BACKGROUND: It has been suggested that atrial natriuretic peptide (ANP) 
contributes to the glomerular hyperfiltration of diabetes mellitus. Infusion of 
ANP increases the urinary excretion of albumin in patients with type I diabetes 
mellitus (IDDM). Although the increased albuminuria is attributed to a rise in 
glomerular pressure, alterations in tubular protein handling might be involved.
PATIENTS AND METHODS: We have studied the effects of ANP in nine 
microalbuminuric IDDM patients. After obtaining baseline parameters, ANP was 
infused over a 1-h period (bolus 0.05 microgram kg-1, infusion rate 0.01 
microgram kg-1 min-1). Renal haemodynamics, sodium and water clearance and 
tubular protein handling were studied.
RESULTS: The glomerular filtration rate (GFR) increased from 116.4 +/- 8.9 to 
128.3 +/- 8.8 mL min-1 1.73 m-2, whereas the effective renal plasma flow (ERPF) 
decreased from 534.3 +/- 44.3 to 484.9 +/- 33.3 mL min-1 1.73 m-2 (P < 0.05). As 
a result, the filtration fraction was significantly higher during infusion of 
ANP. ANP attenuated proximal tubular sodium reabsorption. Urinary albumin 
excretion rose from 87.57 +/- 21.03 to 291.40 +/- 67.86 micrograms min-1 (P < 
0.01). Changes in the urinary excretion of beta 2-microglobulin and free kappa 
light chains were more marked, the excretion of beta 2-microglobulin increasing 
from 0.28 +/- 0.21 to 51.87 +/- 10.51 micrograms min-1 (P < 0.01), and of free 
kappa-light chains from 4.73 +/- 1.74 to 46.14 +/- 6.19 micrograms min-1 (P < 
0.01).
CONCLUSIONS: The observed rise in albuminuria during infusion of ANP does not 
simply reflect a change in glomerular pressure, but might at least partly result 
from an attenuation of tubular protein reabsorption.