Photoperiodic Control of the Rat Pineal Arylalkylamine-N-Acetyltransferase and Hydroxyindole-O-Methyltransferase Gene Expression and Its Effect on Melatonin Synthesis

Abstract

Photoperiodic changes of pineal melatonin (MEL) profile are accompanied by parallel changes of arylalkylamine-N-acetyltransferase (AA-NAT) activity. In the present study, the authors investigated, for the first time, whether two other important variables of pineal metabolism, AA-NAT and hydroxyindole-O-methyltransferase (HIOMT) gene expression, also may be affected by the photoperiod. Evening rises in AA-NAT and HIOMT mRNA and in circulating MEL occurred concomitantly with an increased delay from dark onset as scotophase shortened. On the opposite, the morning declines of all three variables occurred with different kinetics but were locked to light onset. These observations demonstrate that the daily rhythms in AA-NAT and HIOMT gene expression are modulated by the photoperiod and bring further evidence in favor of nor adrenaline as the possible link between the endogenous clock and MEL. Interestingly, the duration of the nocturnal peak in HIOMT mRNA was positively correlated with HIOMT activity. In conclusion, this study adds two important links to the chain of mechanisms involved in the photoperiodic control of pineal metabolism. First, photoperiodic modulation of the MEL rhythm primarily results from changes in the AA-NAT gene expression. Second, the photoperiodic regulation of HIOMT activity occurs at the transcriptional level.

Melatonin in mice: rhythms, response to light, adrenergic stimulation, and metabolism

“…It is possible that small amounts of N-acetylserotonin produced by other transferases are methylated by residual pineal HIOMT enzyme. The rhythm could then come from a low-amplitude rhythm in pineal HIOMT activity similar to the rhythm reported in rats (29). It should be pointed out that very low levels of pineal melatonin synthesis have also been reported elsewhere in C57Bl mice (33,35).…”

Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters

“…We are currently investigating the neurotransmitters and mechanisms implicated in this regulation. In the rat, the photoperiodic variation in HIOMT activity is positively correlated with the rate of Hiomt gene transcription, thus suggesting an involvement of the NAergic stimulation (Ribelayga et al, 1999a). In the pineal gland of the European hamster, the increase in HIOMT activity is associated with a large increase in the number of NPYergic fibers but not in TH-positive fibers from the end of October to mid-December .…”

“…In vivo, in the rat, we have observed that the duration of the nocturnal peak of Hiomt mRNA is longer under SP (8L/16D) than under LP (16L/8D). The SP increase in Hiomt gene expression led to a significant increase (30 to 40%) in mean HIOMT activity throughout 24 h, probably related to an augmentation of protein synthesis (Ribelayga et al, 1999a;Fig. 6).…”

“…The rat pineal HIOMT activity is between 0.7 and 2 nmol/mg protein/h (Sugden et al, 1987b;Ribelayga et al, 1997Ribelayga et al, , 1998bRibelayga et al, , 1999a. HIOMT activity has been measured in the retina and the Harderian gland, although at much lower levels (Quay, 1965;Cardinali and Rosner, 1971;Cardinali and Wurtman, 1972;Nagle et al, 1972Nagle et al, , 1973Pévet et al, 1980a;Wiechmann and Hollyfield, 1989;Bernard et al, 1995;Gauer and Craft, 1996;Djéridane et al, 1998;Ribelayga et al, 1998a).…”

Estudo da presença, da função e das vias de produção da melatonina em invertebrados.

“…O passo final da produção ocorre quando a enzima hidroxindole-O-metiltransferase (HIOMT) converte a NAS em melatonina 10 . A atividade da HIOMT no período noturno apresenta um aumento de 1,5 vez, enquanto o seu RNAm tem um aumento de 2 vezes (17,18).…”