Diurnal Profiles of Blood Glucose in Relation to Time of Administration of Melatonin in Male Spotted Munia (Lonchura punctulata)

The study was aimed at demonstration of the effect of a single acute dose of melatonin (0.5 mg/ 100 g body wt.) on the diurnal profile of blood glucose in male spotted munia in relation to the administration of hormone at the onset of light (i.e., at 06.00 h) or at the onset of darkness (i.e., at 18.00 h) under natural photoperiodic (~12L : 12D) conditions. Blood samples from all birds belonging to the control, sham-control (administered only with the vehicle of hormone, i.e., ethanol-saline 1:9 v/v), and melatonin treated groups were collected at four time points, i.e. 06.00 h, 12.00 h, 18.00 h, and 24.00 h, in a 24 hour cycle. The blood glucose levels in control and sham-control birds showed marked variation with regard to the time of sampling, with a mid-day peak and morning nadir. Exogenous melatonin induced a significant alteration in this diurnal pattern of blood glucose with a marked variation in relation to the time of administration of melatonin. While morning administration of melatonin resulted in hypoglycemia at 12.00 h and 24.00 h and hyperglycemia at 18.00 h, the response to evening injection of melatonin was only hypoglycemic at 24.00 h leaving the glycemic values at other time-points almost unaltered compared to the blood glucose levels in control and sham-control munias. The results of this investigation demonstrate for the first time that a schedule of morning administration of melatonin induces a more broad range of variations in the blood glucose levels than a schedule of evening administration does.     

Ultrastructural circadian variation of mast cells in the pinna of the mouse

It has been found previously under the light microscope that there was a circadian variation in mast cell number in the pinna of mice. The mast cell number was increased at 18.00 h and decreased at 06.00 h. In the current study, 5 mice of each group were synchronized for 4 weeks with a standard lighting regimen (light: 06.00-20.00 h; dark: 20.00-06.00 h). Both pinnas of every mouse of each group were removed at 06.00, 12.00, 18.00 and 24.00 h, respectively. Under the electron microscope, it was observed that more degranulated mast cells were found at 06.00 h and more intact mast cells were visible at 18.00 h. It appeared that the mast cell numbers, decreased and increased under the light microscope, were due to mast cell degradation and regranulation. This finding suggests that a functional circadian variation exists in the mast cell under physiological conditions.     

Detailed profile of prolactin secretion in the immature female rat: evidence for the existence of an ultradian rhythm

The detailed profile of prolactin (PRL) secretion in 22-24 and 29-31 days old female rats was investigated by serial blood sampling through an intracardiac cannula at 15-min intervals for each of the 9 or 10-h periods beginning at 09.00 or 10.00 and 22.00 h. By analysis of the power spectrum and the least squares method the time series of PRL concentrations which were measured by RIA were found to have approximately a 3-h period ultradian rhythm in either sampling period of both the 22-24 and 29-31 days old rats. The peak times calculated based on the acrophase estimated through the calculation of periodicity were concentrated around 12.00, 15.00 and 18.00 h for the sampling period 10.00-19.00, and 24.00, 03.00 and 06.00 h for the sampling period 22.00-07.00 h. However, in more than half of the animals at 22-24 days of age, one secretory episode around 12.00 h, and two secretory episodes around 24.00 and 03.00 h had markedly small amplitudes, making the remaining secretory episodes distinct diurnal and nocturnal surges, respectively. In the animals at 29-31 days of age, the amplitudes of the PRL episodes occurring around 12.00 h were markedly small, making the remaining two episodes as diurnal surges, whereas the amplitudes of PRL secretory episodes during the period 22.00-07.00 h were analogous to each other. These findings indicate that the semicircadian rhythm of PRL secretion is established on the basis of PRL secretion with the 3.0-h period ultradian rhythm.     

Quantitative study of circadian variations in mast cell number in different regions of the mouse

The tongue, pinna and dorsal skin of adult male C-1 mice were removed at 03.00, 06.00, 09.00, 12.00, 15.00, 18.00, 21.00 and 24.00 h, fixed in basic lead acetate and stained with Alcian blue-safranin or 0.5% toluidine blue. The mast cell numbers of these regions were counted and analyzed statistically by analysis of variance. It was found that there were circadian variations in the mast cell number in the tongue, pinna and dorsal skin. The difference between the minimum and maximum of circadian variation in mast cell number in all three regions was highly significant (p less than 0.01). Furthermore, the time points of the maximum and minimum of mast cell number varied between the different regions. The time point of the minimum in the tongue and pinna was at 06.00 h, whereas it was at 09.00 h in the dorsal skin. The time point of the maximum in the tongue and dorsal skin was at 21.00 h, but in the pinna it was at 18.00 h.     

Circadian variations of the plasma proteins in the adult male rat under natural synchronisation (author's transl)]

Circadian rhythms of blood total proteins, albumin, alpha 1-, alpha 2-, beta- and gamma-globulins were documented in 80 Wistar SPF adult male rats, synchronized by natural light (06.00-18.00 h) and darkness (18.00-06.00 h) during the month of October 78. Blood was sampled at four fixed time points in the 24 h scale (i.e. 04.00, 10.00, 16.00 or 24.00 h). Total proteins, albumin, alpha 2- and gamma-globulins showed a statistically significant rhythm with a maximum at 04.00 h. The data obtained in anaesthetized rats under artificial synchronization and in man are compared, taking into account that the rat is a nocturnally active rodent. The present work partially confirms the hypotheses of previous chronopharmacological studies, thus e.g. curarizing substances have a mimimum activity when the protein plasma level, especially albumin, is the highest.     

Drop off rhythm and survival periods of <Emphasis Type="Italic">Amblyomma lepidum</Emphasis> (Acari: Ixodidae) under field conditions

In this study, engorged Amblyomma lepidum ticks were found to drop off in two peaks, one in the morning and one in the evening. Most larvae and females engorged during the morning hours between 06.00 h and 10.00 h with a peak around 08.00 h, whereas the majority of the nymphs dropped in the evening between 18.00 h and 24.00 h with the peak around 22.00 h. Although the effect of time on drop-off patterns of the ticks was statistically significant (p≤ 0.001), there were no significant seasonal influences. Survival of unfed stages of A. lepidum was also studied and was found to increase from larvae to adult ticks. The longest survival periods of 10, 11 and 14 weeks were recorded during the wet season for larvae, nymphs and adults, respectively. It is concluded that environmental conditions required for survival of A. lepidum are optimal only during the wet season and that during other seasons the tick depends primarily on prevailing micro-climatic conditions for its survival.     

Diurnal Profiles of Serum Triiodothyronine and Thyroxine Levels: A Study in Male Roseringed Parakeets (Psittacula krameri) Following Exogenous Administration of Melatonin

This study demonstrates that under subtropical environmental conditions the circulating levels of triiodothyronine (T 3 ) and thyroxine (T 4 ) in adult male roseringed parakeets undergo parallel changes according to a diurnal cycle with a trough in the early morning and a peak in the evening. Chronic afternoon administration of melatonin (25 µg/ 100 g body wt./ day for 30 consecutive days) abolishes time-bound changes in the concentrations of T 3 by suppressing its evening peak, but does not abolish the diurnal rhythm of T 4 . Exogenous melatonin, however, causes a significant increase in the evening value of serum T 4 and a decrease in its value at midnight resulting in phase-shifting of the diurnal fluctuations of T 4 compared to that in the control birds. It appears that exogenous melatonin can alter the diurnal profiles of serum thyroid hormones in a wild psittacine bird.     

Diurnal Profiles of Serum Triiodothyronine and Thyroxine Levels: A Study in Male Roseringed Parakeets (Psittacula krameri) Following Exogenous Administration of Melatonin

This study demonstrates that under subtropical environmental conditions the circulating levels of triiodothyronine (T 3) and thyroxine (T 4) in adult male roseringed parakeets undergo parallel changes according to a diurnal cycle with a trough in the early morning and a peak in the evening. Chronic afternoon administration of melatonin (25 µg/ 100 g body wt./ day for 30 consecutive days) abolishes time-bound changes in the concentrations of T 3 by suppressing its evening peak, but does not abolish the diurnal rhythm of T 4. Exogenous melatonin, however, causes a significant increase in the evening value of serum T 4 and a decrease in its value at midnight resulting in phase-shifting of the diurnal fluctuations of T 4 compared to that in the control birds. It appears that exogenous melatonin can alter the diurnal profiles of serum thyroid hormones in a wild psittacine bird.     

Spontaneous wheel running in laboratory rats genetically selected for activity level in a novel environment

Wistar rats were genetically selected for either high (+A) or low (-A) locomotor activity level in a new environment. The response to the novelty was tested in all filial generations at the age between 75-80 days of life. Groups of 15 +A male rats selected from the 11th and 12th generations were placed in the individual cages connected with rotation wheels at the age 149 +/- 9 days. For a period of 32 days, the spontaneous wheel running activity was recorded for the time intervals 0.00-6.00 a.m., 6.00-12.00, 12.00-18.00, and 18.00-24.00 h. The -A group exhibited a generally low level of running activity over the entire experimental period, whereas the time of running in the +A tended to increase. Inside the +A group, homogeneous as to the short- term activity level, there gradually differentiated two sub-groups, one with relatively constant medium values and the other which showed an enormous prolongation of the time spent with running. The +A and -A groups differed also in their daily activity rhythm. Whereas the +A rats reached maximum of their activity between 18-24 h., followed by a rapid decrease in the morning hours, the -A animals showed a tendency to a later onset of night-type activity, and a higher level continued to morning hours.     

Circadian changes in the RNA content of rat hypothalamic nuclei in relation to food intake

The ribonucleic acid (RNA) and protein content of the ventromedial hypothalamic nuclei (VMH), the lateral hypothalamic areas (LHA) and the cortex (C) of adult male Wistar rats followed free access to food and water were determined at 6-hour intervals (at 6.00, 12.00, 18.00 and 24.00 h); the RNA and protein content of the suprachiasmatic nuclei (SCN) were determined at 12.00 and 24.00 h. The RNA content of the VMH, LHA and SCN differed at various intervals; in the cortex it did not alter significantly. The highest RNA concentration in the VMH was recorded at 18.00 h and in the LHA at 24.00 h, after which, in both areas, it fell. The lowest RNA content in the LHA and the VMH was found at 12.00 h. In the SCN, the RNA concentration at 24.00 h was significantly higher than at 12.00 h. The protein content did not alter significantly during the circadian cycle in any of the structures examined.     

Renal excretion and saline intake during post-stress immobilization period in rats

An experiment in which the rats access either to 0.5% or 1.5% saline was designed in order to further characterise the relationship between sodium intake and renal excretion after acute immobilization stress. A saline solution for 3 days was provided to the rats previous to the experimental day. On that day, after finishing acute immobilization stress, all variables under observation were measured every 6 h for 24 h. These periods were denominated as follows: T1 (12.00 to 18.00 h), T2 (18.00 to 24.00 h), T3 (24.00 to 06.00 h) and T4 (06.00 to 12.00 h). Acute immobilization stress reduced sodium renal excretion in both T1 and T2. Sodium intake in acute immobilization stress rats was lower than in control rats during all observed periods, while the urine volume was only reduced in the stressed animals in T1. These results were similar in both saline solution concentrations. A good correlation was observed between sodium intake and sodium excretion in control rats having access to either 0.5% or 1.5% saline as well as in stressed rats having access to 0.5% saline, this correlation was not observed in stressed rats with 1.5% saline. This suggests that stress impaired the renal capability of rats to handle high sodium but not a slight sodium overload. The inability of the kidney to excrete sodium may be critical to reduce sodium intake after acute immobilization stress.     

Rapid cold-hardening of Drosophila melanogaster in a field setting

Abstract.  Although laboratory studies demonstrate that cooling to ecologically relevant temperatures and/or at ecologically relevant rates induces rapid cold-hardening (RCH) in a variety of insects, little is known of the induction of RCH in nature. In the present study, caged Drosophila melanogaster (1–2 days posteclosion) from a colony established with flies collected locally are placed in a field setting (i.e. in approximately 4-cm deep leaf litter beneath an apple tree in Mount Pleasant, Michigan) during late afternoon (18.00 h EST; 05.00 h GMT). As the cage temperature falls from 22.1 ± 0.8 to 10.1 ± 0.1 °C between 18.00 and 06.00 h, the proportion of flies surviving a transfer to –6 °C for 1 h increases from 10.0 ± 6.2% to 68.1 ± 7.2%. When obtained from field cages, and then cooled from 23 °C at approximately 0.33 °C min⁻¹, more female flies remain behaviourally responsive (clinging to surfaces, exhibiting an active righting response, and/or climbing) at temperatures of 8–12 °C (24.00 h samples) or 7–12 °C (06.00 h samples), than do those sampled from cages kept in an incubator (23 °C). Field cooling reduces chill coma temperature from 8.7 ± 0.2 °C at 06.00 h to 7.1 ± 0.2 °C at 24.00 h, and to 6.6 ± 0.2 °C at 06.00 h. These data demonstrate that, in a recently collected culture of D. melanogaster , natural changes in microenvironmental temperature induce RCH that can benefit the organism at temperatures encountered in nature.     

Blood sugar control in diabetic patients bearing microinfusors: the importance of the dawn phenomenon

Significant early morning hyperglycemia (the so-called "dawn phenomenon") has been observed in insulin-dependent diabetics who were otherwise well controlled. This phenomenon, if present, could lead to errors in adapting the basal insulin infusion in CSII treated diabetic patients, because a normal glucose level in the morning could be associated with asymptomatic hypoglycemic values in the night. In order to observe the occurrence and to quantify the magnitude of this phenomenon 14 well controlled CSII-treated type I diabetics were hospitalized for 1 night and samples for the determination of blood glucose (14 patients) and serum cortisol, free insulin and NEFA (8 patients) were drawn at 24.00, 02.00, 04.00, 06.00, 08.00 h. Blood glucose values were slightly but significantly higher at 06.00 than at 02.00 (106 +/- 7.92 v.s. 88.57 +/- 7.02 mg/dl, p less than 0.025, paired Student t test) while serum free insulin values decreased from midnight to 02.00 and then they remained stable. It is concluded that the small increase of blood glucose values in the morning is not a major clinical problem in CSII treated diabetic patients.     

Suppression of circadian rhythms of pineal and testicular hormones following lithium treatment in normal and reversed light-dark cycles, constant light and constant dark in rats

The aim of the current investigation was to study the effect of lithium on circadian rhythms of pineal - testicular hormones by quantitations of pineal and serum serotonin, N-acetylserotonin and melatonin, and serum testosterone at four time points (06.00, 12.00, 18.00 and 24.00) of a 24-hr period under normal photoperiod (L:D), reversed photoperiod (D:L), constant light (L:L) and constant dark phase (D:D) in rats. Circadian rhythms were observed in pineal hormones in all the combinations of photoperiodic regimens, except in constant light, and in testosterone levels in all the photoperiodic combinations. Pineal and serum N-acetylserotonin and melatonin levels were higher than serotonin at night (24.00 hr), in natural L:D cycle, in reversed L:D cycle or similar to normal L:D cycle in constant dark phase, without any change in constant light. In contrast, testosterone level was higher in light phase (12.00 hr through 18.00 hr) than in the dark phase (24.00 hr through 06.00 hr) in normal L:D cycle, in reversed L:D cycle, similar to normal L:D cycle in constant dark (D:D), and reversed to that of the normal L:D cycle in constant light (L:L). Lithium treatment (2 mEq/kg body weight daily for 15 days) suppressed the magnitude of circadian rhythms of pineal and serum serotonin, N-acetylserotonin and melatonin, and testosterone levels by decreasing their levels at four time points of a 24-hr period in natural L:D or reversed D:L cycle and in constant dark (D:D). Pineal indoleamine levels were reduced after lithium treatment even in constant light (L:L). Moreover, lithium abolished the melatonin rhythms in rats exposed to normal (L:D) and reversed L:D (D:L) cycles, and sustained the rhythms in constant dark. But testosterone rhythm was abolished after lithium treatment in normal (L:D)/reversed L:D (D:L) cycle or even in constant light/dark. The findings indicate that the circadian rhythm exists in pineal hormones in alternate light - dark cycle (L:D/D:L) and in constant dark (D:D), but was absent in constant light phase (L:L) in rats. Lithium not only suppresses the circadian rhythms of pineal hormones, but abolishes the pineal melatonin rhythm only in alternate light - dark cycles, but sustains it in constant dark. The testosterone rhythm is abolished after lithium treatment in alternate light - dark cycle and constant light/dark. It is suggested that (a) normal circadian rhythms of pineal hormones are regulated by pulse dark phase in normal rats, (b) lithium abolishes pineal hormonal rhythm only in pulse light but sustains it in constant dark phase, and (c) circadian testosterone rhythm occurs in both pulse light or pulse dark phase in normal rats, and lithium abolishes the rhythm in all the combinations of the photoperiod. The differential responses of circadian rhythms of pineal and testicular hormones to pulse light or pulse dark in normal and lithium recipients are discussed.     

Influence of exogenous thyroxine on plasma melatonin in juvenile Atlantic salmon (Salmo salar)

One of the most clearly defined endocrine changes during the parr-smolt transformation of anadromous salmonids is an increase in plasma levels of thyroid hormones. The role of pineal hormone melatonin in timing and synchronisation of smoltification is widely discussed. The effect of administration of exogenous thyroxine (T4) on plasma melatonin was investigated in juvenile Atlantic salmon (Salmo salar) at the early stages of parr-smolt transformation. Fish were kept in fresh water under simulated-natural photoperiod and exposed to exogenous T4. Fish were sampled at 12.00 and 24.00 h from treatment and control tanks, 2 and 14 days after treatment started. Plasma melatonin and L-thyroxine were measured using RIA and competitive enzyme immunoassay, respectively. After 2 days of T4 treatment, marked difference in plasma melatonin concentration measured at 12.00 and 24.00 h was still observed in both groups. However, 2-week exposure to T4 caused a reduction in night-time plasma melatonin level and thus, probably, inhibited melatonin related time-keeping system in juvenile salmon. Additional studies are needed to clarify the mechanism of the described phenomenon.     

The effects of nocturnal life on endocrine circadian patterns in healthy adults

We observed the 24-hour patterns of endocrine in medical students who lived either a diurnal life or nocturnal life. Nocturnal life was designed by skipping their breakfast but consuming much (>50% of their daily food intake) in the evening and at night with the sleep from 0130 h to 0830 h the next morning. After 3 weeks in the experimental life, the 24-hour plasma concentrations of melatonin, leptin, glucose and insulin were measured every three hours. Both plasma melatonin and leptin showed peaks at 0300 h in the diurnal lifestyle group, and the night peaks decreased in the nocturnal lifestyle group. The changes in the patterns of melatonin and leptin were highly consistent with that of night-eating syndrome (NES). Plasma glucose increased after all meals in both groups. Its concentration maintained a high level in the nocturnal lifestyle group between midnight and early morning while insulin secretion decreased markedly during this period. Furthermore, the strong association between glucose and insulin in the diurnal lifestyle group after meals was damaged in the nocturnal lifestyle group. It was suggested that nocturnal life leads to the impairment of insulin response to glucose. Taking these results together, nocturnal life is likely to be one of the risk factors to health of modern people, including NES, obesity and diabetes.     

Circadian rhythms of folate and vitamin B12 concentration in relation to convulsive thresholds of mice

Circadian rhythms of folate and vitamin B₁₂ concentrations in the liver, brain and blood of Swiss mice have been determined. The relation of the changes in vitamin concentration to circadian rhythms in locomotor activity, drinking activity and convulsive thresholds (maximal electroshock seizure threshold) have been determined also. Both free folic acid (FFA) and total folic acid (TFA) of liver and blood showed minimum values at 21.00–24.00 h and maximum values at 06.00–09.00 h. Liver TFA declined at a steady rate from the peak value at 09.00 h whereas liver FFA and plasma folate maintained constant values from 09.00–18.00 h then declined rapidly. Brain folate (TFA and FFA) showed no rhythm. The concentrations of vitamin B₁₂ in plasma, liver and brain showed only minor fluctuations. Locomotor and drinking activities showed very similar rhythms with a sustained period of high activity between 12.00–21.00 h followed by a much shorter second period of high activity (23.00–03.00 h). Convulsive threshold declined during the first period of increased locomotor and drinking activities reaching a minimum value at 21.00 h thus just preceding the nadir in folate concentrations in liver and blood.     

Influences of graded dose of melatonin on the levels of blood glucose and adrenal catecholamines in male roseringed parakeets (Psittacula krameri ) under different photoperiods

Effects of daily evening (just before the onset of darkness in a 24 h light dark cycle) administration of graded doses (25, 50, or 100 microg/100 g body wt./day for 30 days) of melatonin on the concentrations of blood glucose and adrenal catecholamines were studied in sexually active male roseringed parakeets under natural (NP; approximately 12L: 12D) and artificial long (LP; 16L: 8D) and short (SP; 8L: 16D) photoperiods. Blood samples and adrenal glands were collected from each bird during the mid-day on the following day of the last treatment. The concentrations of glucose in blood and epinephrine (E) and norepinephrine (NE) in the adrenals were measured. The results of the study indicated that exogenous melatonin induces hypo- or hyperglycemia depending on the dose of hormone administered as well as to the length of photoperiod to which birds were exposed. The levels of E and NE in the adrenals were shown also to vary in relation to photoperiod and the dose of melatonin administered. But the nature of the influence of melatonin becomes different under altered photoperiodic conditions. It appears that short photoperiods are more effective than long photoperiods as a modulator of glycemic and adrenal catecholaminergic responses to exogenous melatonin. A statistically significant correlation between the levels of blood glucose and that of E and NE in the adrenals was found in the control birds, but not in the melatonin treated birds. The results suggested that the responses of blood glucose and adrenal catecholamines to the treatment with melatonin in the roseringed parakeets may not be dependent on each other.     

Circadian rhythm of aldosterone in dairy cattle during the summer

Twelve Holstein heifers, pregnant from 120–150 days were used to study the circadian rhythm of aldosterone, cortisol, progesterone, sodium and potassium in dairy cattle during the summer in Louisiana. Cortisol was not significantly influenced by time (time 1 = 06.00 h). Aldosterone, sodium, potassium and progesterone changed significantly (P<.01) with time. Aldosterone peaked (116.5±17.2 pg/ml) at 08.00 h and then generally declined to 16.00 h (26.7±2.0 pg/ml). Sodium generally increased from 06.00 h (320.1±7.3 mg%) to 18.00 h (377.9±6.1 mg%), and then declined. Potassium generally increased from 06.00 h (20.9±0.5 mg%) to 22.00 h (23.0±0.3 mg%). Progesterone generally increased from 07.00 h (2.8±0.4 mg/ml) to 24.00 h (7.5±1.4 mg/ml). Aldosterone was significantly related to temperature associated with the time of the day samples were taken (r = 0.66, P<.02).     

Diel biting activity of Culex (Melanoconion) caudelli in Trinidad, West Indies

The diel biting periodicity of the arbovirus vector Culex (Melanoconion) caudelli Dyar and Knab (Diptera; Culicidae) in the Aripo-Wallerfield forest, Trinidad, was studied by collecting mosquitoes attracted to mouse-baited traps at 2-hourly intervals during eight 24 h periods. Biting females of Cx caudelli were collected during all night-time hours, 18.00-06.00 hours, with an overall unimodal pattern, i.e. one well-defined peak between 22.00 and 04.00 hours. This contrasts with previous reports that Cx caudelli is diurnally active. During the four moon phases, the period of peak biting activity varied from 22.00 to 24.00 hours at fullmoon, from 22.00 to 04.00 hours at first quarter, and from 24.00 to 02.00 hours at new moon and last quarter phases. The number of mosquitoes collected varied significantly with moon phases, the highest (152/24 h) being collected in the first lunar quarter and the lowest (71/24 h) in the last lunar quarter. Cloud cover and rainfall had no significant effect on the diel biting periodicity of Cx caudelli.