Association between type 2 diabetes and depressive symptoms after a 1-year follow-up in an older adult Mediterranean population.

OBJECTIVES: To examine the cross-sectional association between baseline depressive symptoms and the presence of type 2 diabetes (T2D), and its association with glycated hemoglobin (HbA1c) and other metabolic variables, and the prospective association of depressive symptoms and HbA1c after 1 year of follow-up. METHODS: n = 6224 Mediterranean older adults with overweight/obesity and metabolic syndrome (48% females, mean age 64.9 ± 4.9 years) were evaluated in the framework of the PREDIMED-Plus study cohort. Depressive symptoms were assessed using the Beck Depression Inventory-II and HbA1c was used to measure metabolic control. RESULTS: The presence of T2D increased the likelihood of higher levels of depressive symptoms (χ2 = 15.84, p = 0.001). Polynomial contrast revealed a positive linear relationship (χ2 = 13.49, p = 0.001), the higher the depressive symptoms levels, the higher the prevalence of T2D. Longitudinal analyses showed that the higher baseline depressive symptoms levels, the higher the likelihood of being within the HbA1c ≥ 7% at 1-year level (Wald-χ2 = 24.06, df = 3, p < .001, for the full adjusted model). Additionally, depressive levels at baseline and duration of T2D predicted higher HbA1c and body mass index, and lower physical activity and adherence to Mediterranean Diet at 1 year of follow-up. CONCLUSIONS: This study supports an association between T2D and the severity of depressive symptoms, suggesting a worse metabolic control from mild severity levels in the short-medium term, influenced by lifestyle habits related to diabetes care. Screening for depressive symptoms and a multidisciplinary integrative therapeutic approach should be ensured in patients with T2D.

Mediterranean alcohol-drinking pattern, low to moderate alcohol intake and risk of atrial fibrillation in the PREDIMED study.

BACKGROUND AND AIMS: There is ongoing controversy about the effect of a low to moderate alcohol consumption on atrial fibrillation (AF). Our aim is to assess the association between adherence to a Mediterranean alcohol drinking pattern and AF incidence. METHODS AND RESULTS: A total 6527 out of the 7447 participants in the PREDIMED trial met our inclusion criteria. A validated frequency food questionnaire was used to measure alcohol consumption. Participants were classified as non-drinkers, Mediterranean alcohol drinking pattern (MADP) (10-30 g/d in men and 5-15 g/day in women, preferably red wine consumption with low spirits consumption), low-moderate drinking (<30 g/day men y and < 15 g/day women), and heavy drinking. We performed multivariable Cox regression models to estimate hazard ratios (HR) with 95% confidence intervals (95% CI) of incident AF according to alcohol drinking patterns. After a mean follow up of 4.4 years, 241 new incident AF cases were confirmed. Alcohol consumption was not associated to AF incidence among low-moderate drinkers (HR: 0.96; 95%CI: 0.67-1.37), adherents to MADP (HR: 1.15 95%CI: 0.75-1.75), or heavy drinkers (HR: 0.92; 95%CI: 0.53-1.58), compared with non-drinkers. CONCLUSIONS: In a high cardiovascular risk adult population, a Mediterranean alcohol consumption pattern (low to moderate red wine consumption) was not associated with an increased incidence of AF. CLINICAL TRIALS: URL: http://www.controlled-trials.com. Unique identifier: ISRCTN35739639.

Intensive Weight-Loss Lifestyle Intervention Using Mediterranean Diet and COVID-19 Risk in Older Adults: Secondary Analysis of PREDIMED-Plus Trial.

OBJECTIVES: We tested the effects of a weight-loss intervention encouraging energy-reduced MedDiet and physical activity (PA) in comparison to ad libitum MedDiet on COVID-19 incidence in older adults. DESIGN: Secondary analysis of PREDIMED-Plus, a prospective, ongoing, multicentre randomized controlled trial. SETTING: Community-dwelling, free-living participants in PREDIMED-Plus trial. PARTICIPANTS: 6,874 Spanish older adults (55-75 years, 49% women) with overweight/obesity and metabolic syndrome. INTERVENTION: Participants were randomised to Intervention (IG) or Control (CG) Group. IG received intensive behavioural intervention for weight loss with an energy-reduced MedDiet intervention and PA promotion. CG was encouraged to consume ad libitum MedDiet without PA recommendations. MEASUREMENTS: COVID-19 was ascertained by an independent Event Committee until December 31, 2021. COX regression models compared the effect of PREDIMED-Plus interventions on COVID-19 risk. RESULTS: Overall, 653 COVID-19 incident cases were documented (IG:317; CG:336) over a median (IQR) follow-up of 5.8 (1.3) years (inclusive of 4.0 (1.2) years before community transmission of COVID-19) in both groups. A significantly lowered risk of COVID-19 incidence was not evident in IG, compared to CG (fully-adjusted HR (95% CI): 0.96 (0.81,1.12)). CONCLUSIONS: There was no evidence to show that an intensive weight-loss intervention encouraging energy-reduced MedDiet and PA significantly lowered COVID-19 risk in older adults with overweight/obesity and metabolic syndrome in comparison to ad libitum MedDiet. Recommendations to improve adherence to MedDiet provided with or without lifestyle modification suggestions for weight loss may have similar effects in protecting against COVID-19 risk in older adults with high cardiovascular risks.

Characterization of two different melatonin binding sites in peripheral tissues of the teleost Tinca tinca.

The aim of the present study was to localize and characterize 2-iodo-melatonin ([(125)I]Mel) binding sites in peripheral tissues of the teleost Tinca tinca. A wide distribution of [(125)I]Mel binding sites in peripheral locations of the tench is found, with highest densities being measured in the heart, gills and kidney, and low density of [(125)I]Mel binding sites in gastrointestinal tract, spleen, liver and gonads. Saturation, kinetics, and pharmacological approaches revealed the presence of, at least, two different [(125)I]Mel binding sites in the tench peripheral tissues. The unique characterized subtype in the heart fulfils all the criteria for a canonical melatonin receptor belonging to MT(1) family (the binding is saturable, reversible, and inhibited by GTP analogs), and gives support for the presence of a functional melatonin receptor in the heart of the tench. In contrast, kinetic and pharmacological studies in the kidney revealed the preponderance of a melatonin binding site belonging to the MT(3)-like receptor subtype. Moreover, the decrease of specific binding in both, heart and kidney membranes, and the decrease of affinity in the kidney, produced by the addition of a non-hydrolysable GTP analog, and sodium cations suggest the presence of G(i/o)-proteins (that mediate inhibition of cAMP formation) coupled to such melatonin binding sites. Our results also point to different G(i/o)-proteins involved in the underlying mechanism of melatonin binding sites activation in the kidney. Additionally, the kinetics of [(125)I]Mel binding in kidney membrane preparations is a highly thermosensitive process, being necessary to perform the assays at 4 °C since the equilibrium was not reached at 25 °C assay temperature. The time needed to complete association of [(125)I]Mel at such low temperature is only 15s, whereas 100s is required to displace [(125)I]Mel specific binding by the unlabeled melatonin in kidney membranes. Present results support previous reports on melatonin effects in the regulation of different physiological functions in teleost (as cardiovascular physiology and osmoregulation) acting through peripheral specific receptors.

Caffeinated coffee consumption and risk of atrial fibrillation in two Spanish cohorts.

AIMS: The association between caffeinated coffee consumption and atrial fibrillation remains unclear. Recent studies suggest an inverse association only between a moderate caffeinated coffee consumption and atrial fibrillation, but others have reported no association. The aim of our study was to prospectively assess the association between caffeinated coffee consumption and atrial fibrillation in two Spanish cohorts, one of adults from a general population and another of elderly participants at high cardiovascular risk. METHODS AND RESULTS: We included 18,983 and 6479 participants from the 'Seguimiento Universidad de Navarra' (SUN) and 'Prevención con Dieta Mediterránea' (PREDIMED) cohorts, respectively. Participants were classified according to their caffeinated coffee consumption in three groups: ≤3 cups/month, 1-7 cups/week, and >1 cup/day. We identified 97 atrial fibrillation cases after a median follow-up of 10.3 years (interquartile range 6.5-13.5), in the SUN cohort and 250 cases after 4.4 years median follow-up (interquartile range 2.8-5.8) in the PREDIMED study. No significant associations were observed in the SUN cohort although a J-shaped association was suggested. A significant inverse association between the intermediate category of caffeinated coffee consumption (1-7 cups/week) and atrial fibrillation was observed in PREDIMED participants with a multivariable-adjusted hazard ratio = 0.53 (95% confidence interval 0.36-0.79) when compared with participants who did not consume caffeinated coffee or did it only occasionally. No association was found for higher levels of caffeinated coffee consumption (>1 cup per day), hazard ratio = 0.79 (95% confidence interval 0.49-1.28). In the meta-analysis of both PREDIMED and SUN studies, the hazard ratio for intermediate consumption of caffeinated coffee was 0.60 (95% confidence interval 0.44-0.82) without evidence of heterogeneity. Similar findings were found for the association between caffeine intake and atrial fibrillation risk. CONCLUSION: Intermediate levels of caffeinated coffee consumption (1-7 cups/week) were associated with a reduction in atrial fibrillation risk in two prospective Mediterranean cohorts.

Circadian clock genes of goldfish, Carassius auratus: cDNA cloning and rhythmic expression of period and cryptochrome transcripts in retina, liver, and gut.

Clock genes are known to be the molecular core of biological clocks of vertebrates. They are expressed not only in those tissues considered central pacemakers, but also in peripheral tissues. In the present study, partial cDNAs for 6 of the principal clock genes (Period 1-3 and Cryptochrome 1-3) were cloned from a teleost fish, the goldfish (Carassius auratus ). These genes showed high homology (approximately 90%) with the respective cDNAs of zebrafish (Danio rerio), the only other teleost from which clock genes have been cloned. The daily expression pattern of each gene in retina, gut, and liver of goldfish was investigated using quantitative RT-PCR and cosinor analysis. All clock genes analyzed in the retina showed circadian rhythmicity; however, only Per 2-3 and Cry 2-3 were rhythmic in goldfish liver and gut. The amplitude and phase of the expression in liver and gut were different from those found in goldfish retina. Such differences suggest that other cues, such as feeding time, may contribute to the entrainment of oscillators in goldfish liver and gut. Our results support the use of goldfish as a teleost model to investigate the location and functioning of the circadian oscillators.

Longitudinal changes in Mediterranean diet and transition between different obesity phenotypes.

BACKGROUND & AIMS: Little is known about the impact of specific dietary patterns on the development of obesity phenotypes. We aimed to determine the association of longitudinal changes in adherence to the traditional Mediterranean diet (MedDiet) with the transition between different obesity phenotypes. METHODS: Data of 5801 older men and women at high cardiovascular risk from PREDIMED trial were used. Adherence to MedDiet was measured with the validated 14p-Mediterranean Diet Adherence Screener (MEDAS). Using the simultaneous combination of metabolic health- and body size-related parameters participants were categorized into one of four phenotypes: metabolically healthy and abnormal obese (MHO and MAO), metabolically healthy and abnormal non-obese (MHNO and MANO). Cox regression models with yearly repeated measures during 5-year of follow-up were built with use of Markov chain assumption. RESULTS: Each 2-point increase in MEDAS was associated with the following transitions: in MAO participants, with a 16% (95% CI 3-31%) greater likelihood of becoming MHO; in MHO participants with a 14% (3-23%) lower risk of becoming MAO; in MHNO participants with a 18% (5-30%) lower risk of becoming MHO. In MANO women, but not in men, MEDAS was associated with 20% (5-38%) greater likely of becoming MHNO (p for interaction by gender 0.014). No other significant associations were observed. CONCLUSIONS: Better adherence to the traditional MedDiet is associated with transitions to healthier phenotypes, promoting metabolic health improvement in MAO, MANO (only in women), and MHO, as well as protecting against obesity incidence in MHNO subjects.

Health-related quality of life in individuals with metabolic syndrome: A cross-sectional study.

INTRODUCTION AND OBJECTIVES: Metabolic syndrome (MetS) is a combination of various cardiovascular risk factors with a major impact on morbidity and premature mortality. However, the impact of MetS on self-reported health-related quality of life (HRQoL) is unknown. This study evaluated the HRQoL in a Spanish adult population aged 55 years and older with MetS. METHOD: A cross-sectional analysis was performed with baseline data from the PREDIMED-Plus multicentre randomized trial. The participants were 6430 men and women aged 55-75 years with overweight/obesity (body mass index ≥27 and ≤40kg/m2) and MetS. The SF-36 questionnaire was used as a tool to measure HRQoL. Scores were calculated on each scale of the SF-36 by gender and age. RESULTS: Participants showed higher scores in the social function (mean 85.9, 95% CI; 85.4-86.4) and emotional role scales (mean 86.8, 95% CI; 86.0-87.5). By contrast, the worst scores were obtained in the aggregated physical dimensions. In addition, men obtained higher scores than women on all scales. Among men, the worst score was obtained in general health (mean 65.6, 95% CI; 65.0-66.2), and among women, in body pain (mean 54.3, 95%CI; 53.4-55.2). A significant decrease was found in the aggregated physical dimensions score among participants 70-75 years old, but an increased one in the aggregated mental dimensions, compared to younger participants. CONCLUSIONS: Our results reflect that the MetS may negatively affect HRQoL in the aggregated physical dimensions, body pain in women, and general health in men. However, this adverse association was absent for the psychological dimensions of HRQoL, which were less affected.

[What should nephrologists know about cardiac illnesses in patients on peritoneal dialysis?]. / ¿Qué debe conocer el nefrólogo de la afectación cardíaca en el paciente en diálisis peritoneal?

Patients on peritoneal dialysis account for approximately 10% of individuals on dialysis and are very variably distributed throughout Spain, with a national mean of 47 procedures per million inhabitants. The high incidence of cardiovascular disease in patients on peritoneal dialysis is determined by the almost universal presence of traditional cardiovascular risk factors (diabetes, hypertension) and other risk factors secondary to uremia and the inflammatory process associated to atherosclerotic disease. The concomitant presence in clinical practice of highly diverse heart diseases in these patients makes relevant a number of considerations from the cardiological viewpoint that may be of interest for specialists in nephrology. This review analyzes some aspects of four cardiological conditions that are very common in patients on peritoneal dialysis: heart failure, coronary heart disease, valve involvement, and atrial fibrillation.

Effect of alpha-helical-CRF[9-41] on feeding in goldfish: involvement of cortisol and catecholamines.

The anoretic effect of corticotropin-releasing factor (CRF) was not dependent on adrenal activation in goldfish (Carassius auratus). Moreover, an interaction between CRF and the hypothalamic catecholaminergic system in the central regulation of food intake was observed. The intracerebroventricular (icv) administration of CRF increased cortisol levels and reduced food intake and hypothalamic norepinephrine and dopamine content at 2 hr postinjection, with these effects reversed by alpha-helical CRF[9-41] pretreatment. The anoretic effect of CRF was independent of the circulating cortisol increase, because it was only evoked after icv injections but not after intraperitoneal (ip) administration. Furthermore, the increase in plasma cortisol levels induced by ip administration of this steroid did not modify feeding.

Differential characteristics and regulation of arylamine and arylalkylamine N-acetyltransferases in the frog retina (Rana perezi).

Arylamine N-acetyltransferase activity (A-NAT: E.C.2.3.1.5) from Rana perezi retina was studied using p-phenetidine as specific substrate. Enzyme characteristics and regulation were compared with respect to the arylalkylamine N-acetyltransferase (AA-NAT: E.C.2.3.1.87) from the same tissue. A-NAT activity is distributed in both neural retina and choroid-pigmented epithelium complex, showing a 10-fold higher specific activity in neural retina. In contrast, AA-NAT activity is restricted to neural retina. Subcellular localization in neural retina indicated that both enzymatic activities are in the supernatant fraction (39,000 g, 20 min). p-Phenetidine acetylation was linear as a function of the neural retina amount in the assay (1/16 to 1 retina), and it is insensitive to phosphate buffer pH in the range 6.5-8.4. A-NAT kinetic showed a hyperbolic shape for both cosubstrates. Kinetic constants were KM = 11.2 microM, Vmax = 0.49 nmol/h/mg prot. for p-phenetidine (50 microM acetyl-CoA), and KM = 113.4 microM, Vmax = 3.1 nmol/h/mg prot. for acetyl-CoA (5 mM p-phenetidine). The additivity test for both enzymatic activities in retina homogenates demonstrated that both acceptor amines do not compete for the catalytic sites. Serotonin addition in the assay modifies differentially the kinetic characteristics of both enzymes. Serotonin acted as a strong mixed inhibitor, mainly competitive in nature (competitive Ki = 18.1 microM; non-competitive Ki = 1.9 mM) for AA-NAT. However, it acted as a weak inhibitor with respect to A-NAT, mainly non-competitive, (competitive Ki = 5.7 mM; non-competitive Ki = 8.7 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin biosynthesis in photoreceptor-enriched chick retinal cell cultures: role of cyclic AMP in the K(+)-evoked, Ca(2+)-dependent induction of serotonin N-acetyltransferase activity.

The roles of cyclic AMP and calcium in the regulation of serotonin N-acetyltransferase (NAT) activity were studied in low density monolayer cultures of chick retinal photoreceptors and neurons. Photoreceptor-enriched retinal cell cultures were prepared from embryonic day 6 retinas and cultured for 6 days. NAT activity in these cultures could be induced by treatment with cyclic AMP protagonists, 8Br-cyclic AMP, forskolin, and 3-isobutyl-1-methylxanthine (IBMX), or by treatment with depolarizing concentrations of extracellular K+. The stimulatory effect of K+, which involves Ca2+ influx through dihydropyridine-sensitive channels, was mediated at least in part by cyclic AMP, as indicated by the following observations. Depolarizing concentrations of K+ stimulated the formation of cyclic AMP, and the stimulatory effects of K+ on both cyclic AMP formation and on NAT activity were synergistically potentiated by the cyclic nucleotide phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). MDL 12,330A, a putative adenylate cyclase inhibitor, inhibited K(+)-evoked cyclic AMP accumulation and induction of NAT activity over the identical concentration range. In contrast, MDL 12,300A failed to inhibit the induction of NAT elicited by 8Br-cyclic AMP. H-89, an inhibitor of cyclic AMP-dependent protein kinase, antagonized the induction of NAT activity by either forskolin or K+ with equal potency for both stimuli. These results suggest that cyclic AMP plays an essential role in the induction of NAT activity that occurs as a consequence of membrane depolarization. Cyclic AMP and Ca2+ may also interact at a step distal to adenylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal rhythms of tryptophan hydroxylase activity in Xenopus laevis retina: opposing phases in photoreceptors and inner retinal neurons.

Tryptophan hydroxylase (TPH) is the first enzyme in the biosynthetic pathways of melatonin in photoreceptor cells and of serotonin in amacrine cells. To assess the regulation of TPH activity in photoreceptor cells, we pretreated retinas with kainic acid. The neurotoxin selectively killed inner retinal neurons while sparing photoreceptors. TPH activity in both control and kainate-treated retinas undergoes a day-night rhythm. The rhythms in both preparations fit sinusoidal functions. However, the rhythm in intact retinas peaks at midday while that in kainate-lesioned retinas does so at midnight. The daily rhythm of tryptophan hydroxylase activity in photoreceptors parallels that of melatonin release. Comparing the mean level of activity in rhythms of intact and lesioned retinas, we calculate that the TPH activity in photoreceptors represents 24% of the total activity. Therefore, the TPH activity measured in intact retinas reflects mainly the enzymatic activity in serotonergic neurons, masking that from photoreceptors. In contrast, the levels and diurnal variation of TPH mRNA did not differ in intact and kainate-lesioned retinas indicating that measurements of TPH mRNA content reflect primarily that in photoreceptor cells. Thus, TPH mRNA levels and enzyme activity are differentially regulated in amacrine neurons and photoreceptor cells. This differential regulation markedly impacts the patterns of daily rhythms observed in the intact retina.

Binding characteristics and daily rhythms of melatonin receptors are distinct in the retina and the brain areas of the European sea bass retina (Dicentrarchus labrax).

Melatonin is synthesized, with a circadian rhythm, in the pineal organ of vertebrates, high levels being produced during the scotophase and low levels during the photophase. The retina also produces melatonin, although in the case of the European sea bass, its secretion pattern appears to be inverted. In the study described here, radioreceptor assay techniques were used to characterize the melatonin binding sites, their regional distribution and their daily variations. Brain and retina membrane preparations were used in all the binding assays and 2-[125I]iodomelatonin ([125I]Mel) as radioligand at 25 degrees C. The specific binding of [125I]Mel was seen to be saturable, reversible, specific and of high affinity. In all the tissues assayed, the power of the ligands to inhibit [125I]Mel binding decreased in the following order: melatonin>>4-P-PDOT>luzindole> or =N-acetylserotonin, which points to the presence of Mel1-like receptors. The inhibition curves of 4-P-PDOT suggested the presence of two different binding sites in the brain areas, but only one type of site of low affinity in the neural retina. No daily variations in [125I]Mel binding capacity (Bmax) or affinity (Kd) were detected in the brain areas, while a clear rhythm in Kd melatonin receptor affinity and Bmax binding capacity was observed in the retina. Kd and Bmax retinal rhythms were out of phase with the lowest Kd and the highest Bmax occurring at scotophase. This result suggests that retinal melatonin is a paracrine factor able to control receptor desensitization during photophase when ocular melatonin is higher in this species.

Thermal sensitivity and effect of temperature acclimation on ocular serotonin N-acetyltransferase activity in Rana perezi.

The thermal sensitivity and the response to thermal acclimation of the serotonin N-acetyltransferase (NAT) activity in frog ocular tissue were studied. The ocular NAT shows a positive thermal modulation for both cosubstrates (tryptamine and acetyl-CoA). The higher NAT activity in the cold-acclimated group (4 degrees C) with respect to the warm-acclimated one (24 degrees C) implies a partial thermal compensation of the enzyme. The present results suggest that frog ocular NAT response to temperature entails a modulation of thermal sensitivity of the enzyme rather than changes in enzyme concentration.

The inhibition by indoleamines (tryptamine and serotonin) of ocular serotonin-N-acetyltransferase from Rana perezi is temperature-dependent.

Temperature effects on ocular serotonin N-acetyltransferase (NAT) kinetics characteristics from Rana perezi have been studied with respect to tryptamine and serotonin as substrates. Monoamine oxidase (MAO) activity does not interfere in NAT assay at acceptoramine concentrations used in NAT kinetics characterization from R. perezi retina. NAT shows an inhibition by high substrate (serotonin) concentration, which is temperature-dependent. NAT follows the Michaelis-Menten equation at low temperature, whereas at high temperatures (> 10 degrees C) an inhibition by serotonin is observed. This inhibition of NAT activity by serotonin could act as an amplification mechanism to increase daily melatonin rhythm amplitude in the retina of ectotherms.

Day/night variations of dopamine ocular content during Xenopus laevis ontogeny.

Concentration of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid is quantified by high-pressure liquid chromatography with a coulometric detection system in the eye of Xenopus laevis through ontogeny and in adults at two times during photocycle (midday and midnight). Ocular dopaminergic activity remains low during pre- and prometamorphosis and significantly rises in postmetamorphic froglets. This increase is more pronounced at midnight than at midday. The dualism of DA content versus DA release in Xenopus ocular tissue is studied in an eyecup culture system. On a 24-h cycle of DA release from adult Xenopus eyecups the highest DA release by eyecups is produced during daytime, and significantly decreases in darkness. From these results it can be concluded that in spite of the early development of the retinal dopaminergic system in the ontogeny of Xenopus, the final maturation must occur during the metamorphic climax. Endogenous DA release is significantly inhibited by light offset, which explains the higher ocular DA content found at midnight as compared to midday in postmetamorphic froglets and adults.

Melatonin synthesis in the greenfrog retina in culture: I. Modulation by the light/dark cycle, forskolin and inhibitors of protein synthesis.

Melatonin is synthesized in the pineal gland and the retina of vertebrates. Retinal serotonin N-acetyltransferase (NAT) activity and melatonin show a daily rhythm with high levels during the dark phase of the photocycle. In some vertebrates, these retinal NAT and melatonin rhythms are maintained in vitro. The aim of present work is to develop an eyecup culture system for the greenfrog (Rana perezi), suitable to analyze the mechanisms of regulation of melatonin synthesis by simultaneous determination of NAT activity and melatonin release. The R. perezi eyecups released melatonin to the culture medium in a rhythmic manner at least over a 27-h period under photocycle conditions. NAT activity and melatonin rhythms were similar to that observed in vivo under natural environmental conditions. Rana perezi retina exhibits a pronounced photosensitivity in vitro. Forskolin increased up to 2-fold the NAT activity and 4-fold the melatonin production at any lighting conditions. The addition of the translation inhibitor, cycloheximide, to the medium reduced significantly both nocturnal NAT activity and melatonin release, suggesting that de novo protein synthesis is produced daily during darkness. Actinomycin D, a transcription inhibitor, needs a longer time of action, because pre-existing mRNA must be depleted before the inhibition of melatonin release can be observed. The eyecup culture system is highly sensitive to light and chemical factors, which makes it particularly suitable as a model for the neurochemical analysis of melatonin biosynthesis in the retina of Rana perezi.

Melatonin synthesis in the greenfrog retina in culture: II. Dopaminergic and adrenergic control.

Serotonin N-acetyltransferase (NAT) activity and melatonin show a daily rhythm with high levels at night. Although the rhythmic properties of NAT and melatonin are similar in pineal gland and retina, great differences in the light perception and transmission mechanisms exist. We have analyzed the effects of adrenergic and dopaminergic agents on greenfrog (Rana perezi) eyecup culture, in order to identify the receptors involved in the regulation of retinal melatonin synthesis. A D2-like receptor is directly involved in the regulation of NAT activity and melatonin release in R. perezi retina. Quinpirole mimics the effect of light, reducing the darkness-stimulated NAT activity and melatonin release, while sulpiride antagonized these actions. Neither D1-agonist (SKF 38393) nor D1-antagonist (SCH 23390) had effect on NAT activity. However, a significant inhibition of darkness-evoked melatonin release was produced by SKF 38393 after 6 hours of culture. The beta- and antagonist1-agonists showed a clear inhibition. However, a direct effect of beta, alpha1 and D1-agonists on photoreceptors is unproven, being more probable that the adrenergic actions imply a non-photoreceptor retinal cell. In conclusion, eyecup culture of Rana perezi revealed a dopaminergic control of melatonin synthesis and a possible modulation of dopaminergic tone by adrenergic receptors. Melatonin release is a more sensitive parameter than NAT activity to the action of neuroactive agents, suggesting that melatonin synthesis can be regulated by more than one enzymatic step in Rana perezi.

Food intake inhibition by melatonin in goldfish (Carassius auratus).

Feeding regulation by monoamines, neuropeptides and certain hormones has been studied in fish, but a possible role of melatonin is unknown. The purpose of the present study was to investigate the effects of melatonin on food intake in goldfish. Fishes were housed in 12L:12D and injected with different doses of either melatonin or 2-iodomelatonin. Two routes of administration, intracerebroventricular and intraperitoneal injections, and two times of the daily photocycle, midday and midnight, were tested. Food intake was measured at 2, 5 and 8 h postinjection. Melatonin and its analog, 2-iodomelatonin intracerebroventricularly injected had no effect on food intake at any time. However, intraperitoneal injections of both indoleamines significantly reduced food intake at different postinjection times. The inhibitory effect of melatonin was blocked by intraperitoneal administration of its antagonist, luzindole. These results demonstrate the in vivo efficiency of luzindole as melatonin antagonist, and thus provide a useful experimental tool to investigate melatonin functions. In conclusion, both melatonin and its agonist 2-iodomelatonin administered peripherally, inhibit food intake in goldfish, and this inhibitory effect appears to be mediated via luzindole-sensitive melatonin receptors. Our results strongly suggest that melatonin is involved in the peripheral satiety mechanisms in goldfish.