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There is a temporal relationship between the secretory activity of the rat adrenal gland and the stage of the oestrous cycle. In previous studies, adrenal venous blood has been sampled, but because of the stress of a lengthy operation, the gland is subjected to maximum stimulation. A new surgical approach has been developed in which samples of adrenal venous blood are taken within 3 min of contact. A competitive binding radioassay was used to determine the level of corticosterone in samples of plasma of both adrenal venous and peripheral arterial origin obtained before (3 min) and after (15 min) the onset of (presumably) ACTH-induced secretion. A reassessment of adrenal function indicated that adrenal activity peaked in pro-oestrus with higher values in the afternoon than the morning and both values were significantly higher than at any other stage in the oestrous cycle. The variations in the concentration of corticosterone in adrenal venous plasma were reflected by a similar pattern of variation in the level of corticosterone in peripheral arterial plasma. In samples of adrenal venous plasma obtained at 15 min, the level of corticosterone was approximately 25 times higher than the basal value during pro-oestrus and approximately 140 times higher than the values during the other stages of the cycle; for peripheral arterial blood the values were eight and 22–30 times higher respectively, without any significant difference when samples of either type of blood were obtained under stress. This indicates maximum stimulation by endogenous ACTH.
Results obtained after treatment of ovariectomized rats with progesterone and/or oestradiol and the fact that LH, but not ACTH, plays a stimulatory role in the non-stressed metoestrous animal, suggest that the peak of adrenal activity at the time of pro-oestrus might be biphasic: in the morning it is influenced by a high level of oestrogen and a low level of progesterone; in the afternoon this balance is reversed. The effect is secondary to the surge of LH which may have a direct effect on the peak of adrenal activity at this critical period.
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Wolfson Laboratory for Research in Gerontology, Department of Zoology, University of Hull, Hull, HU6 7RX
(Received 20 June 1977)
A relative lack of adrenocortical responsiveness to stress has been described in the rat during the period from day 2 to about day 16 of neonatal life (Schapiro, Geller & Eiduson, 1962; Levine, Glick & Nakane, 1967; Corte & Yasumura, 1975) and the reports to date seem to implicate a lack of response of the pituitary gland as the primary cause (Zarrow, Philpott & Denenberg, 1968; Donovan, 1970; Corte & Yasumura, 1975). Since very little work has been done on the response of the pituitary gland to stress in the neonatal rat, the present study was undertaken.
Female Sprague–Dawley rats weighing 300 g were housed at 22 °C with a light : darkness cycle of 12 : 12 h. Mated female rats were isolated on day 1 of pregnancy, and after
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Wolfson Laboratory for Research in Gerontology, Department of Zoology, University of Hull, Hull, HU6 7RX
(Received 5 April 1911)
Jones, Brush & Neame (1972) reported that the level of adrenocorticotrophin (ACTH) in the plasma returned to the control value as early as 10 min after sham adrenalectomy. In contrast, Cook, Kendall, Greer & Kramer (1973) observed no decline in the level of radioimmunoreactive ACTH in the plasma until 40 min after the onset of a 2·5 min ether stress. Furthermore, the stress levels of ACTH were maintained for 2 h in animals subjected to continual ether stress. Therefore, the levels of both ACTH and corticosterone in sequential samples of plasma from control and dexamethasone-treated rats were measured, in order to see whether a negative feedback mechanism, that acts on the pituitary gland as the level of corticosterone increases, operates even in the presence of continuous stress.
Blood samples were taken
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The influence of treadmill exercise on corticosterone secretion has been determined in domestic ducks. In birds unused to such exercise the concentrations of plasma corticosterone were markedly increased (> fourfold) after 15 or 30 min of treadmill exercise (1·1 km/h at 3 ° grade) and the level remained high (between 30 and 40 ng/ml) throughout 90 min of exercise. This increase in corticosterone secretion accompanied a similar increase in colon temperature and was independent of the plasma glucose level. After exercise the corticosterone concentration declined to the pretreatment level within 60 min of recovery. In birds used to the exercise the corticosterone response to a standard (30 min) period of exercise was diminished (by 77·6% in comparison with untrained birds and was no greater than the response (1·7-fold) in stationary control birds after handling and bleeding. The diminution of the corticosterone response to exercise may be due to the trained birds becoming fitter and better able to perform the work involved.
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During the course of an investigation designed to define the seasonal functional changes in the adrenal gland of the Cobra, Naja naja (Linn.), two interesting structural features were observed. After routine staining with Heidenhain's iron haematoxylin and picro-aniline blue or Ehrlich's haematoxylin and eosin a distinct 'zonation' of the gland is apparent. As in other reptiles (Chester Jones, 1957; Deane, 1962), the adrenocortical cells are arranged in cords with an overall anterior-posterior orientation. In saggital sections, therefore, the cells of the cords appear as parallel rows, while in transverse sections circular cords with radiating cells predominate. However, peripherally placed cords of cells in the sub capsular part of the gland are distinct from the remainder (Plate, fig. 1), an arrangement reminiscent of the zona glomerulosa of the mammalian adrenal gland. This subcapsular zone completely surrounds the remaining part of the gland and is thickened at the poles, especially at the
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The nasal glands of the domestic duck secrete a sodium chloride solution after the administration of solutions hypertonic to the plasma. The response is abolished by adrenalectomy and restored on treatment of adrenalectomized animals with corticosteroids (Phillips, Holmes & Butler, 1961). Although the secretory activity is dependent on the presence of circulating hormones of the cortisol-corticosterone type, the concentration of these hormones in plasma is not affected by stimuli that result in secretion (Donaldson & Holmes, 1965; Macchi, Phillips, Brown & Yasuna, 1965). In the following report, the tissue distribution of corticosteroids and their metabolites was examined in ducklings in order to clarify the role of the adrenal cortex in the control of the nasal glands.
Male ducklings (Anas platyrhynchos) of the Peking white or Aylesbury strain were used. The treatment of animals and the operative procedures were as described previously (Phillips & Bellamy, 1962). To determine inulin space, inulin
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SUMMARY
The pituitary prolactin levels were measured in the domestic duck (Anas platyrhynchos) and in juvenile gulls from a mixed population of herring and lesser black-backed gulls. In the domestic duck the pituitary prolactin levels increased on the 2nd and 3rd days of maintenance on 0·3 m-NaCl, but by the 5th day they had fallen appreciably below the control levels. Maintenance of gulls with 0·3 m-NaCl produced no change in pituitary prolactin levels after 5 days, but a marked fall in prolaction levels when the birds were maintained on 0·7 m-NaCl for 5 days. This difference in response between the two species may be related to their degree of adaptation to a marine environment.
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SUMMARY
Hypophysectomy resulted in a lengthening of the sloughing cycle for about 25 days as compared with the normal cycle. The increase is only in the resting phase, the renewal phase remains unaffected. Thyroid-stimulating hormone did not affect the epidermis directly but increased the activity of the thyroid gland in the hypophysectomized geckos as judged by the uptake of 131I and follicular cell height, and reduced the resting phase by about 7 days. Corticotrophin inhibited sloughing for at least 65 days, and possibly entirely, with the epidermis remaining in the resting condition.
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SUMMARY
Hypophysectomized—thyroidectomized geckos failed to slough during the experimental period of about 120 days. The resting phase of the sloughing cycle persisted so that the outer epidermal generation remained incomplete. These results indicate that one important endocrine component of the sloughing cycle is the normal functioning of the pituitary—thyroid system.
Prolactin administration at 0·4 i.u./g body wt on alternate days restored sloughing by reducing the length of the resting phase; the outer generation was completed and was shed after the appearance of a new inner unit.
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SUMMARY
Prolactin injected into hypophysectomized geckos restored the length of the sloughing cycle to normal (about 35 days) when given in doses of 0·26 i.u./g body wt on alternate days. When the doses of prolactin were increased to 0·4 i.u. the length of the sloughing cycle was reduced to about 30 days. Prolactin given to thyroidectomized geckos shortened the length of the sloughing cycle to about 28 days when administered in doses of 0·4 i.u./g on alternate days. Prolactin probably acts directly on the epidermis and not through the thyroid gland, since prolactin restored sloughing in thyroidectomized animals. Moreover, prolactin had no effect on the activity of the thyroid gland in the hypophysectomized animals as judged by the percentage uptake of 131I or the histological structure. Prolactin in doses of 0·4 i.u./g on alternate days reduced the length of the resting phase of the sloughing cycle; the renewal phase remained unaltered.
