Sympatho-adrenomedullary Outflow In Rats Research Articles

Possible role of adrenoceptors in the hypothalamic paraventricular nucleus in corticotropin-releasing factor-induced sympatho-adrenomedullary outflow in rats.

A functional interaction between the corticotropin-releasing factor (CRF) system and noradrenergic neurons in the brain has been suggested. In the present study, we investigated the interrelationship between the central CRF-induced elevation of plasma catecholamines and adrenoceptor activation in the paraventricular nucleus of the hypothalamus (PVN) using urethane-anesthetized rats. In rats under urethane anesthesia, a femoral venous line was inserted for infusion of saline, and a femoral arterial line was inserted for collecting blood samples. Next, animals were placed in a stereotaxic apparatus for the application of test agents. Catecholamines in the plasma were extracted by alumina absorption and were assayed with high-performance liquid chromatography with electrochemical detection. Quantification of noradrenaline in rat PVN microdialysates was performed with high-performance liquid chromatography with electrochemical detection. We showed that centrally administered CRF elevated noradrenaline release in the PVN. Furthermore, we demonstrated that microinjection of phenylephrine into the PVN induced elevation of plasma levels of adrenaline, but not of noradrenaline, whereas microinjection of isoproterenol into the PVN induced elevation of plasma levels of noradrenaline, but not of adrenaline. Bilateral blockade of adrenoceptors in the PVN revealed that phentolamine significantly suppressed the CRF-induced elevation of plasma adrenaline level, while propranolol significantly CRF-induced elevation of plasma noradrenaline level. Our results suggest that centrally administered CRF-induced elevation of plasma levels of adrenaline and noradrenaline can be mediated via activation of α-adrenoceptors and β-adrenoceptors, respectively, in the rat PVN.

Effects of centrally administered prostaglandin E 3 and thromboxane A 3 on plasma noradrenaline and adrenaline in rats: Comparison with prostaglandin E 2 and thromboxane A 2

Previously, we reported the involvement of brain ω-6 prostanoids, especially prostaglandin E 2 and thromboxane A 2, in the activation of central sympatho-adrenomedullary outflow in rats. ω-3 Prostanoids, including prostaglandin E 3 and thromboxane A 3, are believed to be less bioactive than ω-6 prostanoids, although studies on the functions of ω-3 prostanoids in the central nervous system have not been reported. In the present study, therefore, we compared the effects of centrally administered ω-3 prostanoids, prostaglandin E 3 and thromboxane A 3, with those of ω-6 prostanoids, prostaglandin E 2 and thromboxane A 2, on the plasma catecholamines in anesthetized rats. Intracerebroventricularly (i.c.v.) administered prostaglandin E 2 (0.15, 0.3 and 1.5 nmol/animal) and prostaglandin E 3 (0.3 and 3 nmol/animal) predominantly elevated plasma noradrenaline but not adrenaline, but the latter was less efficient than the former. On the other hand, U-46619 (an analog of thromboxane A 2) (30, 100 and 300 nmol/animal, i.c.v.) and Δ 17-U-46619 (an analog of thromboxane A 3) (100 and 300 nmol/animal, i.c.v.) both elevated plasma catecholamines (adrenaline ≫ noradrenaline) to the same degree. These results suggest that centrally administered prostaglandin E 3 is less effective than prostaglandin E 2 to elevate plasma noradrenaline, and that thromboxane A 3 is almost as equipotent as thromboxane A 2 to elevate plasma catecholamines in rats.

Nitric oxide synthase isozymes in spinally projecting PVN neurons are involved in CRF-induced sympathetic activation

In the brain, corticotropin-releasing factor (CRF) has been shown to activate the sympatho-adrenomedullary outflow, but the central mechanisms of action are still not fully understood. Previously, we reported that inducible nitric oxide synthase (iNOS) is involved in central CRF-induced elevation of plasma catecholamines in rats. Nitric oxide is mainly synthesized by neuronal NOS (nNOS) and iNOS in many areas in the brain. Of these areas, the paraventricular hypothalamic nucleus (PVN) contains neurons projecting to the intermediolateral cell column (IML) of the spinal cord, thereby directly affecting the sympathetic activity. Therefore, in the present study, we investigated the effect of intracerebroventricularly (i.c.v.) administered CRF on plasma catecholamine levels and expression of NOS isozymes (iNOS and nNOS) and Fos (a marker for neuronal activation) in the spinally projecting PVN neurons, using rats microinjected with a monosynaptic retrograde tracer into the IML. CRF (1.5 nmol/animal, i.c.v.) effectively elevated plasma catecholamine levels. The spinally projecting neurons labeled with a tracer were detected in the dorsal cap, ventral part and posterior part of the PVN. CRF significantly increased the number of spinally projecting neurons triple-labeled with Fos and iNOS in all of these PVN subnuclei. On the other hand, CRF significantly increased the number of spinally projecting neurons triple-labeled with Fos and nNOS only in the ventral part of the PVN. These results suggest that in spinally projecting PVN neurons, iNOS mainly contributes to the centrally administered CRF-induced activation of the sympatho-adrenomedullary outflow in rats.

Brain nuclear factor kappa B is involved in the corticotropin-releasing factor-induced central activation of sympatho-adrenomedullary outflow in rats

Using urethane-anesthetized rats, we examined whether an activation of nuclear factor kappa B is involved in the corticotropin-releasing factor-induced increase in plasma levels of catecholamines. An intracerebroventricularly administered corticotropin-releasing factor (1.5 nmol/animal)-induced increase of plasma catecholamines was dose-dependently reduced by pyrrolidine dithiocarbamate (a nuclear factor kappa B antagonist) (1 and 9 nmol/animal, intracerebroventricularly) and SN50 (a peptide inhibiting nuclear factor kappa B translocation) (9 and 18 nmol/animal, intracerebroventricularly), while SN50M (an inactive control peptide for SN50, 19 nmol/animal, intracerebroventricularly) had no effect on the corticotropin-releasing factor-induced elevation of both catecholamines. Furthermore, the corticotropin-releasing factor-induced responses were also attenuated by rosiglitazone (a peroxisome proliferator-activated receptor-γ agonist)(50 nmol/animal, intracerebroventricularly). These results suggest the involvement of brain nuclear factor kappa B in the corticotropin-releasing factor-induced central activation of the sympatho-adrenomedullary outflow in rats.

Role of brain adrenoceptors in the corticortopin-releasing factor-induced central activation of sympatho-adrenomedullary outflow in rats

We investigated the role played by catecholamine-dependent pathways in modulating the ability of centrally administered corticotropin releasing factor (CRF) to activate sympatho-adrenomedullay outflow, using urethane-anesthetized rats. The CRF (1.5 nmol/animal, i.c.v.)-induced elevations of both plasma noradrenaline and adrenaline were attenuated by phentolamine (a non-selective α adrenoceptor antagonist) [125 and 250 µg (0.33 and 0.66 µmol)/animal], Heat (a selective α 1 adrenoceptor antagonist) [10 and 30 µg (30 and 90 nmol)/animal, i.c.v.] and clonidine (a selective α 2 adrenoceptor agonist) [100 µg (0.375 µmol)/animal, i.c.v.]. On the other hand, the CRF (1.5 nmol/animal, i.c.v.)-induced elevation of both catecholamines was not influenced by RS 79948 (a selective α 2 adrenoceptor antagonist) [10 and 30 µg (7.2 and 72 nmol)/animal, i.c.v.]. Furthermore, the CRF (1.5 nmol/animal, i.c.v.)-induced elevation of noradrenaline was attenuated by sotalol (a non-selective β adrenoceptor antagonist) [125 and 250 µg (0.4 and 0.8 µmol)/animal, i.c.v.], while that of adrenaline was not influenced by sotalol. These results suggest that centrally administered CRF-induced elevation of plasma noradrenaline is mediated by an activation of α 1 and β adrenoceptors in the brain, and that of plasma adrenaline is mediated by an activation of α 1 adrenoceptors in the brain. Furthermore, central α 2 adrenoceptors are involved in modulating the CRF-induced elevation of both plasma catecholamines.

Brain phospholipase C/diacylglycerol lipase are involved in bombesin BB 2 receptor-mediated activation of sympatho-adrenomedullary outflow in rats

Bombesin receptors are mainly divided into two subtypes: BB 1 receptor (neuromedin B-preferring receptor) and BB 2 receptor [gastrin-releasing peptide (GRP)-preferring receptor]. Previously, we reported that intracerebroventricularly (i.c.v.) administered bombesin elevates plasma noradrenaline and adrenaline by production of brain arachidonic acid in rats. Arachidonic acid is released mainly by phospholipase A 2 (PLA 2)-dependent pathway or phospholipase C (PLC)/diacylglycerol lipase-dependent pathway. In the present study, bombesin and GRP elevated plasma catecholamines in a dose-dependent manner (1 and 5 nmol/animal, i.c.v.), while neuromedin B (1, 5 and 10 nmol/animal, i.c.v.) had no effect in urethane-anesthetized rats (bombesin = GRP ≫ neuromedin B). The bombesin (1 nmol/animal, i.c.v.)-induced response was dose-dependently attenuated by [ d-Phe 6, des-Met 14]-bombesin (6–14) ethylamide (bombesin BB 2 receptor antagonist) (15.3 and 30.6 nmol/animal, i.c.v.) and also by U-73122 (PLC inhibitor) (10 and 100 nmol/animal, i.c.v.) and RHC-80267 (diacylglycerol lipase inhibitor) (1.3 and 2.6 μmol/animal, i.c.v.). However, d-Nal-cyclo[Cys-Tyr- d-Trp-Orn-Val-Cys]-Nal-NH 2 (bombesin BB 1 receptor antagonist) (30 and 100 nmol/animal, i.c.v.), mepacrine (PLA 2 inhibitor) (1.1 and 2.2 μmol/animal, i.c.v.) and U-73343 (inactive analog of U-73122) (100 nmol/animal, i.c.v.) had no effect. These results suggest the involvement of brain PLC/diacylglycerol lipase in the brain bombesin BB 2 receptor-mediated activation of sympatho-adrenomedullary outflow in rats.

Inducible nitric oxide synthase is involved in corticotropin-releasing hormone-mediated central sympatho-adrenal outflow in rats

Brain nitric oxide (NO), recognized as a neurotransmitter or a neuromodulator, is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. NO has been shown to activate cyclooxygenase (a prostaglandin-forming enzyme) in addition to guanylate cyclase. Recently, we reported that the intracerebroventricularly (i.c.v.) administered corticotropin-releasing hormone (CRH) increases plasma catecholamines through brain cyclooxygenase-dependent mechanisms in rats [Eur. J. Pharmacol. 419 (2001) 183]. In the present experiments, therefore, we examined whether NO is involved in the CRH-induced increase of plasma catecholamines using urethane-anesthetized rats. I.c.v. administered CRH increased plasma noradrenaline and adrenaline in a dose-dependent manner (0.5, 1.5, and 3.0 nmol/animal). The CRH (1.5 nmol/animal, i.c.v.)-induced increase of plasma catecholamines was reduced by N ω-nitro- l-arginine methyl ester (a non-selective inhibitor of NOS) [111 nmol (30 μg)/animal, i.c.v.], but not by the same dose of N ω-nitro- d-arginine methyl ester (an inactive isomer of N ω-nitro- l-arginine methyl ester). The CRH-induced increase of plasma catecholamines was also reduced either by cycloheximide (an inhibitor of protein synthesis) [107 nmol (30 μg)/animal, i.c.v.] or by S-methylisothiourea (an inhibitor of inducible NOS) [71 nmol (20 μg) and 711 nmol (200 μg)/animal, i.c.v.]. These results suggest the involvement of brain inducible NOS in the CRH-induced activation of the central sympatho-adrenomedullary outflow in rats.

Brain phospholipase C and diacylglycerol lipase are involved in corticotropin-releasing hormone-induced sympatho-adrenomedullary outflow in rats

Previously, we reported that the elevation of plasma noradrenaline and adrenaline induced by intracerebroventricularly (i.c.v.) administered corticotropin-releasing hormone (CRH) was abolished by i.c.v. administered indomethacin, an inhibitor of cyclooxygenase, in rats [Yokotani et al., Eur. J. Pharmacol. 419, 183-189, 2001]. The result suggests the involvement of active metabolites of brain arachidonic acid in the CRH-induced activation of the central sympatho-adrenomedullary outflow. Arachidonic acid is released mainly by two different pathways: phospholipase A 2-dependent pathway; phospholipase C- and diacylglycerol lipase-dependent pathway. In the present study, therefore, we tried to identify which pathway is involved in the CRH-induced elevation of plasma catecholamines in urethane-anesthetized rats. CRH (1.5 nmol/animal, i.c.v.)-induced elevation of plasma noradrenaline and adrenaline was abolished by neomycin [0.55 μmol (500 μg)/animal, i.c.v.] and 1-(6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U-73122) [5 nmol (2.3 μg)/animal, i.c.v.] (inhibitors of phospholipase C), and also by 1,6-bis-(cyclohexyloximinocarbonylamino)-hexane (RHC-80267) [1.3 μmol (500 μg)/animal, i.c.v.] (an inhibitor of diacylglycerol lipase). On the other hand, mepacrine [1.1 μmol (500 μg)/animal, i.c.v.] (an inhibitor of phospholipase A 2) and 1-(6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-2,5-pyrrolidinedione (U-73343) [5 nmol (2.3 μg)/animal, i.c.v.] (an inactive analog of U-73122) had no effect. These results suggest that CRH activates the central sympatho-adrenomedullary outflow by the brain phospholipase C- and diacylglycerol lipase-dependent mechanisms in rats.

Vasopressin V 1 receptor-mediated activation of central sympatho-adrenomedullary outflow in rats

The present study was designed to characterize the vasopressin receptor subtype involved in the vasopressin-induced activation of the central sympatho-adrenomedullary outflow using urethane-anesthetized rats. Intracerebroventricularly (i.c.v.) administered vasopressin (0.1, 0.2 and 0.5 nmol/animal) dose-dependently elevated plasma levels of adrenaline and noradrenaline (adrenaline>noradrenaline). The vasopressin (0.2 nmol/animal)-induced elevation of both catecholamines was significantly attenuated by [d(CH 2) 5 1,Tyr(Me) 2,Arg 8]-vasopressin, a selective vasopressin V 1 receptor antagonist, in a dose-dependent manner (0.1 and 0.2 nmol/animal, i.c.v.). The same doses (0.1 and 0.2 nmol/animal, i.c.v.) of [1-adamantaneacetyl 1, d-Tyr(Et) 2,Val 4,Abu 6, Arg 8,9]-vasopressin, a potent vasopressin V 2 receptor antagonist, had no effect; however, a large dose of this antagonist (1.6 nmol/animal, i.c.v.) effectively reduced the vasopressin-induced elevation of catecholamines. On the other hand, [5-dimethylamino-1-{4-(2-methylbenzoylamino)benzoyl}-2,3,4,5-tetrahydro-1 H-benzazepine], a selective vasopressin V 2 receptor antagonist (5 and 10 nmol/animal, i.c.v.), had no effect on the vasopressin-induced elevation of catecholamines. The vasopressin-induced elevation of catecholamines was abolished by indomethacin, an inhibitor of cyclooxygenase (1.2 μmol/animal, i.c.v.). These results suggest that the vasopressin activates the central sympatho-adrenomedullary outflow by brain vasopressin V 1 receptor- and cyclooxygenase-dependent mechanisms in rats.

Roles of brain prostaglandin E 2 and thromboxane A 2 in the activation of the central sympatho-adrenomedullary outflow in rats

We examined the effects of centrally administered active metabolites of the arachidonic acid cascade on activation of the central sympatho-adrenomedullary outflow using urethane-anaesthetized rats. Intracerebroventricularly (i.c.v.) administered prostaglandin E 2 (0.3 nmol/animal) significantly elevated plasma levels of noradrenaline while levels of adrenaline were not affected. Prostaglandin D 2, prostaglandin F 2α and prostaglandin I 2 at the same dose (0.3 nmol/animal, i.c.v.) had no effect on plasma levels of either catecholamine. Thromboxane A 2 mimetic, 7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo [2.2.1]hept-2-yl], [1 S-[1α,2α( Z),3β(1 E,3 S),4α]]-5-heptenoic acid (I-BOP) (5 and 10 pmol/animal) microinjected into the paraventricular nucleus of the hypothalamus significantly elevated plasma levels of adrenaline, but had little effect on plasma levels of noradrenaline. The I-BOP-induced (10 pmol/animal) elevation of plasma adrenaline levels was abolished by (+)-(1 R,2 R,3 S,4 S)-(5 Z)-7-(3-[4- 3H]-phenylsulphonyl-aminobicyclo[2.2.1]hept-2-yl)hept-5-enoic acid sodium salt [(+)-S-145] (a blocker of thromboxane A 2 receptors) [625 nmol (250 μg)/animal, i.c.v.]. These results suggest that brain prostaglandin E 2 and thromboxane A 2 are respectively involved in the activation of the central sympathetic and adrenomedullary outflow in rats.

Role of brain arachidonic acid cascade on central CRF 1 receptor-mediated activation of sympatho-adrenomedullary outflow in rats

The present experiments were designed to characterize the mechanisms involved in the corticotropin releasing factor (CRF)-induced activation of central sympatho-adrenomedullary outflow in rats. Intracerebroventricularly (i.c.v.) administered CRF and urocortin (0.5, 1.5 and 3.0 nmol/animal) effectively and dose-dependently elevated plasma levels of adrenaline and noradrenaline, and the effect of urocortin was almost the same as that of CRF. The elevation of catecholamines induced by CRF and urocortin (1.5 nmol/animal) was reduced by CP-154,526(butyl-ethyl-{2,5-dimethyl-7-(2,4,6trimethylphenyl)-7 H-pyrrolo [2,3- d] pyrimidin-4-yl]amine), a selective CRF 1 receptor antagonist, in a dose dependent manner (1.2 and/or 2.4 μmol/animal, i.c.v.), and abolished by indomethacin (1.2 μmol/animal, i.c.v.), an inhibitor of cyclooxygenase. Furegrelate (1.8 μmol/animal, i.c.v.), an inhibitor of thromboxane A 2 synthase, abolished the CRF-induced elevation of adrenaline, but had no effect on the evoked release of noradrenaline. These results suggest that activation of brain CRF 1 receptor facilitates the central sympathetic and adrenomedullary outflow in distinct central pathways in rats: brain thromboxane A 2 is involved in the central adrenomedullary outflow; an active metabolite of arachidonic acid other than thromboxane A 2 (probably prostaglandin E 2) may be involved in the central sympathetic outflow.

Brain phospholipase A 2-arachidonic acid cascade is involved in the activation of central sympatho-adrenomedullary outflow in rats

The present experiments were designed to explore the role of the brain phospholipase A 2-arachidonic acid cascade in the activation of central sympatho-adrenomedullary outflow in rats, using melittin (an activator of phospholipase A 2) and arachidonic acid. Intracerebro-ventricularly administered melittin (2.5, 10, and 25 μg/animal) or arachidonic acid (75, 150, 300 μg/animal) effectively and dose dependently elevated plasma levels of adrenaline and noradrenaline. The elevation of both catecholamines induced by melittin (10 μg/animal) was abolished by centrally administered mepacrine (an inhibitor of phospholipase A 2), but not by neomycin (an inhibitor of phospholipase C). However, mepacrine had no effect on the increase induced by arachidonic acid (150 μg/animal). Indomethacin (an inhibitor of cyclooxygenase) abolished all responses induced by melittin and arachidonic acid. Furegrelate (an inhibitor of thromboxane A 2 synthase) abolished the elevation of adrenaline induced by melittin and arachidonic acid, but had no effect on the elevation of noradrenaline induced by these compounds. These results suggest that activation of the brain phospholipase A 2-arachidonic acid cascade facilitates the central sympatho-adrenomedullary outflow in rats. Brain thromboxane A 2 is involved in the activation of central adrenomedullary outflow and an active metabolite of arachidonic acid other than thromboxane A 2 may be involved in activation of the central sympathetic outflow.

P-449 - The inhibitory role of melatonin released from the pineal gland in the centrally mediated sympatho-adrenomedullary outflow in rats

P-449 - The inhibitory role of melatonin released from the pineal gland in the centrally mediated sympatho-adrenomedullary outflow in rats

Brain phospholipase A2-arachidonic acid cascade is involved in the activation of central sympatho-adrenomedullary outflow in rats

Brain phospholipase A2-arachidonic acid cascade is involved in the activation of central sympatho-adrenomedullary outflow in rats

Melatonin inhibits the central sympatho-adrenomedullary outflow in rats.

Central effects of melatonin on the sympatho-adrenomedullary outflow were investigated in urethane-anesthetized rats. In the intact animals, intracerebroventricularly (i.c.v.) administered interleukin-1beta (IL-1beta) (100 ng/animal) slightly, but significantly, elevated the plasma level of noradrenaline (NA), but not the level of adrenaline (Ad). Melatonin (100 microg/animal, i.c.v.) did not modulate the effects of IL-1beta on plasma levels of catecholamines. In the pinealectomized animals, however, the same dose of IL-1beta markedly elevated plasma levels of both Ad and NA, and the elevation of Ad was more potent than that of NA. In these pinealectomized animals, the serum level of melatonin was significantly lower than that in the sham-operated control animals. Furthermore, the IL-1beta-induced elevations of plasma catecholamines in these pinealectomized animals were attenuated by i.c.v. administered melatonin. These results suggest that melatonin plays an inhibitory role in the central regulation of sympatho-adrenomedullary outflow in rats.

Melatonin Inhibits the Central Sympatho-adrenomedullary Outflow in Rats

Central effects of melatonin on the sympatho-adrenomedullary outflow were investigated in urethane-anesthetized rats. In the intact animals, intracerebroventricularly (i.c.v.) administered interleukin-lβ (IL-1β) (100 ng/animal) slightly, but significantly, elevated the plasma level of noradrenaline (NA), but not the level of adrenaline (Ad). Melatonin (100 μg/animal, i.c.v.) did not modulate the effects of IL-lβ on plasma levels of catecholamines. In the pinealectomized animals, however, the same dose of IL-1β markedly elevated plasma levels of both Ad and NA, and the elevation of Ad was more potent than that of NA. In these pinealectomized animals, the serum level of melatonin was significantly lower than that in the sham-operated control animals. Furthermore, the IL-1β-induced elevations of plasma catecholamines in these pinealectomized animals were attenuated by i.c.v. administered melatonin. These results suggest that melatonin plays an inhibitory role in the central regulation of sympatho-adrenomedullary outflow in rats.

Recombinant interleukin-1β inhibits gastric acid secretion by activation of central sympatho-adrenomedullary outflow in rats

The inhibitory mechanism of gastric acid secretion induced by human recombinant interleukin-1β was investigated in bilaterally vagotomized, urethane-anesthetized rats. Intracerebroventricular administration of interleukin-1β (10, 50 and 100 ng/animal) dose dependently inhibited the gastric acid secretion induced by electrical stimulation of the vagus nerve at 3 Hz. Inhibition of gastric acid secretion induced by interleukin-1β (50 ng/animal) was abolished both by splanchnectomy and by phentolamine (5 mg/kg i.m.). Greater splanchnic nerves ramify into the adrenal branch and gastric sympathetic preganglionic branch. The interleukin-1β (50 ng/animal)-induced inhibition was also abolished by intracerebroventricular pretreatment with indomethacin (500 μg/animal), while pretreatment with the same dose of this reagent by the intraperitoneal route was without effect. These results suggest that centrally administered interleukin-1β induces a prostaglandin-mediated central excitation of the sympatho-adrenomedullary system, and the resultant activation of gastric α-adrenoceptors inhibits the vagally stimulated gastric acid secretion in rats.