kidney donors and recipients, the THP excretion rate/GFR ratio tended to be lower in the recipients but the difference was not significant. The correlation between excretion rate of THP and GFR was significant (r = 0.66; p < 0.01). To conclude, uninephrectomy in healthy man was associated with a marked increase of around 40% in the excretion of THP from the kidney that remained in the donor. In the kidney that was transplanted, the THP excretion rate was unchanged. The THP excretion rate was correlated with GFR. The mechanism underlying this association is unknown as THP does not undergo glomerular filtration.

Effects of captopril on renal function in healthy uninephrectomized subjects and in healthy control subjects

OBJECTIVES

To study the importance of the renin-angiotensin-II system for renal haemodynamics and sodium and water handling in the adapted remnant kidney in healthy uninephrectomized subjects.

DESIGN

Case-control study.

SETTING

All subjects were investigated at laboratory C, Department of Medicine and Nephrology, Skejby Hospital.

SUBJECTS

Fourteen healthy uninephrectomized (Unx) and 14 matched healthy control subjects (Cs).

INTERVENTION

Captopril, 25 mg orally.

MAIN OUTCOME MEASURES

The glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured by the constant infusion clearance technique using 125I-iothalamate and 131I-hippuran as reference substances, tubular function was evaluated by the lithium clearance technique (CLi), urinary flow rate (V), sodium excretion (UNaV), fractional sodium excretion (FENa), mean blood pressure (MBP) and heart rate (HR) were measured by conventional methods and plasma levels of angiotensin II (Ang-II), aldosterone (Aldo), arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) were measured by radioimmunoassay.

RESULTS

In both groups captopril ingestion resulted in a significant decrease in the MBP (Unx: 87.1 to 83.5 and Cs: 86.8 to 83.8 mmHg, median values), filtration fraction (Unx: 24.6 to 22.1 and Cs: 24.1 to 22.5%, median values) and Ang-II (Unx: 10.5 to 7.7 and Cs: 12 to 7.6 pmol-1, median values). Single kidney GFR, V, and CLi were unchanged in both groups. FENa and single kidney RPF were significantly increased in only the Cs group; FENa (Unx: 1.81 to 1.91 and Cs: 1.56 and 1.90%, median values). The plasma level of ANP was significantly decreased in only the Unx group.

CONCLUSION

The data suggest that sodium handling in the remnant kidney in uninephrectomized subjects could be less sensitive to Ang-II than in healthy control subjects, and that this might be as a result of adaptive changes in the distal parts of the nephron.