Effects of indirectly acting 5-HT receptor agonists on circulating melatonin levels in rats (original) (raw)
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Evidence for 5-HT1A receptor control of pineal melatonin concentrations in the rat
European Neuropsychopharmacology, 1998
The effect of some serotonin agonists on day and night-time melatonin in the pineal gland was investigated in male rats. Dose dependent increases in nocturnal melatonin concentrations were observed for all serotonin agonists investigated. Statistically significant increases were observed only for D-fenfluramine (20 mg / kg) and the full 5-HT agonists S(1)-20499 (10 mg / kg, 20 mg / kg) and 1A flesinoxan (20 mg / kg). Both paroxetine and D-fenfluramine dose dependently increased daytime pineal melatonin, but only for D-fenfluramine (20 mg / kg) was there a statistically significant increase. The data suggest that acute increases in synaptic serotonin concentrations can be used to manipulate day-or night-time melatonin. Data suggests an influence of the 5-HT receptor subtype in 1A mediating nocturnal melatonin concentrations, perhaps through a functional coupling to b-adrenoceptors on the pineal gland.
Neuroscience Letters, 1989
The interaction between rnelatonin and two 5-hydroxytryptamine (5-HT2) compounds was studied on sleep patterns in rats. Administration of the 5-HT2 receptor antagonist ritanserin (0.63 mg/kg, i.p.) resulted in a significant increase of deep slow wave sleep (SWS2) and a decrease of paradoxical sleep (PS). The 5-HT2 receptor agonist DOM (l-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane) (0.63 mg/kg, i.p.) produced a significant reduction of both SWS2 and PS. Melatonin (1 mg/kg, i.p.) alone did not alter sleep but counteracted the sleep effects induced by ritanserin as well as DOM. It is proposed that melatonin modulates the sensitivity of 5-HT2 receptor-mediated sleep response probably by an indirect route. . Therefore, the differential sleep effects of ritanserin during the light and dark periods in the rat could be related to the circadian variations in melatonin production. In order to test this hypothesis, sleep--wakefulness patterns were analyzed after pharmacological blockade or stimulation of 5-HT2 receptors by ritanserin and DOM, respectively in melatonin-pretreated rats.
A brief review about melatonin, a pineal hormone
2018
Melatonin is a ubiquitous molecule in nature, being locally synthesized in several cells and tissues, besides being a hormone that is centrally produced in the pineal gland of vertebrates, particularly in mammals. Its pineal synthesis is timed by the suprachiasmatic nucleus, that is synchronized to the light-dark cycle via the retinohypothalamic tract, placing melatonin synthesis at night, provided its dark. This unique trait turns melatonin into an internal synchronizer that adequately times the organism's physiology to the daily and seasonal demands. Besides being amphiphilic, melatonin presents specific mechanisms and ways of action devoted to its role as a time-giving agent, being widely spread in the organism. The present review aims to focus on melatonin as a pineal hormone with specific mechanisms and ways of action, besides presenting the clinical syndromes related to its synthesis and/or function disruptions. Arch Endocrinol Metab. 2018;62(4):472-9
Indian journal of biochemistry & biophysics, 2008
Melatonin (N-acetyl-5-methoxytryptamine) was first purified and characterized from the bovine pineal gland extract by Aron Lerner and co-workers in 1958. Since then, a plethora of information has piled up on its biosynthesis, metabolism, time-bound periodicity, physiological and patho-physiological functions, as well as its interactions with other endocrine or neuro-endocrine organs and tissues in the body. Melatonin has wide range of applications in physiology and biomedical fields. In recent years, a significant progress has been made in the understanding mechanism of its actions at the cellular and molecular levels. Consistent efforts have uncovered the mystery of this indoleamine, and demonstrated its role in regulation of a large as well as diverse body functions in different groups of animals in general, and in humans in particular. Current review, in commemoration of 50 years of discovery of melatonin, while revisiting the established dogmas, summarizes current information on...
Journal of Pineal Research, 1988
The presence of type-I1 thyroxine 5'-deiodinase (5'-D) activity in rat pineal gland has been previously described. In the present paper, 5'-D activity, N-acetyltransferase (NAT) activity, and melatonin content were measured in the same rat pineal. Each of these constituents exhibits a nocturnal increase with peak values at 0100 h for melatonin (1.20 4 0.12 ndgland) and at 0300 h for both 5'-D (39.5 t 11.9 fmol/gland/h) and NAT (8.38 t 1.04 nmol/gland/h) activities. In vivo treatment with iopanoic acid (IOP) completely prevented the nocturnal increase in 5'-D activity (14.1 4 2.6 fmoVgIand/h at 0300 h) with no modification in either the NAT activity or melatonin content. Thyroidectomy greatly enhanced the 5'-D activity during the dark period (102.9 4 10.2 vs. 31.6 ? 4.2 fmol/gland/h), reaching a peak at 0200 h; thyroidectomy, however, did not affect daytime pineal 5'-D activity (3.1 1 2 0.78 vs.
Melatonin: New Places in Therapy
Bioscience Reports, 2007
The fact that the full extent of the function of the pineal gland has not yet been elucidated, has stimulated melatonin research worldwide. This review introduces melatonin’s mechanism of action, direct and indirect antioxidant actions as well as the antioxidant properties of its metabolites, 6-hydroxymelatonin (6-OHM) and N-acetyl-N-formyl-5-methoxykynurenamine (AFMK). At present the mechanism of action is proposed to be receptor-, protein- and nonprotein-mediated. From its popular role in the treatment of jetlag, melatonin is now implicated in the reduction of oxidative stess, both as a free radical scavenger and antioxidant. Melatonin’s direct scavenging action in respect of the following will be discussed: superoxide anions, hydrogen peroxide, hydroxyl radicals, singlet oxygen, peroxy radicals and nitric oxide/peroxy nitrite anions. In addition melatonin also possesses indirect antioxidant activity and the role of its metabolites, AFMK and 6-OHM will be presented. It is these free radical scavenging and antioxidant properties of melatonin that has shifted the focus from that of merely strengthening circadian rhythms to that of neuroprotectant: a new place in therapy.