Presence of liver CGRP/amylin receptors in only nonparenchymal cells and absence of direct regulation of rat liver glucose metabolism by CGRP/amylin.

Human calcitonin gene-related peptide (hCGRP-1) and human amylin (hA) have been reported to increase hepatic glucose output in vivo and to bind with high affinity to rat liver plasma membranes, resulting in increased cAMP production. These observations have led to the hypothesis that CGRP or amylin may be physiological regulators of liver glucose metabolism. Liver plasma membranes are derived from several cell types, including parenchymal (hepatocyte), Kupffer, endothelial, lipid storage, and smooth muscle cells. Because the parenchymal cell is responsible for the contribution of the liver to whole-body glucose homeostasis, it is important to verify the location and activity of the CGRP/amylin receptor to this cell. These studies separate liver cells prepared by collagenase digestion into parenchymal and nonparenchymal fractions by metrizamide gradient and differential centrifugation. 125I-labeled [Tyr-0]hCGRP-1 bound with high affinity to nonparenchymal cell fraction and was displaced by both hCGRP-1 and hA. hCGRP-1 bound with greater affinity than hA (Kd = 2.1 +/- 1.6 x 10(-11) vs. 2.6 +/- 1.2 x 10(-8) M) in a manner similar to the binding reported for liver plasma membrane fraction. Linear regression of receptor concentration against nonparenchymal cell count per milliliter was significant (r = 0.999, P = 0.026), leading to an estimate of 3000 receptors/cell. The parenchymal cell fraction bound very little 125I-[Tyr-0]hCGRP-1, and regression of receptor concentration against parenchymal cell count per milliliter was not significant (r = -0.708, P = 0.29), suggesting that binding was not due to parenchymal cells but instead to contamination by nonparenchymal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

LY290181, an inhibitor of diabetes-induced vascular dysfunction, blocks protein kinase C-stimulated transcriptional activation through inhibition of transcription factor binding to a phorbol response element.

Previous studies have shown that high glucose levels and diabetes induce an elevation in protein kinase C (PKC) activity in vascular cells and tissues susceptible to diabetic complications. In addition, PKC activation has been shown to modulate vascular cell growth, permeability, and gene expression, processes thought to be involved in the development of vascular complications. Using two in vivo model systems, we have identified a novel inhibitor of diabetic vascular dysfunction, LY290181. LY290181 prevented glucose-induced increases in blood flow and permeability in rat granulation tissue and corresponding vascular changes in the retina, sciatic nerve, and aorta of diabetic rats. Tested for its ability to inhibit PKC-regulated processes, LY290181 inhibited phorbol ester-stimulated plasminogen activator activity in a dose-dependent manner in bovine retinal endothelial cells and in human dermal fibroblasts. In addition, LY290181 inhibited phorbol ester-stimulated activation of the porcine urokinase plasminogen activator (uPA) promoter (-4600/+398) linked to the chloramphenicol acetyltransferase (CAT) reporter gene (p4660CAT). More detailed analysis of the uPA promoter revealed that LY290181 inhibited phorbol ester-stimulated activation of the uPA phorbol response element (-2458/-2349) located upstream of the thymidine kinase promoter (puPATKCAT). LY290181 appears to inhibit uPA promoter activation by blocking phorbol ester-stimulated binding of nuclear proteins to the uPA PEA3/12-0-tetradecanoylphorbol 13-acetate responsive element (TRE). These results suggest that LY290181 may inhibit diabetes-induced vascular dysfunction by inhibiting transcription factor binding to specific PKC-regulated genes involved in vascular function.