Circadian and ultradian variation in pancreatic secretion of meal-fed pigs after weaning

Aging disrupts the temporal organization of antioxidant defenses in the heart of male rats and phase shifts circadian rhythms of systolic blood pressure

Aging is one of the main risk factors for cardiovascular diseases, and oxidative stress is a key element responsible for the development of age-related pathologies. In addition, the alteration of circadian rhythms also contributes to cardiovascular pathology, but the underlying mechanisms are not well defined. We investigated the aging consequences on the temporal patterns of antioxidant defenses, the molecular clock machinery, and the blood pressure, in the heart of male rats maintained under constant darkness (free running) conditions. Male Holtzman rats from young adult (3-month-old) and older (22-month-old) groups were maintained under constant darkness (12-h dark:12-h dark, DD) condition during fifteen days before the experiment. After the DD period, heart ventricle samples were isolated every 4-h throughout a 24-h period. We observed circadian rhythms of catalase (CAT) and glutathione peroxidase (GPx) mRNA expression, as well as ultradian rhythms of Nrf2 mRNA levels, in the heart of young adult rats. We also found circadian oscillations of CAT and GPx enzymatic activities, reduced glutathione (GSH) and BMAL1 protein in the same group. Interestingly, aging abolished the rhythms of CAT and GPx enzymatic activities, phase-shifted the rhythm's acrophases of GSH and BMAL1 protein levels and turned circadian the ultradian oscillation of Nrf2 expression. Moreover, aging phase-shifted the circadian pattern of systolic blood pressure. In conclusion, aging modifies the temporal organization of antioxidant defenses and blood pressure, probably, as a consequence of a disruption in the circadian rhythm of the clock's transcriptional regulator, BMAL1, in heart.

Evidence for a Coupled Oscillator Model of Endocrine Ultradian Rhythms

Whereas long-period temporal structures in endocrine dynamics have been well studied, endocrine rhythms on the scale of hours are relatively unexplored. The study of these ultradian rhythms (URs) has remained nascent, in part, because a theoretical framework unifying ultradian patterns across systems has not been established. The present overview proposes a conceptual coupled oscillator network model of URs in which oscillating hormonal outputs, or nodes, are connected by edges representing the strength of node-node coupling. We propose that variable-strength coupling exists both within and across classic hormonal axes. Because coupled oscillators synchronize, such a model implies that changes across hormonal systems could be inferred by surveying accessible nodes in the network. This implication would at once simplify the study of URs and open new avenues of exploration into conditions affecting coupling. In support of this proposed framework, we review mammalian evidence for (1) URs of the gut-brain axis and the hypothalamo-pituitary-thyroid, -adrenal, and -gonadal axes, (2) UR coupling within and across these axes; and (3) the relation of these URs to body temperature. URs across these systems exhibit behavior broadly consistent with a coupled oscillator network, maintaining both consistent URs and coupling within and across axes. This model may aid the exploration of mammalian physiology at high temporal resolution and improve the understanding of endocrine system dynamics within individuals.

Effects of ileal digesta collection time on standardized ileal digestibility of amino acids in corn, soybean meal, and distiller's dried grains with solubles fed to growing pigs

The objective of this experiment was to determine the minimum collection time needed to obtain representative samples of ileal digesta from pigs fed different types of diets. Eight barrows with an initial BW of 34.6 kg (SD 2.1) were individually fitted with a T-cannula in the distal ileum and randomly allotted to a replicated 4 × 4 Latin square design with 4 diets and 4 periods per square. Three diets contained corn, soybean meal (SBM), or distiller's dried grains with solubles (DDGS) as the sole source of CP. An N-free diet was also prepared. All diets contained 0.5% chromic oxide as an indigestible marker. Equal meals were provided at 0800 and 2000 h. Ileal digesta samples were collected in 2-h intervals from 0800 to 2000 h during the last 3 d of each 7-d period. When pigs were fed the corn diet, the standardized ileal digestibility (SID) of most indispensable AA and dispensable AA increased and then decreased (quadratic, < 0.05) during each of the six 2-h periods. The SID of most AA were less ( < 0.05) if the ileal digesta samples were collected from 1800 to 2000 h or from 1600 to 2000 h compared with the SID values from the ileal samples collected over the entire 12-h period. When pigs were fed the SBM diet, the SID of Ile, Leu, Thr, Trp, Val, Ala, and Cys increased and then decreased (quadratic, < 0.05) but the SID of all other AA linearly decreased ( < 0.05) during the six 2-h periods. The SID of almost all AA were greater ( < 0.05) if the ileal samples were collected from 0800 to 1000 h, from 0800 to 1200 h, from 1000 to 1400 h, or from 0800 to 1400 h but less ( < 0.05) if collected from 1600 to 1800 h, from 1800 to 2000 h, from 1600 to 2000 h, or from 1400 to 2000 h compared with the SID values from the ileal samples collected over the entire 12-h period. When pigs were fed the DDGS-based diet, the SID of Ile, Leu, Lys, Phe, Trp, Val, and Tyr increased and then decreased (quadratic, < 0.05) during the six 2-h periods. The SID of most AA were less ( < 0.05) if the ileal samples were collected from 1800 to 2000 h compared with the SID values from the ileal samples collected over the entire 12-h period. In conclusion, diurnal variations in SID of AA in pigs indicate that 6 h of ileal sample collection starting 4 or 6 h after feeding may provide representative samples of ileal digesta from pigs fed different types of diets.

Aging modifies daily variation of antioxidant enzymes and oxidative status in the hippocampus

BACKGROUND

Aging is a complex and multifactorial biological process that leads to the progressive deterioration of physiological systems, including the circadian system. In addition, oxidative stress has been associated with the aging of the normal brain and the development of late-onset neurodegenerative diseases. Even though, functional weakening of circadian rhythms and antioxidant function has been observed during aging, the mechanisms by which the circadian system signaling and oxidative stress are interrelated have not yet been elucidated. The objectives of this study were to evaluate the consequences of aging on the temporal organization of the antioxidant defense system and oxidative status as well as to analyze the endogenous clock activity, in the hippocampus of aged rats.

METHODS

Young adults (3-month-old) or older (22-month-old) male Holtzman rats were maintained under constant darkness conditions, during 15days before the sacrifice. Levels of catalase (CAT) and glutathione peroxidase (GPx) mRNA and activity, reduced glutathione (GSH), lipoperoxidation (LPO) and BMAL1 protein were analyzed in hippocampus samples isolated every 4h during a 24-h period. Locomotor activity was recorded during 20days before the experiment.

RESULTS

Our results show that aging modifies temporal patterns of CAT and GPx expression and activity in the hippocampus in a different way. On the one hand, it abolishes the oscillating CAT expression and specific enzymatic activity while, on the other, it increases the mesor of circadian GPx activity rhythm (p<0.01). Additionally, we observed increased GSH (p<0.05) and reduced LPO (p<0.01) levels in the hippocampus of aged rats. Moreover, the nocturnal locomotor activity was reduced in the older animals in comparison to the young adult rats (p<0.01). Interestingly, the 22month-old animals became arrhythmic and showed a marked fragmentation as well as a significant decline in daily locomotor activity when they were maintained under constant darkness conditions (p<0.05). Aging also abolished circadian rhythms of the core clock BMAL1 protein.

CONCLUSION

The loss of temporal organization of the antioxidant enzymes activity, the oxidative status and the cellular clock machinery could result in a temporally altered antioxidant defense system in the aging brain. Learning about how aging affects the circadian system and the expression of genes involved in the antioxidant defense system could contribute to the design of new strategies to improve the quality of life of older people and also to promote a healthy aging.

Circadian regulation of metabolic homeostasis: causes and consequences

Robust circadian rhythms in metabolic processes have been described in both humans and animal models, at the whole body, individual organ, and even cellular level. Classically, these time-of-day-dependent rhythms have been considered secondary to fluctuations in energy/nutrient supply/demand associated with feeding/fasting and wake/sleep cycles. Renewed interest in this field has been fueled by studies revealing that these rhythms are driven, at least in part, by intrinsic mechanisms and that disruption of metabolic synchrony invariably increases the risk of cardiometabolic disease. The objectives of this paper are to provide a comprehensive review regarding rhythms in glucose, lipid, and protein/amino acid metabolism, the relative influence of extrinsic (eg, neurohumoral factors) versus intrinsic (eg, cell autonomous circadian clocks) mediators, the physiologic roles of these rhythms in terms of daily fluctuations in nutrient availability and activity status, as well as the pathologic consequences of dyssynchrony.

Daily rhythms of catalase and glutathione peroxidase expression and activity are endogenously driven in the hippocampus and are modified by a vitamin A-free diet

OBJECTIVES

Alterations in enzymatic antioxidant defense systems lead to a deficit of cognitive functions and altered hippocampal synaptic plasticity. The objectives of this study were to investigate endogenous rhythms of catalase (CAT) and glutathione peroxidase (GPx) expression and activity, as well as CREB1 mRNA, in the rat hippocampus, and to evaluate to which extent the vitamin A deficiency could affect those temporal patterns.

METHODS

Rats from control and vitamin A-deficient (VAD) groups received a diet containing 4000 IU of vitamin A/kg diet, or the same diet devoid of vitamin A, respectively, during 3 months. Rats were maintained under 12-hour-dark conditions, during 10 days before the sacrifice. Circadian rhythms of CAT, GPx, RXRγ, and CREB1 mRNA levels were determined by reverse transcriptrase polymerase chain reaction in hippocampus samples isolated every 4 hours during a 24-hour period. CAT and GPx enzymatic activities were also determined by kinetic assays. Regulatory regions of clock and antioxidant enzymes genes were scanned for E-box, RXRE, and CRE sites.

RESULTS

E-box, RXRE, and CRE sites were found on regulatory regions of GPx and CAT genes, which display a circadian expression in the rat hippocampus. VAD phase shifted CAT, GPx, and RXRγ endogenous rhythms without affecting circadian expression of CREB1.

DISCUSSION

CAT and GPx expression and enzymatic activity are circadian in the rat hippocampus. The VAD affected the temporal patterns antioxidant genes expression, probably by altering circadian rhythms of its RXR receptors and clock factors; thus, it would impair the temporal orchestration of hippocampal daily cognitive performance.

Nutrition and the circadian timing system

Life on earth has evolved under the daily rhythm of light and dark. Consequently, most creatures experience a daily rhythm in food availability. In this review, we first introduce the mammalian circadian timing system, consisting of a central clock in the suprachiasmatic nucleus (SCN) and peripheral clocks in various metabolic tissues including liver, pancreas, and intestine. We describe how peripheral clocks are synchronized by the SCN and metabolic signals. Second, we review the influence of the circadian timing system on food intake behavior, activity of the gastrointestinal system, and several aspects of glucose and lipid metabolism. Third, the circadian control of digestion and metabolism may have important implications for several aspects of food intake in humans. Therefore, we review the human literature on health aspects of meal timing, meal frequency, and breakfast consumption, and we describe the potential implications of the clock system for the timing of enteral tube feeding and parenteral nutrition. Finally, we explore the connection between type 2 diabetes and the circadian timing system. Although the past decade has provided exciting knowledge about the reciprocal relation between biological clocks and feeding/energy metabolism, future research is necessary to further elucidate this fascinating relationship in order to improve human health.

Retinoic acid receptors move in time with the clock in the hippocampus. Effect of a vitamin-A-deficient diet

An endogenous time-keeping mechanism controls circadian biological rhythms in mammals. Previously, we showed that vitamin A deficiency modifies clock BMAL1 and PER1 as well as BDNF and neurogranin daily rhythmicity in the rat hippocampus when animals are maintained under 12-h-light:12-h-dark conditions. Retinoic acid nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs), have been detected in the same brain area. Our objectives were (a) to analyze whether RARα, RARβ and RXRβ exhibit a circadian variation in the rat hippocampus and (b) to investigate the effect of a vitamin-A-deficient diet on the circadian expression of BMAL1, PER1 and retinoic acid receptors (RARs and RXRβ) genes. Holtzman male rats from control and vitamin-A-deficient groups were maintained under 12-h-light:12-h-dark or 12-h-dark:12-h-dark conditions during the last week of treatment. RARα, RARβ, RXRβ, BMAL1 and PER1 transcript and protein levels were determined in hippocampus samples isolated every 4 h in a 24-h period. Regulatory regions of RARs and RXRβ genes were scanned for clock-responsive sites, while BMAL1 and PER1 promoters were analyzed for retinoic acid responsive elements and retinoid X responsive elements. E-box and retinoid-related orphan receptor responsive element sites were found on regulatory regions of retinoid receptors genes, which display an endogenously controlled circadian expression in the rat hippocampus. Those temporal profiles were modified when animals were fed with a vitamin-A-deficient diet. Similarly, the nutritional vitamin A deficiency phase shifted BMAL1 and abolished PER1 circadian expression at both mRNA and protein levels. Our data suggest that vitamin A deficiency may affect the circadian expression in the hippocampus by modifying the rhythmic profiles of retinoic acid receptors.

Effects of dietary metabolizable energy and crude protein content on the activities of digestive enzymes in jejunal fluid of Peking ducks

The response of digestive enzymes activities in the jejunal fluid of Peking ducks to dietary ME and CP content was investigated. In experiment 1, jejunal digesta from 24 cannulated male white Peking ducks of 18 wk of age were collected for 1 h out of every 4 h beginning at 0930 h on d 16, 18, and 20 of the experiment. The activities of amylase, trypsin, and chymotrypsin in jejunal fluid were determined. In experiment 2, 72 male cannulated ducks were randomly sorted into 4 groups. Four treatments consisted of combinations of 3,050 and 2,800 kcal/kg of ME, and 17.50 and 14.40% CP content were available ad libitum. Jejunal digesta samples were collected for 1 h every 4 h from 0930 to 1830 h on d 31, 33, and 35 of the experiment according to the results of experiment 1. The activities of amylase, trypsin, chymotrypsin, lipase, sucrase, and maltase in jejunal fluid were determined. In experiment 1, significant differences were found in the average activities of amylase and chymotrypsin among days. The collection time significantly affected the 3 enzyme activities, and average enzyme activities during the day were higher and more stable than during the night. In experiment 2, the effect of dietary ME content on the 6 digestive enzymes activities was not significant. But the dietary protein content significantly changed amylase, trypsin, and chymotrypsin activities.

Nonparallel secretion of antibacterial activity and protein in porcine pancreatic juice

The antimicrobial activity of exocrine pancreatic juice is an important component of gastrointestinal tract innate defenses, yet little is known about whether secretion is regulated in parallel with digestive enzymes. In this study, we used 8 pigs with pancreatic catheters to quantify antibacterial activity and measure protein content (indicator of enzyme secretion) of pancreatic juice collected hourly from 0700 to 1900, with the animals adapted to being fed at 0800 and 1600. Antibacterial activity in the samples of pancreatic juice was quantified by comparing the growth inhibition of Staphylococcus aureus subsp. aureus strain ATCC 6538P relative to a known concentration of gentamicin. Antibacterial activity (U/mL and /min) was highest in samples collected 1 hour prior to feeding (equivalent to 0.6 microgram gentamicin/mL), declined as the meal was consumed, and was lower (P < 0.05) in samples collected while the meals were being digested (0.41 microgram gentamicin/mL). Protein content was negatively correlated with antibacterial activity, with protein secretion lower (mg/mL and /min) before feeding, with an increase as the pigs ate and digested the meals (P < 0.05). The results indicate that the antibacterial activity in pancreatic juice is not secreted in parallel with protein secretion, suggesting that regulation involves alternative signaling pathways or contrasting responses to shared signals.

The enzyme levels in blood are not affected by oral administration of a pancreatic enzyme preparation (Creon 10,000) in pancreas-insufficient pigs

After oral intake, small amounts of intact protein may be absorbed into the blood circulation. The current study investigated whether orally administered pancreatic enzymes were absorbed from the intestine. The study included 28 pigs; 3 control pigs with intact pancreatic function and 25 pigs that were made exocrine pancreas insufficient by duct ligation (20 pigs) or total pancreatectomy (5 pigs). The pigs received a pancreatic enzyme preparation (0, 2, 4, or 8 g of Creon 10,000) together with the feed. The blood plasma was analyzed for pancreatic lipase activity with a [3H]-triolein substrate assay, while (pro)colipase and cationic trypsin(ogen) levels were measured with enzyme-linked immunosorbent assay (ELISA). Administration of Creon (0-8 g) caused no significant changes in plasma (pro)colipase or cationic trypsin(ogen) levels. Lipase activity peaks in plasma samples were found, but they did not correspond to the administration of Creon. The potential source of these plasma lipase activity peaks is discussed. The results showed no absorption into blood of pancreatic enzymes after oral administration (0, 2, 4, or 8 g of Creon mixed with 100 g of feed) to pancreas-insufficient pigs.

Circadian pancreatic enzyme pattern and relationship between secretory and motor activity in fasting humans

It is unknown whether nonparallel pancreatic enzyme output occurs under basal conditions in humans. We aimed to determine whether the circadian or wake-sleep cycle influences the relationship among pancreatic enzymes or between pancreatic secretory and jejunal motor activity. Using orojejunal multilumen intubation, we measured enzyme outputs and proximal jejunal motility index during consecutive daytime and nighttime periods in each of seven fasting, healthy volunteers. Enzyme outputs were correlated tightly during daytime phases of wakefulness and nighttime phases of sleep (r > 0.72, P < 0.001). During nocturnal phases of wakefulness, output of proteases (r = 0.84, P < 0.001), but not of amylase and trypsin (r = 0.12), remained associated. Nocturnally, particularly during sleep, pancreatic secretory activity was directly correlated with jejunal motility index (r > 0.50, P < 0.001). In conclusion, parallel secretion of pancreatic enzymes dominates throughout the circadian cycle. Nonparallel secretion during nocturnal phases of wakefulness may be due to merely circadian effects or to the coupling of the wake-sleep and the circadian cycle. The association between fluctuations of secretory and motor activity appears to be particularly tight during the night.

Associations by signatures and coherences between the human circulation and helio- and geomagnetic activity

Helio-geomagnetic influences on the human circulation are investigated on the basis of an 11-year-long record from a clinically healthy cardiologist, 35 years of age at the start of monitoring. He measured his blood pressure and heart rate around the clock with an ambulatory monitor programmed to inflate an arm cuff, mostly at intervals of 15-30 minutes, with only few interruptions, starting in August 1987. While monitoring is continuing, data collected up to July 1998 are analyzed herein by cosinor rhythmometry and cross-spectral coherence with matching records of solar activity, gauged by Wolf numbers (WN) and of the geomagnetic disturbance index, Kp. A direct association between heart rate (HR) and WN is found to be solar cycle stage-dependent, whereas an inverse relationship between heart rate variability (HRV) and WN is found consistently. An inverse relation is also observed between WN and the variability in systolic blood pressure (SBP), and to a lesser extent, diastolic blood pressure (DBP). Moreover, HR is cross-spectrally coherent with WN at a frequency of one cycle in about 7.33 months. The results support previously reported associations on morbidity and mortality statistics, extending their scope to human physiology monitored longitudinally.