Effect of melatonin treatment on 24-hour rhythms of serum ACTH, growth hormone, prolactin, luteinizing hormone and insulin in rats injected with Freund's adjuvant

Melatonin, the circadian multioscillator system and health: the need for detailed analyses of peripheral melatonin signaling

Evidence is accumulating regarding the importance of circadian core oscillators, several associated factors, and melatonin signaling in the maintenance of health. Dysfunction of endogenous clocks, melatonin receptor polymorphisms, age- and disease-associated declines of melatonin likely contribute to numerous diseases including cancer, metabolic syndrome, diabetes type 2, hypertension, and several mood and cognitive disorders. Consequences of gene silencing, overexpression, gene polymorphisms, and deviant expression levels in diseases are summarized. The circadian system is a complex network of central and peripheral oscillators, some of them being relatively independent of the pacemaker, the suprachiasmatic nucleus. Actions of melatonin on peripheral oscillators are poorly understood. Various lines of evidence indicate that these clocks are also influenced or phase-reset by melatonin. This includes phase differences of core oscillator gene expression under impaired melatonin signaling, effects of melatonin and melatonin receptor knockouts on oscillator mRNAs or proteins. Cross-connections between melatonin signaling pathways and oscillator proteins, including associated factors, are discussed in this review. The high complexity of the multioscillator system comprises alternate or parallel oscillators based on orthologs and paralogs of the core components and a high number of associated factors with varying tissue-specific importance, which offers numerous possibilities for interactions with melatonin. It is an aim of this review to stimulate research on melatonin signaling in peripheral tissues. This should not be restricted to primary signal molecules but rather include various secondarily connected pathways and discriminate between direct effects of the pineal indoleamine at the target organ and others mediated by modulation of oscillators.

Long-term melatonin administration attenuates low-LET gamma-radiation-induced lymphatic tissue injury during the reproductively active and inactive phases of Indian palm squirrels (Funambulus pennanti)

A comparative analysis of low linear energy transfer (LET) gamma-radiation-induced damage in the lymphatic tissue of a tropical seasonal breeder, Indian palm squirrel (Funambulus pennanti), during its reproductively active phase (RAP) and inactive phase (RIP) was performed with simultaneous investigation of the effects of long-term melatonin pre-treatment (100 microg/100 g body weight). A total of 120 squirrels (60 during RAP and 60 during RIP) were divided into 12 groups and sacrificed at 4, 24, 48, 72 and 168 h following 5 Gy gamma-radiation exposure; control groups were excluded from exposure. Total leukocyte count and absolute lymphocyte count (ALC) and melatonin only of peripheral blood, stimulation index, thiobarbituric-acid-reactive substances (TBARS) level, superoxide dismutase (SOD) activity, and the apoptotic index of spleen as analysed by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labelling (TUNEL) noted at observed time-points were significantly reduced in melatonin pre-treated groups during RAP and RIP. Long-term melatonin pre-treatment mitigated radiation-induced alterations more prominently during RIP, as assessed by ALC, TBARS, SOD, TUNEL and caspase-3 activity, at some time-points. Our results demonstrate an inhibitory role of melatonin on caspase-3 activity in splenocytes during RAP and RIP following gamma-radiation-induced caspase-mediated apoptosis. Hence, we propose that melatonin might preserve the viability of immune cells of a seasonal breeder against background radiation, which is constantly present in the environment.

24-Hour Changes in Circulating Prolactin, Follicle-Stimulating Hormone, Luteinizing Hormone, and Testosterone in Young Male Rats Subjected to Calorie Restriction

This work analyzes the effect of calorie restriction on the 24h variation of pituitary-testicular function in young male Wistar rats by measuring the circulating levels of prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone. Control animals were provided an equilibrium calorie diet and the experimental animals a calorie-restriction diet equivalent to 66% of food restriction for four weeks starting on day 35 of life. Different groups of control and experimental rats were killed at 6h intervals around the clock, beginning I h after light on (HALO). Compared to the control animals, the mean secretion of prolactin was augmented and that of LH and testosterone decreased in calorie-restricted rats, whereas FSH release remained unchanged. Significant changes in the 24 h secretory pattern of circulating prolactin, LH, and testosterone occurred in the calorie-restricted rats. These include the appearance of a second maximum of plasma prolactin at 21 HALO, blunting of the LH peak seen at 13 HALO, and phase-shift of the testosterone peak from 13 HALO in controls to 17 HALO in calorie-restricted rats. The significant positive correlation between individual LH and testosterone levels found in controls was no longer observed in calorie-restricted rats. Availability of nutrients presumably affects the mechanisms that modulate the circadian variation of the pituitary-gonadal axis in growing male rats.

Effect of aging on 24-hour pattern of stress hormones and leptin in rats

This work analyzes the 24-hour changes of hypothalamic-pituitary-adrenal (HPA) axis activity and leptin release in aged rats. Three- and 22-month-old male Wistar rats were killed at 6 time intervals during a 24-hour cycle (n=8-10 rats/group). Aging augmented plasma ACTH while it decreased plasma and adrenal gland corticosterone levels. Plasma and adrenal corticosterone levels attained high levels during all the scotophase, concomitantly with the maxima in ACTH levels, whereas in aged rats only a brief plasma corticosterone peak at the early scotophase and no time of day variations of adrenal corticosterone were observed. Aging augmented circulating leptin, with a significant interaction "agextime" in the factorial ANOVA, i.e. only in young rats time of day changes were significant, with the lowest values of leptin at the middle of the light period and higher values at night. When plasma leptin was expressed on body weight basis, the age-related differences became not significant but the daily pattern of plasma leptin found in young rats persisted. Plasma and adrenal corticosterone levels correlated significantly with plasma ACTH only in young rats. Likewise, plasma leptin correlated with plasma corticosterone only in young rats. These changes can be attributed to a disrupting effect of aging on the homeostatic mechanisms modulating HPA activity and leptin release.

Effect of a high-fat diet on 24-h pattern of circulating levels of prolactin, luteinizing hormone, testosterone, corticosterone, thyroid-stimulating hormone and glucose, and pineal melatonin content, in rats

Circadian rhythmicity is affected in obese subjects. This article analyzes the effect of a high-fat diet (35% fat) on 24-h changes circulating prolactin, luteinizing hormone (LH), testosterone, corticosterone, thyroid-stimulating hormone (TSH) and glucose, and pineal melatonin content, in rats. When body weight of rats reached the values of morbid obesity, the animals were sacrificed at six different time intervals throughout a 24-h cycle, together with age-matched controls fed a normal diet (4% fat). Plasma hormone levels were measured by specific radioimmunoassays and glucose concentration by an automated glucose oxidase method. In rats under a high-fat diet, a significant disruption of the 24-h pattern of plasma TSH, LH, and testosterone and a slight disruption of prolactin rhythm were found. Additionally, high-fat fed rats showed significantly lower total values of plasma TSH and testosterone and absence of correlation between testosterone and circulating LH levels. Plasma corticosterone levels increased significantly in high-fat fed rats and their 24-h variation became blunted. In obese animals, a significant hyperglycemia developed, individual plasma glucose values correlating with circulating corticosterone in high-fat fed rats only. The amplitude of the nocturnal pineal melatonin peak decreased significantly in high-fat fed rats. The results underlie the significant effects that obesity has on circadian organization of hormone secretion.

Effects of moderate consumption of distilled and fermented alcohol on some aspects of neuroimmunomodulation

Alcoholic beverages are characterized by their fermented versus distilled origin and also by their degree of alcohol. The toxic effects of chronic alcohol consumption have been widely studied. However, there is less evidence about possible beneficial effects of moderate alcohol intake. This work was aimed at evaluating the effects of moderate alcohol consumption (beer or ethanol) on plasma hormone concentrations, blood and thymus lymphocyte phenotypes and brain neurotransmitter levels. For this purpose, 40 adult Wistar male rats were administered ethanol or beer for 4 weeks (experimental groups). Age-matched rats were administered beer without alcohol or water to be used as controls. Rats were killed by decapitation and plasma from the trunk blood was collected to measure plasma prolactin, growth hormone and ACTH concentrations by homologous specific double antibody radioimmunoassays. Thymus and blood lymphocyte subsets were measured by flow cytometry. Neurotransmitter concentrations [dopamine, gamma-aminobutyric acid (GABA) and taurine] were measured by high pressure liquid chromatography in the median eminence and the pituitary. Blood and thymus lymphocyte subsets were not significantly changed by either ethanol or beer consumption, compared to controls. Plasma prolactin levels significantly decreased in ethanol-administered groups (p < 0.05) compared to control animals drinking water, although plasma levels of growth hormone and ACTH were not modified by either alcohol used. Dopamine and GABA concentrations in the median eminence or in the adenohypophysis remained unmodified by moderate beer or ethanol consumption. However, taurine concentration was significantly increased in the pituitary (p < 0.05) in the group drinking ethanol compared to those groups drinking beer with or without alcohol. These data suggest that moderate alcohol consumption may change the regulatory mechanism of prolactin secretion. Whether these modifications have a physiological significance deserves further research.

Effect of social isolation on 24-h pattern of stress hormones and leptin in rats

This work analyzes the effect of social isolation of growing male rats on 24-h changes of plasma prolactin, growth hormone, ACTH and leptin, and on plasma and adrenal corticosterone concentrations. At 35 days of life, rats were either individually caged or kept in groups (6-8 animals per cage) under a 12:12 h light/dark schedule (lights on at 08:00 h). A significant arrest of body weight gain regardless of unchanged daily food intake was found in isolated rats after 2 weeks of isolation. On the 4th week, rats were killed at 6 time intervals during a 24-h cycle, beginning at 09:00 h. In isolated rats the 24-h pattern of all parameters tested became distorted, as assessed by Cosinor analysis. When analyzed as a main factor in a factorial analysis of variance, isolation decreased plasma prolactin and growth hormone, increased plasma leptin and corticosterone while decreased adrenal corticosterone. Plasma corticosterone levels correlated significantly with plasma ACTH and with adrenal corticosterone levels in group-caged rats only. These changes can be attributed to an effect of mild stress on the endogenous clock that modulates the circadian hormone release.

24-hour changes in ACTH, corticosterone, growth hormone, and leptin levels in young male rats subjected to calorie restriction

Calorie restriction of young male rats increases plasma prolactin, decreases luteinizing hormone (LH) and testosterone, and disrupts their 24 h secretory pattern. To study whether this could be the consequence of stress, we examined the 24 h variations of plasma adrenocorticotropic hormone (ACTH) corticosterone, growth hormone (GH), leptin, and adrenal corticosterone. Rats were submitted to a calorie restriction equivalent to a 66% of usual intake for 4 weeks, starting on day 35 of life. Controls were kept in individual cages and allowed to eat a normal calorie regimen. Significantly lower ACTH levels were detected in calorie-restricted rats. Plasma corticosterone levels during the light phase of the daily cycle were significantly higher in calorie-restricted rats. Time-of-day variation in plasma ACTH and corticosterone levels attained significance in calorie-restricted rats only, with a maximum toward the end of the resting phase. The daily pattern of adrenal gland corticosterone mirrored that of circulating corticosterone; however, calorie restriction reduced its levels. Plasma ACTH and corticosterone correlated significantly in controls only. Calorie restriction decreased plasma GH and leptin, and it distorted 24h rhythmicity. In a second study, plasma ACTH and corticosterone levels were measured in group-caged rats, isolated control rats, and calorie-restricted rats during the light phase of the daily cycle. Plasma ACTH of calorie-restricted rats was lower, and plasma corticosterone was higher, compared with isolated or group-caged controls. The changes in the secretory pattern of hormones hereby reported may be part of the neuroendocrine and metabolic mechanisms evolved to maximize survival during periods of food shortage.

Effect of interferon-gamma treatment on 24-hour variations in plasma ACTH, growth hormone, prolactin, luteinizing hormone and follicle-stimulating hormone of male rats

OBJECTIVE

Interferon-gamma (IFN-gamma) is a cytokine produced by T helper cells on antigenic challenge that may affect the release of several pituitary hormones. However, in vitro or in vivo studies have yielded disparate results with stimulatory, inhibitory or absent effects of IFN on pituitary hormone release. One of the reasons for these discrepancies could be that hormone changes were commonly assessed at a single time point in the day-night cycle. In this study we measured the circadian pattern of plasma ACTH, growth hormone (GH), prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) at 6 different time points within a 24-hour cycle in adult male Wistar rats.

METHODS

Groups of 6-8 rats kept under light from 08:00 to 20:00 h daily received 5 daily injections intraperitoneally of human IFN-gamma (10(5) IU/kg body weight) or saline at 08:30 h. Plasma ACTH, GH, prolactin, LH and FSH levels were measured by a homologous specific double antibody RIA.

RESULTS

A factorial ANOVA for main effects indicated a significant 43% increase of circulating prolactin in IFN-gamma-treated rats. Time of day changes were significant for the five hormones examined and these diurnal variations became altered by IFN-gamma administration, with a phase advance of ACTH peak, a suppression of the rest phase peak of GH, the appearance of a second peak of prolactin at an early phase of daily photoperiod, and the blunting of the 24-hour variations of plasma FSH.

CONCLUSION

The data point out an effect of IFN-gamma on the mechanisms responsible for the circadian organization of pituitary hormone release.

Effect of melatonin on biochemical variables of the blood in dairy cows

In order to examine the effect of exogenous melatonin on selected biochemical variables of the blood in ruminants, dairy cows were given the pineal gland hormone in the dose of 0.1 mg/kg body weight. One and four hours after melatonin administration blood samples were collected from the cows in the control and the treated group in order to determine the levels of glucose, insulin, total cholesterol, triglycerides, free fatty acids, as well as the activities of alanine and aspartate aminotransferase. The pineal gland hormone caused a significant increase in the levels of total cholesterol and triglycerides, slight increases in glucose and insulin levels, and a significant decrease in the concentration of free fatty acids. Melatonin did not exert an effect on the activity of liver enzymes.

Daily profiles of plasma prolactin (PRL), growth hormone (GH), insulin-like growth factor-1 (IGF-1), luteinizing hormone (LH), testosterone, and melatonin, and of pituitary PRL mRNA and GH mRNA in male Long Evans rats in acute phase of adjuvant arthritis

We studied the effects of adjuvant arthritis (AA) on the endocrine circadian rhythms of plasma prolactin (PRL), growth hormone (GH), insulin-like growth factor-1 (IGF-1), luteinizing hormone (LH), testosterone, and melatonin and of pituitary PRL and GH mRNA in male Long Evans rats. Groups of control and AA rats (studied 23 days after AA induction) that were housed under a 12/12 h light/dark cycle (light on at 06:00 h) were killed at 4 h intervals starting at 14:00 h. Cosinor analysis revealed a significant 12 h rhythm in PRL and PRL mRNA (p < 0.001) in controls with peaks at 14:00 h and 02:00 h, respectively. The peak at 02:00 h was abolished in the AA group resulting in a significant 24 h rhythm in parallel with that of PRL (p < 0.05) and PRL mRNA (p < 0.0001). Growth hormone showed no rhythm, but a significant rhythm of GH mRNA was present in both groups (p < 0.0001). Insulin-like growth factor-1 showed a 24 h rhythm in control but not in AA rats. The mean values of GH, GH mRNA, and IGF-1 were significantly reduced in AA. Luteinizing hormone displayed a significant 24 h rhythm (p < 0.01) peaking in the dark period in the control but not AA group. Testosterone showed in phase temporal changes of LH levels with AA abolishing the 02:00 h peak. Melatonin exhibited a significant 24 h rhythm in control (p < 0.001) and AA (p < 0.01) rats with maximum levels during the dark phase; the mesor value was higher in the AA males. These results demonstrate that AA interferes with the rhythms of all the studied hormones except the non-24 h (arrhythmic) GH secretion pattern and the rhythm in melatonin. The persistence of a distinct melatonin rhythm in AA suggests the observed disturbances of hormonal rhythms in this condition do not occur at the level of the pineal gland.

Immune function in turkey breeder hens during the short day prelighting period and renewal of photosensitivity for egg production

Photorefractoriness (PR) in the turkey breeder hen is characterized by a lack of responsiveness to photoperiods that previously induced or maintained egg production. The consequence of PR is spontaneous regression of ovarian function and cessation of lay. Photosensitivity (PS) may be regained by giving at least 8 wk of short photoperiod (8L:16D) (light restriction). Following the transition from PR to PS, the birds may be photostimulated with long photoperiods, which allows for the recrudescence of ovarian function and normal egg production. Although the return of reproductive viability is the parameter for determining the successful recycle of ovarian function, there are no known reports of the physiological costs of this transition on immune function in the turkey breeder hen. We conducted an experiment to determine the immune responsiveness at various stages of recycle in the turkey breeder hen. Fifty photorefractory birds were selected and distributed equally among five treatment groups (time points). All birds were given an 8-wk period of light restriction (8L:16D) followed by a 12-wk period of photostimulation (16L:8D). The cellular (cutaneous basophil hypersensitivity CBH) and humoral (antibody titer) immune responses were determined in each treatment group (sequential time points): prelight restriction, 2-wk light restriction, 7-wk light restriction, 2-wk photostimulation, and 12-wk photostimulation. After 2-wk light restriction, there was a reduction in the cellular (64.1%) and humoral (59.5%) immune responses from that of the PR hens at the start. After 7-wk light restriction, the humoral responses increased (33.5%) as compared to the 2-wk light restriction time point Upon photostimulation, both the cellular (23.3%) and humoral (52.4%) immune responses were reduced at 2 wk of photostimulation as compared to the prior 7-wk light restriction time point. Finally, there was a rise in cellular (45.7%) and humoral (72.3%) immune responses after 12 wk of photostimulation as compared to the prior 2-wk photostimulation time point. We concluded that recycling of PR turkey hens was associated with altered cellular and humoral immune responses characterized by initial decline then recovery in both the light restriction and the postphotostimulation periods.

Effect of melatonin on 24h changes in plasma protein levels during the preclinical phase of Freund's adjuvant arthritis in rats

The 24h rhythms in plasma protein concentration were examined in rats on the third day after injection of Freund's complete adjuvant or adjuvant's vehicle, performed 3h after light on. In rats treated with adjuvant's vehicle, peak values of albumin and gamma globulin occurred during the nocturnal activity span (P < .02 and P < .0001, respectively), while those of alpha-1, alpha-2, and beta globulins were found late during the rest span (P < .002, P < .0001, and P < .0004, respectively). Freund's adjuvant administration abolished temporal changes in plasma albumin and beta globulin levels. It also decreased the amplitude of daily changes in alpha-1 and alpha-2 globulin (P < .05) and diminished mean values of alpha-2 globulin (P < .01). Pretreatment of rats with melatonin (30 microg daily) for 11 days, 11h after light on, counteracted mycobacterial adjuvant-induced suppression of the 24h rhythms in albumin and alpha-1, alpha-2, and beta globulins. The results further support the existence of preventive properties of a pharmacological dose of melatonin in situations in which a lost of circadian rhythmicity is expected.

Effect of superior cervical ganglionectomy on 24-h variations in hormone secretion from the anterior hypophysis and in hypothalamic monoamine turnover during the preclinical phase of Freund's adjuvant arthritis in rats

The effect of superior cervical ganglionectomy (SCGx) on 24-h rhythms of circulating adrenocorticotropic hormone (ACTH), growth hormone (GH), prolactin and luteinizing hormone (LH) and of hypothalamic noradrenaline content and dopamine and serotonin turnover, was assessed in rats 3 days after administering Freund's complete adjuvant. In sham-operated rats, Freund's adjuvant injection increased serum ACTH without affecting its diurnal rhythmicity. SCGx, performed 10 days earlier, suppressed 24-h rhythmicity and augmented mean values of circulating ACTH. A depressive effect of immunization on GH release was found in both sham-operated and SCGx rats. GH concentrations did not exhibit diurnal rhythmicity and decreased after immunization. Time-of-day-related changes in serum prolactin were significant for all examined groups, except for SCGx-immunized rats. Freund's adjuvant administration augmented prolactin secretion. Daily changes in serum LH concentration and a decrease after immunization were found in both sham-operated and SCGx rats. SCGx: (i) counteracted inhibition of daily variations of noradrenaline content in medial hypothalamus of Freund's adjuvant-injected rats; (ii) decreased anterior hypothalamic dopamine turnover and augmented it in the medial hypothalamus; (iii) lowered amplitude of serotonin turnover rhythm in medial hypothalamus. The data indicate that several early changes in levels and 24-h rhythms of circulating ACTH and prolactin, and in hypothalamic noradrenaline content and dopamine and serotonin turnover, were modified by a previous SCGx in Freund's adjuvant-injected rats.