Circadian rhythm in Schistosoma haematobium egg excretion

The usual peak daily egg excretion period in persons harbouring Schistosoma haematobium is the late morning and early afternoon. No evidence was found to support a hypothesis that the rhythm is mechanical in origin being due to rapid increase of bladder activity in the early morning.A partial reversion of the rhythm occurred when day shift workers changed to night shift.The possible role in the circadian rhythm of host factors—temperature and metabolism and of proteolytic enzyme secretion by miracidia are discussed.     

Circadian rhythm of spontaneous locomotor activity in the bed bug, Cimex lectularius L.

Bed bugs must avoid detection when finding hosts and returning to hidden harborages. Their stealthy habits include foraging when hosts are asleep. Characteristics of spontaneous locomotor activity rhythm of bed bugs with different feeding histories were studied. In the absence of host stimuli, adults and nymphs were much more active in the dark than in the light. The onset of activity in the scotophase commenced soon after lights-off. The free-running period (τ) for all stages was longer in continuous darkness (DD) than in continuous light (LL). The lengthening of τ in DD is an exception for the circadian rule that predicts the opposite in nocturnal animals. Activity in all stages was entrained to reverse L:D regimes within four cycles. Short-term starved adults moved more frequently than recently fed adults. While bed bugs can survive for a year or more without a blood meal, we observed a reduction in activity in insects held for five weeks without food. We suggest that bed bugs make a transition to host-stimulus dependent searching when host presence is not predictable. Such a strategy would enable bed bugs to maximize reproduction when resources are abundant and save energy when resources are scarce.     

Circadian rhythm of blood glucose and tissue glycogen in fed and fasted rats

Blood glucose and tissue glucogen circadian rhythms were determined in male Wistar rats adapted 3 weeks to an artificial lighting regimen of 12 hours' light and 12 hours' darkness. Over a period of 24 hours we examined at 3-hour intervals the blood glucose concentration and the glycogen content of the liver, heart, skeletal muscle (quadriceps femoris) and white (epididymal) and brown (interscapular) adipose tissue of fed rats and rats fasted for 24 hours. The experiments were carried out in the autumn and the results were evaluated statistically by an analysis of variance and the cosinor test. The blood glucose level and the glycogen concentration in all the given tissues, in both fed and starved rats, displayed rhythmic oscillations with a 24- or 12-hour period in the course of the day, with the exception of glycogen in the white adipose tissue of fed rats, in which cosinor analysis failed to demonstrate any rhythm. One day's fasting did not affect the character of circadian rhythm.     

Circadian rhythm of gravitaxis in Euglena gracilis.

Euglena gracilis, a unicellular, photosynthetic flagellate is a model system for environmentally controlled behavioral reactions. One pronounced reaction is the orientation with respect to gravity. In synchronized cultures with no cell growth a distinct circadian rhythm of negative gravitactic orientation could be observed. The main maximum of sensitivity was detected 5 h after the beginning of the subjective day, the main minimum 5 h before the beginning of the subjective day. Transferring synchronized cultures to continuous light resulted in an almost instantaneous loss of rhythmicity. In contrast, after transfer to permanent darkness cells exhibited a circadian rhythm with a progressive shortening of the period for more than 5 days. These findings are in contrast to the circadian rhythm of phototaxis in Euglena, where a free-running period of 24 h was observed. Parallel measurements of negative gravitactic orientation, velocity, cell shape as well as cAMP concentration in synchronized cultures revealed a circadian rhythm of all reactions. The results are discussed with regard to the possible role of cell shape and cAMP in gravitactic orientation.     

Diurnal and seasonal variations of glycogen content in the rat brain.

The effect of seasonal and diurnal variations on glycogen content in the brain was investigated in 3-month old Wistar rats. In the first experimental series, the glycogen content in the brain was determined every 2-months, throughout a whole year. In each experiment, the material was taken at the same time of a day. The results indicated that the brain glycogen content did not change significantly, during the periods of a year examined. In the second series of experiments, the glycogen content in the rat brain was assayed every 3 hours, during a 24-hour-period. A low content of glycogen in the rat brain was found during the night, with a pronounced decrease of this value between 9.00 p.m. and midnight. A possible relationship between the diurnal changes in the brain glycogen content and catecholamine metabolism in the central nervous system is discussed.     

Circadian rhythm of the endopeptidase 22.19 (EC 3.4.22.19) in the rat brain.

The endopeptidase 22.19 (EC 3.4.22.19) has been associated with the metabolism of neuropeptides by its ability to convert small enkephalin-containing peptides (8 to 13 amino acids) into enkephalins. In addition, this enzyme cleaves the Arg8-Arg9 bond of neurotensin and the Phe5-Ser6 bond of bradykinin. We analyzed the circadian variation of endopeptidase 22.19 in the whole and individual areas of the rat brain. Endopeptidase 22.19 activity was analyzed by high-performance liquid chromatography (HPLC) using bradykinin as an operative substrate. Enzymatic specific activities were analyzed by rhythmometric methods and indicate a circadian fluctuation of endopeptidase 22.19 specific activity (mU of enzyme/mg of protein) in the whole brain [p less than 0.001, mesor (M) = 7.62, amplitude (A) = 2.89, and acrophase (phi) = 23:08 h], striatum (p less than 0.001, M = 2.92, A = 0.62, phi = 23:03 h), hypothalamus (p less than 0.001, M = 3.15, A = 0.86, phi = 01:12 h), periaqueductal gray matter (p less than 0.005, M = 2.62, A = 0.34, phi = 22:35 h), and cerebellum (p less than 0.014, M = 4.27, A = 0.88, phi = 17:12 h). The circadian rhythmicity in endopeptidase 22.19 specific activity suggests that light may have an effect on the peptidase activity in whole brain and in areas of the central nervous system and may be essential for the mechanisms of circadian fluctuations of neuropeptides in the brain.     

Circadian rhythm of covalent modifications in liver DNA.

32P-postlabeling analysis recently revealed that in addition to 5-methylcytosine, mammalian DNA contains covalently modified nucleotides of unknown structures and functions termed I-compounds whose levels increase with age. I-compound levels, in addition, depend on species, strain, sex, tissue, and diet and are generally lowered by carcinogen exposure. As shown here, levels of several non-polar I-compounds in liver DNA of untreated male C3H mice were elevated 2 to 8.5 times at 1800 h and 2400 h as compared to 0600 h and 1200 h, while polar I-compounds and persistent carcinogen-DNA adducts induced by safrole were unaffected by time of day. In liver DNA of male F-344 rats 4 non-polar I-compounds and 4 polar I-compounds showed significant circadian rhythm at 2000 h compared to 0800 h. This novel circadian variation of DNA structure implies mechanisms precisely regulating I-compound levels in vivo and may conceivably be linked to diurnal differences of DNA synthesis and gene expression.     

Circadian rhythm of hypothalamo-hypophyseal-adrenal activity in the chicken.

Corticosteroid production, ACTH content in the adenohypophysis and CRF content in the median eminence were studied in vitro and in vivo in the 3-weeks-old chicken according to SAFFRAN and SCHALLY in four different parts of the day: at 6 and 12 a.m., and 6 and 12 p.m. The chicken adrenals in vitro produced only corticosterone in fluorimetrically measurable amounts, with the maximum during the day and the minimum in the evening and at night. Sensitivity to ACTH of the adrenals in vitro was higher during the day than in the evening or at night. After paper-chromatographic separation, steroid hormones equivalent to corticosterone and cortisol could be detected fluorimetrically in the plasma. The "cortisol" level was about 2-2.5 times higher than the corticosterone level. Plasma "cortisol" level displayed the peak at 6 a.m. and the minimum at 12 p.m., while corticosterone at 12 a.m. and 12 p.m., respectively. ACTH content in the adenohypophysis was lowest at 6 a.m. then increased gradually until 12 p.m. CRF level in the median eminence fell during the forenoon, was lowest at noon, to rise up to 6 p.m. and persist at a high level between 6 p.m. and 6 a.m. Thus, in the 3-week-old chicken the functioning of the hypothalamo-hypophyseal-adrenal system displays a circadian rhythm characteristic of animals showing diurnal activity.     

Studies on the circadian rhythm of phosphoenolpyruvate carboxykinase. III. Circadian rhythm in the kidney.

Phosphoenolypyruvate carboxykinase [EC 4.1.1.21] activity in rat kidney shows a circadian rhythm with the highest activity between 0200 h and 0800 h and the lowest activity between 1400 h and 2000 h. The rhythm was observed in both sexes and throughout the year. Actinomycin D and cycloheximide effectively blocked the circadian increase in enzyme activity. These findings suggest that the circadian increase in phosphoenolypyruvate carboxykinase activity is due to net synthesis of enzyme protein through newly synthesized mRNA. In experiments with kidney cortex slices, gluconeogenesis from the radioactive precursor, [14C]malic acid, was considerably higher at 0200 h than at 1400 h, varying in parallel with the change in the enzyme activity.