Renal angiotensin II receptors and protein kinase C in diabetic rats: effects of insulin and ACE inhibition

Abstract

It has been shown that glomerular ANG II receptors are downregulated and protein kinase C (PKC) activity is enhanced in diabetes mellitus. Therefore, we investigated glomerular and preglomerular vascular ANG II receptors and PKC isoform regulation in streptozotocin (STZ)-diabetic rats treated with insulin and/or captopril. Diabetic rats were prepared by injecting STZ (60 mg/kg). Those that developed diabetes after 48 h were treated with low or high doses of insulin, or with a low dose of insulin as well as captopril, and killed 14 days later. Their glomeruli and preglomerular vessels were purified, competitive binding studies were performed by using the ANG II antagonists losartan and PD-123319, and PKC analysis was carried out by Western blotting. Competitive binding studies showed that the AT1 receptor was the only ANG II receptor detected on both glomeruli and preglomerular vessels of all groups. Preglomerular vascular AT1 receptor density (Bmax) was significantly upregulated in low insulin-treated STZ rats, whereas glomerular AT1 Bmax was downregulated. Furthermore, both the captopril- and high insulin-treated groups had less glomerulosclerosis and vascular damage than the low insulin-treated group. PKCα, PKCδ, PKCε, and PKCμ isoforms found in preglomerular vessels were upregulated by captopril and high insulin doses, respectively, whereas no such regulation occurred in glomeruli. We conclude that in STZ-diabetic rats ANG II receptors and PKC isoforms on preglomerular vessels and glomeruli are differentially regulated by treatment with insulin and/or captopril.