Increase in neurogenic nitric oxide metabolism by endothelin-1 in mesenteric arteries from hypertensive rats

A Blunted Sympathetic Function and an Enhanced Nitrergic Activity Contribute to Reduce Mesenteric Resistance in Hyperthyroidism

We aimed to determine whether an experimental model of hyperthyroidism could alter the function of sympathetic and nitrergic components of mesenteric innervation. For this purpose, male Wistar rats were divided into (1) control rats (CT) and (2) rats infused with L-Thyroxine (HT). Body weight gain and adipose tissue accumulation were lower in HT rats, while systolic blood pressure and citrate synthase activity in the soleus muscle were increased by HT. In segments from the superior mesenteric artery, the application of an electrical field stimulation (EFS) induced a vasoconstrictor response, which was lower in arteries from HT animals. The alpha-adrenoceptor antagonist phentolamine diminished EFS-induced vasoconstriction to a lower extent in HT arteries, while the purinergic receptor antagonist suramin reduced contractile response to EFS only in segments from CT. In line with this, noradrenaline release, tyrosine hydroxylase expression and activation and dopamine β hydroxylase expression were diminished in HT. The unspecific nitric oxide synthase (NOS) inhibitor L-NAME increased EFS-induced vasoconstriction more markedly in segments from HT rats. NO release was enhanced in HT, probably due to an enhancement in neuronal NOS activity, in which a hyperactivation of both PKC and PI3K-AKT signaling pathways might play a relevant role. In conclusion, perivascular mesenteric innervation might contribute to reduce the vascular resistance observed in hyperthyroidism.

Nitrergic perivascular innervation in health and diseases: Focus on vascular tone regulation

For a long time, the vascular tone was considered to be regulated exclusively by tonic innervation of vasoconstrictor adrenergic nerves. However, accumulating experimental evidence has revealed the existence of nerves mediating vasodilatation, including perivascular nitrergic nerves (PNN), in a wide variety of mammalian species. Functioning of nitrergic vasodilator nerves is evidenced in several territories, including cerebral, mesenteric, pulmonary, renal, penile, uterine and cutaneous arteries. Nitric oxide (NO) is the main neurogenic vasodilator in cerebral arteries and acts as a counter-regulatory mechanism for adrenergic vasoconstriction in other vascular territories. In the penis, NO relaxes the vascular and cavernous smooth muscles leading to penile erection. Furthermore, when interacting with other perivascular nerves, NO can act as a neuromodulator. PNN dysfunction is involved in the genesis and maintenance of vascular disorders associated with arterial and portal hypertension, diabetes, ageing, obesity, cirrhosis and hormonal changes. For example defective nitrergic function contributes to enhanced sympathetic neurotransmission, vasoconstriction and blood pressure in some animal models of hypertension. In diabetic animals and humans, dysfunctional nitrergic neurotransmission in the corpus cavernosum is associated with erectile dysfunction. However, in some vascular beds of hypertensive and diabetic animals, an increased PNN function has been described as a compensatory mechanism to the increased vascular resistance. The present review summarizes current understanding on the role of PNN in control of vascular tone, its alterations under different conditions and the associated mechanisms. The knowledge of these changes can serve to better understand the mechanisms involved in these disorders and help in planning new treatments.

Thyroid hormones affect nitrergic innervation function in rat mesenteric artery: Role of the PI3K/AKT pathway

We aimed to determine the influence of nitrergic innervation function on the decreased mesenteric arterial tone induced by high levels of triiodothyronine (T3), as a model of acute thyroiditis, as well as the mechanism/s implicated. We analysed in mesenteric segments from male Wistar rats the effect of 10 nmol/L T3 (2 h) on the vasomotor response to electrical field stimulation (EFS) in the presence/absence of specific neuronal NOS (nNOS) inhibitor L-NPA, or superoxide anion scavenger tempol. Nitric oxide (NO) release was measured in the presence/absence of tempol or PI3K inhibitor LY294002. Superoxide anion and peroxynitrite releases, nNOS, PI3K, AKT and superoxide dismutase (SOD) 1 and 2 expressions, nNOS and AKT phosphorylation, and SOD activity were analysed. T3 decreased EFS-induced vasoconstriction. L-NPA increased EFS-induced vasoconstriction more markedly in T3-incubated segments. T3 increased NO release. Tempol decreased EFS-induced vasoconstriction and augmented NO release only in segments without T3. LY294002 decreased NO release in T3-incubated segments. T3 diminished superoxide anion and peroxynitrite formation, enhanced SOD-2 expression, nNOS and AKT phosphorylations and SOD activity, and did not modify nNOS, PI3K, AKT and SOD-1 expressions. In conclusion, these results show a compensatory mechanism aimed at reducing the enhanced blood pressure that appears during acute thyroiditis.

Rosuvastatin restored adrenergic and nitrergic function in mesenteric arteries from obese rats

BACKGROUND AND PURPOSE

We investigated whether high-fat diet (HFD)-induced obesity was associated with changed function of components of the mesenteric innervation (adrenergic, sensory and nitrergic), the mechanisms involved and the possible effects of rosuvastatin on these changes.

EXPERIMENTAL APPROACH

Male Wistar rats were divided into three groups. (i) rats fed a standard diet (control group); (ii) rats fed a HFD (33.5% fat) for 7 weeks; and (iii) rats fed a HFD and treated with rosuvastatin (15 mg·kg(-1) ·day(-1) ) for 7 weeks. Segments of isolated mesenteric arteries were exposed to electric field stimulation (EFS) with or without tetrodotoxin, phentolamine, 7-nitroindazole (7NI) or N(ω) nitro-L-arginine methyl ester (L-NAME). Noradrenaline, ATP and NO release, and nNOS expression were also measured.

KEY RESULTS

EFS induced a greater frequency-dependent contraction in obese than in control rats. In HFD rats, phentolamine reduced contractions elicited by EFS, but noradrenaline release was greater and ATP release decreased. L-NAME and 7NI increased contractions to EFS in segments from control rats, but not in those from HFD rats. NO release and nNOS expression were lower in arterial segments from HFD rats than in control rats. All these changes in HFD rats were reversed by treatment with rosuvastatin.

CONCLUSIONS AND IMPLICATIONS

Neural control of mesenteric vasomotor tone was altered in HFD rats. Enhanced adrenergic and diminished nitrergic components both contributed to increased vasoconstrictor responses to EFS. All these changes were reversed by rosuvastatin, indicating novel mechanisms of statins in neural regulation of vascular tone.

Electroacupuncture Delays Hypertension Development through Enhancing NO/NOS Activity in Spontaneously Hypertensive Rats

Using spontaneously hypertensive rats (SHR), this study investigated whether electroacupuncture (EA) could reduce early stage hypertension by examining nitric oxide (NO) levels in plasma and nitric oxide synthase (NOS) levels in the mesenteric resistance artery. EA was applied to the acupuncture point Governor Vessel 20 (GV20) or to a non-acupuncture point in the tail twice weekly for 3 weeks under anesthesia. In conscious SHR and normotensive Wistar Kyoto (WKY) rats, blood pressure was determined the day after EA treatment by the tail-cuff method. We measured plasma NO concentration, and evaluated endothelial NO syntheses (eNOS) and neuronal NOS (nNOS) protein expression in the mesenteric artery. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were lower after 3 weeks of GV20 treatment than EA at non-acupuncture point and no treatment control in SHR. nNOS expression by EA was significantly different between both WKY and no treatment SHR control, and EA at GV20 in SHR. eNOS expression was significantly high in EA at GV 20 compared with no treatment control. In conclusion, EA could attenuate the blood pressure elevation of SHR, along with enhancing NO/NOS activity in the mesenteric artery in SHR.

Cirrhosis decreases vasoconstrictor response to electrical field stimulation in rat mesenteric artery: role of calcitonin gene-related peptide

Our study determines alterations in the vasoconstrictor response elicited by electric field stimulation (EFS) in mesenteric arteries from cirrhotic rats treated with CCl(4), and how calcitonin gene-related peptide (CGRP) participates in this response. Vasoconstriction induced by EFS was analysed in the absence and presence of the CGRP receptor antagonist CGRP(8-37) in arterial segments from control and cirrhotic rats. The vasodilator response to exogenous CGRP was tested in both groups of rats, and the interference of the guanylate cyclase inhibitor ODQ or the K(ATP) channel blocker glibenclamide was analysed only in segments from cirrhotic rats. The vasodilator response to the K(ATP) channel opener pinacidil and to 8-bromo-cyclic GMP was tested. The K(ATP) currents were recorded using the patch-clamp technique. Expression of receptor activity-modifying protein 1 (RAMP1), calcitonin receptor-like receptor, Kir 6.1 and sulfonylurea receptor 2B (SUR2B) was also analysed. Release of CGRP and cGMP was measured. The EFS-elicited vasoconstriction was less in segments from cirrhotic rats. The presence of CGRP(8-37) increased the EFS-induced response only in segments from cirrhotic rats. The CGRP-induced vasodilatation was greater in segments from cirrhotic rats, and was inhibited by ODQ or glibenclamide. Both pinacidil and 8-bromo-cyclic GMP induced a stronger vasodilator response in segments from cirrhotic rats. Pinacidil induced greater K(ATP) currents in cirrhotic myocytes. Expression of RAMP1, calcitonin receptor-like receptor, Kir 6.1 and SUR2B was not modified by liver cirrhosis. Liver cirrhosis increased CGRP release, but did not modify cGMP formation. The decreased vasoconstrictor response to EFS in cirrhosis is mediated by increased vasodilator response to CGRP, as well as increased K(ATP) channel gating. This effect of CGRP may play a role in the splanchnic vasodilatation present in liver cirrhosis.

Control of systemic and pulmonary blood pressure by nitric oxide formed through neuronal nitric oxide synthase

Nitric oxide formed by neuronal nitric oxide synthase (nNOS) in the brain, autonomic inhibitory (nitrergic) nerves, and heart plays important roles in the control of blood pressure. Activation of nitrergic nerves innervating the systemic vasculature elicits vasodilatation, decreases peripheral resistance, and lowers blood pressure. Impairment of nitrergic nerve function, as well as endothelial dysfunction, results in systemic and pulmonary hypertension and decreased regional blood flow. Blockade of nNOS activity in the brain, particularly the medulla and hypothalamus, causes systemic hypertension. Under hypertensive states, such as those in spontaneously hypertensive and Dahl salt-sensitive rats, the expression of the nNOS gene in the brain is increased; this appears to counteract the activated sympathetic function in the vasomotor center. The present article summarizes information concerning the modulation of systemic and pulmonary hypertension through nNOS-derived nitric oxide produced in the brain and periphery.

Aging increases neuronal nitric oxide release and superoxide anion generation in mesenteric arteries from spontaneously hypertensive rats

We hypothesized that neuronal NO release as well as its bioavailability and vasomotor response could be affected when aging and hypertension are present simultaneously. The neuronal nitric oxide (NO) release, its metabolism and vasomotor response induced by electrical field stimulation was analyzed in isolated segments of endothelium-denuded mesenteric arteries from young and old spontaneously hypertensive rats (SHR). The nitric oxide synthase (NOS) inhibitor N(G)-nitro-arginine-methyl ester (L-NAME) and NOS inhibitor 7-nitroindazole both strengthened electrical field stimulation-elicited contractions more in arteries from young than aged SHR rats. Superoxide dismutase (SOD) potentiated the L-NAME effect in segments from old rats, whereas catalase decreased the contractions induced by electrical field stimulation and noradrenaline but did not modify the L-NAME effect. In noradrenaline-precontracted segments, sodium nitroprusside induced a similar relaxation in arteries from both experimental groups. This relaxation was increased by SOD in old SHR. 8Br cGMP induced greater relaxation in segments from old than from young SHR. Electrical field stimulation induced a tritium release in arteries preincubated with [(3)H]-noradrenaline, that was similar in both young and old SHR rats. Electrical field stimulation induced NO(2)(-) formation, which was greater in segments from old than young SHR rats. Basal cGMP levels and those stimulated with sodium nitroprusside were similar in segments from both groups. Superoxide anion production was greater from old than young SHR rats. Peroxynitrite production induced by electrical field stimulation was only detected in segments from old SHR. The results obtained in mesenteric arteries from old SHR showed increased neuronal NO release and superoxide anion production with respect to those observed in arteries from young SHR rats. This induced decreased NO bioavailability through peroxynitrite formation. The final effect is to decrease the involvement of neuronal NO in electrical field stimulation-induced vasomotor response in arteries from old SHR rats.

Effect of pH changes on reactivity of rat mesenteric artery segments at different magnitude of stretch

The reaction to noradrenaline (NA) (10 microM) and electrical field stimulation (EFS) was studied in rat mesenteric artery segments at different magnitude of stretch and the solution pH. Alkaline solution (pH 7.8) potentiated and acidic solution (pH 7.0 or 6.6) inhibited the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 5-200 mmHg. These pH changes failed to alter resting tension at any magnitude of stretch. Acedic solution of pH 6.6 caused 2-fold decrease in noradrenaline- and 5-15-fold decrease in the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 50, 125, and 200 mmHg. In segments pre-contracted with noradrenaline (10 microM) acidification caused the decrease of the dilation and appearance of the constriction induced by the EFS. The effect of acidosis on the EFS-evoked response was diminished and the effect on noradrenaline-evoked response was abolished in the presence of nitric oxide synthase blocker, NG-nitro-L-arginine (100 microM). These results suggest that acidosis effectively impairs reactivity of the rat mesenteric artery in a wide range of its stretch, and the inhibition of the response to noradrenaline occurs completely, while to EFS only partially due to nitric oxide (NO) release, presumably by the endothelium. In addition, it was shown that acidosis is able to act not only as the commonly known dilator agent, but also as an agent potentiating constriction in case of the high noradrenaline-induced tone.