Diabetic nephropathy, a microvascular complication, is still a hallmark of diabetes mellitus. Although the etiology of diabetic nephropathy remains to be elucidated, previous study suggested that renal vascular structural changes could not be
sole
pathogenesis for decreased renal blood flow in streptozotocin-induced diabetic rats(STZR). Basal values of total renal blood flow (using an electromanetic flowmeter), mean arterial pressure and renal vascular resistance of
secobarbitalanesthetized
STZR(n=10) and age-matched control rats(CR; n=9) were 6.1±0.4 vs. 7.5±0.5ml/min/g kidney weight(p<0.05), 118±3 vs. 114±3mmHg, and 20.1±1.4 vs. 15.6±0.9 mmHg/ml/min/g kidney weight(p<0.01), respectively. this study evaluated the
participation
of
renin-angiotensin system on increased renal vasoconstriction in STZR by determining the reactivity to exogenously administered angiotensins and by determining the effect of captopril on renal vascular tone. Elicited renal vasocostriction in
response to
intravenously administered angiotensin I (50~200 ng/kg) or angiotensin II (4~128ng/kg) under the presence or absence of endogenous converting enzyme, respectively, were quite similar between two groups. Captopril at 0.5 mg/kg followed by
10㎍/kg/min
produced similar degree of renal vasodilation between STZR and CR, thus, did not normalize higher baseline resistance in STZR kidneys. In addition, chronic administration of captopril (100 mg/1 of drinking water) did ameliorate microalbuminuria
but
not
renal hypoperfusion associated with diabetes. Electron microscopic obseravation revealed that only proximal tubules, not glomeruli, of STZR were affected the microvilli which involves in protein reabsorption were reduced in STZR and chronic
administration of captopril prevented it.
Taken together, the data suggest that I) other factors than renin-angiotensin system may play a role in renal vasoconstriction of short-term diabetic STZR, ii) amelioration of microalbuminuria by captopril do not result from the effect on renal
hemodynamics but from an improvement of renal function.
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