bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melatonin Suppression of the Colloid Droplet Formation in the Thyroid Is Not Related to the Alteration of Prostacyclin Synthesis
Authors: Lewiński Andrzej , Pawlikowski Marek 
Published: February 2007

The goal of the present investigation has been to compare the effect of melatonin on the early secretory event in the thyroid follicular cells (thyroglobulin endocytosis; colloid droplet [CD] formation) and the effect of this pineal indoleamine on the release of a stable prostacyclin (PGI2) metabolite, 6‐keto‐PGF1α from the thyroid. 6‐keto‐PGF1α is believed to be a good index of PGI2 synthesis, since PGI2 is not stored within the tissue, but is continuously formed and released. We found that melatonin, administered to rats as daily subcutaneous injections at a dose of 25 μg and/or 250 μg for a total of 3 days, inhibited the CD formation. Moreover, melatonin partially suppressed the stimulatory effect of TSH on the CD formation. In turn, melatonin did not affect 6‐keto‐PGF1α release in basal conditions, but blocked the stimulatory effect of TSH.It is concluded that melatonin decreases the thyroid secretion acting by a mechanism that is independent of the effect of this hormone on PGI2, synthesis.
Cyclic Nucleotide Metabolism in Pineal Homogenates
Authors: Sweat B. F. W. , Carmack C. F. , Jewell L. S. 
Published: February 2007

Adenylate cyclase (AC) in pineal paniculate fractions from rabbit, rat, cow, and the vole Microtus montanus was stimulated by L‐norepinephrine (NE) and L‐isopro‐terenol (ISO). NE stimulation of rabbit and bovine pineal AC was biphasic, with a plateau between 0.01 μM and 1.0 μM and additional stimulation by NE above 1.0 μM. Stimulation by different ISO concentrations gave a typical hyperbolic curve, and optimal stimulation by ISO exceeded that by NE.Melatonin decreased ISO and NE stimulation of AC 10–20%. Although α‐ad‐renergic agonists increase β‐agonist‐mediated adenosine‐3′, 5′‐cyclic monophosphate (cyclic AMP) accumulation in intact pinealocytes, similar amplification of AC stimulation was not seen with broken‐cell preparations.Most (60–70%) pineal guanylate cyclase (GC) was recovered in supernatant fractions after centrifugation of homogenates at 110,000 × g; this soluble GC was unaffected by potential agonists. Low concentrations (0.01–1 nM) of NE, ISO, and phenylephrine (PE) stimulated GC in impure and purified membrane fractions, but each inhibited at concentrations above 10 μM. All concentrations of ISO and NE inhibited GC in the presence of the a‐agonist PE. Melatonin alone did not affect particulate GC, but L‐ISO stimulation was not seen in the presence of equivalent concentrations of melatonin.The in vitro data are consistent with both α‐ and β‐receptor regulation of cyclic nucleotide metabolism in pinealocytes. Endogenous NE may differentially regulate cyclic AMP and guanosine‐3′, 5′‐cyclic monophosphate (cyclic GMP) in pineal; low NE concentrations that stimulate GC have only a slight effect on AC, but higher NE concentrations that inhibit GC maximally stimulate AC. Particulate GC and AC also were resolved by equilibrium centrifugation, to give several discrete peaks of enzyme activity. The results support the existence of several forms of AC and GC, which have different responses to adrenergic agonists.
Effects of melatonin treatment on the gonadotropin‐releasing hormone neuronal system and on gonadotropin secretion in male mink, Mustela vison, in the presence or absence of testosterone feedback
Authors: NToumi F. , Martinet L. , Mondain‐Monval M. 
Published: February 2007

NToumi F, Martinet L, Mondain‐Monval M. Effects of melatonin treatment on the gonadotropin‐releasing hormone neuronal system and on gonadotropin secretion in male mink, Mustela vison, in the presence or absence of testosterone feedback. J. Pineal Res. 1994: 16: 18–25.AbstractThe effects of subcutaneous melatonin capsules on the gonadotropin‐releasing hormone (GnRH) immunoreactive (ir) system and the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) have been tested in intact, castrated, and castrated adult male mink supplemented with testosterone. Animals were transferred in July, i.e., during the period of sexual rest, under a daily light: dark cycle of 16‐hr light and 8‐hr darkness and studied over 13 weeks. GnRH (ir) perikarya, visualized by immunocytochemistry, were counted on serial coronal sections from the diagonal band of Broca to the infundibulum. Serum FSH and LH concentrations were measured by radioimmunoassay. In intact mink, melatonin induced a significant increase in the number of (ir) perikarya and in FSH and LH concentrations 3 and 8 weeks, respectively, after melatonin capsule implantation. In castrated mink, the number of perikarya and the concentrations of FSH, which had increased within 2 weeks after castration, did not change during melatonin treatment. In contrast, the concentrations of LH, which were not altered by castration, increased 3–6 weeks after the onset of melatonin administration, suggesting a stimulation of GnRH release. In castrated testosterone‐treated mink, the number of perikarya was increased as in castrated males, but the elevation of FSH in response to castration was prevented. Within 2 weeks after melatonin capsule implantation, the concentrations of FSH decreased while those of LH remained low, indicating an inhibition of GnRH release. These results show that testosterone modulates the effect of melatonin on the activity of the GnRH–gonadotropin system.
Different patterns of light exposure in relation to melatonin and Cortisol rhythms and sleep of night workers
Authors: Koller Margit , Härma Mikko , Laitinen Jarmo T. , Kundi Michael , Piegler Brigitte , Haider Manfred 
Published: February 2007

Koller M, Harma M, Laitinen JT, Kundi M, Piegler B, Haider M. Different patterns of light exposure in relation to melatonin and Cortisol rhythms and sleep of night workers. J. Pineal Res. 1994: 16: 127–135.AbstractThere is strong evidence to suggest that circadian psychophysiological adaptation processes are modified by light, depending on its intensity and timing. To characterize such modifications and determine whether they are associated with an alteration in the day/night pattern of melatonin excretion, measurements were obtained around the clock in 14 permanent night workers, each studied over a 48 hr period in the field. The light exposure behavior of these workers was studied with a newly developed light dosimetry by measuring light intensity at eye level. Physical activity was continuously registered and sleep indices were obtained by sleep logs and activity markings. Circadian rhythms of melatonin and Cortisol were analysed from salivary samples collected for 24 hr at 2 hr intervals. The inter individual variation of melatonin acrophase determined by cosinor analysis was greater than 180 degrees (from around midnight to noon) and that of Cortisol was about 135 degrees (from early morning to afternoon). Hormonal phase positions coincided significantly with light exposure: the more bright light pulses in the morning (maximum lux between 0600 and 0900), the less were the melatonin and Cortisol acrophases shifted into the day. There was also a negative correlation between melatonin acrophase shift and duration of the overall light exposure above 1500 lux. Morning light maximum and sleep onset correlated highly significantly. Night workers were divided into those with less than (‘non‐shifters’, n = 9) and more than 6 hr deviation from midnight (‘shifters’, n = 5) of the melatonin acrophase. The group comparison revealed a marked difference of the mean melatonin concentrations at night, and at 0700. Shifters did not experience bright light exposure in the morning and showed a tendency towards shorter overall exposure of light above 1500 lux. In conclusion, light avoidance behavior during morning hours, as observed in 5 out of 14 night workers, coincided significantly with a phase delay of melatonin acrophase. Light avoidance also correlated with an earlier sleep onset and a tendency to longer sleep hours. Thus our data suggest that the interaction of a phase shifted activity cycle and the light/dark exposure leads in the field situation to different degrees of adaptation to the prevailing activity/rest requirements, depending on dose and phase position of bright light exposure.
Melatonin and farm animals: Endogenous rhythms and exogenous applications
Authors: Paterson Andrew M. , Foldes Andrew 
Published: February 2007

Paterson AM, Foldes A. Melatonin and farm animals: Endogenous rhythms and exogenous applications. J. Pineal Res. 1994:16:167–177.AbstractStudies on farm animals have contributed significantly to our increased understanding of basic melatonin‐related physiological mechanisms, as well as to the regulation of reproduction and pelage in individual domestic species. This review concentrates on recent work on the role of melatonin in the regulation of porcine reproduction, cervine endocrine, and behavioral cycles and wool and cashmere production which has added to this knowledge base. Early studies of the domestic pig indicated that melatonin secretion in this species differed markedly from that in other domestic and laboratory animals. There is now clear evidence that this is not the case and that the domestic pig uses a circadian rhythm of melatonin release for the transduction of photoperiodic information. Apparent inconsistencies among reports may be due, in part, to differences in the conditions under which the experiments were performed and to the assay systems employed to measure circulating melatonin, the concentrations of which are much lower than in other domestic species. Appropriately administered exogenous melatonin advances the onset of puberty in gilts, and may prove to be effective in overcoming seasonal infertility in female pigs. Appropriately timed melatonin and/or photoperiod treatments, administered to ruminants in utero, influence the reproductive physiology of the offspring, indicating that even in species which don't develop an endogenous melatonin rhythm till some weeks postnatally, awareness of photo environment, presumably via maternal melatonin, predates birth. Pre‐ or early postnatal melatonin‐related treatments also influence the development/cycle frequency of pelage. Areas requiring further investigation include the hormonal/growth factors involved, reasons for the transient nature of the effects in sheep and goats, and the reason for similar effects on pelage of augmenting or inactivating melatonin. Aspects of endogenous melatonin rhythms in farm species which require further study include: the significance of the abolition of the nocturnal melatonin peak in the sheep by prolonged short day exposure; the increased pineal bloodflow in sheep bred to produce high wool yields; the presence of high daytime melatonin levels immediately prior to the rut in the fallow buck; and the low amplitude of the rhythm in the domestic pig.
Effects of aging on photoperiodic responsiveness and specific 2‐[125I]‐iodomelatonin binding sites in the pars tuberalis and suprachiasmatic nuclei of Siberian hamsters
Authors: Duncan Marilyn J. , Purvis Cheryl C. 
Published: February 2007

Duncan MJ, Purvis CC. Effects of aging on photoperiodic responsiveness and specific 2‐[125I]‐iodomelatonin binding sites in the pars tuberalis and suprachiasmatic nuclei of Siberian hamsters. J. Pineal Res. 1994:16:184–187.AbstractSiberian hamsters undergo reproductive quiescence during exposure to a short day photoperiod, but this response appears to diminish with age. This study investigated whether age‐related losses in photoperiodic responsiveness may be related to decreases in specific 2‐[125I]‐iodomelatonin binding sites in the suprachiasmatic nuclei or pars tuberalis. Adult male Siberian hamsters (group 1: 3–6 months of age and group 2: 9–12 months of age) were exposed to short photoperiod (10 hr of light/day) for 10 weeks. Profound testicular regression was evident in the majority of the hamsters in group 1, but in only a few of the hamsters in group 2. There were no significant differences between the groups in the density or affinity of the specific 2‐[125I]‐iodomelatonin binding sites in either the suprachiasmatic nuclei or the pars tuberalis. These findings suggest that the failure of older hamsters to respond to short photoperiod is not caused by a loss of specific 2‐[125I]‐iodomelatonin binding sites in the suprachiasmatic nuclei or pars tuberalis.
Pharmacological effects of melatonin treatment on both locomotor activity and brain serotonin release in rats
Authors: Chuang Jih‐lng , Lin Mao‐Tsun 
Published: February 2007

Chuang J‐I, Lin M‐T. Pharmacological effects of melatonin treatment on both locomotor activity and brain serotonin release in rats. J. Pineal Res. 1994: 17: 11–16.AbstractThe effects of intraperitoneal administration of pharmacological doses of melatonin (60 mg/kg) on both locomotor activity and brain monoamine release were assessed in rats. The spontaneous levels of either horizontal motion, vertical motion, or total distance traveled were decreased following melatonin injection. On the other hand, the spontaneous levels of postural freezing increased after treatment. External heat exposure (36°C) produced increases in locomotion (including horizontal motion, vertical motion, and total distance traveled) as well as decreases of postural freezing in rats. The heat‐induced increases of horizontal motion and total distance traveled as well as decreases of postural freezing were attenuated by melatonin treatment. In addition, cold exposure (4 C) produced increases of vertical motion as well as decreases of postural freezing. Again, the cold‐induced behavioral responses were attenuated by melatonin treatment. Biochemical data revealed that the serum levels of melatonin were decreased by both heat and cold exposure in rats. Furthermore, voltammetric data revealed that intraperitoneal administration of melatonin (60 mg/kg) decreased serotonin, but not the dopamine, release in the hypothalamus, the corpus striatum or nucleus accumbens of rat brain. Neither the locomotor activity responses to thermal stress nor brain monoamine release was affected by a smaller dose of melatonin (30 mg/kg, i. p.). The results suggest that systemic administration of melatonin, at pharmacological doses, inhibits brain serotonin release and results in a reduction in both the spontaneous locomotion and the thermal stress‐induced locomotor activity responses in rats.
Pharmacologic characterization of melatonin mediated phosphoinositide hydrolysis in pigeon brain
Authors: Mullins U. Lena , Eison Arlene S. 
Published: February 2007

Mullins UL, Eison AS. Pharmacologic characterization of melatonin‐mediated phosphoinositide hydrolysis in pigeon brain. J. Pineal Res. 1994: 17: 33–38.AbstractHigh densities of [125I]‐iodomelatonin binding sites have been demonstrated in pigeon brain. Melatonin binding sites have been shown to be linked to signal transduction mechanisms in other species. The present study investigated the melatonin‐mediated second messenger response of phosphoinositide hydrolysis in slices of telencephalon, optic tectum, cerebellum, hypothalamus, and pons medulla of pigeon brain. The highest rates of melatonin‐mediated phosphoinositide hydrolysis were observed in telencephalon and pons/medulla. Relative potencies of melatonin agonists to induce phosphoinositide hydrolysis were as follows: 2‐iodomelatonin > 6‐chloromelatonin > N‐acetylserotonin > melatonin ≫ serotonin (5‐HT). Agonist‐induced phosphoinositide hydrolysis was blocked by N‐acetyltryptamine (NAT), a melatonin antagonist, but not by ketanserin, a 5HT2A/2C receptor antagonist, demonstrating that phosphoinositide hydrolysis did not result from 5HT2A or 5HT2C receptor stimulation. In addition, the effects of melatonin agonists were sensitive to prazosin, an alpha‐adrenergic antagonist reported to exhibit nanomolar affinity for melatonin binding sites in hamster brain, but not to phentolamine, an alpha‐adrenergic antagonist that shows no affinity for melatonin binding sites. These data provide evidence that signal transduction associated with melatonin in pigeon brain involves the induction of phosphoinositide hydrolysis as a second messenger.
Melatonin is involved in cholecystokinin‐induced changes of ileal motility in rats
Authors: Benouali‐Pellissier S. 
Published: February 2007

Benouali‐Pellisier S. Melatonin is involved in cholecystokinin‐induced changes of ileal motility in rats. J. Pineal Res. 1994: 17: 79–85. ©Munksgaard 1994AbstractThe aim of this study was to determine, in the rat, the interaction between melatonin and cholecystokinin in the regulation of the ileal interdigestive motility. This was analyzed by the chronic electromyography technique. Ileal motility was defined by the presence of intermittent spike bursts corresponding to the contractile activity of the organe. In control rats, these spike bursts were organized in cyclic myoelectrical complexes. Each complex is characterized by two successive spiking activity phases: the irregular phase (ISA) followed by the regular phase (RSA). Pinealectomy suppressed the RSA phase so ileal motility was constituted only by the ISA phase. When melatonin (1 mg/kg i. v.) was injected into pinealectomized rats, RSA phases were immediately and definitively restored. RSA phases were also re‐established when the “alimentary” type of cholecystokinin receptors (CCKA) were blocked by selective antagonists such as L364,718 or SR27897 (1 mg/kg i. v.). The latter had better brain accessibility than L364,718. Unlike the effects of melatonin, the effect of these antagonists was neither immediate (the latency is longer for L364,718 than for SR27897) nor definitive. In control rats, cholecystokinin (5 |μg/kg i. v.) induced a characteristic long‐lasting (29 |Mp 2 min) excitomotor effect on the ileum. This effect was suppressed in pinealectomized rats and was restored after melatonin treatment. These results suggest that, via the central nervous system, melatonin is involved in the modulation of cholecystokinin action on ileal motility.
Apamin blocks the direct relaxant effect of melatonin on rat ileal smooth muscle
Authors: Reyes‐Vázquez C. , Naranjo‐Rodríguez E.B. , García‐Segoviano J.A. , Trujillo‐Santana J. , Prieto‐Gómez B. 
Published: February 2007

Reyes‐Vázquez C, Naranjo‐Rodríguez EB, García‐Segoviano JA, Trujillo‐Santana J, Prieto‐Gómez B. Apamin blocks the direct relaxant effect of melatonin on rat ileal smooth muscle. J. Pineal Res. 1997; 22:1–8. © Munksgaard, CopenhagenAbstractThe present study investigated the mechanisms of melatonin‐induced inhibition of the ileal smooth muscle contraction. Rat isolated ileal smooth muscle strips were stimulated in an organ bath using carbachol (CAR) or potassium chloride (KC1) depolarization. Under these conditions, melatonin produced a concentration‐dependent inhibition of muscle contraction (mean inhibitory concentration, IC50: 17.3 times 10‐6 M), which was not blocked by either tetrodotoxin (10‐6 M), hexamethonium (10‐4M), or phentolamine (10‐6M). The inhibitory effect of melatonin during CAR stimulation was blocked in a concentration‐dependent manner by the presence of apamin (4.8 times 10‐9 M), a K+‐channel blocker. By contrast, other K+‐channel blockers such as 4‐aminopyridine (lf‐4M to 5 times 10‐3 M), tetraethylammonium (10‐4 M to 10‐1 M), and glibenclamide (10‐5 M) were ineffective. Additionally, the Ca2+‐channel antagonists nitrendipine (IC50: 2.4 times 10‐9 M) and verapamil (IC50: 1.1 times 10‐7 M) also blocked the inhibitory action of melatonin. These results suggest that melatonin may interact with an apamin‐sensitive, possibly Ca2+‐activated, K+ channel and thus cause an inhibition of ileal smooth muscle contractions.
Nocturnal urinary 6‐sulphatoxymelatonin excretion is decreased in primary breast cancer patients compared to age‐matched controls and shows negative correlation with tumor‐size
Authors: Bartsch Christian , Bartsch Hella , Karenovics Angela , Franz Heiko , Peiker Gertrud , Mecke Dieter 
Published: February 2007

Bartsch C, Bartsch H, Karenovics A, Franz H, Peiker G, Mecke D. Nocturnal urinary 6‐sulphatoxymelatonin excretion is decreased in primary breast cancer patients compared to age‐matched controls and shows negative correlation with tumor‐size. J. Pineal Res. 1997; 23:53–58. © Munksgaard, CopenhagenAbstractIn previous studies a tumor‐size dependent decline of the circadian amplitude of serum melatonin was found in primary unoperated breast cancer patients, which was not due to changes of the hepatic metabolism of melatonin since its main peripheral metabolite, 6‐sulphatoxymelatonin (aMT6s), showed similar serum levels. The aim of the current study was to verify these previous results by measurements of the nocturnal excretion of aMT6s in urine. The determination of aMT6s was carried out by radioimmunoassay. 17 primary unoperated breast cancer (BC) patients and 34 age‐matched control patients with different types of benign gynecological diseases awaiting operation (breast diseases, n=13; ovarian diseases, n=12; and uterine diseases, n=9) were analysed. The median nocturnal urinary aMT6s excretion (22:00–6:00 hr) was significantly lower (‐48%, P =0.033) in BC patients than in controls. Controls showed a significant negative linear regression with age (r = ‐0.419, P= 0.014). According to multivariate linear regression analysis, BC revealed no age‐dependency but a significant negative effect of increasing tumor‐size on aMT6s‐excretion (P= 0.036) was detected. These results confirm previous findings of a decreased pineal melatonin secretion in BC patients as well as an inverse relationship with tumor‐size excluding a possible distortion due to age. The mechanisms involved are unknown but indicate that BC may lead to an impaired production of pineal melatonin. The clinical relevance of these findings from therapeutic and diagnostic point of view is discussed.
Melatonin entrainment of the circadian N‐acetyltransferase rhythm in the newborn rat pineal gland
Authors: Trávníčková Zdeňka , Illnerová Helena 
Published: February 2007

Trávníčková Z, Illnerová H. Melatonin entrainment of the circadian N‐acetyltransferase rhythm in the newborn rat pineal gland. J. Pineal Res. 1997; 23:136–141. © Munksgaard, CopenhagenAbstractIn 15‐day‐old control and vehicle‐treated rats, the evening rise of the pineal N‐acetyltransferase occurred at the same time as in their mothers, whereas in 5‐day‐old pups, the rise occurred by 2–3 hr earlier. Four‐day administration of melatonin in the late day phase advanced the N‐acetyltransferase rise in 15‐day‐old rats as compared with the rise in the vehicle‐treated animals; a slight melatonin induced phase advance in 5‐ and 27‐day‐old rats was not significant. The data indicate that the newborn rat's circadian pacemaker controlling the rhythmic N‐acetyltransferase rise may be entrained by exogenous melatonin. It appears, however, that the maternal melatonin transferred via milk cannot entrain the pup's pacemaker by phase advancing it, since the N‐acetyltransferase rise in the pups begins earlier or at the same time as maternal melatonin production driven by the N‐acetyltransferase rhythm.