Stress and adrenal function

Adrenocortical and heterophil/lymphocyte responses to challenge in hens showing short or long tonic immobility reactions

1. Adult White Leghorn hens showing short or long tonic immobility reactions were classified as low-fear (LF) or high-fear (HF) responders, respectively. Following cannulation, their adrenocortical responsiveness to ACTH administration and the effects of chronic frustration induced by thwarting of feeding on plasma corticosterone concentrations and heterophil/lymphocyte (H/L) ratios were measured at regular intervals. 2. ACTH injection elicited significant and similar mean increases in circulating corticosterone concentrations in both the LF and HF groups. 3. Absolute H/L ratios were higher in HF than in LF hens after cannulation, although both groups showed similar proportional increases from pre-operation ratios. 4. Plasma corticosterone concentrations and H/L ratios were significantly increased at 20 h and 44 h respectively after the frustration of feeding regime began. Thus, adrenocortical activation preceded increases in H/L ratios but, whereas the elevated plasma corticosterone concentrations found after 20 h remained virtually constant thereafter, H/L ratios rose progressively throughout the 68 h frustration period. 5. There were no significant differences between groups in their plasma corticosterone and H/L responses to frustration. However, a consistent trend towards greater adrenocortical activation was observed in the HF than in the LF hens.

Changes in the adrenal steroidogenic responsiveness of the mallard duck (Anas platyrhynchos) during early post-natal development

1. Plasma concentrations of corticosterone (B), aldosterone (Aldo) and deoxycorticosterone (DOC) were measured in mallard ducklings immediately before and after exposure to acute immobilization stress. 2. Except for transient declines in B and DOC between the 4th and 14th days after hatching, the resting concentration of each hormone did not change significantly during post-natal development. 3. The stress-induced in Aldo was maximal at hatching while maximal increases in B and DOC did not occur until one day later. 4. Thereafter the magnitude of the stress-induced increases in the concentrations of all of the hormones decreased steadily and on the 21st and 28th days after hatching only B increased significantly in response to stress.

Effects of short-term changes in electrolyte intake on the adrenal steroidogenic responses of juvenile mallard ducks (Anas platyrhynchos)

1. Adjusting the Na+ and K+ intake of juvenile mallard ducks caused the plasma concentrations of corticosterone (B) and aldosterone (Aldo) to increase independently of one another, but none of these changes in electrolyte intake had a significant effect on the deoxycorticosterone (DOC) concentration. 2. With the exception of DOC in birds consuming the control diet, the plasma concentration of each hormone, regardless of diet, increased significantly following exposure to stress. 3. Stress-induced increases in Aldo concentration were greatest in birds given diets containing low concentrations of Na+. 4. Unlike the mammal and some other species of birds, Na+ may be the primary secretagogue responsible for the regulation of both corticosterone and aldosterone synthesis in the mallard duck.

Stimulation of corticosterone release in the fowl by recombinant DNA-derived chicken growth hormone

The effects of recombinant DNA-derived chicken growth hormone (rcGH) on plasma corticosterone in young broiler cockerels were investigated. A single injection of 200 micrograms/kg rcGH significantly increased plasma corticosterone concentrations 2 hr (but not 20 or 40 min) after treatment. Administration of 10 or 100 micrograms/kg rcGH also significantly increased plasma corticosterone levels after 2 hr, with the higher dose eliciting greater responses. Chronic treatment with seven daily injections of the same doses of rcGH gave similar increases in plasma concentrations of corticosterone. No obvious difference in magnitude of plasma corticosterone was observed between acute and chronic exposure to rcGH. In a further experiment in which serial blood sampling was performed after a single injection or five daily injections of vehicle or 200 micrograms/kg rcGH, there were significant increases in plasma corticosterone concentrations 40 min after acute rcGH treatment and 40 and 80 min after chronic treatment when compared with plasma corticosterone concentrations of vehicle-injected controls. However, the increases could have incorporated a stress response due to repeated sampling because the control birds also showed elevated plasma corticosterone concentrations. The corticosterone response did not diminish with repeated GH challenge. These results suggest that GH may play a role in the acute regulation of corticosterone secretion in intact chickens.

Tonic immobility and heterophil/lymphocyte responses of the domestic fowl to corticosterone infusion

The tonic immobility (TI) fear reactions, plasma corticosterone concentrations and heterophil/lymphocyte (H/L) ratios of adults laying hens were measured before and at intervals of 4 and 11 days after the subcutaneous implantation of osmotic minipumps delivering either corticosterone solution (15 micrograms/hr) or only polyethylene glycol vehicle. The dummy pumps exerted no apparent behavioral or endocrine effects, whereas tonic immobility was significantly prolonged and circulating corticosterone concentrations significantly elevated at 4 and 11 days after implantation of the corticosterone minipumps. H/L ratios were significantly elevated from pre-treatment levels in both groups. However, H/L ratios were considerably higher at both post-treatment points among birds receiving corticosterone rather than vehicle. The present findings suggest that chronic elevations of plasma corticosterone not only alter the haematological profile but may also predispose birds to react more fearfully to alarming stimulation.

The influence of methimazole on the thyrotrophic and peripheral activity of thyrotrophin and thyrotrophin-releasing hormone in the chick embryo and growing chicken

Plasma concentrations of thyroxine (T4) and triiodothyronine (T3) were profoundly depressed both in chick embryos and growing chickens after methimazole (MMI) treatment. There was no response of T4 and T3 levels to TRH or TSH injections in the MMI group, either in embryos or growing chickens. Peroxidase activity measured in the thyroid gland was significantly higher in embryos and growing chickens treated with MMI. However, neither TRH nor TSH affected this activity 2 hr after injection in either control or the MMI-treated group. Hepatic 5'-monodeiodinase activity was significantly stimulated in the MMI-treated groups of embryos and growing chickens but only when additional sulphydryl groups (DTT) were provided. In embryos, monodeiodination activity 2 hr after TSH injection was not significantly different from control values for either DTT-stimulated or unstimulated conditions within the control and MMI-infused groups. However, in both control and MMI-treated embryos monodeiodination activity significantly increased 2 hr after TRH injection. In the growing chickens, monodeiodination activity 2 hr after TRH or TSH injection was not significantly different from control values in either stimulated or unstimulated conditions of each group.

Hematology of Japanese quail selected for high or low serum corticosterone responses to complex stressors

Blood was collected from random-bred male Coturnix coturnix japonica and from quail selected genetically for high or low serum corticosterone responses to complex stressors after chronic exposure to short daily photoperiods and after exposure to long photoperiods. When compared to the low response quail, high response quail exhibited increased mean cellular hemoglobin values, reticulocyte numbers and heterophil percentages, and decreased monocyte and eosinophil numbers after exposure to long photoperiods. The data indicate that these corticosterone response lines can be partitioned by their hematological responses to photoperiodic manipulation.

Plasma concentrations of corticosterone and thyroid hormones in laying fowls from different housing systems

Plasma concentrations of corticosterone, thyroxine (T4) and triiodothyronine (T3) were measured in representative mature female domestic fowls from three housing systems: cages, covered strawyard and range. There were no between-system differences for T4 but T3 was lower in birds from range than in those from cages. Corticosterone concentrations were lower in birds from strawyards than in those from range and cages. In the strawyards there were no differences in corticosterone concentrations between normal and low-ranking hens. The latter were selected on the basis that they remained apart from the flock, were under-weight, poorly feathered and unable to feed at will. Low-ranking hens had significantly higher plasma concentrations of T3 and T4 than normal birds. This was attributed mainly to the poor feather covering of most low-ranking birds. It was concluded that, in the assessment of different housing systems, plasma corticosterone and thyroid hormones were not useful measures of long-term stress or welfare. Different factors relevant to welfare may have contrary effects on the plasma concentrations of these hormones.

Performance of White Leghorn hens in response to cage density and the introduction of cage mates

Hens reared at densities of 344 and 516 cm2/bird produced significantly fewer hard-shelled (HS) and shell-less (SL) eggs than hens reared at a density of 1031 cm2/bird. Soft-shelled (SS) egg production was not affected by the density treatment. A decline in ovulation rate would account for the decrease in total hen-day production in response to the higher density treatments. To determine if the introduction of new cage mates would cause hens to lay fewer eggs with poorer shell quality, the performance of hens with visitors was compared with those with nonvisitors. Visitors were introduced monthly for 13 months. Visitors vs. nonvisitors showed no significant difference with regard to HS, SS, and SL egg production, feed efficiency, mortality, egg weight, and specific gravity.

Corticosterone secretion through long incubation shifts in Diomedea albatrosses

Blood samples were collected from free-living incubating Diomedea albatross during single incubation shifts, both daily (wandering albatross D. exulans and every 2 days (grey-headed albatross D. chrysostoma and black-browed albatross D. melanophris), and the concentration of corticosterone was determined. Within 48 hr a significant increase in the corticosterone concentration was observed in each species. The magnitude of the increase was greater in the grey-headed and black-browed albatrosses than in the wandering albatross. Corticosterone concentrations rose steadily through the incubation shift in grey-headed and black-browed albatrosses, but fluctuated erratically in wandering albatrosses. All three species of albatross fast during incubation and the increase in adrenocortical activity is probably related to the voluntary deprivation of food and water.

Flight stimulates adrenocortical activity in pigeons (Columba livia)

The influence of long-distance flight on corticosterone secretion has been examined in trained racing pigeons. Flights of 315-561 min from release sites 115-557 km from the home loft greatly increased the circulating corticosterone concentration in comparison with the levels in nonexercised controls sampled before release or bled in the loft at the times of release or arrival. The increase in corticosterone concentration was unrelated to the distance flown or duration of flight. Flights of less than 1 min duration (from release sites 100 m from the loft) increased the corticosterone concentration, in comparison with that in the loft controls, but to levels much lower (P less than 0.001) than those following long-distance flights and to concentrations similar to those in birds that were returned to the loft by hand.

Haemorrhage and adrenocortical activity in the fowl (Gallus domesticus)

Plasma aldosterone concentrations were markedly elevated in chickens by the removal of 10-30% of their total blood volume. This aldosterone response to haemorrhage was delayed and of reduced magnitude in birds pretreated for 48 hr with dexamethasone (100 micrograms/kg every 12 hr), in which the basal aldosterone level was also suppressed. Corticosterone concentrations were elevated in both haemorrhaged and nonhaemorrhaged birds, although these responses were completely abolished by dexamethasone pretreatment, which also reduced the basal corticosterone concentration. Prolactin concentrations were unaffected by haemorrhage. These results demonstrate that haemorrhage specifically affects adrenocortical function by increasing aldosterone release and suggests that factors other than the pituitary-adrenal axis are responsible for this stimulation of secretion.

Adrenergic stimulation of adrenocortical secretion in immature fowl

In 5-6-week-old cockerels the circulating corticosterone concentration was significantly increased in birds i.m. injected 30 and 60 min previously with adrenaline (0.33 mg/kg), noradrenaline (0.33 mg/kg) or a beta-adrenergic agonist (isoprotorenol, 1 mg/kg), but was reduced in birds pretreated with an alpha-adrenergic agonist (phenylephrine, 1 mg/kg). The stimulation of corticosterone secretion induced by a 30 min period of forced exercise (0.04 km/hr; 0 degree incline) was potentiated by noradrenaline, isoprotorenol and phentolamine pretreatment. In response to exogenous adrenocorticotrophin (ACTH, 8 i.u./kg), administered i.v., the increase in the plasma corticosterone concentration was elevated above that in the controls in birds pretreated with adrenaline, noradrenaline, isoprotorenol or phentolamine (an alpha antagonist administered at 1 mg/kg). The corticosterone response to ACTH was suppressed by phenylephrine pretreatment. These results demonstrate that both basal and stimulated levels of adrenocortical activity may be subtly regulated by adrenergic mechanisms acting at a site(s) within the hypothalamo-pituitary-adrenal axis.