Indole metabolism in the pineal gland of the rat; some regulatory aspects

Effects of cycloheximide and aminophylline on 5-methoxytryptophol and melatonin contents in the chick pineal gland

The chick pineal gland rhythmically synthesizes two 5-methoxyindoles, melatonin and 5-methoxytryptophol. These rhythms are circadian in nature and have opposite phases. The aim of this study was to determine the effects of cycloheximide, a protein synthesis inhibitor, and aminophylline, an inhibitor of phosphodiesterase, on 5-methoxytryptophol content in the chick pineal gland and to compare this with the drugs' action on pineal melatonin production. Inhibition of melatonin biosynthesis by cycloheximide (1 mg/kg, i.p. ), revealed by a marked reduction in the nighttime activity of serotonin N-acetyltransferase (AA-NAT; a key regulatory enzyme in melatonin synthesis) and melatonin concentrations, was accompanied by a significant increase in 5-methoxytryptophol content. In contrast, administration of aminophylline (100 mg/kg, i.p.) to light-exposed chicks significantly increased pineal AA-NAT activity and melatonin levels and decreased 5-methoxytryptophol concentrations. It is concluded that in the chick the production of pineal 5-methoxytryptophol and melatonin is inversely correlated.

Fos-like immunoreactivity in cultured rat pinealocytes

The expression of Fos-like proteins in cultured rat pinealocytes was investigated immunocytochemically. Pineal glands of 2-day-old rats were dissociated and maintained in culture for 13 days, the last 24 h deprived of animal sera. The pinealocytes were identified morphologically and by serotonin-immunostaining. Incubations with phorbol dibutyrate (PDBu), 8-bromo-cAMP and isoprenaline were carried out for 2 h to test whether Fos-like protein synthesis is activated via serum response element (SRE), calcium/cyclic AMP response element (Ca/CRE) and beta-receptors, respectively. In untreated serum-deprived control cultures, one third of pinealocytes were Fos-immunoreactive suggesting that Fos protein may have a homeostatic role. In cultures incubated with PDBu, more than 70% of the pinealocytes had Fos-like immunoreactive material in their nuclei. Similarly, in cultures incubated with 8-bromo-cAMP or isoprenaline, more than 70% of the pinealocytes were Fos positive. The c-fos gene could be involved in the regulation of pineal melatonin synthesis and SRE and Ca/CRE probably participate in its activation process in pinealocytes.

Low temperature in the golden hamster accelerates the gonadal atrophy induced by short photoperiod but does not affect the daily pattern of melatonin secretion

Male golden hamsters were exposed to short photoperiod at either 20 degrees C or 5 degrees C. After 4 weeks a complete gonadal inhibition was observed in animals kept at 5 degrees C while in animals kept at 20 degrees C such an inhibition was much less. No significant difference in the pattern of pineal and plasma melatonin concentrations was observed between hamsters kept at 20 degrees C and 5 degrees C. If in the golden hamster pineal melatonin secretion is implicated in the transduction of the photoperiodic information, it is probably not implicated in the transduction of thermal information.

Pinealectomy and constant release of melatonin or 5-methoxytryptamine induce testicular atrophy in the European hamster (Cricetus cricetus, L.)

The role of the pineal and of photoperiod in the regulation of gonadal activity has been studied in the European hamster, a wild hamster commonly found in the vicinity of Strasbourg, France. Besides the presence of a probable endogenous circannual rhythm in reproductive capacities, it appears that, as in all other hamster species studied to date, the sexual activity of this animal is directly regulated by changes in the photoperiodic environment. Pinealectomy as well as a constant release of melatonin or of 5-methoxytryptamine has no effect on the gonadal atrophy induced by short photoperiod, but induces testicular regression in animals kept under long photoperiod. The pineal in this species appears thus to be involved in the maintenance of sexual activity in long photoperiod, while it is apparently not required for the gonadal inhibitory effect of short photoperiod. These results are similar to those obtained in the Turkish hamster. 5-Methoxytryptophol is not implicated in the phenomenon of synchronization of the sexual activity with the photoperiodic changes.

Production of methoxyindoles in vitro from methoxytryptophan by rat pineal gland

Pineal glands were incubated in the presence of [3H] methoxytryptophan with and without methoxamine, epinephrine, and norepinephrine. The beta-adrenoceptor-stimulated pineal glands were capable of converting methoxytryptophan to methoxytryptamine, melatonin, methoxyindole acetic acid, and methoxytryptophol, albeit in small quantities. Only methoxyindole acetic acid was detectable after incubation of unstimulated and alpha-adrenergic-agonist-treated pineal glands. These results support the proposal that melatonin can be formed from methoxytryptophan although this is a minor synthetic pathway, and the classic pathway from serotonin via N-acetylserotonin should be considered to be responsible for the majority of pineal melatonin production.

Temporal effects of norepinephrine on pineal serotonin in vitro

The purpose of this study was to examine the temporal effects of norepinephrine (NE) stimulation on pineal serotonin (5HT) in vitro. Rat pineal glands were individually incubated in nutrient media for 6 h. After a 2-h preincubation, the glands were exposed to tryptophan (TRYP) or TRYP + norepinephrine (10(-4)M each) for 4 additional h. Media and pineals were then analyzed for 5HT and 5HIAA content. Initial exposure to TRYP increased 5HT levels in the media. Norepinephrine increased media 5HT concentrations further and also caused 5HIAA levels to rise significantly. These findings suggest that 5HT secretion and/or oxidation is an early response to stimulation of the pineal gland by NE. Following prolonged NE exposure, media 5HT declined to control values while 5HIAA remained high. Similarly, intrapineal levels of 5HT fell after prolonged stimulation with NE. Thus, pineal responses to initial and continued stimulation with NE are differentiable as early and late effects upon 5HT. Early effects may include secretion and/or oxidation of 5HT followed later by utilization of 5HT in N-acetylation pathways such as that leading to melatonin synthesis. The finding that 5HT is secreted in response to NE suggests that the indoleamine may be a hormone of the pineal gland. Based upon its known influence on physiologic rhythms, daily secretion of 5HT from the pineal may be an important part of the gland's time-keeping function.

In vitro uptake and metabolism of [3H]indole compounds in the pineal organ of the pike. I. A radiochromatographic study

Thin layer chromatography analysis of [3H]serotonin and [3H]melatonin metabolites synthetized in vitro by the pineal organ of the pike was performed. After a 10-min pulse, [3H]serotonin was mainly converted into [3H]-5-hydroxyindoleacetic acid (37%), [3H]-5-hydroxytryptophan and [3H]-5-methoxytryptophan (12 to 14%), and [3H]-5-hydroxytryptophol and [3H]-5-methoxytryptophol (3.5 and 9%) at the onset of darkness. When the pulse was followed by postincubations (in a cold medium) of increasing duration (15, 30, and 60 min), it appeared that the amount of [3H]-5-hydroxyindoleacetic acid decreased, that of [3H]-5-hydroxytryptophol decreased faster than that of [3H]-5-methoxytryptophol, and the amounts of [3H]-5-hydroxy- and [3H]-5-methoxytryptophan increased. [3H]-N-acetylserotonin, [3H]melatonin, and [3H]-5-methoxytryptamine were found in very low amounts. At the beginning of the photophase or at the onset of darkness, the uptake and metabolism of [3H]melatonin (after a 10-min pulse followed by a 10-min incubation in cold medium) resulted mainly in the formation of [3H]-5-methoxytryptophol (23 to 43%) and of [3H]-5-methoxytryptamine (6 to 12%). These results show that the pike pineal organ can synthesize all indoles that are known in the pineal gland of higher vertebrates. Usual, but also unusual, pathways of the indole metabolism were found that will need further clarification. Among these are the possible carboxylation of serotonin and deacetylation of melatonin (leading to the synthesis of 5-methoxytryptophol). Altogether, the results obtained suggest that the indole metabolism might be more complex than what has already been described in vertebrates.

Sex and strain related effects of melatonin and 5-methoxytryptophol on open field behaviour in paired mice

The effects of two methoxyindoles, melatonin (MEL) and 5-methoxytryptophol (5-MTL), on partner investigation and other aspects of pair behaviour in the open field, were observed on male and female mice of the albino TO, and the pigmented C57BL/6 strains. Both indole derivatives are major secretory products of rodent (and human) pineal glands. They were administered by i.p. injection (100 micrograms/kg) to both members of the pair 1 h before each 10 min open field exposure. The testing took place on 3 consecutive days. There were no significant differences in behaviour over days, and group means were used in subsequent data analysis (MANOVA and Dunnet's test). Males, more socially active than the females in both strains, responded to MEL by a reduction in contact time; 5-MTL had the same effect on C57 males (TO males showed no change). Females, on the other hand, did not respond to MEL, and increased their social contact seeking after 5-MTL. There was no consistent effect of either indole on locomotion, and erratic (TO strain only) effects on defaecation. The data are discussed in terms of possible actions of pineal indoles on determinants of social behaviour.

Impact of age-related changes in serotonin and norepinephrine metabolism on reproductive function in female rats: an analytical review

This review attempts to reconcile changes in brain NE and 5HT metabolism with the effects of aging, drug treatment and altered photoperiods on phasic and tonic release of LH in the female. A hypothesis is presented in which 5HT has "indirect" and "direct" effects on LH surges. The "indirect" ones facilitate LH surges via a generalized effect of 5HT on temporal organization within multiple neuroendocrine axes. Thus, 5HT promotes circadian rhythmicity in many systems due to its participation in the biological "clock" mechanism of the hypothalamus. The "direct" ones that are specific to the LH releasing mechanism also occur for 5HT (inhibitory) as well as for NE (facilitory) due to the interaction of these transmitters with LH-RH secreting neurons. It is proposed that metabolic changes during aging that favor 5HT at the expense of NE obliterate the facilitatory effects of both amines while enhancing the inhibitory component of 5HT's influence on LH secretion.

Influence of some pteridines on pineal 5-methoxyindole synthesis in male Wistar rats periodically exposed to either white or red light

In previous investigations the change of circadian rhythmicity in pineal melatonin/5-methoxytryptophol synthesis of rats periodically exposed to red light was similar to that in pineals of rats incubated with pterin-6-aldehyde. These experiments were, however, performed with rats of different age and in different periods of the year. In the present study these two factors influencing pineal indole metabolism have been combined the experiments being carried out in rats aged 28 days and during the same day in the month of January. It was observed that under influence of red light the peak of melatonin/5-methoxytryptophol synthesis shifted towards daytime, whereas incubation with pterin-6-aldehyde did not cause such a shift. If under different experimental conditions the mean amount of melatonin/5-methoxytryptophol which was formed over a 24 hour period was compared, it appeared that pineals of rats exposed to white light incubated with reduced neopterin but not pineals incubated with pterin-6-aldehyde behave in this respect similar to pineals of rats exposed to red light. However, if the ratio between melatonin/5-methoxytryptophol and 5-methoxytryptamine is calculated pineals of white light exposed rats incubated in pterin-6-aldehyde behaved very similar to the pineals of rats exposed to red light. Although the role of pteridines remains obscure, it appears that the parameters 2. circadian rhythmicity and 2. the amount of 5-methoxyindoles and 3. the ratio between these indole derivatives might be of importance in analyzing their physiological effects. The influence of application of light of different wavelengths and year rhythmicity is discussed.

Alterations in the spontaneous activity of cells in the guinea pig pineal gland and visual system produced by pineal indoles

The indoles serotonin (SER), melatonin (MEL), 5-methoxytryptophol (5-MTL) and 5-hydroxytryptophol (5-HTL) were administered during daytime microelectrophoretically to 240 cells in the pineal gland of the guniea-pig. The action of SER and 5-HTL was predominantly depressant on the electrical activity, MEL and 5-MTL caused an excitation in most of the units. Although MEL and 5-MTL caused fairly similar reactions on average, they appear to act on different cells. The effects of microelectrophoretically applied MEL and 5-MTL on the spontaneous or evoked activity in the visual system (retinal ganglion cells, optic tract, lateral lateral geniculate body, superior colliculus) of the guinea-pig were also investigated. Of the 76 cells tested in the visual system 25 of the ON- and OFF-cells increased the rate of discharge when the two indoles were applied. Cells in the optic layer of the superior colliculus showed no measurable response to the application of the two substances. 5-HTL caused no effect on cells in the visual system.

Effect of 5-methoxytryptophan and 5-methoxytryptamine on the reproductive system of the male golden hamster

S.c. injection of 25 microgram of methoxytryptamine (5-MT) in oil into adult male hamsters given between 4.30 and 5 p.m. (light on from 5 a.m. to 7 p.m.: 14 L/10 D) for 51 consecutive days caused involution of the testes. Similar injections of 5-MT given between 8.30 and 9.30 a.m. completely failed to cause regression of the gonads. Under the same conditions, 5-methoxytryptophan (5-MTP) did not induce gonadal atrophy, neither in the morning nor in the late afternoon. These results indicate that, like malatonin, 5-methoxytryptamine is implicated in the control of the reproductive function.

The pineal gland of the mole (Talpa europaea L.). VII. Activity of hydroxyindole-O-methyltransferase (HIOMT) in the formation of 5-methoxytryptophan, 5-methoxytryptamine, 5-methoxyindole-3-acetic acid, 5-methoxytryptophol and melantonin in the eyes and the pineal gland

Using a method in which no substrate is added to the incubation medium, the capacity of HIOMT to synthesize 5-methoxytryptophan, 5-methoxytryptamine, 5-methoxyindole-3-acetic acid, 5-methoxytryptophol and melatonin has been determined in the pineal and the eyes of the mole, a mammal having an atrophied visual system. The results demonstrate that the indoleamine metabolism in the retina is similar to the indoleamine metabolism in the pineal. Moreover, in all animals studied both eyes together synthesize 2 to 30 times more of 5-methoxyindoles than the pineal, a result which proves again that the pineal is not the only and not always the most important source of 5-methoxyindoles. With the exception of 5-methoxyindole-3-acetic acid, the synthesis of which is practically neglectable, the production of all other 5-methoxyindoles in the pineal as well as in the retinae is always larger than that of melatonin. In the pineal, 5-methoxytryptophan, for example, is synthesized in a quantity which is 60 to 170 times larger than that of melatonin, while in the retinae the synthesized amount of 5-methoxytryptophan is even 60 to 1000 times larger than that of melatonin.

The independency of an intact pineal gland of the inhibition by 5-methoxytryptamine of the reproductive organs in the male hamster

Subcutaneous injections fo 25 micrograms of 5-methoxytryptamine (5-MT) in oil into intact and pinealectomized male hamsters given between 4.30 p.m. and 5 p.m. (light on from 5 a.m. to 7 p.m.; 14 L/10 D) for 54 consecutive days caused involution of the testes. 5-MT, however, is more effective when the pineal is present. These results indicate that melatonin is not the only pineal factor inducing gonadal atrophy in the hamster. 5-MT seems even more effective than melatonin in so far as it is, contrary to melatonin under the same experimental conditions, also effective in the absence of the pineal. Like melatonin, 5-MT appears to be implicated in the control of the reproductive function.