Insulin stimulates endothelin binding and action on cultured vascular smooth muscle cells

Abstract

Hyperinsulinemia has been implicated as a separate risk factor for the development of accelerated cardiovascular disease, but the mechanism is unknown. Recently, we and several other groups have shown that insulin stimulates the production and secretion of the vasoconstrictor peptide endothelin-1 (ET-1) from vascular endothelial cells, and hyperinsulinemia results in increased plasma ET levels in vivo. However, the interactive effects of diabetes, insulin, and glucose on ET target tissues, like those on vascular smooth muscle cells (VSMC), are not well defined. In these studies, we examined the effects of the diabetic factors on ET receptors and [3H]thymidine incorporation into cultured cells prepared from control, streptozocin-diabetic, insulin-treated diabetic, and hyperinsulinemic rats. Scatchard analysis of saturation binding studies revealed a 2-fold increase in ET receptor number in normal VSMC treated in vitro with insulin, whereas glucose had no significant effect. Neither treatment affected receptor affinity. Similarly, aortic smooth muscle cells, brain capillary pericytes, and kidney afferent arteriolar smooth muscle cells from rats made hyperinsulinemic in vivo each showed approximately a 2-fold increase in receptor number. This increase in receptor density probably resulted from the stimulation of receptor protein production, because insulin caused a maximal 2.3 +/- 0.3 (+/- SEM) fold increase in the ETA receptor mRNA expressed in cultured VSMC by 4 h. Both insulin and ET significantly increased thymidine incorporation in aortic VSMC, but ET-1 was much more potent in this regard. However, the combined effects of insulin plus ET-1 resulted in a 10-fold increase in this index of cell proliferation, significantly different from the effects of either peptide alone. We postulate that hyperinsulinemia in vivo may potentiate ET release and receptor-mediated action, thereby contributing to vascular disease in the setting of diabetes.

Changes in the density and localisation of endothelin receptors in the early stages of rat diabetic retinopathy and the effect of insulin treatment

“…Insulin treatment during 90 days, however, increased the ETA receptors in the neural retina as well as within the innermost layers of the retina in comparison with age-matched control retina. These alterations could be directly due to the injected insulin, since this hormone increases the ETA receptor mRNA expression in vivo and in vitro [22] or indirectly to the metabolic improvement. The up-regulated ETA receptor could trigger an increase in the mitotic activity of retinal cells since this receptor is implicated in the stimulation of the mitogenesis in a number of cells, including the glial cells [3].…”

“…Insulin activated ET-1 synthesis and secretion in cultured endothelial cells [21], whereas in vascular smooth muscle cells and pericytes insulin increased the ETA receptor subtype density and the expression of ETA receptor mRNA [22,23]. In vivo studies have shown that insulin treatment normalised the retinal blood flow [24], mainly influencing ET-1 action and NO production [25,26].…”

Endothelin Antagonism Uncovers Insulin-Mediated Vasorelaxation In Vitro and In Vivo

“…Insulin stimulates the synthesis, secretion, and gene expression of the potent vasoconstrictor ET-1. [12][13][14] In turn, ET-1 mediates vasoconstriction via ET A and ET B receptors on vascular smooth muscle cells. 15 In certain vascular beds, the endothelial ET B receptor is linked to NO production and vasorelaxation.…”

Vasoactive Peptides Modulate Vascular Endothelial Cell Growth Factor Production and Endothelial Cell Proliferation and Invasion

“…1 The abbreviations used are: EC, endothelial cell(s); bFGF, basic fibroblast growth factor; VSMC, vascular smooth muscle cell(s); VEGF, vascular endothelial cell growth factor; ET, endothelin(s); ANP, atrial natriuretic peptide; CNP, C-type natriuretic peptide; NP, natriuretic peptide(s); hUVSMC, human umbilical vein smooth muscle cells; kb, kilobase(s); Luc, luciferase; MAP, mitogen-activated protein; PKC, protein kinase C. lumens were stripped of the endothelial layer by 30 min of incubation in collagenase-containing medium. This was followed by rinsing and additional exposure to collagenase for 2 h to obtain smooth muscle cells (21). The cells had the typical appearance of smooth muscle cells and did not stain positive for Von Willebrand's factor, but were found to stain for ␣-actin.…”