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ABSTRACT
Glucocorticoids have been found to inhibit reproductive function in most domestic species studied but, in the ewe, preliminary reports suggest that glucocorticoids may have little or no effect. This study investigated the effects of the synthetic glucocorticoid dexamethasone on oestrus and ovulation rate in ewes during the breeding season and gonadotrophin secretion in the breeding and non-breeding seasons. In cyclic ewes, dexamethasone treatment at rates of up to 2 mg/day did not affect the natural or pregnant mare serum gonadotrophin-stimulated ovulation rate, or the timing and incidence of behavioural oestrus (P>0·05). Dexamethasone administration (2 mg/day) had no effect on LH secretion or the plasma LH response to a 1 μg injection of gonadotrophin-releasing hormone (GnRH) in ovariectomized ewes in the breeding and non-breeding seasons, and did not compromise the inhibition of plasma LH levels during chronic treatment with oestrogen. Similarly, dexamethasone had no effect on plasma FSH concentrations, but significantly (P<0·05) reduced the plasma FSH response to a 1 μg GnRH injection during chronic negative treatment with oestrogen in ovariectomized ewes. Collectively, these data show that in these experiments dexamethasone did not significantly modify reproductive function in the ewe, a finding that is in contrast to that found in other domestic species.
Journal of Endocrinology (1990) 126, 289–295
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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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ABSTRACT
The patterns of gonadotrophin-releasing hormone (GnRH) input to the pituitary gland that affect the expression of a positive-feedback event by oestrogen on LH secretion were investigated in ovariectomized ewes with hypothalamo-pituitary disconnection (HPD). In experiment 1, ovariectomized HPD ewes were given hourly i.v. pulses of 250 ng GnRH and an i.m. injection of 50 μg oestradiol benzoate (OB). The ewes were given a bolus pulse of 2·25 μg GnRH 16 h after injection of OB, followed by half-hourly pulses of 250 ng GnRH for 14 h (treatment A). The LH surge response was significantly (P <0·05) greater in these ewes compared with that in ewes given a continuous infusion of GnRH (250 ng/h) after the OB injection, followed by a continuous infusion of 500 ng GnRH/h after the bolus pulse of GnRH (treatment B). When no GnRH was administered after the OB injection, except for the bolus pulse of GnRH (treatment C), the surge response was significantly (P <0·05) reduced compared with that in treatment A, and was reduced compared with treatment B. These data suggest that GnRH pulses are important in the generation of the OB-induced LH surge, but that a baseline secretory component can prime the pituitary to some extent. experiment 2, a doubling of the continuous infusion dose of GnRH used in treatment B to 500 ng/h before the bolus pulse of GnRH and to 1 μg/h afterwards (treatment D) gave a similar response compared with treatment A, suggesting that if the baseline input of GnRH is of sufficient magnitude, it can overcome the lack of pulsatile input. In experiment 3, halving the GnRH pulse amplitude used in treatment A from 250 to 125 ng (treatment E) did not reduce the LH surge response, implying that when the GnRH input is in a pulsatile mode, the amplitude of GnRH pulses is less important than the pulsatile nature per se. In experiment 4, removal of GnRH input after the bolus pulse of GnRH (treatment F) significantly (P <0·05) reduced the surge response compared with when pulses were maintained (treatment A), indicating that GnRH input is still required once the LH surge has been initiated. Collectively, these experiments show that several forms of GnRH delivery, both pulsatile and baseline, can result in the full expression of a positive-feedback response in ovariectomized ewes treated with oestrogen.
Journal of Endocrinology (1990) 127, 223–233
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SUMMARY
Domestic ducks were adenohypophysectomized and 2–3 weeks later were loaded with hypertonic saline. Normal intact ducks and sham-operated ducks were similarly treated. For 2 hr. nasal gland secretion was almost completely inhibited (0·20 g.) in the adenohypophysectomized ducks and was significantly reduced (4·93 g.) in the sham-operated ducks compared with the normal intact controls (14·74 g.).
When the renal response of the adenohypophysectomized ducks was compared with that of the normal intact controls no significant difference was found as far as volume of urine and concentration of Na+ and K+ were concerned. When compared with sham-operated controls, however, these values were significantly lower in adenohypophysectomized ducks.
The adrenal weight was not significantly reduced in the adenohypophysectomized ducks, but the weights of thyroid, nasal gland and testis decreased significantly. Histological examination of the adrenal glands of the adenohypophysectomized ducks showed that the central regions were atrophic while the peripheral regions remained normal. Nasal glands, thyroid glands and testes were also examined.
It is concluded that the adenohypophysis plays a major part in regulating extrarenal excretion.
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SUMMARY
After the injection of cortisol into the toad Xenopus laevis, the concentration of steroid in the main circulatory system was much higher than that in the limb muscles. The concentration of corticosteroids in the blood fell at a faster rate than that in muscle. The particulate fraction of toad muscle homogenate bound added cortisol and some of it was not removed by repeated washing of the tissue with fresh medium. Bound steroid was not confined to any one subcellular fraction. The small particle fraction ('microsomes') contained the greatest proportion of steroid and the highest steroid concentration. The loss of corticosteroids from intact and washed particle preparations of toad gastrocnemius was not influenced by temperature over the range of 17–37°.
Copper, zinc and manganese (between 26 and 31 mm) inhibited the release of cortisol bound to muscle particles; p-chloromercuribenzoate (2 mm) and anoxia had no effect. A variation in pH from 2 to 10 made little difference to the rate of steroid release by muscle particles suspended in 0·15 m-KC1. The results suggest that the release of strongly bound steroids from muscle does not involve an enzymic mechanism.
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SUMMARY
Developing marine birds, but not mature ones, when maintained on sea water failed to grow at the same rate as those maintained on fresh water. In both developing and mature birds maintained on sea water the size of the adrenal glands and supraorbital nasal glands showed dramatic increases. The significance of these changes is discussed in relation to both the results of other workers and our recent work on the salt-loaded domestic duck.
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SUMMARY
Adrenal glands of lizards (Lacerta viridis L.) and snakes (Natrix natrix L.) were incubated in media containing tritiated progesterone. Aldosterone, corticosterone and an unknown steroid were produced. Added ACTH did not affect, though added amphenone markedly reduced, the rate of steroid production.
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An adequate supply of dietary iodine is essential as a substrate for the thyroid gland. In some countries, including Britain and the United States, dietary iodine levels have risen markedly in recent years due to the use of iodized salt or bread to eliminate endemic goitre or to the casual use of iodine in food processing and farming. Iodine intake in some communities now greatly exceeds the recommended daily allowance of 150 μg (Wenlock, Buss, Moxon & Bunton, 1982). Additionally, pharmacological doses of iodine may be ingested in certain drugs, for example amiodarone, in radiographic contrast agents or in iodine-containing mouthwashes. Concern that excess iodine intake may cause thyroid dysfunction has renewed interest in the role of iodine in thyroid metabolism.
As well as being a substrate for the biosynthesis of thyroid hormone, iodine has a number of effects on the thyroid gland including the induction of both hypo- and
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ABSTRACT
The presence of insulin-like growth factors (IGFs) in blood is regulated by their association with specific IGF-binding proteins (IGFBPs). In turn, the level of IGFBPs in the blood is likely to depend on a dynamic equilibrium between peptide production and clearance to extravascular tissues or organ-specific degradation. Since circulating IGFBPs may largely derive from liver we have employed partial hepatectomy in the rat to study the clearance rate of endogenous IGFBPs from blood once a major site of production is removed. Adult male rats were partially hepatectomized and serum and the remaining liver removed between 30 min and 7 days after surgery. Ligand blot analysis revealed two major species of IGFBP, of 28–30 kDa and 40–44 kDa in sera from control rats or sham-operated rats respectively. The larger species corresponded in size to rat IGFBP-3, but the smaller form was not recognized by antisera against rat IGFBP-1, bovine IGFBP-2 or human IGFBP-5 following Western immunoblot. Following hepatectomy, the levels of both IGFBP forms in the serum declined within 30 min and were barely detectable after 3 h or 6 h. They began to increase again in serum 24 h following surgery. The reduction in IGFBPs following hepatectomy was not primarily due to degradation by specific proteases in serum. Circulating levels of insulin were increased fivefold 3 h after hepatectomy but subsequently returned to control values. The rise in insulin was accompanied by a significant (P < 0·05) reduction in circulating IGF-I after 3 h which persisted at 24 h. Glucose levels in serum showed a transient but non-significant reduction between 90 min and 6 h after hepatectomy. Total RNA was extracted from remnant liver and subjected to Northern blot hybridization with 32P-labelled cDNAs encoding rat IGFBP-1, -2 or -3. Messenger RNA encoding IGFBP-1 was barely detectable in liver from control or sham-operated animals, but increased within 30 min of partial hepatectomy and peaked at 3 h. It subsequently declined and was again barely detectable after 24 h. No expression of IGFBP-2 or -3 mRNAs was found by Northern blot analysis in the liver of control animals or following partial hepatectomy. These results suggest that both IGF-I and IGFBPs in rat serum decreased rapidly following partial hepatectomy, and that this was due largely to the rapid clearance of the peptide and its binding proteins once the major source of production was removed. A rapid induction of IGFBP-1 in the remaining liver may be unrelated to the circulating IGFBPs since immunoreactive IGFBP-1 was not detected in rat serum.
Journal of Endocrinology (1993) 137, 271–280
