Prostaglandin E2 receptor EP3 subtype in the paraventricular hypothalamic nucleus mediates corticotropin-releasing factor-induced elevation of plasma noradrenaline levels in rats

Targeting Hypertension: Superoxide Anions are Involved in Apelininduced Long-term High Blood Pressure and Sympathetic Activity in the Paraventricular Nucleus

AIM

To determine whether apelin in paraventricular nucleus (PVN) can be a therapeutic target for hypertension.

BACKGROUND

Apelin is a specific endogenous ligand of orphan G protein-coupled receptor APJ.

OBJECTIVE

This study was designed to determine how apelin chronically regulates sympathetic nerve activity and blood pressure in PVN of rats.

METHODS

Apelin and APJ antagonist F13A were infused into PVN with osmotic minipumps. The NAD(P)H oxidase activity and superoxide anions levels in PVN of rats were determined by chemiluminescence.

RESULTS

Infusion of apelin into PVN of Wistar-Kyoto (WKY) rats induced chronic increases in systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), plasma norepinephrine (NE) level, maximal depressor response to hexamethonium (Hex), NAD(P)H oxidase activity, superoxide anions levels, and Nox4 expression. Infusion of F13A into PVN of spontaneously hypertensive rats (SHRs) caused chronic decreases in SBP, DBP, MAP, plasma NE level, maximal depressor response to Hex, NAD(P)H oxidase activity, and superoxide anions levels. Hex, a sympathetic ganglion blocker, inhibited apelin-induced increases in SBP, DBP and MAP. SOD overexpression in PVN of SHRs inhibited the apelin-induced increase in SBP, DBP, MAP, plasma NE level, and maximal depressor response to Hex. PVN Nox4 knockdown also attenuated the apelin-induced increase in SBP, DBP, MAP, plasma NE level, and maximal depressor response to Hex. Chronic injection of F13A into PVN reduced fibrosis of renal artery, thoracic aorta, and heart in SHRs.

CONCLUSION

These results demonstrated that in PVN apelin induced long-term high blood pressure and sympathetic activity via increasing oxidative stress.

Thromboxane A2 in the paraventricular hypothalamic nucleus mediates glucoprivation-induced adrenomedullary outflow

Glucoprivation stimulates a rapid sympathetic response to release and/or secrete catecholamines into the bloodstream. However, the central regulatory mechanisms involving adrenoceptors and prostanoids production in the paraventricular hypothalamic nucleus (PVN) that are responsible for the glucoprivation-induced elevation of plasma catecholamines are still unresolved. In this study, we aimed to clarify whether glucoprivation-induced activation of noradrenergic neurons projecting to the PVN can induce α- and/or β-adrenergic receptor activation and prostanoids production in the PVN to elevate plasma catecholamine levels. We examined the effects of α- and β-adrenergic receptor antagonists, a cyclooxygenase inhibitor, a thromboxane A synthase inhibitor, and a PGE₂ subtype EP₃ receptor antagonist on intravenously administered 2-deoxy-D-glucose (2-DG)-induced elevation of noradrenaline in the PVN and plasma levels of catecholamine in freely moving rats. In addition, we examined whether intravenously administered 2-DG can increase prostanoids levels in the PVN microdialysates. Intracerebroventricular (i.c.v.) pretreatment with phentolamine (a non-selective α-adrenergic receptor antagonist) suppressed the 2-DG-induced increase in the plasma level of adrenaline, whereas i.c.v. pretreatment with propranolol (a non-selective β-adrenergic receptor antagonist) suppressed the 2-DG-induced elevation of the plasma level of noradrenaline. I.c.v. pretreatment with indomethacin (a cyclooxygenase inhibitor) and furegrelate (a thromboxane synthase inhibitor) attenuated the 2-DG-induced elevations of both noradrenaline and adrenaline levels. Furthermore, 2-DG administration elevated the thromboxane B₂ level, a metabolite of thromboxane A₂ in PVN microdialysates. Our results suggest that glucoprivation-induced activation of α- and β-adrenergic receptor in the brain including the PVN and then thromboxane A₂ production in the PVN, which are essential for the 2-DG-induced elevations of both plasma adrenaline and noradrenaline levels.