Accumulation of rat pineal serotonin N-acetyltransferase mRNA induced by pituitary adenylate cyclase activating polypeptide and vasoactive intestinal peptide in vitro

Abstract

In mammals, pineal melatonin secretion is under the control of adrenergic and peptidergic inputs regulating serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase; AA-NAT) activity. In this study, the accumulation of AA-NAT mRNA induced by norepinephrine (NE) and peptides of the secretin superfamily (pituitary adenylate cyclase activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), growth hormone releasing factor (GRF), secretin) was investigated by a new quantitative reverse transcription-PCR (RT-PCR) assay. We demonstrated that PACAP was the most potent peptide to increase the expression of AA-NAT mRNA and to induce cAMP production in rat pinealocytes. VIP was also able to elevate the AA-NAT mRNA level and cAMP efflux in a dose-dependent manner; however, it was six-and threefold, respectively, less potent than PACAP. The maximal values of AA-NAT mRNA level after PACAP and VIP exposures were similar (523·1±52·5 amol to 640·7±68·8 amol vs 461·5±54·3 amol to 579·2±72·4 amol). These saturable peak values were approximately five-to eightfold less than that after NE (3·0±0·3 fmol to 3·6±0·4 fmol). GRF and secretin were less potent than VIP in inducing AA-NAT gene expression and cAMP efflux. These data suggest that the peptides act mostly on VIP 1 /PACAP (VPAC 1 ) receptors of pinealocytes with different affinity. The peak cAMP efflux always preceded the elevation of AA-NAT gene expression during the 3-h infusion of VIP or NE. The cAMP efflux had declined by the time of onset of maximal AA-NAT gene expression, but remained significantly higher than its basal values. Our data indicate that even a submaximal level of cAMP is sufficient for maintaining the maximal AA-NAT mRNA accumulation. These findings show that, in addition to NE, PACAP and VIP may have an important role in the regulation of AA-NAT mRNA levels in rat pinealocytes.

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…Exposure of pinealocytes to graded concentrations of PACAP enhances cAMP production (Rekasi and Czompoly, 2002) and causes an increase in the activity of two key enzymes of the melatonin biosynthetic pathway, serotonin-N-acetyltransferase (Yuwiler et al, 1995;Schomerus et al, 2002) and hydroxyindole-O-methyltransferase (Ribelayga et al, 1997). Consistent with these observations, PACAP has been found to stimulate melatonin secretion by perifused rat pineal glands (Simonneaux et al, 1993) and cultured pinealocytes (Chik and Ho, 1995;Simonneaux et al, 1998;Schomerus et al, 2002).…”

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

“…PACAP stimulates the synthesis and release of MEL by cultured rat pinealocytes with a high affinity (EC 50 ϭ 0.14 nM) similar to that of VIP . PACAP, like VIP, increases CREB phosphorylation (Schomerus et al, 1996), cAMP accumulation Simonneaux et al, 1997b), Aa-nat gene expression (Rekasi and Czompoly, 2002), AA-NAT activity (Yuwiler et al, 1995), 5-HT synthesis (Simonneaux et al, 1997c), and the long-term activity of HIOMT (Ribelayga et al, 1997). Intensity of these PACAP effects is similar to that of VIP (thus lower than reported following NE stimulation).…”

“…VIP was the first and most studied neuropeptide in the pineal gland. VIP increases the intracellular levels (Kaneko et al, 1980;Yuwiler, 1983a;Simonneaux et al, 1997b) and efflux (Rekasi et al, 1998) of cAMP and therefore activates all cAMP-related events: phosphorylation of CREB Schomerus et al, 1996), increase in Aa-nat gene expression Rekasi and Czompoly, 2002), activation of AA-NAT activity in vitro (Kaneko et al, 1980;Yuwiler, 1983a) and in vivo (Schröder et al, 1989), stimulation of the synthesis and release of 5-HT probably following TPOH activation (Simonneaux et al, 1997c), long-term activation of HIOMT (Ribelayga et al, 1997), and stimulation of MEL release (Simonneaux et al, 1990c. These effects, however, are always lower than what has been reported following ␤-AR stimulation.…”

Effects of PACAP on the Circadian Changes of Signaling Pathways in Chicken Pinealocytes

“…The presence of PACAP has been demonstrated both in the rat and avian pineal gland Moller et al 1999), where PACAP stimulates melatonin synthesis Faluhelyi et al 2006;Nakahara et al 2002;Simonneaux et al 1993). Arylalkylamine N-acetyltransferase (AANAT), which is the key regulatory enzyme in the melatonin biosynthetic pathway, has been shown to be very potently stimulated by PACAP (Rekasi and Czompoly 2002). The chick pineal cells in vitro display a circadian rhythm of melatonin release (Faluhelyi et al 2004).…”