Ontogeny of the circadian rhythm of cortisol in sheep

Daily variation of the cortisol and insulin concentration, glycemia, surface temperature, and behavior patterns due the administration of equine Chorionic Gonadotropin in rams

Sex steroids can modulate the circadian rhythmicity of some physiological and behavioral functions of sheep. During the non-breeding season, Corriedale rams have a low testosterone concentration, but the administration of equine Chorionic Gonadotropin (eCG) stimulates its secretion. Therefore, the daily variation of cortisol and insulin concentrations, glycemia, behavioral pattern (eating, ruminating, standing, lying, and sleeping), and rostral and eye surface temperatures were compared in rams treated or not treated with eCG during the non-breeding season [between August (late winter) and September (early spring)]. Twenty Corriedale adult rams (BW 63.4 ± 7.3 kg; BCS: 3.5 ± 0.5; mean ± SD; age: 2-3 years old) were randomly assigned to 1 of 2 treatments: a) Treated: administration of 1000 IU of eCG intramuscularly and b) Control: control, without application of eCG. All the rams were managed under the same feeding and environmental conditions (individual pens outdoors). All variables were measured each hour for 26 h, except testosterone and insulin that were measured at 09:00, 10:00, 12:00, 15:00, 18:00, 21:00, 22:00, 24:00, 03:00, 06:00, 09:00 and 11:00 h. Testosterone and cortisol concentration were greater in Treated than Control rams (testosterone: 32.7 ± 0.7 nmol/L vs 5.8 ± 0.7 nmol/L; P <0.0001; cortisol: 11.3 ± 0.6 nmol/L vs 9.9 ± 0.6 nmol/L; P =0.02). The eye surface temperature was 0.9°C lower in the Treated than in the Control rams (P =0.004). The characteristics of the daily variation pattern of cortisol, glycemia, glycemia:insulin ratio, and surface temperature were not affected by the treatment, the acrophases being at ∼06:00 h, ∼18:00 h, ∼08:00 h, and ∼11:00 h, respectively. The acrophase of insulin concentration was observed earlier in Treated than in Control rams (13:02 ± 0:56 vs 15:47 ± 0:53; P =0.04). Additionally, the acrophase of the time spent eating was advanced in Treated rams (09:48 ± 00:16 vs 10:20 ± 00:16; P =0.04) and sleeping (21:39 ± 00:57 vs 02:02 ± 01:06; P <0.0001). Treated rams slept less time than Control rams (P =0.04). In conclusion, the administration of eCG modulated the daily variation pattern of insulin concentration and the behavioral pattern (period in which rams were observed eating and sleeping). Nevertheless, although there was a greater cortisol concentration and reduced eye surface temperature, the administration of eCG did not modify their daily variation pattern, suggesting that this is robust, limiting the effect of testosterone on their basal pattern.

Simulated shift work during pregnancy does not impair progeny metabolic outcomes in sheep

KEY POINTS

Maternal shift work increases the risk of pregnancy complications, although its effects on progeny health after birth are not clear. We evaluated the impact of a simulated shift work protocol for one-third, two-thirds or all of pregnancy on the metabolic health of sheep progeny. Simulated shift work had no effect on growth, body size, body composition or glucose tolerance in pre-pubertal or young adult progeny. Glucose-stimulated insulin secretion was reduced in adult female progeny and insulin sensitivity was increased in adult female singleton progeny. The results of the present study do not support the hypothesis that maternal shift work exposure impairs metabolic health of progeny in altricial species.

ABSTRACT

Disrupted maternal circadian rhythms, such as those experienced during shift work, are associated with impaired progeny metabolism in rodents. The effects of disrupted maternal circadian rhythms on progeny metabolism have not been assessed in altricial, non-litter bearing species. We therefore assessed postnatal growth from birth to adulthood, as well as body composition, glucose tolerance, insulin secretion and insulin sensitivity, in pre-pubertal and young adult progeny of sheep exposed to control conditions (CON: 10 males, 10 females) or to a simulated shift work (SSW) protocol for the first one-third (SSW0-7: 11 males, 9 females), the first two-thirds (SSW0-14: 8 males, 11 females) or all (SSW0-21: 8 males, 13 females) of pregnancy. Progeny growth did not differ between maternal treatments. In pre-pubertal progeny (12-14 weeks of age), adiposity, glucose tolerance and insulin secretion during an i.v. glucose tolerance test and insulin sensitivity did not differ between maternal treatments. Similarly, in young adult progeny (12-14 months of age), food intake, adiposity and glucose tolerance did not differ between maternal treatments. At this age, however, insulin secretion in response to a glucose bolus was 30% lower in female progeny in the combined SSW groups compared to control females (P = 0.031), and insulin sensitivity of SSW0-21 singleton females was 236% compared to that of CON singleton female progeny (P = 0.025). At least in this model, maternal SSW does not impair progeny metabolic health, with some evidence of greater insulin action in female young adult progeny.

Deciphering the Function of the Blunt Circadian Rhythm of Melatonin in the Newborn Lamb: Impact on Adrenal and Heart

Neonatal lambs, as with human and other neonates, have low arrhythmic endogenous levels of melatonin for several weeks until they start their own pineal rhythm of melatonin production at approximately 2 weeks of life. During pregnancy, daily rhythmic transfer of maternal melatonin to the fetus has important physiological roles in sheep, nonhuman primates, and rats. This melatonin rhythm provides a circadian signal and also participates in adjusting the physiology of several organs in preparation for extrauterine life. We propose that the ensuing absence of a melatonin rhythm plays a role in neonatal adaptation. To test this hypothesis, we studied the effects of imposing a high-amplitude melatonin rhythm in the newborn lamb on (1) clock time-related changes in cortisol and plasma variables and (2) clock time-related changes of gene expression of clock genes and selected functional genes in the adrenal gland and heart. We treated newborn lambs with a daily oral dose of melatonin (0.25 mg/kg) from birth to 5 days of age, recreating a high-amplitude melatonin rhythm. This treatment suppressed clock time-related changes of plasma adrenocorticotropic hormone, cortisol, clock gene expression, and functional genes in the newborn adrenal gland. In the heart, it decreased heart/body weight ratio, increased expression of Anp and Bnp, and resulted in different heart gene expression from control newborns. The interference of this postnatal melatonin treatment with the normal postnatal pattern of adrenocortical function and heart development support a physiological role for the window of flat postnatal melatonin levels during the neonatal transition.

Short communication: Ovine leukocyte telomere length is associated with variation in the cortisol response to systemic bacterial endotoxin challenge

Stress has been associated with biological aging and numerous age-related diseases. This may be due, in part, to accelerated shortening of telomeres, which are critical genomic structures that cap and protect chromosomal ends. Dysfunction of the hypothalamic-pituitary-adrenal axis may indirectly contribute to telomere shortening if an animal reacts too strongly or weakly to a stressor, leading to accelerated biological aging. In this study, outbred Rideau-Arcott sheep were stress challenged with Escherichia coli endotoxin and classified as high, middle, or low cortisol responders to investigate a potential relationship between cortisol response and age, and telomere length. In the present study, no association was found between age and telomere length. The study, however, revealed shorter telomeres in high and low cortisol responders compared with the middle cortisol responders, which suggests that health and longevity may be compromised in extreme high- and low-stress-responding sheep.

Fetal and Neonatal HPA Axis

Stress is an integral part of life. Activation of the hypothalamus-pituitary-adrenal (HPA) axis in the adult can be viewed as mostly adaptive to restore homeostasis in the short term. When stress occurs during development, and specifically during periods of vulnerability in maturing systems, it can significantly reprogram function, leading to pathologies in the adult. Thus, it is critical to understand how the HPA axis is regulated during developmental periods and what are the factors contributing to shape its activity and reactivity to environmental stressors. The HPA axis is not a passive system. It can actively participate in critical physiological regulation, inducing parturition in the sheep for instance or being a center stage actor in the preparation of the fetus to aerobic life (lung maturation). It is also a major player in orchestrating mental function, metabolic, and cardiovascular function often reprogrammed by stressors even prior to conception through epigenetic modifications of gametes. In this review, we review the ontogeny of the HPA axis with an emphasis on two species that have been widely studied-sheep and rodents-because they each share many similar regulatory mechanism applicable to our understanding of the human HPA axis. The studies discussed in this review should ultimately inform us about windows of susceptibility in the developing brain and the crucial importance of early preconception, prenatal, and postnatal interventions designed to improve parental competence and offspring outcome. Only through informed studies will our public health system be able to curb the expansion of many stress-related or stress-induced pathologies and forge a better future for upcoming generations.

Photoperiod regulates clock gene rhythms in the ovine liver

To investigate the photoperiodic entrainment of peripheral rhythms in ruminants, we studied the expression of clock genes in the liver in the highly seasonal Soay sheep. Animals were kept under long (LD 16:8) or short photoperiod (LD 8:16). Daily rhythms in locomotor activity were recorded, and blood concentrations of melatonin and cortisol were measured by RIA. Per2, Bmal1, and Cry1 gene expression was determined by Northern blot analyses using ovine RNA probes in liver collected every 4h for 24h. Liver Per2 and Bmal1, but not Cry1, expression was rhythmic in all treatments. Under long days, peak Per2 expression occurred at end of the night with a similar timing to Bmal1, whereas, under short days the Per2 maximum was in the early night with an inverse pattern to Bmal1. There was a photoperiodxtime interaction for only Per2 (P < 0.001). The 24-h pattern in plasma cortisol matched the observed phasing of Per2 expression, suggesting that it may act as an endocrine entraining factor. The clock gene rhythms in the peripheral tissues were different in timing compared with the ovine suprachiasmatic nucleus (SCN, central pacemaker) and pars tuberalis (melatonin target tissue), and the hepatic rhythms were of lower amplitude compared with photoperiodic rodents. Thus, there are likely to be important species differences in the way the central and peripheral clockwork encodes external photoperiod.

Gender-specific effects of prenatal stress on emotional reactivity and stress physiology of goat kids

The aims of this study were to investigate the effects of maternal stress during pregnancy on the emotional reactivity, the hypothalamo-pituitary-adrenocortical (HPA) axis, and the sympatho-adrenomedullary (SAM) system of goat offspring according to their gender, and to investigate the role of maternal cortisol in prenatal stress effects. Goats were exposed to ten transports in isolation or ten ACTH injections (0.125 IU/kg body weight) during the last third of pregnancy. Control goats remained undisturbed. No effect of repeated transport during the last third of pregnancy was found on basal cortisol concentrations of the offspring. However, an increase in phenylethanolamine N-methyl transferase activity in the adrenals was observed in prenatally stressed kids compared to control kids (P = 0.031). In the presence of novelty, prenatally stressed female kids were more active (P = 0.049) than control females; they also showed more signs of arousal (P = 0.039) and tended to explore more of their environment (P = 0.053) in reaction to a startling stimulus. On the contrary, prenatally stressed male kids tended to be less active (P = 0.051) than control male kids but showed more signs of distress (P = 0.047) in the presence of novelty. Intermediate effects were found on the emotional reactivity to novelty of kids born from dams given injections of ACTH. In conclusion, transport stress in pregnant goats affects the sympatho-adrenomedullary system and the emotional reactivity of their offspring in a gender-specific manner. Moreover, the effects of prenatal transport and ACTH injections showed some similarities but differed in some critical details.

The Physiological Impact of Wool-Harvesting Procedures in Vicunas (Vicugna Vicugna)

A current programme of wildlife utilisation in the Andean region involves the capture of wild vicunas, their shearing, transport and, in some cases, captive farming. The effects of these interventions on the physiology, and thus welfare, of wild vicunas are unknown. As a first step to quantifying and thus mitigating any adverse welfare consequences of this harvest, we measured the immediate and longer-term physical and physiological effects of capture, shearing and transport. A sample of juvenile male vicunas was captured. Six were shorn at the capture site, six after two weeks in captivity, and the remaining seven animals were kept as controls for 39 days. In general, vicunas showed changes in blood glucose, packed cell volume, cortisol, and neutrophil:lymphocyte ratios within 4-6 h following capture. Creatine kinase was also affected by capture and transport, showing a peak plasma level 24 h after capture, which was followed by a peak plasma level of aspartate aminotransferase four days after capture and transport. After 12 days in captivity, all of the vicunas showed physiological parameters close to expected baseline values for the species. We could detect no differences in physiological parameters between animals that were captured, sheared and transported and those that were only captured and transported. Similarly, we could detect no differences in most responses of vicunas between those sheared after 12 days in captivity and a control group held under similar conditions but from which blood was sampled without shearing. A further comparison between animals sheared immediately after capture and animals sheared after 12 days in captivity revealed that creatine kinase levels were higher in the former group. During transport prior to release back into the wild, only minor injuries (lip bleeding and limb contusions) and a significant increase in rectal temperature were observed. Our results provide a basis for recommendations to improve the welfare of vicunas during the wool harvest, and provide baseline and stress-response data to serve as reference points for further studies of vicuna welfare.

Changes in plasma cortisol concentration in lambs of three ages after three methods of castration and tail docking

Lambs were handled only or castrated and tail docked at five, 21 and 42 days of age by either surgery, rubber ring or rubber ring and Burdizzo. Plasma cortisol was measured in blood samples taken before and at 12, 24, 36, 48, 60, 72, 84, 96, 138 and 180 minutes after castration and docking. Pre-treatment and peak cortisol values were highest in five-day-old lambs. The peak cortisol values, at each age, were similar for surgery and rubber ring groups. However, the peak occurred earlier after surgery and rubber ring Burdizzo than after rubber ring only treatment. The cortisol peak was 28 nmol litre-1 lower after rubber ring Burdizzo than surgery or rubber ring only. Plasma cortisol returned to pretreatment values within 84 minutes after rubber ring Burdizzo, 96 to 138 minutes after rubber ring only but not within 180 minutes after surgery. The changes in plasma cortisol together with the changes in behaviour suggest that the rubber ring Burdizzo method of castration and docking of lambs at all ages, was probably the least painful of the methods tested.

Time of day of birth and absence of endocrine and uterine contractile activity rhythms in sheep

To determine whether 24-h rhythms characterize hormone secretion and uterine activity in the pregnant sheep, blood samples were drawn every 1-4 h for 48 h from ewes and fetuses from day 120 of gestation to term. Repetitive 24-h rhythms were absent for cortisol, progesterone, and prolactin in maternal and fetal circulation and for hourly mean uterine contraction rate and amplitude. To test whether photoperiod or pineal melatonin contributes to the absence of rhythms, pineal-intact and pinealectomized ewes and their fetuses were studied in reverse photoperiod. Again, there was little evidence to suggest 24-h endocrine rhythms except for prolactin in two fetuses by cosinor analyses. Prolactin concentrations were increased in pinealectomized ewes and their fetuses. In the apparent absence of rhythms, 20 of 21 pineal-intact ewes gave birth at night; however, 6 out of 7 pinealectomized ewes gave birth during the day. Thus photoperiod and the maternal pineal gland profoundly influenced the time of day of birth in the absence of circadian endocrine or uterine activity rhythms.