Ambient salinity modifies the action of triiodothyronine in the air-breathing fish Anabas testudineus Bloch: Effects on mitochondria-rich cell distribution, osmotic and metabolic regulations

The hydromineral and metabolic actions of thyroid hormone on osmotic acclimation in fish is less understood. We, therefore, studied the short-term action of triiodothyronine (T₃), the potent thyroid hormone, on the distribution and the function of gill mitochondria-rich (MR) cells and on the whole body hydromineral and metabolic regulations of air-breathing fish (Anabas testudineus) adapted to either freshwater (FW) or acclimated to seawater (SA; 30 g L⁻¹). As expected, 24 h T₃ injection (100 ng g⁻¹) elevated (P < 0.05) plasma T₃ but classically reduced (P < 0.05) plasma T₄. The higher Na⁺, K⁺-ATPase immunoreactivity and the varied distribution pattern of MR cells in the gills of T₃-treated FW and SA fish, suggest an action of T₃ on gill MR cell migration, though the density of these cells remained unchanged after T₃ treatment. The ouabain-sensitive Na⁺, K⁺-ATPase activity, a measure of hydromineral competence, showed increases (P < 0.05) in the gills of both FW and SA fish after T₃ administration, but inhibited (P < 0.05) in the kidney of the FW fish and not in the SA fish. Exogenous T₃ reduced glucose (P < 0.05) and urea (P < 0.05) in the plasma of FW fish, whereas these metabolites were elevated (P < 0.05) in the SA fish, suggesting a modulatory effect of ambient salinity on the T₃-driven metabolic actions. Our data identify gill MR cell as a target for T₃ action as it promotes the spatial distribution and the osmotic function of these cells in both fresh water and in seawater. The results besides confirming the metabolic and osmotic actions of T₃ in fish support the hypothesis that the differential actions of T₃ may be due to the direct influence of ambient salinity, a major environmental determinant that alters the osmotic and metabolic strategies of fish.     

Ambient salinity modifies the action of triiodothyronine in the air-breathing fish Anabas testudineus Bloch: effects on mitochondria-rich cell distribution, osmotic and metabolic regulations

A model of thyroidectomized sheep intravenously supplemented with thyroid hormone (TH) was developed to mimic endogenous TH exposure and to analyze the impact on plasma TH homeostasis of xenobiotic interference with TH binding to plasma proteins. TH was displaced from plasma protein binding sites by using phenylbutazone (PBZ) as a test xenobiotic, to compare the effect of PBZ on steady state free and total plasma TH concentrations between the in vivo situation and an in vitro system. While PBZ increased free TH in vitro, PBZ administration in vivo produced an immediate reduction in both total and free plasma TH. The decrease in the total TH was consistent with a PBZ-induced displacement of TH from its plasma binding proteins, leading to an increase in total TH plasma clearance. However, this reduction in total TH was not expected to be accompanied by a parallel decrease in free plasma TH since the free TH is determined by the clearance of the free plasma TH. This suggested that PBZ may also have interfered with the clearance mechanisms of free TH.It can be concluded that our thyroidectomized sheep model enables a dual action of a xenobiotic on plasma TH to be distinguished, namely a displacement of TH from its binding proteins leading to a decrease in the total plasma concentration, which is not relevant to thyroid function versus an interference with the intrinsic TH clearance leading to a change in the free plasma TH, which has a major impact in terms of thyroid disruption.     

Cortisol promotes and integrates the osmotic competence of the organs in North African catfish (Clarias gariepinus Burchell): Evidence from in vivo and in situ approaches

The short-term in situ and long-term in vivo effects of cortisol were examined in North African catfish (Clarias gariepinus) to identify how this major corticosteroid integrates the osmotic competence of fish organs. In the in situ approach, the hydromineral effects of cortisol perfusion (75-300 ng ml⁻¹) for 20 min were tested and the indices of hydromineral and metabolic regulations were measured in our in vivo experimental fish after three alternate intraperitoneal cortisol injections (40 and 200 ng g⁻¹ body mass) for 5 days. Na⁺, K⁺-ATPase activity, a measure of cellular osmotic competence, responded to in situ and in vivo cortisol treatments. In situ cortisol delivery increased the Na⁺, K⁺-ATPase activity in the gill (P < 0.001) and kidney (P < 0.001) but decreased (P < 0.01) in the liver and showed no effect on intestine. In vivo cortisol treatment, on the contrary, increased Na⁺, K⁺-ATPase activity in the gills (P < 0.01), intestine (P < 0.05) and liver (P < 0.01) but decreased (P < 0.05) in the kidney. As expected, plasma cortisol increased (P < 0.001) with increasing doses of cortisol injections which produced direct effects on the metabolites and the mineral contents including the elevations of glucose (P < 0.05), lactate (P < 0.05) and Mg²⁺ (P < 0.05) and reductions of urea (P < 0.05), Na⁺ (P < 0.05) and K⁺ (P < 0.05) in the plasma. A decline of triiodothyronine (P < 0.01) occurred in the catfish after in vivo cortisol treatment and that implies a direct cortisol action on the homeostatic integration in this fish. Evidence is thus presented that in catfish cortisol regulates the whole body hydromineral and metabolite homeostasis by promoting and integrating the osmotic and metabolic functions of the multiple organ systems including liver.     

Androgen support of lacrimal gland function

The effects of dihydrotestosterone (DHT) (1 mg/kg) on biochemical parameters related to lacrimal secretion, basal tear flow rate, and pilocarpine-stimulated lacrimal gland fluid secretion, in mature ovariectomized rabbits were studied. The effects of the synthetic estrogen, diethylstilbestrol (DES) (100 μg/kg), on lacrimal gland biochemical parameters in normal mature female rabbits was also studied. Ovariectomy decreased the total serum levels of testosterone (T) by 88.5% and androstenedione by 35.9%, without changing the levels of dehydroepiandrosterone (DHEA) or its sulfate. Ovariectomy caused a significant regression of the lacrimal glands, decreasing total DNA by 35%, and total protein by 22%. DHT treatment of ovariectomized animals prevented lacrimal gland regression, increasing total gland DNA (31%) and total protein (18%). DHT treatment also increases Na⁺,K⁺-ATPase activity (29%) and ?-adrenergic receptor binding sites (23%) compared to the ovariectomized group. DHT increased pilocarpine stimulated lacrimal gland fluid secretion (13.26±1.47 μL/min) compared to the ovariectomized group (7.72±0.41 μL/min), but DHT treatment paradoxically decreased basal tear flow rate (1.02±0.04 μL/min) as compared to the ovariectomized rabbits (1.96±0.12 μL/min). DES decreased the total serum T from 59.33±10.54 pg/mL to 21.5±6.06 pg/mL. DES decreased total Na⁺,K⁺-ATPase by 12% and increased ?-adrenergic receptor binding sites by 83.3%. These results suggest that androgens play a major role in supporting lacrimal gland secretory function. Additionally, they suggest that estrogens may influence certain aspects of lacrimal functions, although it is not clear to what extent those actions are elicited directly or indirectly.     

Effects of short-term acid and aluminum exposure on the parr-smolt transformation in Atlantic salmon (Salmo salar): disruption of seawater tolerance and endocrine status

Episodic acidification resulting in increased acidity and inorganic aluminum (Al_i) is known to interfere with the parr-smolt transformation of Atlantic salmon (Salmo salar), and has been implicated as a possible cause of population decline. To determine the extent and mechanism(s) by which short-term acid/Al exposure compromises smolt development, Atlantic salmon smolts were exposed to either control (pH 6.7–6.9) or acid/Al (pH 5.4–6.3, 28–64 μg l⁻¹ Al_i) conditions for 2 and 5 days, and impacts on freshwater (FW) ion regulation, seawater (SW) tolerance, plasma hormone levels and stress response were examined. Gill Al concentrations were elevated in all smolts exposed to acid/Al relative to controls confirming exposure to increased Al_i. There was no effect of acid/Al on plasma ion concentrations in FW however, smolts exposed to acid/Al followed by a 24 h SW challenge exhibited greater plasma Cl⁻ levels than controls, indicating reduced SW tolerance. Loss of SW tolerance was accompanied by reductions in gill Na⁺,K⁺-ATPase (NKA) activity and Na⁺,K⁺,2Cl⁻ (NKCC) cotransporter protein abundance. Acid/Al exposure resulted in decreased plasma insulin-like growth factor (IGF-I) and 3,3′,5′-triiodo-l-thyronine (T₃) levels, whereas no effect of treatment was seen on plasma cortisol, growth hormone (GH), or thyroxine (T₄) levels. Acid/Al exposure resulted in increased hematocrit and plasma glucose levels in FW, but both returned to control levels after 24 h in SW. The results indicate that smolt development and SW tolerance are compromised by short-term exposure to acid/Al in the absence of detectable impacts on FW ion regulation. Loss of SW tolerance during short-term acid/Al exposure likely results from reductions in gill NKA and NKCC, possibly mediated by decreases in plasma IGF-I and T₃.     

Osmoregulatory action of PRL,GH, and cortisol in the gilthead seabream (Sparus aurata L)

The osmoregulatory actions of ovine prolactin (oPRL), ovine growth hormone (oGH), and cortisol were tested in the euryhaline gilthead seabream Sparus aurata. Acclimated to sea water (SW, 40 ppt salinity, 1000 mOsm/kg H(2)O) or brackish water (BW, 5 ppt, salinity, 130 mOsm/kg H(2)O), injected every other day for one week (number of injections, 4) with saline (0.9% NaCl), oPRL (4 microg/g body weight), oGH (4 microg/g body weight) or cortisol (5 microg/g body weight), and transferred from SW to BW or from BW to SW 24h after the last injection. Fish were sampled before and 24h after transfer. Gill Na(+), K(+)-ATPase activity, plasma osmolality, plasma ions (sodium and chloride), plasma glucose, and muscle water moisture were examined. SW-adapted fish showed higher gill Na(+), K(+)-ATPase activity, plasma osmolality, and plasma ions levels than BW-adapted fish. Transfer from SW to BW decreased plasma osmolality and ions levels after 24h, while transfer from BW to SW increased these parameters, whereas gill Na(+),K(+)-ATPase activity was unaffected. oPRL treatment significantly decreased gill Na(+),K(+)-ATPase activity and increased plasma osmolality and ions in SW- and BW-adapted fish. This treatment minimizes loss of osmolality and ions in plasma after transfer to BW and increased these values after transfer to SW. No significant changes were observed in gill Na(+),K(+)-ATPase activity, plasma osmolality, and plasma ions in oGH-treated group with respect to saline group before or after transfer from SW to BW or from BW to SW. Treatment with cortisol induced, in SW-adapted fish, a significant increase of gill Na(+),K(+)-ATPase activity and decrease of plasma osmolality and plasma ions. In BW-adapted fish this treatment induced a significant increases in gill Na(+),K(+)-ATPase activity, plasma osmolality, and plasma ions. After transfer to SW cortisol-treated fish had higher plasma osmolality than the saline group. Our results support the osmoregulatory role of PRL in the adaptation to hypoosmotic environment in the gilthead seabream S. aurata. Further studies will be necessary to elucidate the osmoregulatory role of GH in this species. Cortisol results suggest a "dual osmoregulatory role" of this hormone in S. aurata.     

Effect of phenylalanine and p-chlorophenylalanine on Na+, K+-ATPase activity in the synaptic plasma membrane from the cerebral cortex of rats

Na⁺, K⁺-ATPase activity was measured in synaptic plasma membrane from cerebral cortex of Wistar rats subjected to experimental phenylketonuria, i.e., chemical hyperphenylalaninemia induced by subcutaneous administration of 5.2 μmol phenylalanine /g body weight (twice a day) plus 0.9 μmol p-chlorophenylalanine /g body weight (once a day). The treatment was performed from the 6^th to the 14^th postpartum day and rats were killed 12 h after the last injection. Synaptic plasma membrane from cerebral cortex was prepared by a discontinuous density sucrose gradient for Na⁺, K⁺-ATPase activity determination. The results showed that the enzyme activity was decreased by 30% in animals subjected to experimental phenylketonuria when compared to control. Thein vitro effects of the drugs on Na⁺, K⁺-ATPase activity were also investigated. Phenylalanine and p-chlorophenylalanine inhibited the enzyme activity and this inhibition was reversed by alanine. In addition, competition between phenylalanine and p-chlorophenylalanine for binding to the enzyme was observed, suggesting a common binding site for these substances. Our results suggest that reduction of Na⁺, K⁺-ATPase activity may be one of the mechanisms related to the brain dysfunction observed in human PKU.     

Platelet Na+,K+-ATPase activity as a possible peripheral marker for the neurotoxic effects of phenylalanine in phenylketonuria

Thein vitro effects of phenylalanine or alanine alone or combined on Na⁺,K⁺-ATPase activity in membranes from human platelets were investigated. The enzyme activity was assayed in membranes prepared from platelet-rich plasma of healthy donors. Phenylalanine or alanine were added to the assay to final concentrations of 0.3 to 1.2 mM, similar to those found in plasma of phenylketonuric patients. Phenylalanine inhibited Na⁺,K⁺-ATPase activity by 20–50% [F(4,25)=11.47; p<0.001]. Alanine had no effect on Na⁺,K⁺-ATPase activity but when combined with phenylalanine prevented the enzyme inhibition. These results, allied to others previously reported on brain Na⁺,K⁺-ATPase activity, may reflect a general inhibitory effect of phenylalanine on this important enzyme activity. Therefore, it is possible that measurement of Na⁺,K⁺-ATPase activity in platelets from PKU patients may be a useful peripheral marker for the neurotoxic effects of phenylalanine.     

Effect of hypermethioninemia on some parameters of oxidative stress and on Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase activity in hippocampus of rats

In the present study we investigated the effect of chronic administration of methionine, a metabolite accumulated in many inherited pathological conditions such as methionine adenosyltransferase deficiency and homocystinuria, on some parameters of oxidative stress, namely thiobarbituric acid reactive substances (TBARS), catalase activity and total thiol content, as well as on Na⁺,K⁺-ATPase activity in rat hippocampus. For chronic treatment, rats received subcutaneous injections of methionine (1.34–2.68 μmol/g of body weight), twice a day, from the 6th to the 28th day of age and controls received saline. Animals were killed 12 h after the last injection. Results showed that chronic hypermethioninemia significantly increased TBARS, decreased Na⁺,K⁺-ATPase activity but did not alter catalase and total thiol content. Since chronic hypermethioninemia altered TBARS and Na⁺,K⁺-ATPase activity at 12 h after methionine administration, we also investigated the effect of acute administration of this amino acid on the same parameters studied after chronic methionine administration. For acute treatment,29-day-old rats received one single injection of methionine (2.68 μmol/g of body weight) or saline and were killed 1, 3 or 12 h later. Results showed that rats subjected to acute hypermethioninemia presented a reduction of Na⁺,K⁺-ATPase activity and an increase in TBARS when the animals were killed at 3 and 12 h, but not at 1 h, after methionine administration. These data indicate that hypermethioninemia increases lipid peroxidation which may, at least partially, explain the effect of methionine on the reduction in Na⁺,K⁺-ATPase activity. If confirmed in human beings, our findings could suggest that the induction of oxidative stress and the inhibition of Na⁺,K⁺-ATPase activity caused by methionine might contribute to the neurophysiopathology observed in patients with severe hypermethioninemia.     

Relative abundance of alpha2 Na(+) pump isoform influences Na(+)-Ca(2+) exchanger currents and Ca(2+) transients in mouse ventricular myocytes

In the mouse, genetic reduction in the Na(+), K(+)-ATPase alpha1 or alpha2 isoforms results in different functional phenotypes: heterozygous alpha2 isolated hearts are hypercontractile, whereas heterozygous alpha1 hearts are hypocontractile. We examined Na(+)/Ca(2+) exchange (NCX) currents in voltage clamped myocytes (pipette [Na(+)]=15 mM) induced by abrupt removal of extracellular Na(+). In wild-type (WT) myocytes, peak exchanger currents were 0.59+/-0.04 pA/pF (mean+/-S.E.M., n=10). In alpha1(+/-) myocytes (alpha2 isoform increased by 54%), NCX current was reduced to 0.33+/-0.05 (n=9, P<0.001) indicating a lower subsarcolemmal [Na(+)]. In alpha2(+/-) myocytes (alpha2 isoform reduced by 54%), the NCX current was increased to 0.89+/-0.11 (n=8, P=0.03). The peak sarcolemmal Na(+) pump currents activated by abrupt increase in [K(+)](o) to 4 mM in voltage clamped myocytes in which the Na(+) pump had been completely inhibited for 5 min by exposure to 0 [K(+)](o) were similar in alpha1(+/-) (0.86+/-0.12, n=10) and alpha2(+/-) myocytes (0.94+/-0.08 pA/pF, n=16), and were slightly but insignificantly reduced relative to WT (1.03+/-0.05, n=24). The fluo-3 [Ca(2+)](i) transient (F/F(o)) in WT myocytes paced at 0.5 Hz was 2.18+/-0.09, n=34, was increased in alpha2(+/-) myocytes (F/F(o)=2.56+/-0.14, n=24, P=0.02), and was decreased in alpha1(+/-) myocytes (F/F(o)=1.93+/-0.08, n=28, P<0.05). Thus the alpha2 isoform rather than the alpha1 appears to influence Na(+)/Ca(2+) exchanger currents [Ca(2+)](i) transients, and contractility. This finding is consistent with the proposal that alpha2 isoform of the Na pump preferentially alters [Na(+)] in a subsarcolemmal micro-domain adjacent to Na(+)/Ca(2+) exchanger molecules and SR Ca(2+) release sites.     

Mechanism of glucose-induced (Na+, K+)-ATPase inhibition in aortic wall of rabbits

Summary Hyperglycaemia decreases (Na⁺, K⁺)-ATPase activity in specific tissues by a mechanism whose effects are prevented by aldose reductase inhibitors and by raising plasma myo-inositol. This mechanism was activated and studied in vitro in normal rabbit aortic intima-media. Raising medium glucose to 10 mmol/l for 60 min inhibited a major component of (Na⁺, K⁺)-ATPase-mediated ⁸⁶Rb ⁺ /K⁺ uptake normally operative in resting aortic intima-media in medium containing normal plasma levels of glucose (5 mmol/l) and myo-inositol (70 mol/l); 20 or 30 mmol/l glucose had no greater effect. This effect occurred under conditions in which the aortic intima-media's normal myo-inositol content is not detectably decreased. The inhibition was prevented by sorbinil (10 mol/l) and by raising medium myo-inositol from 70 to 500 mol/l, which had no effect on (Na⁺, K⁺)-ATPase activity when the medium glucose remained at 5 mmol/l. Raising medium glucose selectively inhibited a component of (Na⁺, K⁺)-ATPase activity that requires medium myo-inositol, because it is maintained by a regulatory system through rapid basal phosphatidylinositol turnover in a discrete pool, which is replenished by a fraction of basal de novo phosphatidylinositol synthesis that is selectively dependent on myo-inositol uptake. Medium myo-inositol at a normal plasma level became inadequate to maintain this fraction of basal de novo phosphatidylinositol synthesis ([1,3-¹⁴C]glycerol incorporation) when the medium glucose was raised. When sorbinil was added raising medium glucose did not alter the ability of 70 umol/l medium myoinositol to maintain the (Na⁺, K⁺)-ATPase activity that requires medium myo-inositol. The inhibition caused by raising medium glucose was reproduced by a competitive inhibitor of active myo-inositol transport, scyllo-inositol (500 mol/l). The effect of medium glucose in an elevated plasma level on (Na⁺, K⁺)-ATPase activity in aortic intima-media appears to result from increased polyol pathway activity that makes myoinositol uptake at a normal plasma level inadequate to maintain the normal operation of a regulatory system.     

Intrastriatal Hypoxanthine Reduces Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase Activity and Induces Oxidative Stress in the Rats

The main objective of this study was to investigate the effects of a single intrastriatal injection of hypoxanthine, a metabolite accumulated in Lesch Nyhan disease and possibly involved in its neuropathology, on Na⁺,K⁺-ATPase activity, as well as on some parameters of oxidative stress, namely chemiluminescence (an index of lipid peroxidation), total radical-trapping antioxidant parameter—TRAP (an index of total antioxidant capacity of the tissue) and total thiol protein membrane content, in striatum, cerebral cortex and hippocampus of rats. Results show that hypoxanthine significantly decreased Na⁺,K⁺-ATPase activity and TRAP while increased chemiluminescence in all ipsislateral structures tested. However, no effect on total thiol protein membrane content was detected. We suggest that hypoxanthine induces oxidative stress in all cerebral structures studied (striatum, hippocampus and cerebral cortex) and that the reduction of Na⁺,K⁺-ATPase activity was probably mediated by reactive oxygen species.     

Myocardial (Na+k+)-Atpase Activity in Daul Salt-Sensitive and Resistant Rats

Vascular (Na⁺K⁺)-punp activity (ouabain-sensitive ⁵⁶Rb⁺uptake) and myocardial (Na⁺K⁺)-ATPase activity are reduced in. animals with various forms of low renin, experimental hypertersion. On the other hand, vascular (Na⁺, K⁺)-puinp activity is increased in Dahl salt-sensitive relative to resistant rats (a genetic model of hypertension), regardless of salt intake or blood pressure and it is also increased in Dahl salt-sensitive rats on high salt (3% NaCl) relative to low salt (0.4% NaCl) diets. It has been suggested that this increase in vascular (Na⁺K⁺)-pump activity may be secondary to an increase in the vascular sarcolemmal permeability to Na⁺in these salt-sensitive rats. In the present study, (Na⁺K⁺)-ATPase activity of left ventricular microsomal fractions, was increased in Dahl salt-sensitive relative to resistant rats on low salt diets; however, this difference disappeared when these salt-sensitive and resistant rats were placed on high salt diets. In contrast, mvocardial (Na⁺K⁺)-ATPase activity was decrease in Dahl salt-sensitive rats on high relative to low salt diets. Evidence that this decrease in (Na⁺K⁺)-ATPase activity is not secondary to myocardial hypertrophy in the hypertensive salt-sensitive rats, and mechanisms by which decreased cardiovascular (Na⁺K⁺)-pump activity, increased sarcolemmal permeability or both, might contribute to elevated blood pressure, are discussed.     

Intrastriatal Administration of Guanidinoacetate Inhibits Na+, K+-ATPase and Creatine Kinase Activities in Rat Striatum

Guanidinoacetate methyltransferase deficiency (GAMT deficiency) is an inherited neurometabolic disorder clinically characterized by epilepsy and mental retardation and biochemically by accumulation of guanidinoacetate (GAA) and depletion of creatine. Although this disease is predominantly characterized by severe neurological findings, the underlying mechanisms of brain injury are not yet established. In the present study, we investigated the effect of intrastriatal administration of GAA on Na⁺, K⁺-ATPase activity, total (tCK), cytosolic (Cy-CK), and mitochondrial (Mi-CK) creatine kinase (CK) activities in rat striatum. We verified that Na⁺, K⁺-ATPase, tCK, and Mi-CK activities were significantly inhibited by GAA, in contrast to Cy-CK which was not affected by this guanidino compound. Since these enzyme activities can be affected by reactive species, we also investigated the effect of intrastriatal administration of GAA on thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation in rats. We found that this metabolite significantly increased this oxidative stress parameter. Considering the importance of Na⁺, K⁺-ATPase and CK activities for brain metabolism homeostasis, our results suggest that the inhibition of these enzymes by increased intracerebral levels of GAA may contribute to the neuropathology observed in patients with GAMT-deficiency.     

Effects of thyroid hormone on the renal dopaminergic system

This study determined the effects of thyroid hormone on the renal dopaminergic system. Surgical thyroidectomy (Tx) and treatment with 2-thiouracil (Thio) decreased renal cortex Na⁺/K⁺ ATPase activity and urinary volume. Tx also decreased urinary Na⁺ and urinary l-DOPA without changing urinary excretion of Dopamine (DA). Thio treatment decreased slightly urinary l-DOPA and Na⁺, but increased urinary excretion of DA. In both models of thyroid hormone deficiency, the ratio urinary DA/DOPA increased. Changes after Thio treatment were reversed after one month of drug withdrawal. Treatment with T₃ via osmotic minipump increased Na⁺/K⁺ ATPase activity and urinary l-DOPA, did not change urinary DA, and increased the ratio DA/DOPA. To further analyze the effects of thyroid hormone deficiency, we administered selective DA₁ (SCH-23390), DA₂ (Sulpiride), and a non selective (Haloperidol) DA receptor antagonists to Thio treated and control animals. The DA₁ antagonist decreased diuresis, natriuresis and urinary l-DOPA in control, but had no effect in Thio treated rats. Sulpiride had no effect in either group. The combination of SCH-23390 plus Sulpiride decreased urinary l-DOPA and urinary volume only in Thio treated animals. Haloperidol decreased urinary volume in Thio treated animals, but had no effect in controls. Our findings suggest that renal DA synthesis is to some extent dependent on thyroid hormone levels, and that the response of DA receptors is altered by thyroid hormone deficiency, indicating a role of this hormone in the regulation of the renal dopaminergic system.     

PRL and GH synthesis and release from the sea bream (Sparus auratus L.) pituitary gland in vitro in response to osmotic challenge

The endocrine factors prolactin (PRL) and growth hormone (GH) are believed to have counteracting effects in the adaption of fish to changes in environmental salinity. In order to further investigate this interaction sea bream were challenged with full seawater (SW) or freshwater (FW) for 7 days and the response of pituitary glands cultured in vitro to an osmotic challenge (230, 275 and 320 mOsm/kg) was assessed. In vitro PRL secretion from pituitaries of SW-adapted fish was unaltered in response to an osmotic challenge, while GH secretion increased in the lowest osmolality (230 mOsm/kg). In contrast, both GH and PRL secretion by pituitaries from FW challenged fish was significantly increased (p < 0.01) over that of pituitaries from SW fish at the highest osmolality (320 mOsm/kg). After FW challenge pituitary PRL content and de novo synthesised and released PRL were significantly increased (p < 0.01), while total PRL secretion was not different from SW animals. GH pituitary content decreased in FW animals while total secretion and secretion of de novo synthesised protein were significantly increased (p < 0.01). In addition, after transfer of fish to FW expression of PRL and GH increased 3- and 2-fold, respectively. Despite the increase in PRL expression, no increase in total PRL secretion occurred and although in gills a 2-fold increase in the osmoregulatory marker, Na⁺/K⁺-ATPase activity was detected, profound haemodilution and a cumulative mortality of 40% occurred in sea bream placed in FW. Taken together the results suggest that the sea bream pituitary gland fails to respond appropriately to the osmotic challenge caused by low salinity and the physiological response evoked in vivo is not enough to allow this species to withstand and adapt to FW.     

Mechanisms in rabbit aorta for hyperglycaemia-induced alterations in angiotensin II and norepinephrine effects

Summary The (Na⁺, K⁺)-ATPase activity operative in rabbit aortic intima-media incubated with normal plasma levels of glucose and myo-inositol (70 mol/l) is decreased when the glucose content of the medium is raised from 5 to 10 mmol/l or higher; this effect is prevented by aldose reductase inhibitors and by raising the myo-inositol content of the medium to 500 mol/l. The decrease in (Na⁺, K⁺)-ATPase activity results from the loss of a component normally regulated (stimulated) by endogenously released adenosine through a receptor that stimulates phosphatidylinositol turnover in a discrete pool. The replenishment of this phosphatidylinositol pool selectively requires myo-inositol transport and is inhibited when increased polyol pathway activity impairs myo-inositol transport at a normal plasma level. Adenosine is a vasodilator, some endothelium-released vasodilators modulate the responses to vasoconstrictors by stimulating an increase in (Na⁺, K⁺)-ATPase activity in vascular smooth muscle. Whether adenosine mediates this effect in angiotensin II or norepinephrine-stimulated aorta was examined. Angiotensin II (100 nmol/l) and norepinephrine (1 mol/l) evoked marked increases in (Na⁺, K⁺)-ATPase activity in aortic intima-media incubated with 5 mmol/l glucose and 70 mol/l myo-inositol, which were inhibited when adenosine deaminase was added or the medium myo-inositol omitted to inhibit myo-inositol transport. Raising the medium glucose to 30 mmol/l inhibited the angiotensin II and norepinephrine evoked increases in (Na⁺, K⁺)-ATPase activity, and this was prevented when tolrestat (10 mol/l) was added or the myo-inositol content of the medium was raised from 70 to 500 mol/l. Hyperglycaemia causes decreased (Na⁺, K⁺)-ATPase activity prevented by aldose reductase inhibitors and by raising plasma myo-inositol by a mechanism which inhibits an adenosine-(Na⁺, K⁺)-ATPase regulatory system, which modulates the responses to angiotensin II and norepinephrine in some blood vessels.     

Effect of Lipopolysaccharide on Small Intestinal l-Leucine Transport in Rabbit

In the present study, we have investigated whether the lipopolysaccharide (LPS) endotoxin from Escherichia coli is able to alter the jejunal transport of l-leucine when the tissue is exposed to endotoxin. The results have shown that the LPS at 3 × 10^-5 g/ml decreases the uptake of l-leucine into the enterocyte, as well as the mucosal to serosal flux of l-leucine. The secretagogue effect of LPS on the gut did not affect the inhibitory effect of LPS on the intestinal absorption of the amino acid. The endotoxin did not modify amino acid diffusion across the intestinal epithelium. However, from the mediated transport, only the Na⁺-dependent transport system was affected by LPS with a diminution of the transporter affinity (the apparent K_m was increased). In addition, we found a reduction of the Na⁺, K⁺-ATPase activity, which could explain the l-leucine Na⁺-dependent transport inhibition.     

Neurostimulatory and antioxidative effects of L-deprenyl in aged rat brain regions

This study investigated the influence of chronically administered L-deprenyl on normal ageing-related parameters: multiple unit action potentials, the activities of the enzymes Na⁺,K⁺-adenosinetriphosphatase, glutathione-s-transferase and glutathione peroxidase, and the levels of lipid peroxidation products and lipofuscin contents in the brain regions (cerebral cortex, hippocampus, striatum and thalamus) of 24-month-old rats. The drug increased the activity of Na⁺,K⁺-ATPase and glutathione-s-transferase. The activity of glutathione peroxidase remained unaffected. The drug also increased the multiple unit action potentials activity. The levels of lipid peroxidation products were, however, decreased, and lipofuscin accumulation was diminished by the drug. The results essentially indicated that chronic treatment of rats with L-deprenyl significantly influenced the ageing-related alterations in: multiple unit action potentials, Na⁺,K⁺-adenosinetriphosphatase, glutathione-s-transferase, lipid peroxidation products and lipofuscin accumulation. These novel data on the effect of L-deprenyl on parameters of normal ageing provide new additional evidence concerning the anti-ageing therapeutic potential of L-deprenyl. This revised version was published online in July 2006 with corrections to the Cover Date.