Effects of Melatonin on Blood Pressure in Stress‐induced Hypertension in Rats

Abstract

Melatonin, acting through its receptors, is involved in numerous physiological processes, including blood pressure (BP) regulation. In present study, the effect of melatonin inhibition on stress-induced hypertension was investigated. The hypertensive model consisted of male Sprague-Dawley rats subjected to electrical foot-shock combined with noise. Microinjection of melatonin (0.1 and 1.0 mmol/L) into the anterior hypothalamic area (AHA) produced a fall in BP in nomortensive rats and stress-induced hypertensive rats (SIHR). Luzindole (10 mmol/L), a competitive antagonist of melatonin MT1 and MT2 receptors, almost completely abolished the depressor effect of melatonin, the MT2 receptor-specific antagonist 4-phenyl-2-propionamidotetralin (10 mmol/L) partially blocked (by approximately 60%) the depressor effect of melatonin, whereas the MT3 receptor-selective antagonist prazosin (10 mmol/L) failed to antagonize the effects of melatonin. Brain microdialysis was performed in the AHA and the rostral ventrolateral medulla (RVLM). Melatonin and amino acids in the dialysate samples collected were detected by high-performance liquid chromatography combined with fluorescence detection. The results indicated that melatonin concentrations in the AHA were reduced in SIHR. Microinjection of melatonin into the AHA decreased glutamate release and increased GABA and taurine release in the RVLM, which were paralleled by a decrease in arterial pressure. The mRNA expression of MT2 in the AHA of SIHR was higher than that in normotensive control rats, whereas there was no significant difference in MT1 mRNA expressin between the two groups. The results of the present study suggest that both a decrease of melatonin and an increase in the MT2 receptor in the AHA are involved in the manifestation of stress-induced hypertension. Both MT1 and MT2 receptors participated in the antihypertensive effect of melatonin in the AHA. The antihypertensive effect of melatonin was related to the decreases in the excitatory amino acid glutamate and increases in the inhibitory amino acids taurine and GABA in the RVLM.

Design of Novel Melatonin Analogs for the Reduction of Intraocular Pressure in Normotensive Rabbits

“…The effects of INS48848 were completely blocked by prazosin, an antagonist of MT 3 melatonin receptors (Paul et al, 1999;Pintor et al, 2003;Xia et al, 2008), and were potently inhibited by luzindole, a nonselective antagonist of melatonin receptors (Pintor et al, 2003). However, DH97, an MT 2 receptor antagonist (Chen et al, 2005;Alarma-Estrany et al, 2007;Mendoza-Vargas et al, 2009), had little effect against INS48848.…”

Melatonin secretion is impaired in women with preeclampsia and an abnormal circadian blood pressure rhythm

“…Moreover, in animal models melatonin has been proven as a pathogenetic link in the development of stress induced and metabolic syndromerelated hypertension. 43,44 Therefore, it is probable that the significant association of melatonin with circadian rhythm of BP is observed in any forms of hypertension.…”

The Presence and Localization of Melatonin Receptors in the Rat Aorta

“…In rats, pinealectomy results in the development of hypertension (Karppanen et al 1973;Zanoboni et al 1978) that in turn can be lowered by MEL treatment (Holmes and Sugden 1976). Likewise, MEL reduced BP in spontaneously hypertensive rats (Pechanova et al 2007), L-NAME (N(G)-nitro-L-arginine-methyl ester)-treated hypertensive rats (Paulis et al 2010), and in rats hypertensive as a result of high fructose diet (Leibowitz et al 2008) or due to stress (Xia et al 2008).…”