Shingo Takatori

Hypertension and dysregulated proinflammatory cytokine production in receptor activity-modifying protein 1-deficient mice

Calcitonin gene-related peptide (CGRP) is thought to be a prominent neuropeptide in cardiovascular regulation and neuroimmune modulation. There are two isoforms of CGRP (αCGRP and βCGRP), and the main CGRP receptors are probably composed of a calcitonin receptor-like receptor (CLR) and a receptor activity-modifying protein (RAMP)1. However, the physiological functions of CGRP that are mediated through the CLR/RAMP1 receptors remain to be clarified. For an improved understanding of the functions, we generated mice deficient in RAMP1, a specific subunit of CGRP receptors, by a conditional gene-targeting technique. The RAMP1-deficient mice (RAMP1−/−) exhibited high blood pressure, with no changes in heart rate. αCGRP was found to have a potent vascular relaxant activity compared with βCGRP in the artery of the WT (RAMP1+/+) mice. The activities of both CGRP isoforms were remarkably suppressed in the arteries of the RAMP1−/− mice. The LPS-induced inflammatory responses of the RAMP1−/− mice revealed a transient and significant increase in the serum CGRP levels and high serum levels of proinflammatory cytokines compared with the RAMP1+/+ mice. αCGRP and βCGRP equally suppressed the production of TNF-α and IL-12 in bone marrow-derived dendritic cells stimulated with lipopolysaccharide. Their inhibitory effects were not observed in the bone marrow-derived dendritic cells of the RAMP1−/− mice. These results indicate that CGRP signaling through CLR/RAMP1 receptors plays a crucial role in the regulation of both blood pressure by vascular relaxation and proinflammatory cytokine production from dendritic cells.

Chronic hyperinsulinemia enhances adrenergic vasoconstriction and decreases calcitonin gene-related peptide-containing nerve-mediated vasodilation in pithed rats.

The present study investigated the influence of chronic hyperinsulinemia on vascular responsiveness induced by adrenergic nerves and calcitonin gene–related peptide–containing (CGRPergic) nerves in pithed rats with insulin resistance. Male Wistar rats (6 weeks old) received 15% fructose solution in drinking fluid for 10 weeks (fructose-drinking rats: FDR), which resulted in significant increases in plasma levels of insulin, total cholesterol and triglyceride, and systolic blood pressure, as compared with control rats. Pithed FDR showed greater adrenergic nerve–mediated pressor response to spinal cord stimulation (SCS) at the lower thoracic vertebra (Th 9–12) and pressor response to exogenous noradrenaline than control rats. In pithed FDR with blood pressure artificially increased by continuous infusion of methoxamine and blockade of autonomic ganglia by hexamethonium, CGRPergic nerve–mediated depressor responses to SCS were significantly smaller than those in control rats, but depressor responses to other vasodilators such as acetylcholine, CGRP and sodium nitroprusside were similar to those in control rats. These results suggest that chronic hyperinsulinemia in FDR facilitates adrenergic nerve–mediated vasoconstriction, which is associated with attenuated CGRPergic nerve–mediated vasodilation.

Ameliorative effect of Eucommia ulmoides Oliv. leaves extract (ELE) on insulin resistance and abnormal perivascular innervation in fructose-drinking rats

AIM OF THE STUDY Eucommia ulmoides Oliv. leaf is a traditional Chinese medicine that exhibits an anti-diabetic action. This study was designed to investigate whether long-term administration of Eucommia ulmoides Oliv. leaves extract (ELE) ameliorates pre-diabetic state of insulin resistance and abnormal perivascular innervation in the hyperinsulinemic state. MATERIALS AND METHODS ELE at doses of 500 and 1000mg/kg was administered orally once daily for 4 weeks in fructose-drinking rats (FDRs). Plasma levels of insulin, blood glucose levels, and perivascular innervation were assessed using biochemical and immunohistochemical methods. RESULTS FDR showed significant increase in plasma levels of insulin, an index for insulin resistance (Homeostasis Model Assessment ratio-HOMA-IR) and systolic blood pressure (SBP), but not blood glucose levels, as compared with control rats. Immunohistochemical study showed significantly greater density of tyrosine hydroxylase (TH)-like immunoreactivity (LI)-containing nerves and significantly lower density of calcitonin gene-related peptide (CGRP)-LI-containing nerves in mesenteric arteries of FDR than those in control. A 4-week treatment with ELE (500 and 1000mg/kg, p.o.) significantly decreased plasma levels of insulin and HOMA-IR without affecting blood glucose levels and significantly lowered SBP in FDR. ELE treatment in FDR resulted in significant increase in CGRP-LI never fiber density and significant decrease in TH-LI never fiber density in mesenteric arteries of FDR. CONCLUSIONS These results suggest that long-term ELE treatment effectively prevents insulin resistance development and ameliorates abnormal perivascular innervation in FDR.

Candesartan Cilexetil Improves Angiotensin II Type 2 Receptor–Mediated Neurite Outgrowth via the PI3K-Akt Pathway in Fructose-Induced Insulin-Resistant Rats

We have shown previously that stimulation of the angiotensin II type 2 receptor (AT2R) results in nerve facilitation. In this study, we determined the capacity of candesartan to correct expression patterns characteristic of neuropathy and AT2R-mediated neurite outgrowth in the fructose-induced insulin-resistant rat, which is one of the human hyperinsulinemia models. Wistar rats received a 15% (w/v) fructose solution in their drinking water for 4 weeks (fructose-drinking rats [FDRs]), with or without candesartan (5 mg/kg/day). We evaluated physiological and behavioral parameters and performed immunohistochemical studies. We found that the FDR developed insulin resistance and downregulated both AT2R neuronal function and phosphorylated Akt expression in dorsal root ganglia (DRG) neurons. Candesartan improved neurite outgrowth in the FDR, which was associated with the restoration of AT2R and phosphorylated Akt expression. Furthermore, downregulation of phosphoinositide 3-kinase (PI3K) inhibited AT2R-mediated neurite outgrowth in control DRG cells. PI3K activation increased AT2R-mediated neurite outgrowth and phosphorylated Akt expression in FDR DRG cells. These results suggest that the decrease of AT2R-mediated neurite outgrowth in FDRs is likely to be the result of decreased PI3K-dependent Akt activation. Candesartan improved AT2R neuronal function and Akt phosphorylation, which were associated with sensory nerve defects and insulin sensitivity in the FDR.

Hyperinsulinemia induces hypertension associated with neurogenic vascular dysfunction resulting from abnormal perivascular innervations in rat mesenteric resistance arteries

We previously reported that chronic hyperinsulinemia and insulin resistance induced by fructose-drinking loading elicited hypertension associated with abnormal neuronal regulation of vascular tone in an in vivo study using pithed rats. Therefore, to further clarify the detailed mechanisms of perivascular nervous system malfunction induced by chronic hyperinsulinemia, we investigated the neurogenic vascular responses and distribution of perivascular nerves using mesenteric vascular beds isolated from fructose-loaded rats with hyperinsulinemia. Male Wistar rats (6 weeks old) received 15% fructose solution as drinking fluid for 10 weeks (fructose-drinking rats, FDR), which resulted in significant increases in plasma levels of insulin, the glucose-insulin index, blood norepinephrine (NE) levels and systolic blood pressure, but not blood glucose levels, when compared with normal water-drinking rats (control rats). In perfused mesenteric vascular beds of FDR, enhanced adrenergic nerve-mediated vasoconstriction with no effect on NE-induced vasoconstriction and decreased calcitonin gene-related peptide (CGRP)-containing nerve-mediated vasodilation with no effect on CGRP-induced vasodilation were observed. Immunohistochemistry studies showed increased density of neuropeptide Y immunopositive adrenergic fibers and reduced density of CGRP immunopositive fibers in mesenteric arteries of FDR. Furthermore, FDR showed decreased CGRP content in dorsal root ganglia. These findings suggest that dysfunction of the neuronal vascular control system resulting from abnormal innervation of mesenteric perivascular nerves induced by the hyperinsulinemic state is responsible for the development of hypertension in FDR.

Pioglitazone opposes neurogenic vascular dysfunction associated with chronic hyperinsulinaemia

Background and purpose: We previously demonstrated that chronic hyperinsulinaemia induced by drinking high levels of fructose augments adrenergic nerve‐mediated vasoconstriction and suppresses vasodilatation mediated by calcitonin gene‐related peptide (CGRP)‐containing (CGRPergic) vasodilator nerves. In this study, the effects of pioglitazone on vascular responses induced by stimulation of adrenergic nerves, CGRPergic nerves and vasoactive agents were investigated in pithed rats given 15% fructose solution to drink (FDR).

Angiotensin II type 2 receptors facilitate reinnervation of phenol-lesioned vascular calcitonin gene-related peptide-containing nerves in rat mesenteric arteries.

The present study was designed to investigate involvement of angiotensin II (Ang II) type 2 receptors (AT2 receptors) in restoration of perivascular nerve innervation injured by topical phenol treatment. Male Wistar rats underwent in vivo topical application of 10% phenol around the superior mesenteric artery. After phenol treatment, animals were subjected to immunohistochemistry of the third branch of small arteries, Western blot analysis of AT2 receptor protein expression in dorsal root ganglia (DRG) and studies of mesenteric neurogenic vasoresponsiveness. Ang II (750 ng/kg/day), nerve growth factor (NGF; 20 microg/kg/day) and PD123,319 (AT2 receptor antagonist; 10 mg/kg/day) were intraperitoneally administered for 7 days using osmotic mini-pumps immediately after topical phenol treatment. Losartan (AT1 receptor antagonist) was administered in drinking water (0.025%). Phenol treatment markedly reduced densities of both calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) and neuropeptide Y (NPY)-LI-containing fibers. NGF restored densities of both nerve fibers to the sham control level. Coadministration of Ang II and losartan significantly increased the density of CGRP-LI-fibers but not NPY-LI-fibers compared with saline control. The increase of the density of CGRP-LI-fibers by coadministration of Ang II and losartan was suppressed by adding PD123,319. Coadministration of Ang II and losartan ameliorated reduction of CGRP nerve-mediated vasodilation of perfused mesenteric arteries caused by phenol treatment. The AT2 receptor protein expression detected in DRG was markedly increased by NGF. These results suggest that selective stimulation of AT2 receptors by Ang II facilitates reinnervation of mesenteric perivascular CGRP-containing nerves injured by topical phenol application in the rat.

Acute hyperglycemia and hyperinsulinemia enhance adrenergic vasoconstriction and decrease calcitonin gene-related peptide-containing nerve-mediated vasodilation in pithed rats.

Recent clinical studies have demonstrated that transient postprandial hyperglycemia and hyperinsulinemia may contribute to the development of hypertension. Therefore, we investigated the influence of acute hyperglycemia and/or hyperinsulinemia induced by glucose or insulin infusion on neuronal and humoral control of vascular tone in rats. Euglycemic male Wistar rats were pithed under anesthesia and arterial blood pressure was measured. Changes in vascular responses to spinal cord stimulation (SCS) and intravenous bolus injections of noradrenaline, angiotensin II, calcitonin gene−related peptide (CGRP), acetylcholine and sodium nitroprusside (SNP) were studied by infusing various concentrations of glucose or insulin. Continuous glucose infusion, which increased both blood glucose and serum insulin levels, significantly augmented adrenergic nerve−mediated pressor responses to SCS without affecting pressor responses to injection of noradrenaline or angiotensin II. In pithed rats with artificially increased blood pressure and blockade of autonomic outflow, glucose infusion attenuated CGRPergic nerve−depressor responses to SCS without affecting depressor responses to injection of CGRP, acetylcholine or SNP. In pithed rats treated with octreotide, which increased blood glucose without increasing serum insulin levels, glucose infusion caused only significant augmentation of adrenergic nerve−mediated pressor responses. Combined infusion of insulin and glucose, which resulted in increased serum insulin levels with euglycemia, significantly augmented adrenergic nerve−mediated pressor responses and attenuated CGRPergic nerve−mediated depressor responses. The present results suggest that acute hyperglycemia and hyperinsulinemia increase adrenergic nerve−mediated vasoconstriction, which in turn blunts CGRPergic nerve function, and that the increase in plasma insulin concentration associated with hyperglycemia may be responsible for the alteration of neuronal vascular regulation.

Paracrine control of mesenteric perivascular axo-axonal interaction

Immunohistochemical study of rat mesenteric arteries showed dense innervation of adrenergic nerves, calcitonin gene‐related peptide (CGRP)‐containing nerves (CGRPergic nerves), nitric oxide‐containing nerves (nitrergic nerves). Double‐immunostaining revealed that most CGRPergic or nitrergic nerves were in close contact with adrenergic nerves. CGRPergic and transient receptor potential vanilloid‐1 (TRPV1)‐immunopositive nerves appeared in the same neurone. In rat perfused mesenteric vascular beds without endothelium and with active tone, perfusion of nicotine, or bolus injection of capsaicin and acetylcholine and periarterial nerve stimulation (PNS) lowered pH levels of out flowed perfusate concomitant with vasodilation. Cold‐storage denervation of preparations abolished pH lowering induced by nicotine and PNS. Guanethidine inhibited PNS‐ and nicotine‐, but not acetylcholine‐ and capsaicin‐, induced pH lowering. Pharmacological analysis showed that protons were released not only from adrenergic nerves but also from CGRPergic nerves. A study using a fluorescent pH indicator demonstrated that nicotine, acetylcholine and capsaicin applied outside small mesenteric artery lowered perivascular pH levels, which were not observed in Ca2+ free medium. Exogenously injected hydrochloric acid in denuded preparations induced pH lowering and vasodilation, which was inhibited by denervation, TRPV1 antagonists and capsaicin without affecting pH lowering. These results suggest that excitement of adrenergic nerves releases protons to activate TRPV1 in CGRPergic nerves and thereby induce vasodilation. It is also suggested that CGRPergic nerves release protons with exocytosis to facilitate neurotransmission via a positive feedback mechanism.

[Effect of propolis on insulin resistance in fructose-drinking rats].

Propolis, a honeybee product, contains a variety of biologically active substances. The present study was designed to investigate the effects of propolis on insulin resistance induced by fructose-drinking rats (FDR; type 2 diabetic animal model). Male Wistar rats (6 weeks old) received 15% fructose solution in drinking water for 8 weeks. FDR showed significant increases in plasma levels of insulin, Homeostasis Model Assessment ratio (HOMA-R, an index of insulin resistance), body weight, and systolic blood pressure but not blood glucose levels, when compared with control rats. Brazilian propolis extract (100 and 300mg/kg, p. o.) treatment for 8 weeks significantly decreased the plasma level of insulin, HOMA-R, and body weight, increased plasma triglyceride levels without affecting blood glucose and total cholesterol levels, and tended to decrease systolic blood pressure. In isolated and perfused mesenteric vascular beds of FDR, propolis treatment resulted in a significant reduction of sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS; 8Hz) and tended to increase the calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator response to PNS, compared with those in untreated FDR. However, propolis treatment did not significantly affect norepinephrine-induced vasoconstriction and CGRP-induced vasodilation. These results suggest that propolis could be an effective functional food to prevent the development of insulin resistance.Propolis, a honeybee product, contains a variety of biologically active substances. The present study was designed to investigate the effects of propolis on insulin resistance induced by fructose-drinking rats (FDR; type 2 diabetic animal model). Male Wistar rats (6 weeks old) received 15% fructose solution in drinking water for 8 weeks. FDR showed significant increases in plasma levels of insulin, Homeostasis Model Assessment ratio (HOMA-R, an index of insulin resistance), body weight, and systolic blood pressure but not blood glucose levels, when compared with control rats. Brazilian propolis extract (100 and 300 mg/kg, p.o.) treatment for 8 weeks significantly decreased the plasma level of insulin, HOMA-R, and body weight, increased plasma triglyceride levels without affecting blood glucose and total cholesterol levels, and tended to decrease systolic blood pressure. In isolated and perfused mesenteric vascular beds of FDR, propolis treatment resulted in a significant reduction of sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS; 8 Hz) and tended to increase the calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator response to PNS, compared with those in untreated FDR. However, propolis treatment did not significantly affect norepinephrine-induced vasoconstriction and CGRP-induced vasodilation. These results suggest that propolis could be an effective functional food to prevent the development of insulin resistance.