Iveta Herichová

Perinatal development of circadian melatonin production in domestic chicks

Abstract: In contrast to the situation in mammals, in which circadian melatonin production by the pineal gland does not begin until some time after birth, the development of pineal gland rhythmicity is an embryonic event in the precocial domestic fowl. A distinct melatonin rhythm was found in 19‐d‐old chick embryos maintained under light:dark (LD) 16:8. No significant variation in melatonin levels was detected in embryos exposed to LD 8:16. The melatonin rhythm in the pineal gland and plasma of chick embryos incubated for 18 d in LD 12:12 persisted for 2 d in constant darkness indicating that melatonin production is under circadian control at least from the end of embryonic life. A I‐d exposure to a LD cycle during the first postembryonic day was sufficient to entrain the melatonin rhythm, and previous embryonic exposure to either LD or constant darkness (DD) neither modified this rapid synchronization nor did it affect the melatonin pattern during the two subsequent days in DD. It is suggested that, in contrast to the situation in mammals, the avian embryo has evolved its own early circadian melatonin‐producing system because, as a consequence of its extrauterine development, it cannot use the system of its mother.

Melatonin content in plasma and large intestine of patients with colorectal carcinoma before and after surgery

Abstract: The distinct melatonin rhythm with higher concentrations during the darktime was found in plasma of both control patients and patients with colorectal carcinoma. Moderate surgery did not induce any changes in plasma melatonin levels, but a pronounced increase in both the day‐ and nighttime melatonin concentrations was found after surgical treatment for colon cancer. The melatonin content in the tumor tissue did not differ from that in the proximal and the distal parts of the resected gut, which were without signs of malignant changes. Neither concentrations of serotonin nor 5‐hydroxyindole acetic acid differed among analyzed parts of the gut. Daytime melatonin concentrations in gut tissue (314.7 ± 87.8 pg/g of wet tissue) were more than ten times higher than the daytime levels in circulation. It was hypothesized that increased levels of this hormone in the gastrointestinal tract may play an important protective role against the development of colorectal cancer via stimulation of the immune system, protection against free radicals, and interaction with fatty acid uptake and metabolism.

Effect of streptozotocin-induced diabetes on daily expression of per2 and dbp in the heart and liver and melatonin rhythm in the pineal gland of Wistar rat.

The circadian system is a flexible framework allowing a proper adjustment of physiological functions to the regularly changing environment. Pathways that are used to synchronize components of the circadian system have been shown to be susceptible to pathophysiological conditions. In our study, we investigated effects of streptozotocin (STZ)-induced diabetes mellitus on function of the circadian system at the level of melatonin synthesis and expression of per2 and dbp in the heart and liver in 8-week-old Wistar rats. Rhythmic pattern of clock gene per2 and transcription factor dbp in controls and STZ-treated animals was determined. Streptozotocin administration had a more substantial effect on per2 expression in the liver than in the heart. Pronounced phase advance in the rhythm of dbp expression in both the liver and the heart was observed. The melatonin rhythm reflecting the phase of the master clock was not affected by STZ application. Changes in per2 and dbp expression in the heart and liver imply alterations in input pathway or peripheral oscillators with possible consequences on function of analysed organs. (Mol Cell Biochem 270: 223–229, 2005)

Rhythms of the pineal N-acetyltransferase mRNA and melatonin concentrations during embryonic and post-embryonic development in chicken

Development of a daily rhythmicity in transcription of a gene encoding a rate-limiting enzyme of melatonin biosynthesis, the arylalkylamine-N-acetyltransferase (AA-NAT) was studied by northern blot analysis in pineal glands of 16 and 19-day-old embryos and 1, 4, 8, 11, and 14-day-old chicks. In a parallel experiment, melatonin content in pineal glands and plasma was measured. A significant rhythm of AA-NAT expression was found at embryonic day (ED) 16, the earliest day assayed in this experiment. Expression was low during the daytime and a clear signal was found in the middle of the darktime. The intensity of the signal was increasing during the ontogeny. The nocturnal pineal melatonin concentrations were increasing over the studied period (from ED 19 until post-embryonic day 21). Midnight plasma melatonin concentrations increased from ED19 to PD 3 and oscillated around this value afterwards. Data show that rhythmic expression of AA-NAT mRNA starts very early in development of chicken and plays a major role in melatonin rhythm generation during embryonic development.

Role of melatonin in the control of growth and growth hormone secretion in poultry

The pineal hormone melatonin controls reproduction of photoperiodic mammals and is an integral part of the circadian organization in birds. Recent findings indicate an involvement of this hormone also in more basic physiological processes, including growth, development, and aging. Melatonin may modulate growth in poultry through interaction with transcriptional factors, through interaction with hormones involved in growth control, and by modulation of energy metabolism and decreasing physical activity. Our studies showed that a single melatonin injection increased plasma growth hormone (GH) concentrations in the Japanese quail. Specific serotonin receptor blocker ketanserin did not preclude a stimulatory action of melatonin on GH synthesis. Serotonin agonist quipazine increased GH levels but failed to enhance the stimulatory effect of melatonin. Pretreatment with melatonin in drinking water did not affect the magnitude of the GH response to subcutaneous (s.c.) administration of thyrotropin releasing hormone (TRH) that considerably stimulated GH secretion. Present data suggest that melatonin modulates rather central neural pathways involved in the control of GH synthesis at the hypothalamic level than the sensitivity of the pituitary gland.

Effect of rhythmic melatonin administration on clock gene expression in the suprachiasmatic nucleus and the heart of hypertensive TGR(mRen2)27 rats.

Objectives Plasma melatonin concentrations in non-dipping patients show a blunted daily rhythm. Melatonin has a capacity to improve disturbances in biological rhythms. Hypertensive TGR(mRen2)27 (TGR) rats with an upregulated renin–angiotensin system and inverted blood pressure profile were used to elucidate whether melatonin is able to influence the control of blood pressure. Design Melatonin was administered in drinking water to normotensive Sprague–Dawley (SD) and hypertensive TGR rats during the dark phase of the light: dark cycle 12: 12 for 4 weeks. Methods The effect of melatonin on blood pressure was monitored, and the expression of clock genes per2 and bmal1 and melatonin receptor MT1 in the suprachiasmatic nucleus (SCN) and the heart was measured by real time polymerase chain reaction during a 24-h cycle. Results and conclusion The administration of melatonin did not influence clock gene expression in the SCN but its effect on clock gene expression in the heart was phase dependent in both SD and TGR rats. Melatonin administration did not decrease the expression of melatonin receptors in the SCN and the heart. Melatonin did not decrease blood pressure in TGR rats but influenced the peripheral oscillator in the heart independently of the SCN. A modified function of molecular circadian oscillators in the heart can interfere with anticipation and disturb the adaptation of this organ to pressure overload.

Evidence for daily rhythms of the expression of proopiomelanocortin, interleukin-1-beta and interleukin-6 in adenopituitaries of male long-evans rats: effect of adjuvant arthritis.

Objective: Several interleukins (ILs) including IL-1β and IL-6 are produced in the anterior pituitary (AP) where they probably participate in the local regulation of hormone production. Immune challenge brings about the dysregulation of immune-endocrine interaction and enhanced the expression of pituitary IL-1β and IL-6. Little is known about regulation of their production, and therefore the purpose of the present work was to describe the relationship between circulating corticosterone and the mRNA expression of proopiomelanocortin (POMC), IL-1β and IL-6 in the AP during a 24-hour cycle in normal rats and rats with acute adjuvant arthritis (AA). Methods: Groups of intact male Long-Evans rats and rats 23 days after induction of AA kept on a 12-hour light/dark cycle (light on at 6:00 a.m.) were killed at 4-hour intervals starting at 2:00 p.m. Trunk blood was used for corticosterone determination by radioimmunoassay. Adenopituitaries were extracted for total RNA and the message of interest was quantitated by real-time PCR using specific primers and TaqMan probes. Parameters of rhythms were evaluated by cosinor analysis. Results: In normal rats, serum corticosterone showed a circadian rhythm with the peak at 6:00 p.m. and the nadir in the morning hours (p < 0.001). POMC mRNA in AP also showed a circadian rhythm (p < 0.05) which was inversely related to corticosterone levels. IL-1β and IL-6 expression in normal rats showed clear-cut daily rhythms (p < 0.001) with the nadirs in the dark period, in contrast to the corticosterone peak in plasma. In arthritic rats, rhythmic corticosterone secretion was suppressed with a plateau pattern of the rhythm. The mean POMC expression was higher than in controls, and the rhythm failed to be significant. IL-1β expression was suppressed by AA (p < 0.001) but the rhythm was still present (p < 0.05). The rhythmic pattern of IL-6 expression was similar to that of controls, but with higher mesor values (p < 0.05). Conclusion: These results suggest a regulatory relationship between circulating corticosterone and the expression of POMC, IL-1β and IL-6 in AP of normal rats. Arthritis induced a higher expression of POMC and IL-6 in the AP and a suppression of IL-1β mRNA during the 24-hour cycle which suggests the involvement of different regulatory mechanisms compared to normal conditions.

Expression of cell cycle regulatory factors hus1, gadd45a, rb1, cdkn2a and mre11a correlates with expression of clock gene per2 in human colorectal carcinoma tissue

Deregulated expression of clock gene per2 has previously been associated with progression of cancer. The aim of the present study was to identify genes related to per2 expression and involved in cell cycle control. Patients surgically treated for colorectal carcinoma with up-regulated and down-regulated per2 expression in cancer versus adjacent tissue were studied. Total RNA from cancer tissue of these patients was used to specify genes associated with altered per2 expression using the Human Cell Cycle RT2 profiler PCR array system. We identified seven genes positively correlated (hus1, gadd45α, rb1, cdkn2a, cdk5rp1, mre11a, sumo1) and two genes negatively correlated (cdc20, birc5) with per2 expression. Expression of these seven genes was subsequently measured by real time PCR in all patients of the cohort. Patients were divided into three groups according to TNM classification. We observed an increase in gene expression in cancer tissue compared to adjacent tissue in the first group of patients in all genes measured. Expression of genes positively associated with per2 gene expression was dependent on tumor staging and changes were observed preferentially in cancer tissue. For genes negatively associated with per2 expression we also detected changes in expression dependent on tumor staging. Expression of cdc20 and birc5 was increasing in the proximal tissue and decreasing in the cancer tissue. These results implicate functional involvement of per2 in the process of carcinogenesis via newly uncovered genes. The relevancy of gene expression for determination of diagnosis and prognosis should be considered in relation to tumor staging.

Melatonin and clock genes expression in the cardiovascular system.

Generation of circadian oscillations is based on rhythmic expression of clock genes and subsequent post-transcriptional and post-translational modifications. In addition to the central circadian oscillator - the suprachiasmatic nucleus (SCN), peripheral oscillators have been demonstrated in many tissues, including the heart and blood vessels. Melatonin mediates cyclic lighting conditions to rhythmic endocrine signal and is able to synchronize neuronal firing in the SCN via membrane receptors. Clock gene expression is melatonin sensitive in the pars tuberalis, genes cry1 and tim1 respond to single injection while neurod1 and npas4 are influenced via long lasting mechanisms. In the rat heart, melatonin phase advanced expression of per2 and bmal1 independently from its effects on the SCN. Melatonin is an important endogenous signal able to synchronize circadian oscillations in the cardiovascular system. It may be effective especially in situations when the circadian control is weakened or organism must adapt to rapid changes in rhythmic environmental conditions.

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.