Effect Of D₃ Dopamine Receptor On Insulin Receptor In Vascular Smooth Muscle Cells From WKY And SHR And Its Role In The Pathogenesis Of Essential Hypertension

Background:Recently, more and more evidences support a linkage between insulin resistance (IR) and essential hypertension (EH), more than 50% of hypertensive patients are with IR. Although the mechanisms of EH are complicated, vascular smooth muscle cells (VSMCs) proliferation is one of the most important target, which plays an important role in the regulation of blood pressure. EH is evident with VSMCs proliferation, which increases contraction force, decreases complaisance and increases conduit vessel stiffness and peripheral vascular resistance. Insulin is a potent factor stimulating VSMCs proliferation and apoptosis by direct regulation of insulin receptor substrate phosphorylation, or indirect regulation of effects of other humoral or hormonal factors, including angiotensin (ANG), insulin-like factor 1 (IGF-1). In the hypertensive patients, the positive relationship between insulin level and the VSMCs proliferation has also been found. Consistent with the above-mentioned results, we also found insulin stimulated VSMCs proliferation in a concentration-dependent manner.Dopamine receptors, which belong to the G protein-couple receptor, play an important role in the regulation of blood pressure. It is classified into D₁ (D₁,D₅)- and D₂-like (D₂,D₃,D)4) subtypes based on their structure and pharmacology. Stimulation of dopamine receptor induces natriuresis and diuresis, which is validated by dopamine receptor deficient mice. Disruption of D₁,D₃,D5 receptor gene in mice leads to hypertension with impaired natriuresis. As a major type of D₂-like receptor, D₃ receptor abundantly expresses in kidney and vessels, stimulation of D₃ receptor induces natriuresis, diuresis or vasorelaxation. Our previous studies showed D₁-like or D₃ receptor, by itself, had no effect on VSMCs proliferation, blocked the stimulatory effect of norepinephrine on VSMCs proliferation. Insulin is potent stimulator of VSMCs proliferation, which, as D₃ receptor, exists on VSMCs. Is there any effect of D₃ receptor on insulin receptor expression and function in VSMCs? Based on our previous studies, we hypothesis that D₃ receptor might have an effect on the insulin receptor expression and the insulin-mediated VSMCs proliferation. Objective:To investigate the role of D₃ receptor on insulin receptor expression and function in VSMCs from spontaneously hypertensive rat (SHR) and Wistar-Kyoto (WKY) rats.Methods:1. A10 cell culture.2. The proliferation of VSMCs were checked by [3H]-TdR,MTT assay,and evaluation of cell number experiment.3. Effects of D₃ receptor on insulin receptor expression were determined by western blot and RT-PCR.4. To investigate whether there is different effect of D₃ receptor on insulin receptor expression and function, we used the primary VSMCs from aorta of WKY and SHR.Result:1. Insulin stimulated VSMCs proliferation in a concentration-dependent manner, D₃ receptor, by itself, had no effect on VSMCs proliferation, but blocked the stimulatory effect of insulin on VSMCs proliferation.2. Stimulation of D₃ receptor, via PKA, decreased the insulin receptor expression in VSMCs, which was blocked in the presence of D₃ receptor antagonist, indicating the specificity of D₃ receptor agonist, PD₁28907.3. The inhibitory effect of D₃ receptor on insulin receptor expression and function not only happened in WKY but also in SHR. However, even stimulation with D₃ receptor, the insulin receptor expressions and the levels of VSMCs proliferation were still higher in SHR than in WKY rats.Conclusion:Stimulation of D₃ receptor reduces insulin receptor expression and the insulin-mediated proliferation in VSMCs from both WKY and SHR, although the basal levels of insulin receptor expression and function is higher in SHR, indicating, unlike theD₃ receptor in kidney, D₃ receptor in artery is still a target to reduce the insulin effect on VSMC proliferation in SHR.