N-Acetyltryptamine

Effect of Melatonin and 5-Methoxycarbonylamino-N-Acetyltryptamine on the Intraocular Pressure of Normal and Glaucomatous Mice.[Pubmed:26941171]

J Pharmacol Exp Ther. 2016 May;357(2):293-9.

Melatonin is a neurohormone that is produced not only by the pineal gland but also by several ocular structures. One of the main physiologic roles of melatonin is the reduction of intraocular pressure (IOP). Using both control C57BL/6J and glaucomatous DBA/2J mice as well as TonoLab tonometry, this study evaluated the effect of melatonin and 5-methoxycarbonylamino-N-Acetyltryptamine (5-MCA-NAT) when glaucomatous pathology was fully established and compared pharmacological behavior in treated mice versus control mice. In addition, 5-MCA-NAT was tested to determine its effects on ameliorating increased IOP in a glaucoma model. The results demonstrate that melatonin and 5-MCA-NAT can reduce IOP in a concentration-dependent manner. The EC50values for melatonin in control and glaucomatous animals were 34microM and 50microM, respectively. Interestingly, melatonin decreased IOP in 19.4% +/- 3.7% and 32.6% +/- 6.0% of control and glaucomatous mice, respectively, when the animals were studied at age 12 months. 5-MCA-NAT reduced IOP in the same manner and was able to stop IOP progression in glaucomatous mice. Use of melatonin receptor antagonists showed that hypotensive effects were blocked by the MT2receptor antagonists luzindole and 4-phenyl-2-propionamidotetralin in the case of melatonin and by only 4-phenyl-2-propionamidotetralin in the case of 5-MCA-NAT. In conclusion, melatonin and 5-MCA-NAT can effectively reduce IOP in a glaucoma model, and their hypotensive effects are more profound in the glaucoma model than in control animals.

Melatonin and its analog 5-methoxycarbonylamino-N-acetyltryptamine potentiate adrenergic receptor-mediated ocular hypotensive effects in rabbits: significance for combination therapy in glaucoma.[Pubmed:23591996]

J Pharmacol Exp Ther. 2013 Jul;346(1):138-45.

Melatonin is currently considered a promising drug for glaucoma treatment because of its ocular hypotensive and neuroprotective effects. We have investigated the effect of melatonin and its analog 5-methoxycarbonylamino-N-Acetyltryptamine, 5-MCA-NAT, on beta(2)/alpha(2A)-adrenergic receptor mRNA as well as protein expression in cultured rabbit nonpigmented ciliary epithelial cells. Quantitative polymerase chain reaction and immunocytochemical assays revealed a significant beta(2)-adrenergic receptor downregulation as well as alpha(2A)-adrenergic receptor up-regulation of treated cells (P < 0.001, maximal significant effect). In addition, we have studied the effect of these drugs upon the ocular hypotensive action of a nonselective beta-adrenergic receptor (timolol) and a selective alpha(2)-adrenergic receptor agonist (brimonidine) in normotensive rabbits. Intraocular pressure (IOP) experiments showed that the administration of timolol in rabbits pretreated with melatonin or 5-MCA-NAT evoked an additional IOP reduction of 14.02% +/- 5.8% or 16.75% +/- 5.48% (P < 0.01) in comparison with rabbits treated with timolol alone for 24 hours. Concerning brimonidine hypotensive action, an additional IOP reduction of 29.26% +/- 5.21% or 39.07% +/- 5.81% (P < 0.001) was observed in rabbits pretreated with melatonin or 5-MCA-NAT when compared with animals treated with brimonidine alone for 24 hours. Additionally, a sustained potentiating effect of a single dose of 5-MCA-NAT was seen in rabbits treated with brimonidine once daily for up 4 days (extra IOP decrease of 15.57% +/- 5.15%, P < 0.05, compared with brimonidine alone). These data confirm the indirect action of melatoninergic compounds on adrenergic receptors and their remarkable effect upon the ocular hypotensive action mainly of alpha(2)-adrenergic receptor agonists but also of beta-adrenergic antagonists.

Tryptamine 5-hydroxylase-deficient Sekiguchi rice induces synthesis of 5-hydroxytryptophan and N-acetyltryptamine but decreases melatonin biosynthesis during senescence process of detached leaves.[Pubmed:21884550]

J Pineal Res. 2012 Mar;52(2):211-6.

Melatonin biosynthesis was examined in Sekiguchi mutant rice lacking functional tryptamine 5-hydroxylase (T5H) activity, which is the terminal enzyme for serotonin biosynthesis in rice. During senescence process, the leaves of Sekiguchi mutant rice produced more tryptamine and N-Acetyltryptamine compared with the wild-type Asahi leaves. Even though T5H activity is absent, Sekiguchi leaves produce low levels of serotonin derived from 5-hydroxytryptophan, which was found to be synthesized during senescence process. Accordingly, both rice cultivars exhibited similar levels of N-acetylserotonin until 6 days of senescence induction; however, only Asahi leaves continued to accumulate N-acetylserotonin after 6 days. In contrast, a large amount of N-Acetyltryptamine was accumulated in Sekiguchi leaves, indicating that tryptamine was efficiently utilized as substrate by the rice arylalkylamine N-acetyltransferase enzyme. An increase in N-Acetyltryptamine in Sekiguchi had an inhibitory effect on synthesis of melatonin because little melatonin was produced in Sekiguchi leaves at 6 days of senescence induction, even in the presence of equivalent levels of N-acetylserotonin in both cultivars. The exogenous treatment of 0.1 mmN-Acetyltryptamine during senescence process completely blocked melatonin synthesis.

Molecular and cellular pharmacological properties of 5-methoxycarbonylamino-N-acetyltryptamine (MCA-NAT): a nonspecific MT3 ligand.[Pubmed:20210850]

J Pineal Res. 2010 Apr;48(3):222-9.

5-Methoxycarbonylamino-N-Acetyltryptamine (MCA-NAT) has been initially described as a ligand at non MT(1), non MT(2) melatonin binding site (MT3) selective versus MT(1) and MT(2), two membrane melatonin receptors. MCA-NAT activity has been reported by others in different models, in vivo, particularly in the intra-ocular pressure (IOP) models in rabbits and monkeys. Its activity was systematically linked to either MT3 or to a new, yet unknown, melatonin receptor. In this article, the melatonin receptor pharmacology of MCA-NAT is described. MCA-NAT has micromolar range affinities at the melatonin receptors MT(1) and MT(2), while in functional studies, MCA-NAT proved to be a powerful MT(1)/MT(2) partial agonist in the sub-micromolar range. These data strongly suggest that MCA-NAT actions might be mediated by these receptors in vivo. Finally, as described by others, we show that MCA-NAT is unable to elicit any type of receptor-like functional responses from Chinese hamster ovary cells over-expressing quinone reductase 2, the MT3.

Melatonin receptors: are there multiple subtypes?[Pubmed:7762083]

Trends Pharmacol Sci. 1995 Feb;16(2):50-6.

There is now evidence for more than one site of action for the hormone melatonin (N-acetyl-5-methoxy-tryptamine). Recent pharmacological and molecular advances are providing the tools to address the characterization of melatonin receptor subtypes. The development of novel melatonin receptor agonists and antagonists, high-affinity radioligands, quantitative bioassays, and the recent cloning of melatonin receptors are furthering our understanding of native and recombinant melatonin receptors. In this article, Margarita Dubocovich discusses the properties of melatonin receptors, and the basis for their classification into at least two subtypes, the ML1 and ML2.

Arylalkylamine (serotonin) N-acetyltransferase assay using high-performance liquid chromatography with fluorescence or electrochemical detection of N-acetyltryptamine.[Pubmed:2327568]

Anal Biochem. 1990 Feb 1;184(2):228-34.

A sensitive, rapid, and economical method has been developed for determination of serotonin N-acetyltransferase activity from a variety of enzyme sources. The assay is based upon separation and detection of N-Acetyltryptamine formed from tryptamine and acetyl coenzyme A, by means of high-performance liquid chromatography with either electrochemical or fluorometric detection. The limit of sensitivity with both detection methods is less than 20 pmol of N-Acetyltryptamine formed per sample. A method for synthesis of N-Acetyltryptamine, used as an external standard in the assay, is described.

Luzindole (N-0774): a novel melatonin receptor antagonist.[Pubmed:2843633]

J Pharmacol Exp Ther. 1988 Sep;246(3):902-10.

The pharmacological potencies of 2-substituted N-Acetyltryptamines were determined on the presynaptic melatonin receptor site of rabbit retina labeled in vitro with [3H]dopamine. Calcium-dependent release of [3H]dopamine was elicited by electrical stimulation at 3 Hz for 2 min (20 mA, 2 msec). Melatonin (5-OCH3-N-Acetyltryptamine) and 6-chloromelatonin were equipotent in inhibiting the calcium-dependent release of [3H]dopamine (IC50 = 40 pM). 2-Substituted N-Acetyltryptamines with a methyl (i.e., 6,7-dichloro-2-methylmelatonin, IC50 = 10 pM) or iodine (i.e., 2-iodomelatonin, IC50 = 5 pM) group were more potent than melatonin in inhibiting [3H]dopamine release. I report here the pharmacological properties of the novel N-Acetyltryptamine, 2-benzyl-N-Acetyltryptamine (N-0774, luzindole) on the presynaptic melatonin receptor of rabbit retina. Luzindole (0.1-10 microM) did not affect the spontaneous outflow of radioactivity or the stimulation-evoked release of [3H]dopamine when added alone. However, luzindole (0.1-10 microM) shifted the concentration effect curve for melatonin to the right in a parallel fashion. The pA2 extrapolated from the Schild plot (slope, 0.91) was 7.7, with a KB = 20 nM. The dissociation constants for luzindole (KB), determined in the presence of 6,7-dichloro-2-methylmelatonin (10 pM-1 nM) or 6-chloromelatonin (10 pM-100 nM) were 16 and 40 nM, respectively. These data suggest that luzindole and the various melatonin agonists are competing for the same presynaptic melatonin receptor site in the rabbit retina.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a retinal melatonin receptor.[Pubmed:2991499]

J Pharmacol Exp Ther. 1985 Aug;234(2):395-401.

Melatonin (5-methoxy-N-Acetyltryptamine) at picomolar concentrations (IC50, 40 pM) inhibited the calcium-dependent release of [3H]dopamine elicited at 3 Hz (2 min, 20 mA, 2 msec) from rabbit retina through activation of a site possessing the pharmacological and functional characteristics of a receptor. The effect of melatonin shows biological specificity as this hormone does not modify [3H]dopamine release from striatum or olfactory tubercle. This paper describes the effects of small modifications of the melatonin structure on the inhibition of calcium-dependent release of [3H]dopamine from retina. The more active melatonin analogs were those possessing a 5-methoxy group on carbon 5 of the indole nucleus and an N-acetyl group on the same position as in melatonin. The potencies of 5-methoxy indoles compounds was as follows (IC50): melatonin (40 pM) = 6-chloromelatonin (40 pM) greater than 6-hydroxymelatonin (1.6 nM) greater than or equal to 6-methoxymelatonin (2 nM) greater than 5-methoxytryptamine (63 nM) greater than 5-methoxy-N,N-di-methyltryptamine (200 nM) much greater than 5-methoxytryptophol (4 microM). The structure activity relationships of melatonin and related indoles indicated that the efficacy of melatonin is determined by the moiety substituted on carbon 5 (i.e., 5-methoxy group), whereas the affinity for the receptor is determined primarily by the moiety substituted on carbon 3 (i.e., ethyl N-acetyl group) of the indole nucleus. N-Acetyltryptamine competitively antagonized the inhibitory effect of melatonin in the chicken retina and appears to be a partial agonist in the rabbit retina.(ABSTRACT TRUNCATED AT 250 WORDS)