Food deprivation alters osmoregulatory and metabolic responses to salinity acclimation in gilthead sea bream Sparus auratus

The influence of acclimation to different environmental salinities (low salinity water, LSW; seawater, SW; and hyper saline water, HSW) and feeding conditions (fed and food deprived) for 14 days was assessed on osmoregulation and energy metabolism of several tissues of gilthead sea bream Sparus auratus. Fish were randomly assigned to one of six treatments: fed fish in LSW, SW, and HSW, and food-deprived fish in LSW, SW, and HSW. After 14 days, plasma, liver, gills, kidney and brain were taken for the assessment of plasma osmolality, plasma cortisol, metabolites and the activity of several enzymes involved in energy metabolism. Food deprivation abolished or attenuated the increase in gill Na⁺,K⁺-ATPase activity observed in LSW- and HSW-acclimated fish, respectively. In addition, a linear relationship between renal Na⁺,K⁺-ATPase activity and environmental salinity was observed after food deprivation, but values decreased with respect to fed fish. Food-deprived fish acclimated to extreme salinities increased production of glucose through hepatic gluconeogenesis, and the glucose produced was apparently exported to other tissues and served to sustain plasma glucose levels. Salinity acclimation to extreme salinities enhanced activity of osmoregulatory organs, which is probably sustained by higher glucose use in fed fish but by increased use of other fuels, such as lactate and amino acids in food-deprived fish.     

Studies on the relationship between osmotic or ionic regulation and thyroid gland activity in two salmonid fishes, Salmo gairdneri Richardson and Oncorhynchus kisutch Walbaum

In freshwater-acclimated rainbow trout a single intraperitoneal injection of ovine TSH significantly elevated plasma thyroxine (T₄) levels within 1 h after the injection. In seawater adapted trout the increase in T₄ after TSH-treatment was not evident until 6 h after the injection. TSH caused a transient fall in plasma Na⁺ and Cl^- between 3 h and 9 h after the injection in seawater-adapted fish and plasma Na⁺ was lowered in freshwater-adapted trout 24 h after the injection. Although there were clear histological changes in the thyroid gland of freshwater-adapted trout after TSH-injection, no such changes were evident in seawater-adapted fish.
Plasma thyroid hormone levels and thyroid histology in freshwater-adapted rainbow trout and coho salmon transferred to sea water, and seawater-adapted trout transferred to fresh water showed no consistent changes compared with controls.
The data are interpreted to indicate that although ambient salinity may have indirect effects on thyroid activity there is no direct involvement in ionic or osmotic regulation in the two species.     

Effect of ovine TSH, thiourea, ovine prolactin and bovine growth hormone on plasma thyroxine and tri-iodothyronine levels in rainbow trout,Salmo gairdneri

Summary A single injection of ovine TSH (1.1 g or 2.2 g/g body weight) effected a significant (P<0.01) increase in plasma T₄ levels in rainbow trout within 9 h and 1 h respectively. In fish given the higher dose the T₄ levels were still significantly higher (P<0.01) than in the controls 24 h after the injection. Ovine TSH had no significant effect on plasma T₃ levels. Plasma T₃/T₄ ratios in fish given the higher TSH dose were significantly lower than the controls at 3 h (P<0.01), 6 h (P=0.01), 9 h and 24 h (P<0.05) while in fish given the lower dose they were significantly lower than in controls at 3 h (P<0.01), 6 h (P=0.01) and 9 h (P<0.05).T₄ levels in TSH-injected fish were significantly higher (P<0.05) than in controls after 3 and 11 injections but were not significantly different after 16 injections. Plasma T₃ and T₃/T₄ ratios did not differ significantly in fish given multiple injections of either TSH or saline.Plasma T₄ levels in fish treated with thiourea were significantly lower (Pº0.01) than in comparable controls after 6, 9 and 15 days and plasma T₃ levels were lower (P<0.05) after 15 days treatment. T₃/T₄ ratios did not differ significantly at any time period.A single injection of bovine STH (10 g/g body weight) effect a significant rise in plasma T₄ levels 9 h (P=0.05) and 24 h (P<0.01) after the injection while ovine prolactin in a similar dose was without effect. Plasma T₃ levels in saline injected fish showed a steady decline over the 24 h following the injection whereas levels in prolactin and STH injected animals tended to rise. T₃ levels in the saline-injected fish were significantly higher (P<0.01) than in prolactin and STH injected animals 1 h after the injection but were significantly lower (P<0.01) than in the hormone-treated fish 24 h after the injection. There were no significant differences in T₃/T₄ ratios in any of the groups. Multiple injections of STH effected a significant increase (P<0.05) in plasma T₄ compared with the controls; prolactin had no significant effect. There was no significant differences in plasma T₃ concentration or T₃/T₄ ratios in any of the groups.     

Thyrotropin-releasing hormone (TRH) is not thyrotropic but somatotropic in fed and starved adult chickens.

Adult fed and starved Warren chickens, 2 yr of age, and approaching the end of the second laying year, were injected iv with 1 of the following products: 10 micrograms of thyrotropin releasing hormone (TRH); 100 micrograms of bovine thyrotropin (bTSH); 100 micrograms of ovine growth hormone (oGH); saline. The influence on plasma concentrations of thyroxine (T4), triiodothyronine (T3) or chicken GH (cGH) were followed. Prior to injection, it was clear from the control values that starvation for 3 d decreased plasma levels of T3 and increased cGH, whereas 7 d of fasting increased T4 and cGH. The plasma levels of cGH were elevated greater than 10-fold at 15 min following the TRH challenge in food-deprived chickens compared to a less than 4-fold increase in normal fed hens. This increase was followed by a rise in T3 after 1 h, which was also more pronounced in the starved animals, whereas T4 decreased or remained unaffected. Increases in T4 can, however, be obtained with 100 micrograms TSH in normal fed (2-fold) or starved animals (greater than 3-fold). Following injection of 100 micrograms oGH, a significant increase in T3 levels was observed which in fed animals was already present at 30 min, but the higher levels persisted for 1 and 2 h in fed and starved hens. At the same time, a decrease in T4 was observed in both groups of GH-treated chickens. It is concluded that TRH at the dose used is not thyrotropic but has a somatotropic effect and is responsible for the peripheral conversion of T4 into T3.     

Insulin and glucagon family peptides in relation to activities of hepatic hexokinase and other enzymes in fed and starved Atlantic salmon (Salmo salar) and cod (Gadus morhua).

1. Plasma levels of insulin, glucagon, and glucagon-like peptide (Glp) were all reduced by starvation of salmon and cod. In the salmon the drop in Glp was larger than in insulin and glucagon. 2. After starvation the activity of hexokinase (EC 2.7.1.1) was increased in salmon liver, but decreased in cod liver. The salmon hepatic hexokinase activity was inversely correlated with the Glp/insulin ratio. 3. Activities of hepatic glycogen phosphorylase (EC 2.4.1.1) and phosphofructokinase (EC 2.7.1.11) were increased in starved as compared to fed salmon. In cod, starvation resulted in decreased or unchanged activity of phosphorylase. This discrepancy may be related to different degrees of environmental and handling stress. 4. Intraperitoneal injection of human insulin in salmon gave increased hepatic phosphorylase and hexokinase activities and reduced plasma levels of glucagon, Glp and endogenous fish insulin at sampling after 30 hr. 5. No differences in hepatic hexokinase activities or plasma hormone levels were observed between cod fed low and high carbohydrate diets. Apparently, regulation of glucose phosphorylation by dietary carbohydrate does not occur.     

Effect of central injection of bradykinin and bradykinin potentiating factor upon release of anterior pituitary hormones in ovariectomized female rats

The effects of third ventricular (IVT) injection of 25 μg of bradykinin (BK) upon plasma levels of LH, FSH, TSH, GH and prolactin were investigated in conscious ovariectomized female rats bearing indwelling jugular cannulae. Some animals were pretreated with bradykinin potentiating factor (BPF). Intravenous administration of BK had no effect upon hormone levels. IVT injection of BK significantly depressed plasma prolactin levels at 15 and 30 min post-drug, with levels returning to control values by 60 min. Pretreatment of animals with BPF (75 μg/3 μl) prolonged the prolactin suppression induced by BK for up to two hours. Plasma LH, FSH, TSH and GH levels in BK-rats were not significantly different from those of saline-injected animals at any time point measured. Neither BPF alone nor in conjunction with BK had any effects upon plasma levels of TSH; however, BK plus BPF suppressed FSH concentrations at 75 min post-BPF, while BPF alone appeared to increase GH levels at 45 min. In vitro incubation of hemipituitaries with 0.083, 0.83 or 8.33 μg/ml BK had no effect upon the release of LH, TSH or prolactin compared to control values. However, the secretion of GH and FSH was suppressed by the lowest dose of BK tested. These results suggest that BK may play a physiological inhibitory role in the regulation of prolactin, which can be augmented by preventing its degradation, i.e. via BPF. The effect of the peptide seems to be mediated by the CNS since neither intravenous injection of BK nor in vitro incubation of pituitaries with the peptide modified prolactin release.     

Growth hormone stimulates the peripheral conversion of thyroxine into triiodothyronine by increasing the liver 5'-monodeiodinase activity in the fasted and normal fed chicken

Normal fed and 2 days fasted Warren chickens were injected intravenously with 100 micrograms of ovine growth hormone (GH) and ovine prolactin and plasma concentrations of thyroid hormones were assayed prior and up to 2 h after injection. Fasting alone decreases T3, but increases T4. An injection of GH resulted in increases of plasma T3 concentrations in two fasting experiments by 40% (after 3/4 h) and 104% (after 1 h). In normal fed animals no increase is observed in the first experiment, whereas a 35% increase occurs in the second one. An injection of 100 micrograms prolactin does not influence T3 in normal fed or fasting animals. Both GH and prolactin, however, may decrease plasma concentrations of T4. In a separate experiment 50 micrograms and 200 micrograms of GH raised the decreased T3 levels after fasting by 39% and 60% respectively 1 h after injection and by 24 and 61% respectively in normal fed chicken, whereas prolactin was ineffective in this regard. Using Hisex chickens, the influence of an injection of 100 micrograms GH on plasma concentrations of thyroid hormones could be confirmed. At the same time GH increases the liver 5'-monodeiodinase activity by 330% after 1 h and by 147% after 2 h. The peroxidase activity is not influenced in normal fed chickens, but GH decreases this activity in food deprived animals after 1 h and 2 h. It is concluded that ovine GH, but not prolactin, stimulates the peripheral conversion of T4 into T3 in both normal fed and food deprived chicken and that this effect is dose dependent.     

Effects of tartrate thyrotropin-releasing hormone treatment on serum thyrotropin, free triiodothyronine, free thyroxine and prolactin levels in patients with spinocerebellar degeneration.

The aim of the present study was to investigate the pituitary-thyroid axis function during the long-term (30 days) intramuscular administration of 4 mg/day of thyrotropin-releasing hormone tartrate (TRH-T) in 15 patients with spinocerebellar degeneration. The study was performed as follows: (1) acute 4 mg TRH-T test with hourly prolactin (PRL) and thyroid-stimulating hormone (TSH) level evaluations for 6 h; (2) placebo; and (3) 4 mg/day of TRH-T administration for 30 days with TSH, PRL, and free T3 and T4 (FT3 and FT4) levels evaluated on days 1, 15 and 30. Hormone determination was performed just before and 1 h after placebo or TRH-T administration. The acute administration of TRH-T caused a sustained rise of TSH which lasted until the 6th hour and of PRL which declined after 1 h (p < 0.01). During placebo administration, no change of TSH, PRL, FT3 or FT4 was observed. On the 1st day of treatment, 1 h after the TRH-T injection, a significant increase of both TSH and PRL levels occurred (p < 0.01). As compared to the 1st day, a significant decrease of the TSH (p < 0.01) levels occurred on the 15th and 30th days before TRH-T: the TSH response to TRH-T administration was present although less than on the 1st day (p < 0.01). Moreover, throughout the whole period of treatment, no difference was recorded for PRL levels before or after TRH-T administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Amiodarone inhibits T4 to T3 conversion and alpha-glycerophosphate dehydrogenase and malic enzyme levels in rat liver

Amiodarone has been found to decrease serum T3 by blocking peripheral T4 5'-deiodinase. This reduction in T3 levels may contribute to the effectiveness of this drug in moderating cardiac arrhythmias. To further characterize the effect of amiodarone on thyroid hormone metabolism and biological action, male Sprague-Dawley rats were thyroidectomized and then fed 500 ug T4 or 50 ug T3 and 500 mg amiodarone/kg of powdered diet for 6 to 8 weeks. Hepatic and cardiac levels of T4, T3, alpha-glycerophosphate dehydrogenase (GPD) and malic enzyme (ME) were used as indicators of thyroid hormone availability and action at the cellular level. Conversion of T4 to T3 was measured in liver homogenates. Serum TSH, T4 and T3 were also measured. Amiodarone reduced hepatic GPD and ME in thyroidectomized rats receiving dietary T4. Liver T4 levels were significantly increased by amiodarone and the T3/T4 ratio was reduced (P less than .05). Amiodarone inhibited hepatic T4 to T3 conversion and decreased serum T3. The decreased T3 action at the cellular level, indicated by the reduction in hepatic GPD and ME, is not due to pharmacologic effects of amiodarone since these enzyme levels were not affected by amiodarone in thyroidectomized rats replaced with T3.     

Effects of a high plant protein diet on the somatotropic system and cholecystokinin in Atlantic salmon (Salmo salar L.)

To investigate the endocrine signalling from dietary plant protein on somatotropic system and gastrointestinal hormone cholecystokinin (CCK), two iso-amino acid diets based on either high plant or high fish meal protein were fed to Atlantic salmon. Salmon with an average starting weight of 641 ± 23 g (N = 180), were fed a fish meal (FM) based diet (containing 40% FM) or diets mainly consisting of blended plant proteins (PP) containing only 13% marine protein, of which only 5% was FM for 3 months. mRNA levels of target genes GH, GH-R, IGF-I, IGF-II, IGFBP-1, IGF-IR in addition to CCK-L, were studied in brain, hepatic tissue and fast muscle, and circulating levels of IGF-I in plasma of Atlantic salmon were measured. We detected reduced feed intake resulting in lower growth, weight gain and muscle protein accretion in salmon fed plant protein compared to a diet based on fish meal. There were no significant effects on the regulation of the target genes in brain or in hepatic tissues, but a trend of down-regulation of IGF-I was detected in fast muscle. Lower feed intake, and therefore lower intake of the indispensable amino acids, may have resulted in lower pituitary GH and lower IGF-I mRNA levels in muscle tissues. This, together with higher protein catabolism, may be the main cause of the reduced growth of salmon fed plant protein diet. There were no signalling effects detected either by the minor differences of the diets on mRNA levels of GH, GH-R, IGF-IR, IGF-II, IGFBP-1, CCK or plasma protein IGF-I.     

Effects of intraventricular injection of gastrin on release of LH,prolactin, TSH and GH in conscious ovariectomized rats

Conscious ovariectomized (OVX) rats bearing a cannula implanted in the 3rd ventricle were injected with 2 μl of 0.9% NaCl containing varying doses of synthetic gastrin and plasma gonadotropin, GH and TSH levels were measured by RIA in jugular blood samples drawn through an indwelling silastic catheter. Control injections of saline iv or into the 3rd ventricle did not modify plasma hormone levels. Intraventricular injection of 1 or 5 μg gastrin produced significant suppression of plasma LH and prolactin (Prl) levels within 5 min of injection. Injection of 1 μg gastrin had no effect on plasma GH, but increasing the dose to 5 μg induced a progressive elevation, which reached peak levels at 60 min. By contrast, TSH levels were lowered by both doses of gastrin within 5 min of injection and the lowering persisted for 60 min. Intravenous injection of gastrin had no effect on plasma gonadotropin, GH and TSH, but induced an elevation in Prl levels. $\text{In}$$\text{vitro}$ incubation of hemipituitaries with gastrin failed to modify gonadotropin, GH or Prl but slightly inhibited TSH release at the highest dose of 5 μg gastrin. The results indicate that synthetic gastrin can alter pituitary hormone release in unrestrained OVX rats and implicate a hypothalamic site of action for the peptide to alter release of a gonadotropin, Prl and GH. Its effect on TSH release may be mediated both via hypothalamic neurons and by a direct action on pituitary thyrotrophs.     

Influence of chronic thyroxine treatment on plasma hormone and metabolite concentrations and on responses to insulin, glucagon and thyrotrophin releasing hormone in adult sheep

Four adult sheep fed twice daily were given daily subcutaneous injections of saline for four weeks, followed by a similar period of daily L-thyroxine (T4) injection (1 mg/day). T4 treatment increased basal plasma concentrations of T4, triiodothyronine (T3), insulin and glucose, together with T3-uptake and the free thyroxine index, while cholesterol and urea concentrations decreased. T4 treatment reduced the rise in prolactin levels after the morning meal. Thyrotrophin releasing hormone (TRH) injection increased plasma T3 only in the control period and T3-uptake only in the T4 treatment period. T4 treatment did not affect the prolactin response to TRH injection or the insulin and glucose responses to glucagon injection. The increase in insulin concentrations after insulin injection and the secondary hyperglycaemia following initial insulin-induced hypoglycaemia were reduced by T4 treatment.     

Prolactin regulation in the coho salmon,Oncorhynchus kisutch

Summary Parr and smolt sea water acclimated coho salmon,Oncorhynchus kisutch were subjected to gradual and direct transfers to fresh water. Plasma osmotic pressure, Na⁺, K⁺, Ca⁺⁺ and Mg⁺⁺ were similar in freshwater (FW) fish and seawater (SW) transferred controls for the 24 h following transfer. In spite of the similarity in osmotic pressure and ion levels, plasma cortisol concentrations were significantly increased immediately following salinity change while both pituitary and plasma prolactin decreased indicating enhanced secretion by the pituitary and clearance from the blood. In vitro experiments showed greater incorporation of tritiated leucine into prolactin (PRL) cells immediately after transfer to FW while prolactin injections into intact fish lowered activity in rostral pars distalis (RPD) cells as measured by the same technique, providing evidence of hormonal feedback. These experiments show that the increased synthesis and release of PRL that occurs in coho following movement into FW is not obviously correlated with plasma osmotic pressure, Na⁺ or Ca⁺⁺ concentrations as has been observed in other species of teleosts.Abbreviations FW freshwater - SW seawater - PRL prolactin - RPD rostral pars distalis     

Fasting modifies Aroclor 1254 impact on plasma cortisol,glucose and lactate responses to a handling disturbance in Arctic charr

Integrated effects of polychlorinated biphenyl (PCB) and nutritional status on responses to handling disturbance were investigated in the Arctic charr (Salvelinus alpinus). The fish were orally contaminated with Aroclor 1254 and held either with or without food for 5 months before they were subjected to a 10-min handling disturbance. Food-deprived fish were given 0, 1, 10 or 100 mg PCB kg(-1) and the fed fish 0 or 100 mg PCB kg(-1). Plasma cortisol, glucose and lactate levels were measured at 0 (pre-handling), 1, 3, 6 and 23 h after the handling disturbance. Food-deprived control fish had elevated plasma cortisol levels compared with fed fish before handling. These basal cortisol levels were suppressed by PCB in food-deprived fish, and elevated by PCB in fed fish. The immediate cortisol and glucose responses to handling disturbance were suppressed by PCB in a dose-dependent way in food-deprived fish. Although these responses were also lowered by PCB in the fed fish, the effect was much less pronounced than in food-deprived fish. There were only minor effects on plasma lactate responses. Our findings suggest that the stress responses of the Arctic charr are compromised by PCB and that the long-term fasting, typical of high-latitude fish, makes these species particularly sensitive to organochlorines such as PCB.     

Unusual features of neonatal thyroid function in small-for-gestational-age lambs. Origin of plasma T4 and T3 deficiencies

Thyroid function was studied in small for gestational age (SGA) or control newborn lambs. Neonatal changes in plasma concentrations of TSH, T3, rT3, total and free T4 were monitored, and thyroid scintigraphs were performed. Responsiveness of the hypothalamic-pituitary-thyroid axis to cold exposure and TRH or TSH administration was assessed. In addition, T4 and T3 kinetic studies were performed. In agreement with results obtained in babies, plasma T3, total T4 and free T4 concentrations were depressed in low birth weight animals, whereas TSH and rT3 levels were not affected. Thyroid size expressed relatively to the body weight was higher in SGA animals, thus suggesting that a partial compensation for low thyroid hormone levels had occurred during the fetal life. Plasma TSH and T4 concentrations increased by a same extent after exposure to cold and TRH or TSH administration in SGA and control lambs; however, the rise in T3 levels was depressed in the former in all stimulation tests. T3 and T4 production rates were similar in the two experimental groups. In SGA lambs, the metabolic clearance rate and the total distribution space of these two hormones were significantly increased; the fast T3 pool was higher, and the slow T3 pool lower than in control animals. All these results demonstrate that, despite low circulating thyroid hormone concentrations, SGA lambs are not hypothyroid. An increased T4 and T3 storage in the extravascular compartment is probably the major factor involved in the occurrence of this plasma deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thyrotropic and peripheral activities of thyrotrophin and thyrotrophin-releasing hormone in the chick embryo and adult chicken

The influence of an intravenous injection of thyrotrophin-releasing hormone (TRH) and bovine thyrotrophin (TSH) on circulating levels of thyroid hormones and the liver 5'-monodeiodination (5'-D) activity is studied in the chick embryo and the adult chicken. In the 18-day-old chick embryo, an injection of 1 microgram TRH and 0.01 I.U. TSH increase plasma concentrations of triiodothyronine (T3) and of thyroxine (T4). TRH, however, preferentially raises plasma levels of T3, resulting in an increased T3 to T4 ratio, whereas TSH preferentially increases T4, resulting in a decreased T3 to T4 ratio. The 5'-D-activity is also stimulated following TRH but not following TSH administration. The increase of reverse T3 (rT3) is much more pronounced following the administration of TSH. In adult chicken an injection of up to 20 micrograms of TRH never increased plasma concentrations of T4, but increases T3 at every dose used together with 5'-D at the 20 micrograms dose. TSH on the other hand never increased T3 or 5'-D, but elevates T4 consistently. It is concluded that TSH is mainly thyrotropic in the chick embryo or adult chicken whereas TRH is responsible for the peripheral conversion of T4 into T3 by stimulating the 5'-D-activity. The involvement of a TRH induced GH release in this peripheral activity is discussed.     

In vivo effects of the steroid analogue RU486 on some aspects of intermediary and thyroid metabolism of brook charr, Salvelinus fontinalis.

The glucocorticoid analogue RU486 was administered by intraperitoneal injection to brook charr (Salvelinus fontinalis) to further explore the role of cortisol on aspects of intermediary and thyroid hormone metabolism of the species. RU486 significantly elevated the hepatosomatic index, hepatic G3PDH activity, and hepatic glycogen content, but was without effect on hepatic protein content, hepatic FPBase activity, or plasma glucose concentration. However, the stressor-related increase in plasma glucose concentration that was evident in brook charr 24 h following handling and injection was suppressed in RU486-treated groups. The distribution volume, turnover rates, and metabolic clearance rates of [3H]cortisol were similar in RU486- and vehicle-treated groups. Plasma T3 and T4 concentrations were similar in RU486- and vehicle-treated groups, but hepatic T3 production and hepatic T3 content were lower in RU486-treated fish; TSH had no effect on hepatic T3 content of vehicle-treated brook charr but significantly increased T3 content in the RU486-treated group. These observations support the concept of a role of cortisol in the control of peripheral monodeiodination of T4 in salmonid fish and suggest that RU486 may be a useful drug for evaluating the role of cortisol in fish in vivo.     

Exposure of goldsinny, rock cook and corkwing wrasse to low temperature and low salinity: survival, blood physiology and seasonal variation

Wrasse used as cleaner fish with farmed Atlantic salmon Salmo salar can be subjected to large and rapid temperature and salinity fluctuations in late autumn and early winter, when summer-warmed surface water is affected by early snowmelt episodes. Because of their containment in sea cages, wrasse which are essentially acclimated to summer temperatures may be rapidly exposed to winter conditions. Short-term tolerance of low temperature and low salinity by three species of wrasse, goldsinny Ctenolabrus rupestris rock cook Centrolabrus exoletus corkwing Crenilabrus melops caught during the summer, and winter-caught corkwing, was investigated. A 3–day period at 30 or 32‰ salinity and temperature 8, 6 or 4° C (for summer-caught fish; 4° C only for winter-caught) was followed by a decline in salinity to 24, 16 or 8‰ over c. 36 h, followed by a further 24 h at these salinities held constant, at each of the three temperatures. Controls in 30 or 32‰ were maintained at 8, 6 or 4° C. Mortality of summer-caught corkwing and rock cook was high at 4° C, whereas the influence of salinity on mortality was small. Mortality of goldsinny was low or zero in all treatments. Surviving corkwing and rock cook after 3 days at 4° C and 32‰ salinity had elevated plasma osmolality: in summer-caught corkwing, plasma [Cl°] and [Na⁺] were high, whereas in rock cook only [Na⁺] was high. Haematocrit was low in summer-caught corkwing, high in rock cook. In survivors of all three species at the end of the experiment, values of all these parameters were comparable with those of fish at the beginning of the experiment, except that survivors at low salinity (8, 16‰) had low plasma osmolality, at all temperatures, and in surviving rock cook in these treatments haematocrit was high and plasma [Cl^?] was low. Winter-caught corkwing had higher osmolality, [Na⁺] and [Cl^?] than summer-caught corkwing; there was no difference in haematocrit. Survival of wintercaught corkwing exposed to four salinities at 4° C was much higher than that of summercaught corkwing under the same conditions. Little change in blood physiology was recorded for winter-caught corkwing, with only fish subjected to 8‰ and 4° C showing signs of osmoregulatory stress. The interspecific and seasonal differences in survival and blood physiology at low temperature and low salinity are discussed in relation to wrasse survival over winter, both in the field and in salmon farms.     

Twenty-four-Hour Rhythms of Serum Acth,Prolactin, Growth Hormone,and Thyroid-Stimulating Hormone,and of Median-Eminence Norepinephrine,Dopamine, and Serotonin,in Rats Injected with Freund's Adjuvant

The effect of Freund's adjuvant injection on 24-h variation of circulating ACTH, prolactin, growth hormone (GH), and thyroid-stimulating hormone (TSH) levels, and of norepinephrine (NE) content, and dopamine (DA) and serotonin (5HT) turnover in median eminence, was examined in adult rats kept under light between 0800 and 2000 h daily. Groups of 6–10 animals Freund's complete adjuvant or its vehicle at 1 lOOh 3 days before sacrifice and were killed by decapitation at six different time intervals throughout a 24-h cycle. In rats injected with adjuvant's vehicle, serum ACTH and prolactin exhibited peak values around the light-dark transition (p < 0.0001 and < 0.04, respectively), while the maximum in TSH was found in the late afternoon (p < 0.0001, one-way ANOVA). GH levels did not vary on a 24-h basis. In Freund's adjuvant-injected rats, 24-h variations of TSH levels became blunted, while 24-h variations of prolactin and ACTH persisted. Freund's adjuvant augmented serum ACTH and prolactin levels, and decreased GH and TSH levels (p < 0.0007, factorial ANOVA). Median-eminence NE content, and turnover of DA, assessed by measuring dihydroxyphenylacetic acid, DOPAC/DA ratio, and of 5HT, assessed by measuring 5-hydroxyindoleacetic acid, HIAA/5HT ratio, varied on a 24-h basis in rats receiving adjuvant's vehicle (p < 0.02). Median-eminence NE content attained its maximum at 1600–2000 h, while maxima in DOPA/DA and HIAA/5HT ratios occurred at 0400 h. Injection with Freund's adjuvant reduced the amplitude of the daily variation of NE content, shifted the maximum of DOPAC/DA ratio toward the light-dark transition, and blunted the daily variation in HIAA/5HT ratio in median eminence. The administration at 1200 of the immunosuppressant drug cyclosporine (5 mg/kg, 5 days) restored the augmented ACTH and prolactin levels (p < 0.0001, factorial ANOVA) and depressed GH and TSH levels (p < 0.02) found in Freund's adjuvant-injected rats. Cyclosporine was also effective in restoring 24-h rhythmicity of serum ACTH and TSH, but not of prolactin, levels. Cyclosporine did not modify the effect of Freund's adjuvant on time-of-day changes of median-eminence NE content, but it was effective in counteracting the changes of DA and 5HT turnover found after immunization. The results are compatible with a significant effect of immune-mediated inflammatory response at an early phase after Freund's adjuvant injection on ACTH, GH, prolactin, and TSH release, which is partially sensitive to immunosuppression by cyclosporine. (Chronobiology International, 14(3), 253–265, 1997)     

The use of intramuscularly administered methyl-TRH to evaluate the pituitary-thyroid axis.

The present study was carried out to evaluate the effectiveness of intramuscular administration of methyl-TRH, a potent analogue of thyrotropin-releasing hormone, for assessing pituitary reserve of TSH and prolactin and for distinguishing euthyroid, hypothyroid and hyperthyroid individuals. Serum samples were taken for 24 hours after intramuscular injection of methyl-TRH, 200 microgram, in 19 euthyroid subjects, 9 hypothyroid men and 9 hyperthyroid men. The mean serum prolactin and TSH concentrations were significantly elevated over baseline levels at 30 min in the euthyroid individuals and remained elevated for 3 to 4 hours. The serum TSH, T3 and T4 responses after intramuscular methyl-TRH in euthyroid subjects were clearly distinguishable from those of hyperthyroid and hypothyroid patients. Significant elevation of the serum T3 and T4 concentrations at 24 hours after intramuscular injection of methyl-TRH shows the sustained effect of this TRH analogue in euthyroid subjects.