Effect of stress-like concentrations of cortisol on the feedback potency of oestradiol in orchidectomized sheep

Relationship between periparturient diseases, metabolic markers and the dynamics of hair cortisol concentrations in dairy cows

Hair cortisol concentration (HCC) might represent a promising marker for retrospective welfare assessment of dairy cows. The objective of the study was to explore the dynamics of HCC in diseased and healthy cows from eight-week ante partum (AP) to eight-week post partum (PP). Twenty-four pregnant cows were followed from drying off to week eight PP. Tail hair was used to measure cortisol at five different time points. The occurrence of peripartum diseases, lameness and the body condition score (BCS) were monitored on a weekly basis. Blood β-hydroxybutyric acid, non-esterified fatty acids, calcium and insulin-like growth factor-1 (IGF-1) concentrations were measured. The temperature-humidity index (THI) was continuously recorded. The median values of HCC in all cows were 0.4, 0.3, 0.6, 0.8 and 0.5 pg/mg at weeks eight, four AP, calving, weeks four, eight PP, respectively. There was no association between HCC and the occurrence of peripartum diseases (P ≥ 0.05). A positive correlation between HCC and BCS loss (P < 0.01) and THI (P < 0.05) was observed. The occurrence of peripartum diseases was associated with low IGF-1 during the study period but no relationship was found between cortisol and IGF-1 levels (P ≥ 0.05). Brown Swiss cows showed higher HCC (P < 0.01) at weeks eight, four AP, and week four PP and lower average milk yield (P < 0.05) than Holstein-Friesian cows. In conclusion, HCC was not a suitable marker for peripartum diseases but it could reflect a stress response, which is linked to BCS loss, heat stress and breed.

Corticosterone Injection Impairs Follicular Development, Ovulation and Steroidogenesis Capacity in Mice Ovary

Simple Summary

Researchers have hitherto established hundreds of animal stress models. However, these models have some limitations due to the complexity in operation and large differences between individual animals. In particular, there are few stress models that are specifically applied in mammalian ovaries. In this study, using intraperitoneal injection of cortisol/corticosterone (CORT), we successfully established a stress model that acts on the ovarian function. Our data showed that CORT inhibits ovarian and follicular development and blocks ovulation. The establishment of this model might provide a living platform for studying ovarian stress in future research.

Abstract

The aim of this study is to establish an ovarian stress model, and to investigate the effects of stress on follicular development. Our data showed that continuous intraperitoneal injection of CORT successfully created a stressful environment in the ovary. To assess the effects of CORT on ovarian functions, 80 three-week-old ICR (Institute of Cancer Research) female mice were randomly divided into control group and treatment group. All mice were injected intraperitoneally with pregnant horse serum gonadotropin (PMSG). At the same time, the treatment group were injected with CORT (1 mg/mouse) at intervals of 8 h; while the control group was injected with same volume of methyl sulfoxide (DMSO). Blood, ovaries, or ovarian granulosa cell samples were collected at 24 h, 48 h, and 55 h after PMSG injection. The results showed that, compared with the control group, CORT-injected mice revealed a significant decrease in ovulation rates, ovarian weight, ovarian index, the number of secondary follicles and mature follicles, levels of estrogen and progesterone, and mRNA expression of steroid synthase-related genes. Collectively, our findings clearly demonstrated that CORT injection could represent an effective practice to simulate stresses that inhibit ovarian functions by reducing follicular development and ovulation.

Faecal glucocorticoid metabolites and body temperature in Australian merino ewes (Ovis aries) during summer artificial insemination (AI) program

Reproductive wastage is a key issue for sheep producers, both regionally and globally. The reproductive output of farm animals can be influenced by physiological and environmental factors. Rapid and reliable quantification of physiological stress can provide a useful tool for designing and testing on-farm management interventions to improve farm animal welfare and productivity. In this study, we quantified physiological stress non-invasively using faecal glucocorticoid metabolites-FGMs analysis and body temperature measurements of 15 superovulated donor merino ewes (Ovis aries) during participation in artificial insemination (AI) program conducted during 2015/2016 Australian summer. We hypothesized that low percentage transferable embryos in donor merino ewes will be associated positively with higher body temperature and/or higher FGMs in these ewes. Temperature humidity index (THI) was calculated and found within high thermal stress range during the two AI trials. Overall, results showed none of the factors (ewe ID, AI trial no., THI or FGMs) were significant for reduced percentage transferrable embryos, except ewe body temperature was highly significant (p = 0.014). Within AI trial comparisons showed significant positive associations between higher FGMs and body temperature with reduced transferrable embryos. These results suggest that Australian merino ewes participating in summer AI trials can experience physiological stress. Prolonged activation of the stress endocrine response and high body temperature (e.g. ensued from heat stress) could impact on ewe reproductive output. Therefore, future research should apply minimally invasive physiological tools to gather baseline information on physiological stress in merino sheep to enable the development of new farm-friendly methods of managing stress.

Cystic ovaries in intermittently-suckled sows: follicle growth and endocrine profiles

This paper presents follicle development and hormone profiles for sows with normal ovulation or cystic follicles during an intermittent-suckling (IS) regime that started at Day 14 of lactation. Sows were subjected to separation from their piglets during blocks of 6h or 12h. In total, 8 out of 52 sows developed cystic follicles; either full cystic ovaries (n=6) or partial ovulation (n=2). Increase in follicle size of these sows was similar to that of normal ovulating sows until pre-ovulatory size at Day 5 after the start of separation, but from then on became larger (P<0.05). LH surge was smaller or absent in sows that developed (partially) cystic ovaries (0.4 ± 0.1 vs 3.6 ± 0.3 ngmL(-1); P<0.01). Peak levels of oestradiol (E2) were similar but high E2 levels persisted in sows that developed (partly) cystic ovaries and duration of oestrus tended to be longer. The risk of developing (partly) cystic ovaries was higher when IS occurred in blocks of 6h versus 12h (33 vs 10%). In conclusion, the appearance of cystic ovaries at approximately Day 20 of ongoing lactation was related to an insufficient LH surge, as is also the case in non-lactating sows.

A glucocorticoid sensitive biphasic rhythm of testosterone secretion

Studies of the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-testicular (HPT) axis have revealed a reciprocal relationship between these two endocrine pathways. In rats, for example, disruption of the HPT axis alters the circadian secretion of corticosterone. Stress, on the other hand, can have varying effects on testosterone secretion in both rats and humans. Furthermore, in contrast to humans, where several pulses of testosterone secretion can be detected across the 24-h period with the largest in the morning, rats appear to exhibit a diurnal rhythm of testosterone secretion. In the present study, we used an automated blood sampling system to investigate the true circadian pattern of testosterone secretion under basal conditions and investigated how this responds to changes in levels of circulating corticosteroids. Analysis of plasma testosterone revealed the expected bimodal pattern of basal testosterone secretion. The two secretory episodes were 12.59 h +/- 41 min apart and 4.04 h +/- 16 min long, with one in the light phase and the other in the dark phase of the cycle. Interestingly, when both testosterone and corticosterone diurnal profile were compared, we found that the circadian rise in plasma corticosterone levels falls neatly between the two testosterone secretory episodes. Treatment of rats with the synthetic glucocorticoid methylprednisolone in their drinking water abolished the normal bimodal profile of testosterone secretion. These rats show transient pulses of testosterone throughout the 24 h, but no circadian pattern. By contrast, adrenalectomised rats maintain their bimodal circadian pattern, suggesting that an intact HPA axis is not necessary for generation of the endogenous HPT rhythm. Thus, although the circadian rhythm of testosterone does not depend on normal HPA function, increased levels of glucocorticoids can abolish normal HPT rhythmicity.

Cerebral neurons involved in the innervation of both the adrenal gland and the ovary: a double viral tracing study

Previous studies using the viral transneuronal tracing technique demonstrated central autonomic circuits involved in the innervation of the adrenal gland and the ovary. Since the pattern of infection of central nervous system structures is similar after virus inoculation of the adrenal gland and the ovary, and, on the other hand, it is well documented that the activity of the hypothalamo-pituitary-adrenal axis exerts an inhibitory effect on the reproductive system, we investigated whether there are neurons that are transneuronally connected both with the adrenal gland and the ovary. The central circuitry involved in the innervation of the left adrenal and the left ovary was studied in individual rats by dual transneuronal tracing using isogenic recombinant strains (BDG and DS-RED) of Bartha strain of pseudorabies virus. Dual-infected neurons were detected in the ventrolateral medulla, nucleus of the solitary tract, caudal raphe nuclei, A5 cell group, and hypothalamic paraventricular nucleus. The results indicate that there are neurons in the central nervous system that contribute to the transneuronal innervation of both the adrenal gland and the ovary. The data suggest a new type of interaction, i.e. interaction at cellular level that might be involved in regulatory processes integrating the functional activity of the two organs.

Psychosocial stress suppresses attractivity, proceptivity and pulsatile LH secretion in the ewe

Various stressors suppress pulsatile secretion of luteinizing hormone (LH) in ewes and cortisol has been shown to be a mediator of this effect under various conditions. In contrast, little is known about the impact of stress and cortisol on sexual behavior in the ewe. Therefore, we tested the hypothesis that both psychosocial stress and stress-like levels of cortisol will reduce the level of attractivity, proceptivity and receptivity in addition to suppressing LH secretion in the ewe. In Experiment 1, a layered stress paradigm of psychosocial stress was used, consisting of isolation for 4 h with the addition of restraint, blindfold and noise of a barking dog (predator stress) at hourly intervals. This stress paradigm reduced LH pulse amplitude in ovariectomized ewes. In Experiment 2, ovariectomized ewes were artificially induced into estrus with progesterone and estradiol benzoate treatment and the layered stress paradigm was applied. LH was measured and sexual behavior was assessed using T-mazes and mating tests. Stress reduced pulsatile LH secretion, and also reduced attractivity and proceptivity of ewes but had no effect on receptivity. In Experiment 3, ewes artificially induced into estrus were infused with cortisol for 30 h. Cortisol elevated circulating plasma concentrations of cortisol, delayed the onset of estrus and resulted in increased circling behavior of ewes (i.e. moderate avoidance) during estrus and increased investigation and courtship from rams. There was no effect of cortisol on attractivity, proceptivity or receptivity during estrus. We conclude that psychosocial stress inhibits LH secretion, the ability of ewes to attract rams (attractivity) and the motivation of ewes to seek rams and initiate mating (proceptivity), but cortisol is unlikely to be the principal mediator of these effects.

Does cortisol acting via the type II glucocorticoid receptor mediate suppression of pulsatile luteinizing hormone secretion in response to psychosocial stress?

This study assessed the importance of cortisol in mediating inhibition of pulsatile LH secretion in sheep exposed to a psychosocial stress. First, we developed an acute psychosocial stress model that involves sequential layering of novel stressors over 3-4 h. This layered-stress paradigm robustly activated the hypothalamic-pituitary-adrenal axis and unambiguously inhibited pulsatile LH secretion. We next used this paradigm to test the hypothesis that cortisol, acting via the type II glucocorticoid receptor (GR), mediates stress-induced suppression of pulsatile LH secretion. Our approach was to determine whether an antagonist of the type II GR (RU486) reverses inhibition of LH pulsatility in response to the layered stress. We used two animal models to assess different aspects of LH pulse regulation. With the first model (ovariectomized ewe), LH pulse characteristics could vary as a function of both altered GnRH pulses and pituitary responsiveness to GnRH. In this case, antagonism of the type II GR did not prevent stress-induced inhibition of pulsatile LH secretion. With the second model (pituitary-clamped ovariectomized ewe), pulsatile GnRH input to the pituitary was fixed to enable assessment of stress effects specifically at the pituitary level. In this case, the layered stress inhibited pituitary responsiveness to GnRH and antagonism of the type II GR reversed the effect. Collectively, these findings indicate acute psychosocial stress inhibits pulsatile LH secretion, at least in part, by reducing pituitary responsiveness to GnRH. Cortisol, acting via the type II GR, is an obligatory mediator of this effect. However, under conditions in which GnRH input to the pituitary is not clamped, antagonism of the type II GR does not prevent stress-induced inhibition of LH pulsatility, implicating an additional pathway of suppression that is independent of cortisol acting via this receptor.

Influence of estradiol on adrenal activity in ovariectomized cows during acute stress

Stress-dependent activation of the hypothalamo-pituitary-adrenal axis (HPA) can compromise reproductive function in animals and humans. In addition, it has been shown that estrogens are also capable of influencing the activity of the adrenal cortex. The objective of this study was to evaluate the effect of estradiol (E2) on adrenocortical secretion of cortisol and progesterone as well as on pituitary LH-release in cows during stress. Five ovariectomized Brown Swiss cows were exposed to acute restraint stress (2-h immobilization in a trimming chute), either with or without E2 treatment. Blood samples were taken every 15 min during a 5-h period for determination of cortisol progesterone and LH. Our results demonstrate that during the 2-h stress period mean cortisol concentrations significantly (P < 0.05) increased in all cows independent of E2 treatment. Mean progesterone concentrations also increased during stress, but the effect was only significant in E2-untreated cows. In contrast to cortisol and progesterone, mean LH values decreased in all animals during stress, but the decline was not significant. However, significantly lower mean LH values were seen at the end of the stress period comparing to values before stress. In cows without stress, E2 treatment had no significant effect on mean values of all three hormones analyzed. From our results it can be concluded that in ovariectomized cows (a) acute stress increases cortisol and progesterone secretion but decreases LH release and (b) the stress induced adrenocortical and pituitary responses were clearly attenuated under the influence of estradiol.

Dexamethasone influences endocrine and ovarian function in dairy cattle

Multiparous nonlactating Holstein cows were used to determine the effect of dexamethasone on ovarian follicular development and plasma hormone concentrations. Animals were randomly divided into two groups, control (C; n = 5) and treatment (T; n = 6), but managed as one group. Both groups were synchronized with two injections of PGF2alpha (25 mg i.m.) 11 d apart. One day after ovulation (d 0) the T group received a daily injection of dexamethasone (44 microg/kg of body weight; i.m.) until the first dominant follicle stopped growing or up to d 12 postovulation. The C group received vehicle injections. Blood samples were collected daily from all cows. Concentrations of LH and FSH did not differ between the C and T cows, whereas progesterone concentrations were lower in T than in C cows from d 4 onward. Treatment x day interaction influenced plasma insulin concentrations such that T cows had insulin concentrations 2.9- to 6.0-fold those of C cows between d 2 and 9. Dexamethasone decreased IGF-I and -II concentrations from d 5 onward. Concentrations of plasma leptin and the various IGF binding proteins were not affected by dexamethasone. Total number of follicles (> or = 5 mm) and plasma estradiol concentrations were less in T than in C cows on d 0, 1, and 4. The growth rate of the dominant follicles and maximum diameter of the dominant and subordinate follicles were not affected by dexamethasone. The diameter of the CL was 21 to 39% larger in T than in C cows between d 6 and 10. Treatment x day interaction influenced plasma cholesterol concentrations such that cholesterol levels decreased 46.8% in T cows and 19.5% in C cows between d 0 and 10. Plasma glucose concentrations were greater in T than in C cows between d 1 and 10. In summary, dexamethasone had significant effects on metabolism without a major impact on growth of the first-wave dominant follicle. Dexamethasone-induced suppression of luteal function was associated with decreased plasma IGF-I and -II concentrations.