J.G. Phillips

The effects of aging and chronic dietary restriction on whole body growth and protein turnover in the rat

Changes in whole body growth, nucleic acids, and protein turnover have been studied in conjunction with ageing and chronic dietary restriction. Normal developmental changes between weaning and senescence included progressive decreases in the fractional rates of growth, protein synthesis, and protein breakdown; the decline in the synthetic rate correlating with decreases in the ribosomal capacity. Dietary intervention was imposed at weaning and involved pair feeding to 50% of the ad libitum food intake. Although this regime slowed whole body growth by retarding the developmental decline in protein turnover, growth was extended into the second and third years of life. The dietary-induced increase in longevity resulting from a retardation of the ageing process(es) appears therefore to be associated with an enhanced turnover of proteins during the major portion of the life span of dietary restricted rats.

Reproductive performance and endocrine responses to ingested petroleum in domestic ducks (Anas platyrhynchos)

Abstract The onset of lay by Khaki Campbell ducks transferred from a short-day (8L:16D) to a long-day photoperiod (16L:8D) was delayed by at least 4 weeks in birds fed 5 ml of North Sea Crude Oil per 100 g day wt of food, compared with birds fed an uncontaminated control diet. Over a 20-week period the oviposition rate and shell thickness of eggs laid by the birds fed 5% oil were greatly reduced. Refeeding the oil-fed birds with the uncontaminated diet increased oviposition rate and egg-shell thickness but not to the level in the controls. Throughout the experiment the plasma levels of prolactin and corticosterone in blood samples taken at weekly intervals were invariably less than those in the control birds. During photostimulation the mean plasma thyroxine concentration in the oil-fed birds was higher than the level in the controls but significant increases in the weekly concentration were only observed after the effects of petroleum on reproduction were manifest. The circulating concentrations of triiodothyronine were unaffected by oil ingestion. These results suggest that decreased ovarian activity in the oil-fed birds was not due to antigonadal effects of increased prolactin secretion or adrenocortical activity and an endocrine dysfunction of the thyroid is unlikely to be causally responsible for the effects of petroleum on avian reproduction.

Growth, growth hormone, and corticosterone secretion in freshwater and saline-adapted ducklings (Anas platyrhynchos)

Abstract Plasma growth hormone (GH) and corticosterone concentrations have been determined in growing male and female ducks during adaptation to hypersaline drinking water (0.1 – 0.4 M NaCl) and fresh water (FW). Saline adaptation resulted in growth retardation, adrenal hypertrophy, and lymphoid (bursa of Fabricus) involution. Basal plasma corticosterone levels increased with age in both FW- and saltwater (SW)-reared birds. Compared with the FW birds corticosterone was temporarily increased three- to fivefold during periods of saline adaptation. Plasma GH cocentrations decreased with age in birds reared on both FW and SW and in each group were directly related to the percentage weekly body weight gain. However, differences between the groups in growth rate were not reflected in corresponding differences in plasma GH level. No differences were seen between the sexes in circulating GH or corticosterone concentrations in the FW birds.

Transitory corticosterone responses of ducks anas platyrhynchos to exercise

Horizontal treadmill exercise induced a marked (P less than 0.001) but transitory increase in the level of circulating corticosterone in the plasma of adult male ducks. The decline in corticosterone concentration during exercise is unlikely to be due to a depletion of adrenocortical stores since a marked (P less than 0.001) corticosterone response to adrenocorticotrophin (ACTH) administration was observed immediately after exercise, and was of similar magnitude to that induced in nonexercised controls. The corticosterone response to repeated exercise is also transitory, habituating completely within 28 days of the start of daily training. The corticosterone response (P less than 0.001) to ACTH challenge is not, however, diminished by training. These results indicate that the habituation of the corticosterone response to either acute or repeated exercise is due to a reduction in endogenous ACTH secretion. A similar mechanism appears to be responsible for the habituation of the corticosterone response to handling and confinement in nonexercised control birds. A marked (P less than 0.001) increase in the level of circulating corticosterone was, however, elicited when these birds were exercised, indicating that despite adaptation to handling and confinement the birds remained responsive to the novel stressor of exercise. The corticosterone response of these birds was, however, less than that in untrained birds indicating that the corticosterone response in untrained birds is due to both workload and the stress of handling and confinement.

Habituation of the corticosterone response of ducks (Anas platyrhynchos) to daily treadmill exercise.

The habituation of the corticosterone response of ducks to treadmill exercise (1.1 km/hr 0 degrees incline for 60 min) has been determined over a 28-day period. In untrained birds 30 min of treadmill exercise resulted in a marked (P less than 0.001) increase in the basal plasma corticosterone level. After 60 min of exercise the corticosterone concentration remained elevated (P less than 0.001) in comparison with basal and control (nonexercised) levels but was less (P less than 0.01) than that at 30 min. Following exercise the concentration declined to basal levels within 60 min. After 7 days of daily training the peak (30 min) corticosterone response to exercise diminished by greater than 50% and was absent in birds trained for 21 days. This habituation of the corticosterone response may be due to adrenocortical stimulation by pituitary adrenocorticotrophin (ACTH) being reduced. As the stimulatory effect of ACTH administration (8 IU/kg) on corticosterone secretion does not habituate in birds treated daily (for 28 days), the reduced corticosterone response to exercise may be due to decreased ACTH release rather than to a reduction in adrenal ACTH sensitivity.

Adrenocortical responses to novel stressors in acutely or repeatedly starved chickens

The effect of starvation on the corticosterone responses of immature cockerels to acute, novel stress has been determined. The marked corticosterone responses of fed birds to either horizontal treadmill exercise (0.04 km/hr) or intravenous adrenocorticotrophic hormone (ACTH) administration (P less than 0.001 in both cases) were reduced by starvation (P less than 0.01 and P less than 0.001, respectively). This reduction did not appear to be due to either feedback inhibition of corticosterone on the hypothalamus or pituitary, or to reduced adrenal responsiveness to endogenous ACTH. Starvation significantly elevated the basal level of circulating corticosterone (P less than 0.001), but the magnitude of this elevation and the level of corticosterone attained were less (P less than 0.05) in birds that were accustomed to starvation. This habituation of adrenocortical activity may be due to reduced pituitary ACTH secretion, and was specific in that the corticosterone responses to novel stressors were unaffected.

The significance of environmental factors in the hormone mediated changes of nasal (salt) gland activity in birds

Abstract The relative importance of environmental pressures on the regulatory demands of the extrarenal (salt gland) excretory route to maintain homeostasis in birds is now becoming known through the experimental approach in which individual natural stresses have been examined in their effect on the hormonal status of the bird. Attempts have been made to interpret these changes in terms of salt gland activity, and emerging from the approach is the view that hormones are involved at possibly three levels within the body viz. directly on the gland at the cellular level, systemically via hormonally induced changes which secondarily affect salt gland activity and finally as a result of hormonal changes which have their basis in behavioral adjustments. The present state of our knowledge is discussed with respect to corticosteroids, thyroxine, ACTH, prolactin and AVT in relation to hypersalinity, heat, cold and water deprivation.

Growth hormone secretion in anaesthetized fowl 1. Refractoriness to repeated stimulation by human pancreatic growth hormone-releasing factor (hpGRF) or thyrotrophin releasing hormone (TRH)

The intravenous (iv) administration of thyrotrophin releasing hormone (TRH, at 1.0 or 10.0 micrograms/kg) or human pancreatic growth hormone-releasing factor (hpGRF(1-44)NH2, at 10 micrograms/kg) markedly increased the growth hormone (GH) concentration in the plasma of immature or adult cockerels anaesthetized by sodium pentabarbitone (30 mg/kg, iv). A second injection of either TRH or hpGRF failed to increase the GH concentration in immature chicks when administered 15, 30, or 60 min after the first injection. However, significant GH responses to TRH or hpGRF were observed when the interval between injections was either 120 or 240 min. The magnitude of the GH responses to TRH were, however, diminished by 83.3 and 26.7% when given 120 or 240 min after the initial TRH injection, and the responses to hpGRF were similarly reduced by 68.3 and 33.6%. A similar period of GH refractoriness to TRH or hpGRF stimulation was also observed in adult birds, although the recovery of GH responsiveness occurred earlier. While a second injection of hpGRF was ineffective in increasing the plasma GH concentration if given within 30 min of the first, it was fully effective when the interval between injections was greater than 60 min. In response to a second injection of TRH, the GH concentration was elevated when the interval between injections was greater than 120 min, after which the magnitude of the response evoked was greater than that induced by the initial injection. Growth hormone secretion secretion in immature and adult fowl is therefore refractory to repeated provocative stimuli, although the mechanism involved is unknown.

Endocrine responses of ducks (Anas platyrhynchos) to treadmill exercise

Variations in the plasma concentrations of immunoreactive glucagon, insulin, triiodothyronine (T3), thyroxine (T4), prolactin, and growth hormone (GH) have been determined in adult domestic ducks during 90 min of treadmill exercise (3° grade, 1.1 km/hr). Plasma glucagon and T3 concentrations were, respectively, increased (P < 0.05 in comparison with pretreatment and sedentary control levels) after 15 and 60 min of treadmill exercise and both remained elevated thereafter. The concentration of plasma glucagon progressively increased in the control birds and was higher (P < 0.05) than the pretreatment level after 60, 75, and 90 min. The concentration of plasma T4 was markedly reduced (P < 0.05) after 15 min of exercise and progressively declined throughout the period of exercise. A similar but lesser decline in the T4 concentration was also observed in nonexercised control birds. In both the exercised and control birds the plasma insulin level declined (P < 0.02) during the course of the study, although no significant difference in the insulin concentration was observed between the groups. Plasma concentrations of GH and prolactin were unaffected by treadmill exercise or by handling and blood sampling. The hormonal responses of ducks to exercise differ from those in mammalian species.

Circadian variation in activity of the duck (Anas platyrhynchos) adrenal gland

Duck adrenal glands were studied with respect to circadian activity by incubating with progesterone-4-14C at 2-hour intervals for 24 hr. The production of deoxycorticosterone, corticosterone, and aldosterone was studied in quadruplicate incubations. Results show that peak production of corticosterone and aldosterone occurred at early morning at 06.00–08.00 hr and again in the late afternoon, 16.00–20.00 hr. Production of these two hormones was at minimum at midday and midnight. Unlike the mammalian species studied which exhibit a 24-hr cycle change in adrenal activity, the duck shows a characteristic 12-hr cycle. This pattern of circadian activity of the adrenal reflects to some degree the physiology of the animals in that the peaks of adrenal activity coincide with times of maximal body activity.