Early diabetes mellitus stimulates proximal tubule renin mRNA expression in the rat.
BACKGROUND
Enhanced intrarenal angiotensin II (Ang II) activity may contribute to diabetic nephropathy. The proximal tubule is a proposed site of significant intrarenal Ang II production. We determined the effect of early diabetes on mRNA expression of components of the proximal tubule renin-angiotensin system.


METHODS
Three groups of male Sprague-Dawley rats were studied after two weeks: (1) control (C), (2) streptozotocin-induced diabetes (STZ), and (3) STZ-induced diabetes, with normoglycemia maintained by insulin implants (STZ-I). Competitive reverse transcription-polymerase chain reaction was used to assay mRNA for renin, angiotensinogen, and angiotensin-converting enzyme in suspensions of proximal tubules; plasma and kidney levels of Ang II were measured by radioimmunoassay, and Western analysis of Ang II subtype 1 (AT1) receptors was performed.


RESULTS
STZ rats tended to have increased plasma and intrarenal levels of Ang II compared with C and STZ-I rats. In proximal tubules, mRNA for renin was significantly increased in STZ rats, with reversal to control values in STZ-I rats (C, 2432 +/- 437 vs. STZ, 5688 +/- 890 fg/0.25 microg RNA, P < 0.05 vs. C, N = 9, vs. STZ-I, 1676 +/- 376 fg/0.25 microg RNA, P = NS vs. C). In STZ rats, the AT1 receptor antagonist losartan caused a further fivefold increase in proximal tubule renin mRNA, associated with proximal tubular renin immunostaining. STZ had no significant effect on mRNA expression for angiotensinogen or angiotensin-converting enzyme in proximal tubules. By Western blot analysis, cortical and proximal tubule AT1 receptor protein expression was significantly decreased in STZ rats.


CONCLUSIONS
These data suggest activation of the proximal tubule renin-angiotensin system in early STZ diabetes, mediated at least partly by enhanced expression of renin mRNA. Increased local production of Ang II could contribute to tubulointerstitial injury in this model.
Zimpelmann
J
J
Departments of Medicine and Cellular and Molecular Medicine, Kidney Research Center, Ottawa Hospital ResearchInstitute, University of Ottawa, Ottawa, Ontario, Canada.
Kumar
D
D
Levine
D Z
DZ
Wehbi
G
G
Imig
J D
JD
Navar
L G
LG
Burns
K D
KD
D000804:Angiotensin II / Q000032:analysis / Q000097:blood; D057911:Angiotensin Receptor Antagonists; D000808:Angiotensinogen / Q000235:genetics; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D015870:Gene Expression / Q000502:physiology; D006984:Hypertrophy; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000737:chemistry / Q000473:pathology / Q000503:physiopathology*; D019808:Losartan / Q000494:pharmacology; D008297:Male; D009395:Nephritis, Interstitial / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000235:genetics; D012083:Renin / Q000032:analysis / Q000235:genetics*; D012084:Renin-Angiotensin System / Q000502:physiology
D057911:Angiotensin Receptor Antagonists; D000959:Antihypertensive Agents; D007004:Hypoglycemic Agents; D007328:Insulin; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D000808:Angiotensinogen; D000804:Angiotensin II; D012083:Renin; D019808:Losartan