Hyperreninemia due to increased renal renin synthesis in BioBreeding Worcester rats

Angiotensin II and its receptors in the diabetic kidney

Studies using either angiotensin-converting enzyme inhibitors or type 1 (AT(1)) angiotensin II (ANG II)-receptor blockers indicate that ANG II is a mediator of progressive injury in diabetic nephropathy. However, suppression of the systemic renin-angiotensin system (RAS) generally has been shown in diabetes mellitus. Evidence suggests that intrarenal RASs within glomeruli and proximal tubules may be activated with hyperglycemia, leading to stimulation of local ANG II production, which may exert feedback inhibition of systemic renin release. Once formed, intrarenal ANG II exerts most of its well-described effects through binding to AT(1) receptors that are abundantly present in cells of the glomeruli, tubules, vasculature, and interstitium. Thus, AT(1)-receptor activation increases vascular resistance, reduces renal blood flow, and stimulates production of extracellular matrix in the mesangium and tubulointerstitium. Recent studies suggest that the adult kidney also expresses type 2 (AT(2)) ANG II receptors in glomeruli, tubular segments, and vasculature. AT(2)-receptor activation is associated with increased intrarenal nitric oxide production, stimulation of natriuresis, and inhibition of cell growth and matrix synthesis, effects that oppose those of kidney AT(1) receptors. A number of studies have shown a reduction in kidney AT(1)-receptor expression in diabetic nephropathy, suggesting that the balance between AT(1)- and AT(2)-receptor-mediated cell-signaling events may be a determinant of progression rate in diabetic nephropathy and that unopposed stimulation of AT(2) receptors by ANG II with use of AT(1)-receptor blockers may contribute to the beneficial properties of these agents. Determination of the expression pattern of AT(2) receptors in diabetes and further definition of the role of AT(2) receptors in opposing the detrimental effects of AT(1) receptors may lead to more selective targeting of the RAS in diabetic nephropathy.

A case of renin-producing juxtaglomerular tumor: effect of ACE inhibitor or angiotensin II receptor antagonist

We report a case of a renin-producing juxtaglomerular cell tumor and the effects of angiotensin-converting enzyme (ACE) inhibitor captopril or angiotensin II receptor antagonist TCV-116. A 19-year-old female visited our clinic because of hypertension (162/122 mmHg). Plasma renin activity (PRA) was 25 ng/ml/h and plasma aldosterone concentration (PAC) was 880 pg/ml. Abdominal sonography revealed a low echoic tumor in the center of the right kidney. The mass was shown to have isodensity on a computed tomography scan, iso- or slightly lower intensity on T1-weighted magnetic resonance imaging (MRI), and low intensity on T2-weighted MRI. Renal angiography disclosed a hypovascular tumor. Plasma renin activity was not decreased in response to oral administration of captopril (50 mg) or TCV-116 (4 mg), which is associated with a marked decrease in PAC and blood pressure. The average of the mean blood pressure determined by an ambulatory monitoring system every hour for 24 h was lowered from 118 +/- 10.6 (SD) to 85 +/- 11.4 mmHg by TCV-116. Plasma renin activity did not show any difference between the right and left renal vein. Removal of the tumor successfully decreased PRA to 0.3 ng/ml/h and PAC to 33 pg/ml, resulting in a decrease in 24-h average of the mean blood pressure to 78 +/- 16.9 mmHg. The tumor was well capsulated and stained with an antibody against mouse renin. In the tumor, but not normal tissues, renin mRNA was detected at 1.6 kb using rat renin cDNA. The content of active renin in the tumor amounted to 182 micrograms/g tissue, which is 109 times higher than that in normal tissue. The plasma- or tumor-inactive renin concentration was 3.6- or 1.8-fold the active renin concentration, respectively. These results suggest that the juxtaglomerular tumor had an MRI image of iso- to low intensity on T1 and low intensity on T2, and that renin secretion from the tumor may be due mainly to the constitutive pathway and angiotensin II receptor antagonist, as well as to ACE inhibitors, and may be very effective for lowering the blood pressure.

Reciprocal changes in left ventricular collagen alpha 1 chain gene expression between types I and IV in spontaneously diabetic rats

The characteristic features of diabetic cardiomyopathy have been reported to be increased collagen formation associated with impairment of ventricular performance, based on experimental models of diabetes. The present study was therefore designed to clarify collagen gene expression in hearts obtained from female spontaneously diabetic BioBreeding Worcester Tokyo (BB/W@Tky) rats. Cardiac hypertrophy was observed as early as 14 weeks in diabetic BB/W@Tky rats, i.e. 4 weeks after the onset of diabetes. Left ventricular gene expression of collagen alpha 1 (I) was decreased to 10.6% of the control level. In 24-week-old diabetic rats, which had more marked cardiac hypertrophy, the level of alpha 1 Type I collagen mRNA was further decreased to 5.7% of the control level, whereas collagen alpha 1 (IV) mRNA demonstrated a 3-fold increase. As a result, a ratio of collagen alpha 1 (IV) to actin mRNA was positively correlated with plasma glucose concentration. These results suggest that hyperglycemia may alter the gene expression of extracellular matrix proteins, resulting in the morphological and functional changes seen in diabetic cardiomyopathy.

Renin and angiotensinogen expression during the evolution of diabetes

The expression of renin and angiotensinogen genes and their proteins were studied during the progression of diabetes using adult BioBreeding spontaneously diabetic rats at 1 day and 2-12 months of diabetes. The number of renin-stained cells per juxtaglomerular apparatus was determined by immunocytochemistry. Initially, at 2 months of diabetes the number of renin-stained cells per juxtaglomerular apparatus increased significantly (p less than 0.0001, 2 months versus resistant groups) and was followed by a decrease in the number and intensity of renin-stained cells after 12 months of diabetes (p = 0.007, 2 months versus 12 months). A significant negative correlation was observed between the number of renin-containing cells and the duration of diabetes (r = 0.99, p = 0.014). Immunoreactive angiotensinogen was restricted to the proximal tubule and appeared increased after 4 and 8 months of diabetes as compared with the 2- and 12-month diabetic groups. Renin messenger RNA (mRNA) levels increased with the onset of diabetes and decreased markedly during chronic diabetes. At 1 day of diabetes, renin mRNA levels were 700% higher than at 12 months of diabetes. Angiotensinogen mRNA levels were unchanged. We conclude that diabetes results in an initial increase in renin gene expression, and as the duration of diabetes lengthens, there is a progressive decrease in renin gene expression and in the number of cells containing renin. These findings suggest that as the duration of diabetes and the age of the animal lengthens, there is a decrease in the number of cells expressing the renin gene.