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1.
The diurnal rhythms of plasma glucose, cortisol, growth hormone (GH) and thyroid hormone (T4, T3) concentrations and hepatic glycogen content were measured in rainbow trout that had been entrained to a specific time of daily feeding (post-dawn, midday, pre-dusk); the purpose of the study was to investigate the significance of feeding time on hormones and metabolite patterns. Plasma GH, cortisol and T4 concentrations all showed evidence of a diurnal rhythm in some treatment groups. There was a significant interaction between the time of feeding and plasma GH and cortisol concentration rhythms; for GH, this appeared to be related to the phase-shifting of the post-prandial increases in plasma GH concentrations, and for cortisol, the rhythms were only evident in fish fed in the post-dawn period [diurnal rhythms were not evident in treatment groups fed in at midday or pre-dusk]. Peak plasma T4 concentrations were evident during the photophase in all three treatment groups; however, the time of feeding had a negligible effect on the timing of those peaks. There were no apparent diurnal rhythms of plasma T3 and glucose concentrations, hepatic glycogen content or hepatosomatic index in any of the three treatment groups. To whom correspondence should be addressed  相似文献   

2.
Clove oil has been demonstrated to be an effective, inexpensive anaesthetic and euthanizing agent for a number of fish species, including rainbow trout, used in aquaculture and fisheries research. However, the potential for clove oil to cause perturbations in important plasma hormone concentrations has not been investigated. The effect of anaesthesia and euthanasia in trout with eugenol (the active ingredient in clove oil) on plasma cortisol, glucose, growth hormone (GH) and two thyroid hormones [tri‐iodothyronine (T3) and thyroxine (T4)] was compared with tricaine methanesulfonate (MS‐222) anaesthesia, and stunning by cranial concussion in two experiments. Effects on blood chemistry were different when comparing the particular anaesthetic method being used. Stunning fish significantly increased plasma cortisol and glucose levels (both P<0.05), while euthanizing fish using either clove oil or MS‐222 had no effect on these hormone levels. In contrast, the levels of GH, T3 and T4 hormones were unaffected regardless of whether fish were euthanized by stunning, MS‐222 or clove oil. Variation in effects between hormones were observed using clove oil eugenol. In fish sampled 10 min after anaesthetizing with 150 mg L?1 of eugenol, cortisol levels were significantly decreased (P<0.03), while there were no differences in either glucose or GH levels. Tri‐iodothyronine and T4 also showed significantly elevated levels (P<0.05) after 10‐min exposure to eugenol. These results highlight the importance of investigating the potential effects of any new anaesthetic or euthanizing compounds on blood plasma parameters, prior to using them in a research setting, or when comparing results to other studies which have utilized alternative anaesthetic compounds.  相似文献   

3.
The study examined the combined effects of time of feeding (post-dawn, midday-pre-dusk) and ration level (1.5%, 2.0%, 2.5%) on the diurnal rhythms of plasma growth hormone (GH), L-thyroxine (T4), triiodo-L-thyronine (T3), cortisol and glucose concentrations in rainbow trout (Oncorhynchus mykiss) maintained under constant ambient water temperature and natural photoperiod.Plasma GH and glucose concentrations exhibited marked diurnal rhythms, with significant postprandial peaks that were phase-shifted with time of feeding. The ration level did not appear to alter these feeding time-entrained rhythms, but the amplitude of the changes (peaks) were more pronounced in trout fed the higher ration levels. Plasma cortisol concentrations showed distinct diurnal rhythms, with peaks during the photophase and the scotophase in all the treatment groups. The time of feeding did not appear to influence these rhythms, and there was no evidence of a postprandial increase in any group.Plasma GH, cortisol and glucose concentrations were significantly higher in groups fed the 2.5% ration compared with animals fed either 1.5 or 2.0% rations.The diurnal rhythms of plasma T4 concentrations were not affected by the time of feeding or ration level; the peak values generally occurred during the photophase in all the treatment groups. Plasma T3 concentrations did not show any significant diurnal patterns, nor were they influenced by ration levels or time of feeding.To whom correspondence should be addressed  相似文献   

4.
The acute and chronic effects of excess iodide (KI or NaI) were studied on thyroid function of rainbow trout at 11±1°C. No Wolff-Chaikoff effect, characteristic of mammals, was observed and instead plasma L-thyroxine (T4) levels increased 6 hr after a single iodide injection. Plasma 3,5,3′-triiodo-L-thyronine (T3) did not change and by 24 hr plasma T4 returned to normal. This iodide-induced elevation in plasma T4 was probably not due to toxic effects demonstrated at higher NaI or KI doses. A single iodide injection also decreased the plasma iodide distribution space, decreased the fractional rate of plasma iodide loss and completely blocked thyroidal uptake of radioiodide. Injections of iodide over a 22-day period elevated plasma iodide 200X with no mortality and no influence on plasma T4 or T3. It is concluded that: (i) apart from the transient 6h increase in plasma T4, trout thyroid function, as judged by plasma hormone levels, is insensitive to considerable iodide excess, (ii) non-invasive iodide suppression of thyroidal radioiodide recycling may be useful in kinetic studies of125I-labeled thyroid hormones, and (iii) fundamental differences in intrathyroidal iodine metabolism appear to exist between mammals and fish.  相似文献   

5.
The circadian patterns of several tissue and plasma metabolites, and several plasma hormone concentrations are described in rainbow trout (Oncorhynchus mykiss) that were held in groups under three different photoperiod regimes, and given free access to a demand-feeder. Regardless of photoperiod regime, all the measured parameters showed significant diel rhythms that appeared to be synchronized by dawn; dawn was represented by the concomitant onset of both light and feeding. The diel increases in hepatic glycogen content, and plasma T4 and cortisol concentrations were in phase with the main period of feeding activity, whereas the peaks in plasma T3 and glucose concentrations that may also be triggered by feeding activity, were delayed by several hours. The peaks in hepatosomatic index, plasma non-esterified fatty acids and plasma growth hormone concentrations were 180° out of phase with the main period of feeding activity, and associated with periods of hypophagia and low activity.  相似文献   

6.
Temporal changes in growth, plasma thyroid hormone, cortisol, growth hormone (GH) and non-esterified fatty acid (NEFA) concentrations, hepatic T3 content and hepatic 5-monodeiodinase activity were measured in rainbow trout (Oncorhynchus mykiss) subjected to a sustained fast for up to eight weeks, and during a four-week re-feeding period. The purpose of the study was to examine aspects of the endocrine control of energy partitioning processes characteristic of short-term (acute; fasting) and long-term (chronic; starvation) food-deprivation states in fish, and to explore the role of the thyroid hormones, cortisol and GH in the energy repartitioning that takes place during an acute anabolic (re-feeding) state following chronic food deprivation.Differences in growth rate between fed and fasted groups were evident after two weeks, but significant weight loss by the fasted groups was not evident until between four and six weeks into the fast. Hepatosomatic indices (HSIs) were significantly reduced in the fasted fish within seven days, and as early as two days in one study; recovery of the HSI in fasted fish was evident within three days of re-feeding. Liver protein content (expressed as % wet weight) was consistently depressed in the fasted fish in only one of the three studies. Liver total lipid content (expressed as % wet weight) was depressed in the fasted fish within two days of food deprivation. Because of the rapid and sustained decrease in the HSI of fasted fish, the hepatic total protein and lipid reserves, when considered on a body weight basis, were markedly lowered within the first few days of the fast. Plasma GH concentrations exhibited a bi-modal pattern of change, with a transient fall in levels, followed by a sustained increase in fasted fish. The indicators of interrenal activity were suggestive of a depressed pituitary-interrenal axis in fasted animals; plasma cortisol levels were elevated to levels of fed animals within one day of re-feeding. The indicators of thyroid hormone economy (plasma thyroid hormone levels, liver triiodothyronine content, hepatic 5-monodeiodinase (MD) activity, thyroid epithelial cell height) were similarly indicative of a depressed pituitary-thyroid axis in fasted animals, with recovery to levels of the fed animals within one week. Despite the compensatory changes in accumulation of reserves (as indicated by a compensatory increase in HSI), there were no apparent compensatory changes in any of the endocrine parameters evident during the re-feeding period.  相似文献   

7.
Rainbow trout fed a 26% canola meal-based (CM) diet for 12 weeks at 15°C exhibited reduced growth, lower feed conversion, enlarged thyroid glands and lower plasma thyroid hormone (TH) levels than comparable fish fed equinitrogenous, equicaloric soybean meal-based (SB) diets. Supplementation of the SB diets with either T4 (20 mg/kg) or T3 (10 or 20 mg/kg) had no effect on the growth rate, feed conversion and thyroid histology of the trout. However, plasma T4 levels weredepressed in trout fed the T4- and high T3-supplemented SB diets. In trout fed T4- and T3-supplemented CM diets the growth rates and feed conversion were not significantly different from those of the SB-fed groups. Moreover, in the T4-supplemented group, plasma T4 levels were in the normal range. However, thyroid enlargement was evident in all the CM-fed fish, and plasma T3 levels were markedly elevated in groups fed the T3-supplemented CM diets. The data suggest that antithyroid components in the CM diets inhibited TH synthesis (but not their release), and impaired TH clearance from the circulation. There were no significant differences in plasma cortisol levels in the 8 treatment groups, nor were there differences in the histological appearance of the interrenal gland. However, when the data from SB- and CM-fed fish were pooled, plasma cortisol levels in the SB-fed fish were significantly lower than in the CM-fed animals. Glucosinolates at a level of 164 mg/kg diet were toxic to young trout, but the effect was ameliorated by dietary TH supplementation.  相似文献   

8.
A factorial experiment was conducted to determine the effect and interaction of dietary carbohydrate level and triiodo-L-thyronine (T3) supplementation on the growth, physiological response and plasma insulin and cortisol levels of rainbow trout. The oral administration of T3 significantly increased the growth, protein efficiency ratio and feed efficiency of trout, indicating an increased protein and perhaps energy utilization in these fish. However, T, administration did not significantly increase the utilization of dietary glucose as an energy source by the trout. Similarly, the administration of T3 did not significantly affect plasma insulin levels in either the fed or the fasted trout. Plasma insulin levels were significantly higher in fed trout reared on the non-T3 supplemented high carbohydrate diet in comparison to trout reared on the low carbohydrate diets. This indicates that increased dietary carbohydrate stimulates increased insulin secretion in the trout. Therefore, although rainbow trout are not insulin-deficient, they can still be considered a diabetic-like animal due to their poor glucose tolerance. Plasma cortisol levels were not affected by diet composition and altered plasma glucose levels.  相似文献   

9.
Brown (BT) and rainbow trout (RT) in freshwater (FW) were treated with ovine growth hormone (GH), GH + iopanoic acid (IOP), and GH + IOP plus triiodothyronine (T3) for RT only. After 1 week of treatment, trout were transferred to 30 o/oo SW and treatment continued. In FW, GH treatment increased significantly plasma T3 level (BT) and T3/T4 ratio (BT and RT) by stimulating T4 to T3 deiodination. In the GH + IOP group, the plasma T3 levels and T3/T4 ratio fell significantly as T4 to T3 deiodination was inhibited. In GH + IOP + T3-treated RT, plasma T3 and T3/T4 ratios increased significantly relative to other groups. No mortality occurred and plasma osmolarity (PO) was not altered by any treatment in FW. After transfer to SW, all IOP + GH trout died within 2 (BT) or 3 days (RT). All GH-treated or control BT survived to the end of the experiment (6 days). RT survival rates tended to be improved in GH and GH + IOP + T3 groups relative to controls. Correlatively on day 1 the PO increase was significantly higher in IOP + GH groups (BT and RT) than in the other groups and significantly lower in GH and GH + IOP + T3 treated RT than in controls from days 1 to 6. These data confirm the requirement of T3 and deiodination of T4 to T3 for the development of hypoosmoregulatory mechanisms in SW as previously shown (Lebel and Leloup 1992). Furthermore, the suppression of the hypoosmoregulatory effect of GH, when conversion of T4 to T3 was inhibited by IOP and the reversal when T3 was added to IOP + GH treatment suggests that GH osmoregulatory action in SW acts via the simulation of T4-5′ monodeiodination which increases T3 production.  相似文献   

10.
The effect of cortisol on the in vitro metabolism of [3H]17-hydroxyprogesterone ([3H]17OHP) was studied during embryonic development of Arctic charr (Salvelinus alpinus) and rainbow trout (Oncorhynchus mykiss). In the absence of cortisol, rainbow trout embryos metabolized [3H]17OHP largely to androstenedione (A4) and androstenetrione (11-KA) with a minor conversion to 17,20ß-dihydroxy-4-pregnen-3-one (17,20P). In the presence of cortisol, this biosynthesis was inhibited. On the other hand, cortisol had no apparent inhibitory effect on the nature of metabolism of [3H]17OHP by Arctic charr embryos. In these embryos [3H]17OHP was metabolized mainly to 17,20P with a minor conversion to A4 and without the formation of 11-KA that was seen in rainbow trout.When incubated in the presence of [3H]cortisol both Arctic charr and rainbow trout embryos produced 11ß-hydroxyandrostenedione (11ß-OHA) as the major metabolite, with a minor conversion to an unknown steroid. The catabolism of the cortisol by salmonid embryos may reflect the ability of the embryo to inactivate or detoxify cortisol to protect itself from the adverse effects of this biologically potent steroid hormone The study indicates the existence of species-specific differences in the nature of metabolism of [3H]17OHP and the inhibitory effect of cortisol on this metabolism.  相似文献   

11.
The fluid uptake rate of the posterior intestine of salmonids increases during the parr-smolt transformation. Intestinal fluid uptake in post-smolt Atlantic salmon was investigated after treatment with cortisol and growth hormone (GH), alone or together. Two replicate experiments were conducted in August 1991 and August 1992. Cortisol was emulsified in vegetable shortening and vegetable oil (1:1) and implanted into the peritoneal cavity. GH was administered as intraperitoneal injections in a saline vehicle on days 0 and 2. On days 5 and 6, plasma cortisol levels, gill Na+,K+-ATPase activity, andin vitro measurements of fluid transport rate (Jv) across the posterior intestine were measured. Implants of cortisol elevated the plasma cortisol levels within a physiological range, and resulted in elevated gill Na+,K+-ATPase activity, as expected. The fluid uptake rate across the posterior intestine was roughly doubled by cortisol treatment. GH treatment did not affect intestinal fluid transport, gill Na+,K+-ATPase activity, or plasma cortisol concentrations. The seawater-adapting increase in the rate of fluid uptake by the posterior intestine of smolting salmon is probably stimulated by elevated plasma cortisol concentrations.  相似文献   

12.
The formation of 11-deoxycortisol from 17-hydroxyprogesterone was studied in rainbow trout (Oncorhynchus mykiss) head kidney and liver microsomes. The K m for head kidney microsomal 17-hydroxyprogesterone 21-hydroxylase measured in pooled microsomes from juvenile rainbow trout was 3.75 M, and the V max was 41.4 pmol/(mg protein × min). The K m for liver microsomal 17-hydroxyprogesterone 21-hydroxylase was 31.0 M, and the V max was 51.0 pmol/(mg protein × min). The intrinsic clearance values suggest that liver, in addition to head kidney, could significantly contribute to the formation of 11-deoxycortisol in rainbow trout. Progesterone inhibited both the head kidney and the liver microsomal 17-hydroxyprogesterone 21-hydroxylase activity competitively. The K i for progesterone in head kidney was 1.8 M and in liver 144 M. The different K m and K i values for microsomal 21-hydroxylation suggest that 21-hydroxylation of 17-hydroxyprogesterone in head kidney and liver is catalysed by different enzyme systems. Treatment of rainbow trout by adrenocorticotrophic hormone (ACTH) for 1.5 or 3 h (single injections) or three weeks (injections every other day) did not affect head kidney or liver17-hydroxyprogesterone 21-hydroxylase activity. ACTH may thus not regulate this enzyme activity. The increase in plasma cortisol levels 1.5 and 3 h after ACTH injection but not following repeated injections suggests that the hormone regulates the initial secretion of cortisol, but does not have a long-term regulatory effect upon cortisol production in rainbow trout.  相似文献   

13.
Juvenile rainbow trout, held at 12°C on a 12 h light :12 h dark photocycle, were fed a constant ration (1 % of body wt day ?1) of isonitrogenous and isoenergetic diets that varied in either arginine content (3.6-56.1 g kg?1 dry matter; experiment 1), or glycine (3.3–118 g kg?1 dry matter) and alanine (5.0-42.3 g kg?1 dry matter) content (experiment 2). In experiment 1, the lowest dietary level of arginine depressed growth, feed efficiency, plasma l -thyroxine (T4) and 3,5,3′-triiodo-l -thyronine (T3) levels and hepatic T4 5’monodeiodinase (5'D) activity responsible for T4-to-T3 conversion. Over the dietary range of 7.1–56.1 g arginine kg?1, there was no change in 5'D activity, despite an arginine stimulation of growth. The optimum level of arginine for growth was within the range of 14.1–28.1 g kg?1 of the diet or 32–63 g kg?1 of dietary protein. In experiment 2, an increase in dietary glycine level, at the expense of glutamic acid, increased 5'D activity without attendant elevation of the plasma T3 level. The latter finding suggests that glycine also induced a compensatory increase in T3 degradation rate. This may explain why the glycine-induced increase in 5'D activity was unaccompanied by any changes in growth indices. Alteration of dietary alanine content did not affect growth or thyroid function. We conclude that of the various dietary amino acids tested, only glycine led to a progressive stimulation of hepatic T4 5'D activity. However, because glycine likely enhanced T3 degradation, no increases in plasma T3 or growth indices were found. Glycine may serve as an advance signal that activates thyroid function immediately preceding or coincident with energy and nutrient (especially protein) intake. This, in turn, may improve the efficiency of nutrient absorption and/or post-absorptive anabolic events.  相似文献   

14.
Serum thyroid hormone concentrations were measured during the seven stages of metamorphosis (1–7) of the southern hemisphere lamprey, Geotria australis. The respective mean concentrations ± SEM of serum thyroxine (T4) and triiodothyronine (T3) fell from 31.73 ± 4.09 and 5.06 ± 0.70 nM in large ammocoetes sampled in February, at the time when metamorphosis was initiated, to 4.54 ± 0.36 and 1.03 ± 0.12 nM at stage 5. Although there was a small, but significant, recovery of serum T4 concentrations during stages 6 and 7, no such corresponding statistically significant rise occurred in serum T3 concentrations. Serum thyroid hormone concentrations in ammocoetes sampled during the period when metamorphosis was taking place, exhibited a marked seasonal increase between February and May–June (late autumn/early winter); serum T3 and T4 concentrations peaked in May–June and were, respectively, > 2 fold and > 8 fold higher than those recorded for samples in late February (mid summer). By mid-July the serum T4 and T3 levels had declined from the peak values. Ammocoetes taken from streams at 16°C in June and acclimated to aquaria water at 25°C or 6°C had significantly lower serum T3 and T4 concentrations at the higher temperature, and also a lower serum T4, but not T3 concentration, at the lower temperature. Treatment of separate groups of ammocoetes with either propylthiouracil or T3 for 70 days significantly depressed and raised respectively, the serum thyroid hormone and hepatic T3 concentrations and caused significant changes in the body weight, but did not induce the onset of metamorphosis.  相似文献   

15.
We have studied the seasonal relationship between growth and circulating growth hormone (GH), hepatic GH-binding and plasma insulin-like growth factor-I immunoreactivity in gilthead sea bream,Sparus aurata. The seasonal increase in plasma GH levels preceded by several weeks the summer increase in growth rates. In contrast, a marked increase in hepatic GH-binding with a high degree of endogenous GH occupancy was found during the period of maximum growth which suggests an enhanced sensitivity of liver to GH action. Thus, circulating levels of immunoreactive IGF-I, probably derived from the liver in response to GH action, were positively correlated with growth throughout the experimental period although a consistent relationship between growth and circulating GH was not found. In spite of this, we consider that, in gilthead sea bream, as in several other teleosts, the availability of endogenous GH can limit growth. Thus, under environmental conditions of suboptimal growth, a single intraperitoneal injection of recombinant rainbow trout GH (rtGH) induced over the dose range tested (0.75, 1.5, 3 μg g BW−1) an increase in plasma IGF-I-like immunoreactivity comparable to that seen during the period of maximum growth.  相似文献   

16.
Tissue T3 (3,5,3′-triiodo-L-thyronine) concentrations were measured in rainbow trout, Salmo gairdneri, after digestion by Pronase or collagenase and extraction with ethanolic ammonia (99:1, v/v) followed by 2N NH4OH and chloroform. Recoveries of [125I]T3 administered in vivo or in vitro were high and consistent and there was close parallelism between sample dilutions and the radioimmunoassay curve, but recoveries of unlabeled T3 administered in vitro were low and variable. Alternatively, trout were brought to isotopic equilibrium by [125I]T3 infusion for 96 h, the extracted [125I]T3 determined by gel filtration and the tissue T3 content calculated from the specific activity of plasma [125I]T3. By the latter method, tissue T3 concentrations were: intestine (4.2 ng/g), kidney (2.5), liver (2.8), stomach (1.5), heart (1.0), muscle (0.7), gill (0.6) and skin (0.3). Muscle (67% of body weight) comprised the largest tissue T3 pool (82% of all tissues examined). Seven days exposure of trout to water acidified with H2SO4 (pH 4.8) or acidified water containing aluminum (21.6 mM), decreased tissue T3 content generally and particularly in muscle (14% of controls). In conclusion, skeletal muscle is the largest T3 tissue pool and seems highly responsive to altered physiologic state.  相似文献   

17.
The absorptions of 3,5,3-triiodo-L-thyronine (T3) and L-thyroxine (T4) from the intestinal lumen of the rainbow trout were compared in vivo. Tracer doses of [125I]T4 (+T4) or [125I]T3 (*T3) were injected through an anal cannula into the duodenum of trout fasted for 3 days at 12°C, and radioactivity was measured in blood and tissues at 4–48 h. *T3 was removed more extensively than *T4 from the intestinal lumen and more radioactivity was absorbed into the blood and tissues of u+T3-injected trout than *T4-injected trout. HPLC analysis showed that a high proportion of the radioactivity in the plasma, liver, kidney and intestinal lumen of *T3-injected trout remained as the parent *T3. However, in *T4-injected trout most plasma radioactivity was in the form of 125I–, and by 24 h a high proportion of luminal radioactivity was 125I–. By 48 h, over 4% of the injected *T3 and 1% of the injected *T4 dose resided in the gall bladder, primarily as derivatives of *T3 or *T4. We conclude that T3 is absorbed more effectively than T4 from the intestinal lumen of fasted trout, indicating the potential for an enterohepatic T3 cycle.  相似文献   

18.
The glutamate agonist, N-methyl-D,L-aspartate (NMA) stimulates the secretion of growth hormone (GH) from pituitary fragments in vitro and increases plasma GH levels in vivo in rainbow trout, Oncorhynchus mykiss (Flett et al. 1994; Holloway and Leatherland 1997a,b); however gonadal steroid hormones appear to modulate this response in experimental situations. This study examines whether steroid hormones also modulate the GH-regulatory actions of NMA during the normal reproductive cycle of rainbow trout by examining the relationship between the stage of sexual maturation and the pituitary release of GH in vitro in response to an NMA (10-8 M) challenge. NMA had no effect on mean GH release from the pituitary glands of fish that were immature (GSI <1.0), from males during early development (GSI 1.0-3.0), or from sexually mature males (with free running milt) and females (ovulated). However, NMA significantly increased GH release from pituitary glands taken from females during the early stages of gonadal growth (GSI 1.0-9.0) and from males and females sampled during the later stages of gonadal growth (males GSI 3.01-6.0; females GSI 9.01-15.0). The GH-stimulatory action of NMA in males and females progressed to a maximum effect during the late stages of gonadal growth, and disappeared in ovulated females and free running males. Moreover, in female fish, the maximal GH release in response to the NMA challenge is positively correlated with plasma 17β-estradiol levels; no such correlation was evident for plasma testosterone levels in males. Changes in the GH response to NMA during maturation while gonadal steroid levels fluctuate provides further evidence to suggest that the effects of NMA on GH secretion are intimately linked to endogenous gonadal steroid hormone levels. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Plasma cortisol levels and the number (Nmax) and affinity (Kd) of specific hepatic cortisol-binding sites were determined in rainbow trout subjected to chronic confinement stress for 14 days. Confinement significantly elevated plasma cortisol levels to 47.3 ± 13.5 ng ml–1 within 24h and although levels declined to 8.0 ± 3.0 ng ml–1 after 14 days, they were significantly higher throughout than levels in unstressed control fish (< 2.0 ng ml–1). There was a 60% reduction in cytosolic Nmax in stressed fish during the first 24h of confinement (35.8 ± 7.9 cf. 129.0 ± 15.2 fmol mg–1 protein), a decline which was sustained at 7 days after the onset of stress but, although numbers of binding sites in the liver of stressed fish were still lower than in unstressed fish, the difference was no longer significant after 14 days of confinement. There was an accompanying significant rise in the Kd of cortisol binding in stressed fish during confinement, from 4.0 ± 0.6 nM at time 0 to 8.4 ± 0.8 nM after 24 h confinement. This increment in Kd was sustained at a level significantly higher than in control fish throughout the 14 day confinement period, despite marked reductions in cortisol levels and increases in Nmax in stressed fish. Throughout the study, specific binding of cortisol could not be consistently detected in high-salt nuclear extracts from stressed or unstressed fish, suggesting either that high-affinity binding sites for cortisol were absent from these preparations, that receptors were present but unable to interact with ligand because they were occupied, or that receptors were present but not being extracted. These possibilities were investigated using a range of extraction procedures, by varying the temperature of incubation, by employing dexamethasone as ligand and by examining binding in purified, intact, nuclei. Estradiol was employed as a methodological control throughout and substantial amounts of specific estradiol binding were detected in all compartments and preparations. Specific cortisol-binding sites were detected in intact nuclei of both stressed and unstressed fish, at levels an order of magnitude lower than estradiol binding in the same preparations. These data demonstrate that activation of the pituitary-interrenal axis leads to significant changes in the nature of target-tissue binding of cortisol in rainbow trout, and reveal a clear difference in the subcellular distribution of binding-sites for estradiol and cortisol, which reflects the situation in mammalian tissues.  相似文献   

20.
Distribution and function of hepatic - and -adrenoceptors were examined in rainbow trout (Oncorhynchus mykiss) injected with slow release hydrogenated coconut oil implants alone (sham) or containing cortisol. - and -Adrenoceptors were assayed on purified hepatic membranes 10–14 days post-implantation using 3H-prazosin () and 3H-CGP (). At 10–14 days, plasma cortisol values were significantly elevated to approximately 220 compared with 35.0 ng ml-1 in cortisol implanted vs. sham trout. No significant differences were found between any of the experimental groups for either the affinity (Kd) or maximal number of binding sites (Bmax) for either receptor type. Epinephrine significantly stimulated glucose release from hepatocytes isolated from sham injected trout, but not from cortisol-treated fish. Epinephrine-induced glucose release was blocked by both - and -antagonists. These studies do not support the hypothesis that rainbow trout exposed to chronic cortisol alter properties of hepatic adrenoceptors.  相似文献   

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