Role of brain prostanoids in glucagon-like peptide-1-induced central activation of sympatho-adrenomedullary outflow in rats.

1. The aim of the present study was to characterize the source of plasma catecholamines induced by centrally administered glucagon-like peptide-1 (GLP-1), with regard to brain prostanoids, in urethane-anaesthetized rats. 2. Glucagon-like peptide-1 and other compounds were administered intracerebroventricularly (i.c.v.) and blood samples were collected via a cannula inserted into the femoral artery. Catecholamines were extracted from plasma with activated alumina and were assayed electrochemically using high-performance liquid chromatography. 3. At 0.3, 1.0 and 3.0 nmol/animal, GLP-1 dose-dependently elevated plasma levels of noradrenaline and adrenaline and the 1.0 nmol GLP-1-induced response was dose-dependently reduced by 5 and 10 nmol/animal exendin (5-39), a selective GLP-1 receptor antagonist. The GLP-1-induced elevation of concentrations of both catecholamines was abolished by 1.2 micromol/animal indomethacin, an inhibitor of cyclo-oxygenase, whereas 1.2 micromol/animal baicalein, a lipoxygenase inhibitor, had no effect. 4. Both furegrelate (1.8 micromol/animal; an inhibitor of thromboxane A(2) synthase) and (+)S-145 (625 nmol/animal; a thromboxane A(2) receptor antagonist) attenuated the GLP-1-induced increases in plasma adrenaline concentrations, but had no effect on the increases in plasma noradrenaline. The GLP-1-induced increase in plasma adrenaline concentrations was abolished by acute bilateral adrenalectomy, but the procedure had no effect on increases in plasma noradrenaline. 5. These results suggest that, in rats, centrally administered GLP-1 induces the secretion of adrenaline from the adrenal medulla by brain thromboxane A(2)-mediated mechanisms, whereas the peptide evokes the release of noradrenaline from sympathetic nerves by brain prostanoids via mechanisms other than those mediated by thromboxane A(2).

Centrally administered N-methyl-d-aspartate evokes the adrenal secretion of noradrenaline and adrenaline by brain thromboxane A2-mediated mechanisms in rats.

Plasma adrenaline mainly originated from adrenaline-containing cells in the adrenal medulla, while plasma noradrenaline reflects the release from sympathetic nerves in addition to the secretion from noradrenaline-containing cells in the adrenal medulla. The present study was undertaken to characterize the source of plasma catecholamines induced by centrally administered N-methyl-d-aspartate with regard to the brain prostanoid, using urethane-anesthetized rats. Intracerebroventricularly (i.c.v.) administered N-methyl-d-aspartate (1.0, 5.0, 10.0 nmol/animal) dose-dependently elevated plasma levels of noradrenaline and adrenaline. The N-methyl-d-aspartate (5.0 nmol/animal, i.c.v.)-induced elevation of both catecholamines was reduced by dizocilpine maleate (5 nmol/animal, i.c.v.), a non-competitive N-methyl-d-aspartate receptor antagonist. Indomethacin (0.6 and 1.2 micromol/animal, i.c.v.), an inhibitor of cyclooxygenase, dose-dependently reduced the N-methyl-d-aspartate (5.0 nmol/animal, i.c.v.)-induced elevation of both catecholamines. The N-methyl-d-aspartate-induced response was dose-dependently attenuated by furegrelate (0.9 and 1.8 micromol/animal, i.c.v.), an inhibitor of thromboxane A2 synthase. Furthermore, the acute bilateral adrenalectomy abolished the N-methyl-d-aspartate-induced responses, indicating that the source of increase in plasma noradrenaline evoked by N-methyl-d-aspartate is due to secretion from the adrenal gland and not due to release from sympathetic nerve terminals. These results suggest that centrally administered N-methyl-d-aspartate induces the secretion of noradrenaline and adrenaline from adrenal medulla by the brain thromboxane A2-mediated mechanisms 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-gamma 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 alpha adrenoceptor antagonist) [125 and 250 microg (0.33 and 0.66 micromol)/animal], Heat (a selective alpha(1) adrenoceptor antagonist) [10 and 30 microg (30 and 90 nmol)/animal, i.c.v.] and clonidine (a selective alpha(2) adrenoceptor agonist) [100 microg (0.375 micromol)/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 alpha(2) adrenoceptor antagonist) [10 and 30 microg (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 beta adrenoceptor antagonist) [125 and 250 microg (0.4 and 0.8 micromol)/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 alpha(1) and beta adrenoceptors in the brain, and that of plasma adrenaline is mediated by an activation of alpha(1) adrenoceptors in the brain. Furthermore, central alpha(2) adrenoceptors are involved in modulating the CRF-induced elevation of both plasma catecholamines.