Periarterial Nerve Research Articles

A ketolide antibiotic, telithromycin, inhibits vascular adrenergic neurotransmission in the rat mesenteric vascular bed

A ketolide antibiotic, telithromycin, has side effects including temporary loss of consciousness in clinical use, but the underlying mechanisms remain unclear. This study investigated the effects of telithromycin on perivascular nerve function in rat mesenteric arteries, in comparison with those of macrolide (erythromycin and clarithromycin) and new quinolone antibiotics (levofloxacin and gatifloxacin). In vitro, vascular responses and release of noradrenaline induced by periarterial nerve stimulation (PNS) of rat perfused mesenteric vascular beds were measured in the presence of each antibiotic. In vivo blood pressure measurement was performed in Wistar rats. In mesenteric preparations with resting tone, telithromycin (10 nM-10 microM) markedly inhibited PNS (4-12 Hz)-induced adrenergic nerve- and exogenous noradrenaline-mediated vasoconstriction, whereas the other antibiotics slightly inhibited PNS-induced responses without affecting noradrenaline-induced responses. Telithromycin significantly reduced PNS (12 Hz)-evoked noradrenaline release in the perfusate. In pre-constricted preparations with or without endothelium, telithromycin (0.1 nM-10 microM) caused a concentration-dependent vasodilation. Telithromycin (10 nM) inhibited calcium-induced vasoconstriction in high KCl and calcium-free medium. None of the antibiotics used affected PNS (0.5-2 Hz)-induced calcitonin gene-related peptide (CGRP) nerve- and exogenous CGRP-mediated vasodilation. Intravenous injection of telithromycin significantly lowered blood pressure in anaesthetized rats. These results suggest that telithromycin causes not only strong inhibition of perivascular adrenergic neurotransmission but also a vasodilator action in mesenteric vascular beds and hypotension. It is thus possible that telithromycin increases visceral blood flow, consequently reducing cerebral blood flow and resulting in a temporary loss of consciousness.

Nerve stimulation induced overflow of neuropeptide Y and modulation by angiotensin II in spontaneously hypertensive rats

The sympathetic nervous system and renin-angiotensin system are both thought to contribute to the development and maintenance of hypertension in experimental models such as the spontaneously hypertensive rat (SHR). We demonstrated that periarterial nerve stimulation (NS) increased the perfusion pressure (PP) and neuropeptide Y (NPY) overflow from perfused mesenteric arterial beds of SHRs at 4-6, 10-12, and 18-20 wk of age, which correspond to prehypertensive, developing hypertensive, and maintained hypertensive stages, respectively, in the SHR. NS also increased PP and NPY overflow from mesenteric beds of Wistar-Kyoto (WKY) normotensive rats. NS-induced increases in PP and NPY were greater in vessels obtained from SHRs of all three ages compared with WKY rats. ANG II produced a greater increase in PP in preparations taken from SHRs than WKY rats. ANG II also resulted in a greater increase in basal NPY overflow from 10- to 12-wk-old and 18- to 20-wk-old SHRs than age-matched WKY rats. ANG II enhanced the NS-induced overflow of NPY from SHR preparations more than WKY controls at all ages studied. The enhancement of NS-induced NPY overflow by ANG II was blocked by the AT1 receptor antagonist EMD-66684 and the angiotensin type 2 receptor antagonist PD-123319. In contrast, ANG II greatly enhanced norepinephrine overflow in the presence of PD-123319. Both captopril and EMD-66684 decreased neurotransmitter overflow from SHR mesenteric beds; therefore, we conclude that an endogenous renin-angiotensin system is active in this preparation. It is concluded that the ANG II-induced enhancement of sympathetic nerve stimulation may contribute to the development and maintenance of hypertension in the SHR.

Endothelium removal augments endothelium‐independent vasodilatation in rat mesenteric vascular bed

The vascular endothelium regulates vascular tone by releasing various endothelium-derived vasoactive substances to counteract excess vascular response. We investigated whether the vascular endothelium regulates vasodilatation via released endothelium-derived contracting factors (EDCFs), by examining the effect of endothelium removal on responses to periarterial nerve stimulation (PNS) and various vasodilator agents. The rat mesenteric vascular bed was perfused with Krebs solution. Vasodilator responses to PNS and 5 min perfusion of vasodilator agents in preparations with endothelium were compared with those in the same preparations without endothelium. The endothelium was removed by 30 s perfusion with sodium deoxycholate. Endothelium removal significantly augmented vasodilator responses to PNS and calcitonin gene-related peptide (CGRP), isoprenaline (beta-adrenoceptor agonist), SNP and 8-bromo-cGMP (8-Br-cGMP; cGMP analogue) but not BAY41-2272 (soluble guanylate cyclase activator). The augmentation of SNP-induced vasodilatation after denudation was much greater than that of CGRP- or isoprenaline-induced vasodilatation. In the preparations with an intact endothelium, L-NAME (nitric oxide synthase inhibitor) significantly augmented vasodilator responses to PNS and CGRP, isoprenaline, SNP and 8-Br-cGMP, but not BAY41-2272. Indomethacin (cyclooxygenase inhibitor) and seratrodast (thromboxane A(2) receptor antagonist), but not phosphoramidon (endothelin-1-converting enzyme inhibitor) or BQ-123 (selective endothelin type A receptor antagonists), significantly augmented vasodilator responses to PNS and CGRP, isoprenaline, SNP and BAY41-2272. These results suggest that the endothelium in rat mesenteric arteries regulates and maintains vascular tone via counteracting not only vasoconstriction through releasing endothelium-derived relaxing factors, but also vasodilatation, in part by releasing an EDCF, thromboxane A(2).

Temperature‐dependent differences in sympathetic neuroeffector transmission in mesenteric arteries and veins in hypertension

Norepinephrine (NE) is released from sympathetic nerves supplying arteries and veins. We studied temperature‐related (28–37 ºC) differences in NE release and clearance using amperometry to measure NE in vitro. Tissues from sham and DOCA‐salt hypertensive rats were studied. Peak NE currents in sham veins declined more with temperature compared to arteries. Peak currents in DOCA‐salt arteries also showed greater temperature sensitivity than those in sham arteries. Currents in sham veins and DOCA‐salt arteries increased faster, decayed more slowly and were more temperature sensitive than those in sham arteries. Idazoxan (blocks α2 adrenergic receptors, α2ARs) and cocaine (blocks the NE transporter, NET) accelerated current rise time in sham arteries only. NE current decay was accelerated by idazoxan in veins but not arteries at 37 ºC and in arteries but not veins at 28 ºC, with a smaller increase in DOCA‐salt arteries at 28 ºC than sham arteries. We conclude that control of NE release from peri‐arterial nerves is more complex and therefore more temperature‐sensitive than in peri‐venous nerves. DOCA‐salt hypertension impairs NE release and clearance in arteries but not veins. α2ARs functional as autoreceptors and possibly as a “clearance receptor” holding NE in the neuroeffector junction. Clearance of NE in sham arteries is NET‐dependent and in sham veins and DOCA‐salt arteries is α2 NE clearance receptor dependent.

Royal Jelly Ameliorates Insulin Resistance in Fructose-Drinking Rats

Royal jelly (RJ) is known to contain excellent nutrition and a variety of biological activities. The present study was designed to investigate the effects of RJ on insulin resistance (hyperinsulinemia) in fructose-drinking rats (FDR; insulin resistance 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 and triglyceride, Homeostasis Model Assessment ratio (HOMA-R, an index of insulin resistance), and systolic blood pressure, but not blood glucose levels, when compared with control rats. RJ (100, 300 mg/kg, p.o.) treatment for 8 weeks significantly decreased the plasma levels of insulin and triglyceride, HOMA-R, without affecting blood glucose or total cholesterol levels and tended to lower systolic blood pressure. In isolated and perfused mesenteric vascular beds of FDR, RJ treatment resulted in a significant reduction in sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS) and tended to increase the calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator response to PNS, compared with those in untreated FDR. However, RJ treatment did not significantly affect norepinephrine-induced vasoconstriction or CGRP-induced vasodilation. These results suggest that RJ could be an effective functional food to prevent insulin resistance associated with the development of hypertension.

Lafutidine Facilitates Calcitonin Gene-Related Peptide (CGRP) Nerve-Mediated Vasodilation via Vanilloid-1 Receptors in Rat Mesenteric Resistance Arteries

Lafutidine is a histamine H2-receptor antagonist with gastric antisecretory and gastroprotective activity associated with activation of capsaicin-sensitive nerves. The present study examined the effect of lafutidine on neurotransmission of capsaicin-sensitive calcitonin gene-related peptide (CGRP)-containing vasodilator nerves (CGRPergic nerves) in rat mesenteric resistance arteries. Rat mesenteric vascular beds were perfused with Krebs solution and vascular endothelium was removed by 30-s perfusion with sodium deoxycholate. In preparations preconstricted by continuous perfusion of methoxamine (α1adrenoceptor agonist), perfusion of lafutidine (0.1 –10 μ M) concentration-dependently augmented vasodilation induced by the periarterial nerve stimulation (PNS, 1 Hz) without affecting vasodilation induced by exogenous CGRP (10 pmol) injection. Perfusion of famotidine (H2-receptor antagonist, 1 –100 μ M) had no effect on either PNS-induced or CGRP-induced vasodilation. Perfusion of lafutidine concentration-dependently augmented vasodilation induced by a bolus injection of capsaicin (vanilloid-1 receptor agonist, 30 pmol). The presence of a vanilloid-1 receptor antagonist, ruthenium red (10 μ M) or capsazepine (5 μ M), abolished capsaicin-induced vasodilation and significantly decreased the PNS-induced vasodilation. The decreased PNS-induced vasodilation by ruthenium red or capsazepine was not affected by perfusion of lafutidine. These results suggest that lafutidine facilitates CGRP nerve-mediated vasodilation by modulating the function of presynaptic vanilloid-1 receptors located in CGRPergic nerves.

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 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.

Functional Antagonism between Endogenous Neuropeptide Y and Calcitonin Gene-Related Peptide in Mesenteric Resistance Arteries

To test the hypothesis that endogenous neuropeptide Y (NPY) counteracts the vasodilator effects of calcitonin gene-related peptide (CGRP), we used isolated mesenteric resistance arteries of rats and mice. With immunohistochemistry, we observed CGRP-containing fibers along and in the vicinity of a subset of NPY- or tyrosine hydroxylase-immunoreactive fibers. The CGRP1 receptor component calcitonin-related-like receptor was expressed by periarterial nerves and smooth muscle cells, whereas receptor activity-modifying protein 1 was observed primarily on the smooth muscle. In organ chambers, exogenous CGRP caused relaxations that were reversed by exogenous NPY. The effects were inhibited by 1-piperidinecarboxamide, N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl]-carbonyl]pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl)-methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl) (BIBN4096BS, a CGRP1 receptor antagonist; pK(B) = 8.54 +/- 0.52) and (R)-NZ-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]argininamide (BIBP3226, a Y1 antagonist; pK(B) = 7.00 +/- 0.49), respectively. Pretreatment with capsaicin (1 muM; 20 min) and the presence of BIBN4096BS (20 nM) increased contractile responses to K(+) (20-40 mM) and electrical field stimulation (EFS; 1-32 Hz). NPY increased contractile responses to K(+) and BIBP3226 (400 nM) reduced contractile responses to EFS. These effects were inhibited by capsaicin and BIBN4096BS, respectively. Furthermore, the relaxing effect of exogenous CGRP (10 nM) during phenylephrine-induced contraction (30 muM) was reversed by EFS, and this effect was reduced in the presence of BIBP3226. We confirmed that bioactive concentrations of endogenous CGRP and NPY can be released from periarterial sensory-motor and sympathetic nerves, respectively, and we demonstrate for the first time functional antagonism between endogenous NPY and CGRP at the level of the smooth muscle.

Effect of Long-term Treatment with Royal Jelly on Insulin Resistance in Otsuka Long-Evans Tokushima Fatty (OLETF) Rats

Royal jelly (RJ) is known to have abundant nutritional properties and a variety of biological activities. To investigate the effects of RJ on insulin resistance, 10-week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 diabetic model, were treated for 4 weeks with RJ (10, 30, and 300 mg/kg, p.o.). RJ treatment tended to decrease systolic blood pressure and significantly decreased serum levels of insulin and the Homeostasis Model Assessment ratio, an index of insulin resistance. In isolated and perfused mesenteric vascular beds of OLETF rats, RJ treatment resulted in significant reduction of the sympathetic nerve-mediated vasoconstrictor response to periarterial nerve stimulation (PNS) and potentiation of the calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator response to PNS, compared with that in untreated OLETF rats. However, RJ treatment did not significantly affect norepinephrine-induced vasoconstriction and CGRP-induced vasodilation. These results suggest that RJ could be an effective and functional food to prevent the development of insulin resistance.

Role of Renal Sympathetic Nerves in Regulating Renovascular Responses to Angiotensin II in Spontaneously Hypertensive Rats

The purpose of this study was to test the hypothesis that renal sympathetic nerves modulate angiotensin II-induced renal vasoconstriction in kidneys from genetically hypertensive rats via Y1 receptors activating the Gi pathway. In isolated, perfused kidneys from spontaneously hypertensive rats, the naturally occurring renal sympathetic cotransmitter neuropeptide Y at 6 nM enhanced angiotensin II (0.3 nM)-induced changes in perfusion pressure by 47 +/- 7 mm Hg, and this effect was inhibited by BIBP3226 [N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)-methyl]-D-arginine amide)], a selective Y1 receptor antagonist (1 microM). We next examined whether periarterial nerve stimulation (5 Hz) enhances renal vascular responses to a physiological level of angiotensin II (100 pM). Kidneys were pretreated with prazosin (a selective alpha1-adrenoceptor antagonist) to block nerve stimulation-induced changes in perfusion pressure. In kidneys from spontaneously hypertensive rats, but not normotensive rats, periarterial nerve stimulation significantly augmented angiotensin II-induced changes in perfusion pressure (177 +/- 26% of response in absence of stimulation). BIBP3226, but not rauwolscine (a selective alpha2-adrenoceptor antagonist), abolished periarterial nerve stimulation-induced enhancement of angiotensin II-mediated renal vasoconstriction. Pretreatment of hypertensive animals with pertussis toxin 3 days prior to kidney perfusion significantly (p < 0.000001) decreased mean blood pressure (203 +/- 2 versus 145 +/- 6 mm Hg in nonpretreated versus pertussis toxin-pretreated spontaneously hypertensive rats) and abolished periarterial nerve stimulation-induced enhancement of angiotensin II-mediated renal vasoconstriction. We conclude that, in spontaneously hypertensive rats but not normotensive rats, sympathetic nerve stimulation enhances renal vascular responses to physiological levels of angiotensin II via a mechanism mainly involving Y1 receptors coupled to Gi proteins.

Innervation and functional changes in mesenteric perivascular calcitonin gene-related peptide- and neuropeptide Y-containing nerves following topical phenol treatment

We have previously shown that age-related reduction of innervation and function in mesenteric perivascular calcitonin gene-related peptide-containing vasodilator nerves takes place in spontaneously hypertensive rats. The present study was performed to investigate innervation and functional changes in perivascular calcitonin gene-related peptide- and adrenergic neuropeptide Y-containing nerves after topical treatment with phenol, which damages nerve fibers, around the rat superior mesenteric artery. Under pentobarbital-Na anesthesia, 8-week-old Wistar rats underwent in vivo topical application of phenol (10% phenol in 90% ethanol) or saline (sham rats) to the superior mesenteric artery proximal to the bifurcation of the abdominal aorta. After the treatment, the animals were subjected to immunohistochemistry of the 3rd branch of small arteries proximal to the intestine and to vascular responsiveness testing on day 3 through day 14. The innervation levels of calcitonin gene-related peptide-like immunoreactivity containing fibers and neuropeptide Y-like immunoreactivity containing fibers were markedly reduced on day 3 to day 14 and on day 5 to day 14 after the treatment, compared with those in sham-operated rats, respectively. In perfused mesenteric vascular beds isolated from phenol-treated rats, adrenergic nerve-mediated vasoconstriction and calcitonin gene-related peptide nerve-mediated vasodilation in response to periarterial nerve stimulation (2–12 Hz) were significantly decreased on day 3 and day 7. Neurogenic release of norepinephrine in phenol-treated rats on day 7 was significantly smaller that that in sham-operated rats. Nerve growth factor content in the mesenteric arteries of phenol-treated rats was significantly lower than that in sham-operated rats. Administration of nerve growth factor using osmotic mini-pumps for 7 days after the phenol treatment resulted in greater density of calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity fibers than in phenol-treated rats and restored decreased vascular responses to periarterial nerve stimulation. These results suggest that topical phenol-treatment of the mesenteric artery effectively induces functional denervation of perivascular nerves, which can be prevented or reversed by nerve growth factor treatment.

Neuronal Nitric-Oxide Synthase Inhibition Facilitates Adrenergic Neurotransmission in Rat Mesenteric Resistance Arteries

The effects of nonselective nitric-oxide synthase (NOS) inhibitors [N-omega-nitro-L-arginine methyl ester (L-NAME) and N-omega-nitro-L-arginine (L-NNA)] and specific neuronal NOS (nNOS) inhibitor [vinyl-L-N-5-(1-imino-3-butenyl)-L-ornithine (L-VNIO)] on adrenergic nerve-mediated vasoconstriction were studied in rat perfused mesenteric vascular beds without endothelium. Perfusion of L-NAME, L-NNA, or l-VNIO markedly augmented vasoconstrictor responses to periarterial nerve stimulation (PNS; 2-8 Hz) without affecting vasoconstriction induced by exogenously injected norepinephrine (NE). Addition of L-arginine, a precursor for the synthesis of nitric oxide (NO), reversed the augmentation of the PNS response by l-NAME. The PNS (8 Hz)-evoked NE release in the perfusate was increased by L-NAME perfusion. In preparations treated with capsaicin [a depleter of calcitonin gene-related peptide (CGRP)-containing nerves], L-NAME did not augment vasoconstrictor responses to PNS or NE injection. Combined perfusion of CGRP(8-37) (a CGRP receptor antagonist) and L-NAME induced additive augmentation of the vasoconstrictor response to PNS but did not affect the response to NE injection. In preparations with active tone produced by methoxamine and in the presence of guanethidine, L-NAME perfusion did not affect the vasodilator response induced by PNS. Immunostaining of the mesenteric artery showed the presence of nNOS-like immunopositive nerve fibers, which were absent in arteries pretreated with capsaicin. These findings suggest that NO, which is released from perivascular capsaicin-sensitive nerves, presynaptically inhibits neurogenic NE release to modulate adrenergic neurotransmission.

Adrenomedullin release in the rat mesenteric resistance artery

Adrenomedullin (AM) is a potent vasodilator peptide whose major source is the vascular wall. In the present study, the mechanism of release of AM was investigated in the rat mesenteric resistance artery. The isolated mesenteric vascular bed was perfused with Krebs solution at a constant flow rate (5 ml/min) and AM in the perfusate was measured by a highly sensitive enzyme immunoassay (Immunoenzymometric assay; IEMA) method. In preparations without endothelium, spontaneous release of AM was detected in the perfusate (68.7 ± 5.8 fmol/ml, n = 45). Periarterial nerve stimulation (PNS, 4 and 8 Hz) caused 11.4 ± 3.9% (4 Hz) and 9.1 ± 3.5% (8 Hz) decreases in the spontaneous release of AM. Removal of Ca 2+ from the medium did not affect the spontaneous AM release, but abolished the PNS-induced inhibition of spontaneous AM release. Perfusion of 10 nM calcitonin gene-related peptide (CGRP) or 0.1 μM capsaicin (inducer of CGRP release) inhibited significantly the spontaneous AM release. PNS (8 Hz)-induced inhibition of spontaneous AM release was antagonized by CGRP(8–37) (CGRP receptor antagonist). These results suggest that AM is mainly released from vascular smooth muscle cells of the rat mesenteric artery and endogenous or exogenous CGRP inhibits AM release.

Up-regulation of nNOS and associated increase in nitrergic vasodilation in superior mesenteric arteries in pre-hepatic portal hypertension

Splanchnic arterial vasodilation in portal hypertension has been attributed largely to vascular NO overproduction. Three NO-synthase (NOS) isoforms have been identified of which e(ndothelial)-NOS has been found up-regulated and i(nducible)-NOS not expressed in the splanchnic circulation in portal hypertension. So far, n(euronal)-NOS has not been investigated and hence, the current study evaluates nNOS-expression and nNOS-mediated vasorelaxation in a model of portal vein-ligated rats (PVL). Mesenteric vasculature of PVL and sham rats was evaluated for nNOS-protein (immunohistochemically and Western blotting). In vitro perfused de-endothelialized mesenteric arterial vasculature was pre-constricted with norepinephrine (EC(80)) and tested for nNOS-mediated vasorelaxation by periarterial nerve stimulation (PNS, 2-12 Hz, 45V) before and after incubation with the NOS-inhibitor L-NAME (10(-4)M). nNOS was localized to the adventitia of the mesenteric arterial tree showing more intense staining and increased protein expression in PVL as compared to sham rats. PNS induced a frequency-dependent vasorelaxation, which was more pronounced in PVL rats. L-NAME abolished this difference in nerval-mediated vasorelaxation, the effect being significantly greater in PVL than in sham animals. Perivascular nNOS-protein expression is enhanced in mesenteric arteries in portal hypertension mediating an increased nerval NO-mediated vasorelaxation. This nNOS-derived NO overproduction may play an important role in the pathogenesis of arterial vasodilation in portal hypertension.

Effect of OS-0689, a novel SERM, on periarterial nerve function in tail arteries of ovariectomized rats

Objective: We have previously shown that OS-0689 attenuates the rise in tail skin temperature of ovariectomized rats, which is believed to be relevant to human symptoms of hot flush. In this study, we elucidate the mechanism underlying the ameliorating effects of OS-0689 on elevated tail skin temperature. Methods: Female Sprague–Dawley rats were ovariectomized and orally treated with OS-0544 (1 mg/kg), OS-0689 (3 mg/kg; (+)-enantiomer of OS-0544) or 17β-estradiol (3 mg/kg; E 2) for 1 week. At 1, 3 or 6 weeks after ovariectomy, the vasoconstrictions and vasorelaxations induced by periarterial nerve stimulation (PNS), l-noradrenaline (NA), and rat calcitonin gene-related peptide (CGRP) in isolated tail arteries were compared between OVX and sham-operated rats. Results: Three weeks after ovariectomy, vasoconstrictions in response to PNS and NA in the arteries of OVX rats were markedly less than those in the arteries of sham-operated rats. However, at 1 and 6 weeks after ovariectomy the stimuli-induced vasoconstrictions in the arteries of OVX rats were greater than those of sham-operated rats. Moreover, NA reactivity was not attenuated in the mesenteric arteries at 3 weeks after ovariectomy. OS-0544, OS-0689 and E 2 prevented the decrease in vasoconstrictions in the tail arteries. Vasorelaxations in response to PNS and rat CGRP were significantly greater in the arteries of OVX rats than in those of the sham-operated rats. OS-0689 inhibited the increase in vasorelaxation induced by both stimuli, whereas E 2 had no effects. Conclusions: Ovariectomy not only decreases adrenergic function but also enhances CGRPergic function in rats’ tail arteries. OS-0689 improves both impairments and thereby improves on rat hot flush.

Effect of Adrenomedullin on Adrenergic Vasoconstriction in Mesenteric Resistance Arteries of the Rat

Adrenomedullin (AM) is a hypotensive peptide that belongs to a family of peptides structurally related to calcitonin gene-related peptide (CGRP). The present study examined the effect of AM on adrenergic nerve-mediated vasoconstriction in rat perfused mesenteric vascular beds without endothelium. Perfusion of AM at 0.1 nM but not 10 nM increased vasoconstrictor responses to periarterial nerve stimulation (PNS) (1 – 4 Hz), while AM at 10 nM significantly attenuated vasoconstriction induced by bolus injection of norepinephrine (NE). In preparations treated with capsaicin (a CGRP depletor), pressor responses to both PNS and NE injection were markedly attenuated by AM. Perfusion of CGRP(8 – 37) (a CGRP-receptor antagonist) significantly potentiated the PNS- but not the NE-induced vasoconstriction. Combined perfusion of CGRP(8 – 37) and AM had no effect on the PNS-induced response and antagonized the inhibitory effect of AM on the NE-induced response. AM(22 – 52) (an AM-receptor antagonist) did not influence the effect of AM. These findings suggest that AM facilitates adrenergic vasoconstriction by inhibiting neurotransmission of CGRP-containing nerves, which counteract adrenergic nerve-mediated vasoconstriction.

Modulation of neurotransmitter release by NO is altered in mesenteric arterial bed of spontaneously hypertensive rats.

Nitric oxide (NO) reacts with catecholamines resulting in their deactivation. In the present study with the use of the perfused mesenteric arterial bed as a model of the sympathetic neuroeffector junction, the NO synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME) resulted in the enhancement of the periarterial nerve stimulation-induced increase in perfusion pressure and norepinephrine overflow while decreasing neuropeptide Y (NPY) overflow. These changes were prevented by l-arginine, demonstrating that the effects of l-NAME were specific to the inhibition of NOS. From the fact that norepinephrine acts on prejunctional alpha(2)-adrenoceptors to inhibit the evoked release of sympathetic cotransmitters, we carried out experiments in the presence of the alpha(2)-adrenergic receptor antagonist yohimbine to investigate the possibility that the decrease in NPY observed in the presence of l-NAME was due to the increase in bioactive norepinephrine acting on its autoreceptor. Periarterial nerve stimulation in the presence of both l-NAME and yohimbine prevented the previously observed decrease in NPY, indicating that the cause of this decrease was, as predicted, due to alpha(2)-adrenoceptor activation. The periarterial nerve stimulation-induced increase of norepinephrine overflow was greater in the spontaneously hypertensive rat compared with normotensive rats. In contrast to what was observed in the isolated perfused mesenteric arterial bed obtained from normotensive animals, inhibition of NOS did not result in a further increase in the overflow of norepinephrine or in a subsequent decrease in NPY. These results demonstrate that, in addition to being a direct vasodilator, NO, by deactivating norepinephrine, can modulate sympathetic neurotransmission and that this modulation is altered in the spontaneously hypertensive rat.

Up-regulation of nNOS and associated increase in vasorelaxation in superior mesenteric arteries in portal hypertension

Splanchnic arterial vasodilatation is the pathophysiological hallmark in the development of the hyperdynamic circulation in portal hypertension. This has been attributed largely to vascular NO overproduction. Three NO-synthase-(NOS)-isoforms have been identified of which e(ndothelial)-NOS has been found up-regulated and I(nducible)-NOS not expressed in the splanchnic circulation in portal hypertension. N(euronal)-NOS so far has not been investigated and hence, the current study evaluates in a model of portal vein-ligated rats (PVL) nNOS-expression and nNOS-mediated vasorelaxation. Methods: Mesenteric vasculature of PVL and sham rats was stained for nNOS immunohistochemically and analyzed for nNOS-protein level by western blots. In-vitro perfused de-endothelialized mesenteric arterial vasculature were preconstricted with norepinephrine (EC80) and tested for nNOS-mediated vasorelaxation by periarterial nerve stimulation (PNS, 2–12 Hz, 45V) before and after incubation with the NO-inhibitor L-NAME (10-4 M). Results: nNOS was localized to the adventitia of the mesenteric arterial tree showing more intense staining in PVL as compared to sham rats. Correspondingly, nNOS protein expression was markedly up-regulated in mesenteric arteries in PVL rats. PNS induced a frequency-dependent vasorelaxation which was more pronounced in PVL rats (Fig.1A). This difference in nerval-mediated vasorelaxation was abolished by incubation with L-NAME (Fig.1B). The effect of NO-inhibition on vasorelaxation, representing nNOS-mediated vasorelaxation, was significantly greater in PVL rats than in sham animals (Fig.1C). Conclusion: Perivascular nNOS protein expression is enhanced in mesenteric arteries in portal hypertension mediating an increased nerval NO-mediated vasorelaxation. This nNOS-derived NO overproduction may play an important role in the pathogenesis of arterial vasodilation and hyperdynamic circulatory syndrome in portal hypertension.

Acetylcholinesterase (AChE) – Positive Innervation of the Guinea-Pig Spleen

The presence and intraorgan distribution of the acetylcholinesterase (AChE)-positive nerve structures in the guinea-pig spleen were studied by means of the direct thiocholine method. Visualized AChE-positive nerve fibres entered the guinea-pig spleen at its hilum in the vicinity of the splenic artery branches and intra parenchyma were gradually distributed to form thicker periarterial nerves and also fine adventitial nerve plexus. In described topography the AChE-positive nerve fibres were identified in association with the central artery running through the white pulp. Some of the perivascular nerve fibres associated with the central artery extended away and passed into the periarterial lymphatic sheath (PALS) to reach the marginal zone and in continuation entered into the mantle zone of lymphatic follicles. Several AChE-positive nerve fibres were seen in the red pulp but less in the splenic capsule. We did not find any AChE-positive nerve cells in the guinea-pig spleen.

Nitric oxide decreases the biological activity of norepinephrine resulting in altered vascular tone in the rat mesenteric arterial bed.

Nitric oxide (NO) reacts with catecholamines resulting in their deactivation. In this study, we demonstrated that coincubation of NO donors with sympathetic neurotransmitters decreased the amount of norepinephrine detected but not ATP or neuropeptide Y (NPY). Furthermore, we found that the ability of norepinephrine to increase perfusion pressure in the isolated perfused mesenteric arterial bed of the rat was attenuated by the incubation of norepinephrine with the NO donor diethylamine NONOate. Conversely, the vasoconstrictive ability of NPY and ATP was unaffected by incubation with NONOate. Periarterial nerve stimulation in the presence of the NO synthase (NOS) inhibitor Nomega-nitro-l-arginine methyl ester (l-NAME) resulted in an increase in both perfusion pressure response and norepinephrine levels. This was prevented by l-arginine, demonstrating that the effects of l-NAME were indeed specific to the inhibition of NOS. To confirm that NO was not altering the release of norepinephrine from the sympathetic nerve via presynaptic activation of guanylate cyclase, we repeated the experiments in the presence of the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxaloine-one (ODQ). Unlike l-NAME, ODQ infusion did not increase norepinephrine overflow, demonstrating that modulation of norepinephrine by NO at the vascular neuroeffector junction of the rat mesenteric vascular bed is not the result of presynaptic guanylate cyclase activation. These results demonstrate that, in addition to being a direct vasodilatator, NO can also alter vascular reactivity at the sympathetic neuroeffector junction in the rat mesenteric bed by deactivating the vasoconstrictor norepinephrine.