Effect of Systemic Insulin and Angiotensin II Receptor Subtype-1 Antagonist on Endothelin-1 Receptor Subtype(s) Regulation and Binding in Diabetic Rat Heart

Abstract

This study reports on the regulation and remodeling role of endothelin-1 (ET-1) and its receptor subtypes, ET(A)-Rs/ET(B)-Rs, at the coronary endothelium (CE) and cardiomyocyte (CM) sites. It is carried out in normal and normotensive rats with streptozotocin-induced diabetes mellitus receiving different treatment modalities. Normal rats were divided into two groups, namely a placebo (N) and a losartan-treated (NL), and diabetic rats into four groups receiving placebo (D), insulin-treated (DI), losartan-treated (DL), and insulin/losartan-treated (DIL) respectively. Binding kinetics of ET-1 to ET(A)-Rs/ET(B)-Rs on CE and CMs were assessed in the above groups to try to explain the effect of therapeutic doses of an angiotensin II receptor subtype-1 blocker on the dynamics of this ligand and its receptor in insulin supplemented diabetic animals. Each group was divided into two subgroups: CHAPS-untreated and CHAPS-treated rat hearts perfused with [125I]ET-1 to respectively estimate ET-1 binding affinity (tau = 1/k-n) to its receptor subtype(s) on CE and CMs using mathematical modeling describing a 1:1 reversible binding stoichiometry. Heart perfusion results revealed that insulin treatment significantly decreased tau on CE but not on CMs in diabetic rats. In diabetics treated with losartan, an increase in tau value on CE but not on CMs was noted. Cotreatment of diabetic rats with insulin and losartan normalized tau on CE but decreased it on CMs. Western blot, using snap-frozen heart tissues, revealed increase in ET(A)-R density in all diabetic groups. However, significant decrease in ET(B)-R density was observed in all groups compared to the normal, and was reconfirmed by immunohistochemical analysis. In conclusion, coadministration of insulin and losartan in nonhypertensive animals suffering from diabetes type 1 may offer new cardiac protection benefits by improving coronary blood flow and cardiomyocyte contractility through modulating ET-1 receptor subtypes density and affinity at CE and CM sites.

Role of glucagon-like peptide-1 and its agonists on early prevention of cardiac remodeling in type 1 diabetic rat hearts

“…Protein samples (100 µg) extracts from (n = 8) homogenized cardiac muscle were loaded and separated on 10% polyacrylamide gel electrophoresis for 1 h (Mini-gel electrophoresis unit, Protean III, Bio-Rad Laboratory, USA) (Karam et al 2005). Protein bands were then transferred for 2 h on nitrocellulose membranes (Transblot unit, PowerPac HC, Bio-Rad Laboratory, USA).…”

Effect of Insulin and Losartan on Modulation of Insulin-Like Growth Factor 1 Receptor at Heart Level in Diabetic Rats

“…Recently, we found that in STZ-induced diabetic rats, the co-treatment with insulin and losartan was almost able to totally prevent myocardial remodeling [8]. We also reported that this treatment modality could improve cardiac contraction as well as coronary blood flow in STZ-induced diabetic rats through the modification of the affinity of endothelin-1 (ET-1) to its receptor subtypes ET A -R and ET B -R [19].…”

“…The procedures as reported by Al-Jaroudi et al (2005) and Karam et al (2005) were followed. Samples of proteins from homogenate extracts of whole heart (n=8) were quantified using the Bio-Rad DC Protein Assay (Bio-Rad Laboratory, CA, USA).…”

Effect of Insulin and Losartan on Modulation of Insulin-Like Growth Factor 1 Receptor at Heart Level in Diabetic Rats

“…Recently, we found that in STZ-induced diabetic rats, the co-treatment with insulin and losartan was almost able to totally prevent myocardial remodeling [8]. We also reported that this treatment modality could improve cardiac contraction as well as coronary blood flow in STZ-induced diabetic rats through the modification of the affinity of endothelin-1 (ET-1) to its receptor subtypes ET A -R and ET B -R [19]. to pH 4.5 with 0.1 mol/L citrate buffer.…”