Responses of gametes to the oviductal environment

Spermatozoa and oocytes are separately formed in highly specialized biological compartments (testes and epididymis, ovarian follicle), then deposited communally in the oviduct in an environment designed to facilitate their final maturation, promote their union, and nurture the resultant zygotes and early embryos. The mammalian oviduct undergoes hormonally-mediated cyclical modifications that climax during the periovulatory period thus ensuring production of the specialized environment required for the gametes. While the number of potential bioeffectors present in the oviduct is immense, there are four classes of modulators that are of particular note for the 'capacitation' or maturation of both the spermatozoa and the eggs or early embryos: beta-amino acids, bicarbonate ion, progesterone, and oviductins. Only the oviductins are unique to the oviduct, while the other three are present either at higher concentrations than in other tissues or arrive within the oviductal milieu coordinately with the gametes. For spermatozoa, beta-amino acids, bicarbonate ion, and progesterone work interactively to promote motility, capacitation, and the acrosome reaction, while oviductins facilitate capacitation and species-specific zona pellucida recognition and adhesion. For embryonic development, progesterone works indirectly by promoting a permissive oviductal environment, bicarbonate ion is required for cleavage, and beta-amino acids, acting as organic osmolytes, membrane stabilizers, and/or antioxidants, are facilitatory. Oviductins adhere to the zona pellucida of the ovulated egg thereby increasing sperm adhesion and speed of sperm penetration. Oviductins in the perivitelline space or endocytosed by the pre-implantation embryo may regulate differentiation during the morula to blastocyst transition. The roles of these mediators and their mechanisms of action for the gametes and early embryos are reviewed and discussed.

[Cardioprotective effect of taurine]

The review analyses data which had been accumulated in the recent years on the pharmacological properties of the inhibiting amino acid taurine concerning its cardiotropic action. The results of experimental and clinical studies of the beneficial effect of this compound on pathologically changed function of the heart are shown, and the mechanisms of this effect both on the cellular and systemic level are discussed.

Cytotoxicity of bile salts against biliary epithelium: a study in isolated bile ductule fragments and isolated perfused rat liver

We evaluated cytotoxic effects of different unconjugated and glycine- and taurine-conjugated bile salts (BS) against bile duct epithelial cells in isolated bile ductule fragments and isolated perfused rat liver. Ultrastructural morphometric studies were performed in polarized rat bile ductule fragments exposed in vitro to increasing concentrations (10-100 micromol/L) of lithocholate (LCA), deoxycholate (DCA), chenodeoxycholate (CDCA), cholate (CA), ursodeoxycholate (UDCA), their taurine-conjugates, and glycoconjugates of cholic (GCA) or chenodeoxycholic acid (GCDCA) for 20, 30, or 75 minutes. To evaluate the cytotoxicity of unconjugated hydrophobic bile salts against biliary epithelium (BDE) in the whole liver, livers were isolated from rats with impaired taurine-conjugation capacity (beta-alanine treatment) and perfused for 70 minutes with 2 micromol/min LCA (n = 6), CDCA (n = 6), CA (n = 6), or 0.5 micromol/min tauro-LCA (n = 4). In isolated bile ductule fragments, hydrophobic unconjugated bile salts (LCA, CDCA, DCA) induced a marked damage of intracellular organelles, mainly mitochondria. The damage started at a concentration of 10 micromol/L and became prominent at concentrations higher than 50 micromol/L. No damage of the apical and basolateral membrane was seen and tight junctions appeared intact. UDCA, taurine and glycoconjugated bile salts failed to induce any evident ultrastructural alteration. In taurine-depleted isolated livers, perfused with LCA, CDCA, or CA, bile duct epithelial cells showed no evidence of intracellular damage, despite the increased biliary excretion of unconjugated BS. Marked alterations of the apical cell membrane were seen only in livers perfused with LCA and in isolated segments of the biliary epithelium. In contrast with biliary epithelium, hepatocytes showed prominent subcellular damage with CA and CDCA, and profound alterations of the canalicular membrane with LCA and tauro-LCA. We have shown that, in vitro, BDE cells are not damaged by taurine- or glycine-conjugated BS, but they are very sensitive to cytotoxicity of hydrophobic unconjugated BS. Such sensitivity is not present in the whole liver, probably because of the specificity of BS transport processes, the microvascular architecture of the bile ductal system, and the presence in bile of a physiological surfactant, such as phospholipids.

Differential effects of lower limb revascularisation on organ injury and the role of the amino acid taurine

Lower torso revascularisation following ischaemia results in a systemic inflammatory response. Endothelial barrier function is disrupted by neutrophil-derived proteases and oxidants. Taurine, an amino acid found in large quantities in neutrophils, is a powerful endogeneous anti-oxidant. The aims of this study were to investigate the systemic effects of reperfusion following lower limb revascularisation and to evaluate the role of taurine administration in preventing this injury. A rat model of aortic occlusion (30 min) followed by 2 h of reperfusion was used. Animals were randomised to one of three groups (n = 10 per group): control; ischaemia reperfusion untreated (IR) and taurine-treated. Taurine (4% solution) was administrated orally for 48 h prior to the experiment. Neutrophil infiltration and microvascular permeability were assessed by measuring tissue myeloperoxidase activity and wet/dry weights respectively in lung, liver, kidney, and in cardiac and skeletal muscle. Statistical analysis was by means of analysis of variance (ANOVA). Reperfusion resulted in pulmonary and renal microvascular injury as assessed by organ oedema. Hepatic tissue, skeletal and cardiac muscle were unaffected by lower limb revascularisation. Taurine was effective in preventing neutrophil-mediated pulmonary but not renal microvascular injury. These data suggest that, whilst reperfusion-induced pulmonary injury is predominantly neutrophil-mediated, agents other than neutrophil-derived oxidative metabolites, capable of independently causing organ injury through direct endothelial damage, are produced during reperfusion.

Regulation of the slow Ca++ channels of myocardial cells

Contraction of the heart is regulated by a number of mechanisms, such as neurotransmitters, hormones, autacoids, pH, intracellular ATP, and Ca++ ions. These actions are mediated, at least in part, by actions on the sarcolemmal slow (L-type) Ca++ channels, exerted directly or indirectly. The major mechanisms for the regulation of the slow Ca++ channels of myocardial cells includes the following. cAMP/PK-A phosphorylation stimulates the slow Ca++ channel activity, whereas cGMP/PK-G phosphorylation inhibits. DAG/PK-C phosphorylation and tyrosine kinase phosphorylation are suggested to stimulate the slow Ca++ channel activity. Intracellular application of Gs alpha protein increases the slow Ca++ currents (ICa(L)). Lowering of intracellular ATP inhibits ICa(L). Acidosis and increase in [Ca]i inhibits ICa(L). A number of changes in the Ca++ channels also occur during development and aging. Thus, it appears that the slow Ca++ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of extrinsic and intrinsic factors, and thereby control can be exercised over the force of contraction of the heart.

Taurine depletion in the intact animal stimulates in vitro phosphorylation of an approximately 44-kDa protein present in the mitochondrial fraction of the rat heart

Sprague-Dawley rats were treated with 1.5% guanidinoethanesulfonic (GES) acid in their water in order to deplete the taurine levels partially in cardiac tissue. After 6 weeks of GES treatment, in vitro phosphorylation of a approximately 44 kDa protein present in the mitochondrial fraction of the rat heart was increased by 85%. The increase in the in vitro phosphorylation of the specific approximately 44 kDa protein after GES treatment was reversed when the animals were subsequently given 1.5% taurine in their drinking water for an additional 6 weeks. Taurine (1.5%) alone for a period of 6 weeks had no effect on the phosphorylation of the approximately 44 kDa protein. These results suggest that taurine has a regulatory role in the phosphorylation of a specific protein in cardiac tissue.

Taurine permeation through swelling-activated anion conductance in rat IMCD cells in primary culture

Whole cell recordings were performed on rat inner medullary collecting duct (IMCD) cells in primary culture. With 140 mmol/l CsCl in bath and pipette we find within 10 min a 60-fold increase in membrane conductance from 0.02 +/- 0.003 to 1.2 +/- 0.1 nS/pF when bath osmolarity is decreased from 600 to 500 mosmol/l. The effect is due to the activation of an outwardly rectifying anion conductance with the anion selectivity SCN- > I- > NO-3 > Br- > Cl- > F- > isethionate > gluconate > or = aspartate > or = glutamate. A relative permeability of the organic osmolyte taurine to Cl- (Ptaurine: PCl-) of 0.15 was detected. With taurine in pipette and bath, the channel exhibits a nearly identical activation and sensitivity profile to a variety of anion channel blockers as under symmetrical Cl- conditions. Furthermore, the 50% inhibitory concentration value for the effect of 5-nitro-2-(3-phenylpropylamino)benzoate on both currents is virtually identical. We conclude that hypotonic stress increases the anion conductance of rat IMCD cells and that this anion conductance mediates taurine efflux.

The role of antioxidants in the prevention of t-butyl hydroperoxide-induced chemiluminescence

An experimental system which assesses the antioxidant potential of ascorbic acid, glutathione, uric acid, and taurine was developed. The system comprised hemoglobin, luminol, t-butyl hydroperoxide, and different concentrations of antioxidants in TRIS-HCl buffer (pH 7.4). Control assays were performed by excluding antioxidants. Chemiluminescence was detected using a liquid scintillation counter in single photon mode. All antioxidants, when applied in the appropriate concentrations, decreased the maximum chemiluminescence values. The minimum concentrations which decreased the chemiluminescence values were defined for each of the antioxidants.

Complementary vascular-protective actions of magnesium and taurine: a rationale for magnesium taurate

By a variety of mechanisms, magnesium functions both intracellularly and extracellularly to minimize the cytoplasmic free calcium level, [Ca2+]i. This may be the chief reason why correction of magnesium deficiency, or induction of hypermagnesemia by parenteral infusion, exerts antihypertensive, anti-atherosclerotic, anti-arrhythmic and antithrombotic effects. Although the amino acid taurine can increase systolic calcium transients in cardiac cells (and thus has positive inotropic activity), it has other actions which tend to reduce [Ca2+]i. Indeed, in animal or clinical studies, taurine lowers elevated blood pressure, retards cholesterol-induced atherogenesis, prevents arrhythmias and stabilizes platelets--effects parallel to those of magnesium. The complex magnesium taurate may thus have considerable potential as a vascular-protective nutritional supplement, and might also be administered parenterally, as an alternative to magnesium sulfate, in the treatment of acute myocardial infarction as well as of pre-eclampsia. The effects of magnesium taurate in diabetes deserve particular attention, since both magnesium and taurine may improve insulin sensitivity, and also may lessen risk for the micro- and macrovascular complications of diabetes.

Release of taurine and its effects on release of neurotransmitter amino acids in rat cerebral cortex

Taurine has been postulated to function as a neurotransmitter or neuromodulator. The possibility of depolarization-evoked release of taurine from nerve terminals, and the effects of taurine on release of endogenous glutamate (Glu), aspartate (Asp), and gamma-aminobutyrate (GABA) were examined using a superfusion of crude synaptosomes prepared from rat cerebral cortex. Taurine contents in cerebral cortex and its synaptosomes were 31.7 and 25.2 nmol/mg protein, respectively. Although the basal rate of taurine release was 35.3 pmol/min/mg protein of synaptosomes (second highest releasing rate), the 2-min stimulation with KCl (30 mM) evoked only a 1.3-fold increase in release of taurine (47.3 pmol/min/mg). The increase was largely Ca(2+)-dependent. The addition of taurine to the perfusion medium significantly reduced the depolarization-evoked increases in Glu, Asp, and GABA release. The taurine-induced reduction in GABA release was attenuated by phaclofen, a GABAB antagonist, but not by bicuculline, a GABAA antagonist. However, these antagonists did not block the effects on Glu and Asp release. These data suggest that taurine may be only partly released from nerve terminals by depolarization in the cerebral cortex, but that taurine may act upon nerve terminals to regulate the release of excitatory and inhibitory amino acid transmitters.

Taurine induces a long-lasting increase of synaptic efficacy and axon excitability in the hippocampus

The physiological role of taurine, one of the most abundant free amino acids in the mammalian brain, is still poorly understood. We have found that bath application of the amino acid taurine induces two opposite actions on field excitatory synaptic potentials (fEPSP) recorded in the CA1 area of hippocampal slices: a decrease in fEPSP slope prevented by GABAA antagonists, and a long-lasting potentiation of fEPSP independent of GABAA or NMDA receptor activation. Two long-lasting processes account for this taurine-induced potentiation: (1) an increase in synaptic efficacy that is accompanied neither by modifications in the basic postsynaptic membrane electrical properties nor by those presynaptic changes involved in fEPSP paired-pulse facilitation; and (2) an increase in the axon excitability revealed by a reduction on the threshold for antidromic action potential activation. In addition, taurine perfusion also induces a long-lasting increase in intracellularly recorded EPSPs and monosynaptically activated IPSPs. A number of experimental observations such as temperature dependence, extracellular Na+ concentration dependence, and saturation studies, although they are not unequivocally conclusive, suggest that the taurine uptake system is required for the taurine-induced fEPSP potentiation. Our data describe a new taurine action defined as a potentiation of synaptic transmission due in part to an increment in presynaptic axon excitability and in synaptic efficacy.

Taurolidine, an antilipopolysaccharide agent, has immunoregulatory properties that are mediated by the amino acid taurine

Taurolidine has bactericidal and antilipopolysaccharide properties. It is broken down into the amino acid taurine, which has been shown to modulate intracellular calcium activity, a critical component in the priming and activation of macrophages and polymorphonuclear leukocytes. We hypothesized that taurolidine may function to enhance immune activity in these cells. The aim of this study was to investigate the immunological effects of taurolidine and correlate findings with survival after a septic challenge in a murine model. Study 1: CD-1 mice underwent cecal ligation and puncture, were randomized to receive taurolidine (200 mg/kg body weight/i.p.) or saline control, and studied for end point survival. Study 2: CD-1 mice were randomized to receive taurolidine (200 mg/kg body weight/i.p.) or saline control. Peritoneal macrophages (PM luminal diameters) were assessed for O2-, NO, tumor necrosis factor-alpha (TNF-alpha), CD11b, phagocytosis, and PMN influx. O2-, TNF-alpha, CD11b expression, and phagocytosis were significantly increased in the taurolidine group. Study 3: PM luminal diameters were cultured in vitro +/- 0.5 mg/ml taurolidine and PM luminal diameter antimicrobial function assessed (O2-, NO, TNF-alpha, and phagocytosis). O2-, TNF-alpha, and phagocytosis were significantly increased, whereas NO was reduced. Study 4: PM luminal diameters were also cultured with taurine (0.5 mg/ml). Similar increase in O2-, TNF-alpha, and phagocytosis were identified. Intracellular PM luminal diameter [Ca2+] was also assessed and increases in free, unbound intracellular [Ca2+] occurred after taurine culture. Thus, in addition to its bactericidal and antilipopolysaccharide activity, taurolidine primes PM luminal diameters for enhanced antimicrobial activity and these effects appear mediated by the amino acid taurine.

The in vivo and in vitro protective properties of taurine

1. Taurine is a ubiquitous, free amino acid found in mammalian systems. 2. The biological functions of taurine are unclear. 3. Various in vivo data suggest that taurine has a variety of protective functions and deficiency leads to pathological changes. 4. Depletion in rats of taurine increases susceptibility to liver damage from carbon tetrachloride. 5. Susceptibility to a variety of hepatotoxicants correlates with the estimated hepatic taurine level. 6. In vitro data suggest that taurine can protect cells against toxic damage. 7. Taurine protects isolated hepatocytes against carbon tetrachloride, hydrazine and 1,4-naphthoquinone but not against allyl alcohol, alpha-naphthylisothiocyanate (ANIT) or diaminodiphenyl methane (DAPM) cytotoxicity. 8. The mechanisms of protection are unclear but may include modulation of calcium levels, osmoregulation and membrane stabilization.

The neuronal environment after subarachnoid haemorrhage--correlation of amino acid and nucleoside levels with post-operative recovery

The study explores biochemically the neuronal environment adjacent to a subarachnoid haemorrhage in 11 patients after neurosurgical clipping of an arterial aneurysm. Extracellular fluid (ECF) from the rectus gyrus and subarachnoid fluid (SAF) were sampled with microdialysis probes. The concentrations of amino acids and nucleosides were monitored in 60 min samples collected over 2-4 days. The patients were 33-67 years of age. Surgery was performed 0-5 days after rupture of the aneurysm in 8 patients. One patient was operated on after 15 months. Clipping of aneurysms without prior haemorrhage was performed in two cases. Markedly elevated concentrations of the excitatory amino acid glutamate was observed in the ECF of only one patient who underwent surgery within 8 hours after the haemorrhage. Moderate glutamate elevations were seen in two patients and of aspartate in another patient. Five patients displayed periods of varying length of specifically elevated taurine concentrations in ECF or SAF. Transient periods of high concentrations of glycine and serine were seen in two patients. Even though average concentrations of all amino acids were fairly similar in the ECF and SAF, the pattern of changes vs. time differed markedly in the two compartments. Presently, we conclude that the level of consciousness in the post-operative phase was inversely related to total amino acid concentration in the ECF. Furthermore, while the ECF concentrations of taurine and glycine increased both specifically and transiently in several patients, excitatory amino acid levels were not appreciably elevated subsequent to the neurosurgical intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of the brain by carnitine

Carnitine (beta-hydroxy-gamma-trimethylammonium butyrate) is widely distributed in the body including the nervous system. Its physiological function, viz. a carrier of long-chain fatty acids through the inner mitochondrial membrane, has been well established. In this review, mainly based on our experiments, we discuss the possibility that carnitine may have effects other than the "physiological" function and that it may be a potent protector of the brain. When mice were exposed to ammonia (intraperitoneal injection of ammonium acetate), they developed seizures and concentrations of brain energy metabolites were altered; ATP and phosphocreatine decreased while ADP, AMP, pyruvate and lactate increased. The seizures and changes in brain energy metabolites were clearly suppressed when the mice were pre-treated with carnitine. Furthermore, changes in energy metabolites in the brain caused by severe ischemia (decapitation) were also suppressed by carnitine. Since D-carnitine showed similar effects as those of L-carnitine, the effects seem due to function(s) of carnitine yet to be defined. Intrinsic substances including carnitine appear to deserve further studies for possible use in protecting the brain.

Taurine depletion and excitation-contraction coupling in rat myocardium

Although the sulfur-containing amino acid taurine is found in high concentrations in mammalian myocardium, its involvement in function of the cardiac myocyte remains unclear. To examine the effects of taurine depletion on cardiac mechanical function, rats were treated in vivo with the taurine transport antagonist guanidinoethane sulfonate (GES). After 6 weeks of treatment, myocardial taurine concentrations were decreased to < 40% of control, with no change in tissue DNA content. Right ventricular trabeculas from taurine-depleted rats exhibited significant reductions (P < .05) in isometric twitch force (Ft) at all [Ca2+]o levels and systolic sarcomere lengths examined. Taurine-depleted trabeculas also exhibited increased passive compliance. A slight (P < .05) rightward shift in the Ft-[Ca2+]o relation suggested a decrease in the sensitivity of the taurine-depleted muscles to [Ca2+]o. No changes were observed in the force-interval relation, suggesting that the transsarcolemmal Ca(2+)-handling mechanisms remained unchanged. The fraction of Ca2+ recirculated through the sarcoplasmic reticulum, inferred from the decay of postextrasystolic potentiation, was also not different in the taurine-depleted muscles. When force was expressed relative to the rate of stimulation, length of rest periods, or postextrasystolic potentiation, virtually all curves were super-imposable for control and taurine-depleted muscles, suggesting that the deficit was not dependent on Ca2+ handling. Thus, we conclude that in taurine-depleted muscles the force-generating processes showed the same regulation as in control muscle. Furthermore, the substantial deficit in force development is consistent with a reduced population of force generators on the basis of three pieces of evidence.(ABSTRACT TRUNCATED AT 250 WORDS)

UDP-N-acetylhexosamines and hypotaurine in human glioblastoma, normal brain tissue and cell cultures: 1H/NMR spectroscopy study

NMR spectroscopy was used to analyse perchloric acid extracts of normal human brain, murine brain cell cultures, glioblastoma tissue and the glioblastoma cell line U-87. 1H NMR spectra revealed the presence of elevated levels of UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine in glioblastoma extracts and the glioblastoma cell line U-87, in comparison with normal brain tissue and primary cell cultures of neurons and astrocytes. UDP-N-acetylhexosamines appear to accumulate in cells that are unable to differentiate. Furthermore, it was found that the culture medium had an effect on the concentration of UDP-N-acetygalactosamine in the glioblastoma cell line. Hypotaurine, previously only associated with oligodendrocytes, has been identified in astrocyte cultures and in cerebellar granule cells. In normal brain it was not observed by NMR spectroscopy, but was easily detectable in glioblastoma tissue extracts. UDP-N-acetylhexoseamines and hypotaurine might be useful markers for brain pathology and play a role in cell differentiation and cell division.

Regulation of mammalian brain cell volume

Maintenance of brain cell volume is of crucial importance for normal central nervous system (CNS) function. This review considers volume regulation primarily in response to disturbances of body fluid osmolality. Brain cells counter the tendency to swell or shrink by appropriate adjustment of their internal osmotic potential. This is achieved by loss or uptake of inorganic ions and low molecular weight organic solutes (osmolytes). The latter comprise mainly amino acids, myoinositol, choline, and methylamines. Taurine may be of particular importance in volume control, especially in young animals. Brain cell volume regulation, however, is only one contributory factor to maintenance of constant brain volume (water content), and operates in parallel with important alterations in bulk fluid and electrolyte movement across the blood-brain barrier and between the interstitium and cerebrospinal fluid, which themselves moderate the requirement for transient alteration in cell volume during acute osmotic imbalance. Although altered cerebral content of inorganic ions and osmolytes are usually regarded as responses, respectively, to acute and chronic osmotic disturbances, osmolytes (especially taurine) may also participate in short-term cell volume regulation.