RESUMEN
The pineal gland and retina of the turkey rhythmically produce melatonin. In birds kept under a daily light-dark (LD) illumination cycle melatonin concentrations in the pineal gland and retina were low during the light phase and high during the dark phase. A similar melatonin rhythm with high night-time values was also observed in the plasma. The pineal and retinal melatonin rhythms mirror oscillations in the activity of serotonin N-acetyltransferase (AANAT; the penultimate enzyme in the melatonin biosynthetic pathway). In contrast, in both the pineal gland and retina the activity of the enzyme hydroxyindole-O-methyltransferase (HIOMT) did not exhibit significant changes throughout the 24-h period. Acute exposure of turkeys to light at night dramatically decreased melatonin levels in the pineal gland, retina and plasma. The rhythms in AANAT activity and melatonin concentrations in the turkey pineal gland and retina were circadian in nature as they persisted under conditions of constant darkness (DD). Under DD, however, the amplitudes of AANAT and melatonin rhythms were significantly lower (by 50-80%) than those found under the LD cycle. The findings indicate that melatonin rhythmicity in the turkey pineal gland and retina is regulated both by light and the endogenous circadian clock. The rapid dampening of the rhythms under DD suggests that of these two regulatory factors, environmental light may be the primary stimulus in the maintenance of the high amplitude melatonin rhythms in the turkey.
Asunto(s)
Ritmo Circadiano/fisiología , Melatonina/biosíntesis , Fotoperiodo , Glándula Pineal/metabolismo , Retina/metabolismo , Pavos/metabolismo , Acetilserotonina O-Metiltransferasa/sangre , Acetilserotonina O-Metiltransferasa/metabolismo , Animales , N-Acetiltransferasa de Arilalquilamina/sangre , N-Acetiltransferasa de Arilalquilamina/metabolismo , Femenino , Luz , Masculino , Melatonina/sangre , Glándula Pineal/enzimología , Retina/enzimología , Pavos/fisiologíaRESUMEN
It has been historically assumed that the pineal gland is the major source of melatonin (N-acetyl-5-methoxytryptamine) in vertebrates. Melatonin plays a central role in fine-tuning circadian rhythms in vertebrate physiology. In addition, melatonin shows a remarkable functional versatility exhibiting antioxidant, oncostatic, antiaging, and immunomodulatory properties. Melatonin has been identified in a wide range of organisms from bacteria to human beings. Its biosynthesis from tryptophan involves four well-defined intracellular steps catalyzed by tryptophan hydroxylase, aromatic amino acid decarboxylase, serotonin-N-acetyltransferase, and hydroxyindole-O-methyltransferase. Here, for the first time, we document that both resting and phytohemagglutinin-stimulated human lymphocytes synthesize and release large amounts of melatonin, with the melatonin concentration in the medium increasing up to five times the nocturnal physiological levels in human serum. Moreover, we show that the necessary machinery to synthesize melatonin is present in human lymphocytes. Furthermore, melatonin released to the culture medium is synthesized in the cells, because blocking the enzymes required for its biosynthesis or inhibiting protein synthesis in general produced a significant reduction in melatonin release. Moreover, this inhibition caused a decrease in IL-2 production, which was restored by adding exogenous melatonin. These findings indicate that in addition to pineal gland, human lymphoid cells are an important physiological source of melatonin and that this melatonin could be involved in the regulation of the human immune system, possibly by acting as an intracrine, autocrine, and/or paracrine substance.
Asunto(s)
Linfocitos/metabolismo , Melatonina/biosíntesis , Acetilserotonina O-Metiltransferasa/sangre , Arilamina N-Acetiltransferasa/sangre , Comunicación Autocrina , Medios de Cultivo Condicionados , Fenclonina/farmacología , Humanos , Interleucina-2/biosíntesis , Interleucina-2/genética , Activación de Linfocitos/efectos de los fármacos , Melatonina/genética , Melatonina/fisiología , Oligonucleótidos Antisentido/farmacología , Comunicación Paracrina , Fitohemaglutininas/farmacologíaRESUMEN
Human blood platelets were tested for the presence of mRNAs coding for tryptophan hydroxylase (TPOH) and hydroxy-indol-o-methyl-transferase (HIOMT). Total RNA was extracted from platelets (12.9 +/- 3.3 mg RNA/100 ml blood, mean +/- SEM of 6 preparations) and cDNA synthesized by reverse transcription using random hexamers, oligo-dT or TPOH- or HIOMT-specific primers, designed to amplify a 254 bp fragment for TPOH and a 301 bp fragment for HIOMT. Positive controls were performed using RNA extracted from human normal or tumoral pineal glands. The PCR products were analyzed by gel electrophoresis, transferred to a nylon membrane and hybridized with a 32P-labeled internal probe. When random hexamers, oligo-dT or specific primers were used for reverse transcription, amplification products of the predicted sizes were detectable following electrophoresis in the case of pineal glands and following transfer and hybridization in the case of platelets. These results show TPOH and HIOMT mRNAs to be present in human blood and support the hypothesis that serotonin and melatonin may be synthesized in blood and, more particularly, in platelets.
Asunto(s)
Acetilserotonina O-Metiltransferasa/genética , Plaquetas/química , ARN Mensajero/sangre , Triptófano Hidroxilasa/genética , Acetilserotonina O-Metiltransferasa/sangre , Southern Blotting , Electroforesis en Gel de Agar , Humanos , Reacción en Cadena de la Polimerasa , Triptófano Hidroxilasa/sangreRESUMEN
An autosomal recessive thrombopathy in pigs is described and characterized functionally, morphologically and biochemically. The affected pigs have a severe bleeding diathesis and a markedly prolonged bleeding time but normal plasma and platelet von Willebrand factor (vWF) levels. Electron micrographs and fluorescence microscopy with mepacrine reveal reduced numbers of dense granules in platelets as compared to normals. This thrombopathy is a pure delta storage pool disease (SPD), as evidenced: a) biochemically by platelet serotonin content and metabolism and by comparative ATP/ADP content and secretion; b) functionally by reduced aggregability to low concentrations of convulxin and collagen but normal aggregability to other agents and normal synthesis of thromboxane B2. The affection was first discovered in a colony of von Willebrand's disease (vWD) pigs, but is biologically and genetically distinct. It is possible to completely separate the SPD from the vWD, although originally animals could be affected by both vWD and SPD. Normal plasma and platelet alpha granule content of vWF are found in diseased animals. An intermediate disorder is also detected in animals not severely affected, which may represent the heterozygous state.