Sympathoexcitation of moxonidine in the caudal ventrolateral medulla is dependent on I1-imidazoline receptors in anesthetized rats

Peripheral versus central effect of intravenous moxonidine on rat carotid sinus baroreflex-mediated sympathetic arterial pressure regulation

AIMS

Moxonidine is a centrally acting antihypertensive agent with a selectivity to I₁-imidazoline receptors higher than that to α₂-adrenergic receptors. The present study aimed to quantify a peripheral effect of moxonidine on carotid sinus baroreflex-mediated sympathetic arterial pressure (AP) regulation separately from its central effect.

MAIN METHODS

In eight anesthetized Wistar rats, changes in efferent sympathetic nerve activity (SNA) and AP in response to a carotid sinus pressure input were compared before and during an intravenous administration of moxonidine (100μgkg^-1 bolus followed by a continuous infusion at 200μg·kg^-1·h^-1).

KEY FINDINGS

Moxonidine significantly narrowed the range of the AP response (55.3±5.8 to 39.1±6.1mmHg, P<0.05) without changing the minimum AP (77.2±6.4 to 80.7±5.1mmHg, not significant). In the neural arc, moxonidine reduced the minimum SNA (56.6±5.9 to 29.7±6.2%, P<0.05) without affecting the range of the SNA response (45.3±5.5 to 40.2±5.0%, not significant). In the peripheral arc, moxonidine increased the intercept (3.0±8.5 to 51.1±7.2mmHg, P<0.01) and reduced the slope (1.28±0.06 to 0.92±0.15mmHg/%, P<0.05).

SIGNIFICANCE

Moxonidine increased AP at any given SNA, suggesting that the peripheral vasoconstrictive effect is stronger than generally recognized. The peripheral vasoconstrictive effect of moxonidine may partly offset the vasodilatory effect attained by centrally-mediated sympathoinhibition.

Centrally acting drug moxonidine decreases reactive oxygen species via inactivation of the phosphoinositide-3 kinase signaling in the rostral ventrolateral medulla in hypertensive rats

OBJECTIVE

Centrally acting antihypertensive action of moxonidine is a result of activation of Imidazoline-1 receptor (I1R) in the rostral ventrolateral medulla (RVLM). Hypertension shows an increase in reactive oxygen species (ROS) in the RVLM. The present objective was to determine the phosphoinositide-3 kinase (PI3K) signaling pathway involved in the effect of moxonidine on ROS generation in the RVLM of spontaneously hypertensive rat (SHR).

METHODS

Wistar-Kyoto rats and SHR received intracisternal infusion (2 weeks) of tested agents which were subjected to subsequent experiments. In-situ ROS in the RVLM was evaluated by the oxidative fluorescence dye. Western blot and PCR analysis were performed to detect the expression levels of PI3K signaling pathway. Lentivirus was injected bilaterally into the RVLM for silencing PI3K signaling.

RESULTS

ROS production in the RVLM was dose-dependently reduced in SHRs treated with infusion of moxonidine (20 nmol/day), which was prevented by the I1R antagonist efaroxan but not by the α2-adrenoceptor antagonist yohimbine. Moxonidine pretreatment significantly blunted cardiovascular sensitivity to injection of tempol (5 nmol) or angiotensin II (10 pmol) into the RVLM in SHR. Expression levels of PI3K/Akt, nuclear factor kappa-B (NFκB), NADPHase (NOX4), and angiotensin type I receptor (AT1R) in the RVLM were markedly decreased in SHR treated with moxonidine. Infection of lentivirus containing PI3K shRNA in the RVLM effectively prevented effects of moxonidine on cardiovascular activity and expression levels of Akt, NFκB, NOX4, and AT1R.

CONCLUSION

The centrally antihypertensive drug moxonidine decreases ROS production in the RVLM through inactivation of the PI3K/Akt signaling pathway in hypertension.

Modulation of stress by imidazoline binding sites: implications for psychiatric disorders

In this review, we present evidence for the involvement of imidazoline binding sites (IBS) in modulating responses to stress, through central control of monoaminergic and hypothalamo-pituitary-adrenal (HPA) axis activity. Pharmacological and physiological evidence is presented for differential effects of different IBS subtypes on serotoninergic and catecholaminergic pathways involved in control of basal and stress-stimulated HPA axis activity. IBS ligands can modulate behavioural and neuroendocrine responses in animal models of stress, depression and anxiety, and a body of evidence exists for alterations in central IBS expression in psychiatric patients, which can be normalised partially or fully by treatment with antidepressants. Dysfunction in monoaminergic systems and the HPA axis under basal and stress-induced activation has been extensively reported in psychiatric illnesses. On the basis of the literature, we suggest a potential therapeutic role for selective IBS ligands in the treatment of depression and anxiety disorders.