Biological signals最新文献

Dinoflagellates are the causative agents of red tides with worldwide occurrence and can be induced to encyst by in doleamines such as melatonin and 5-methoxytryptamine (5-MOT). This biological response may be mediated via indoleamine-binding proteins or receptors. Here we report the initial characterization of the signal transduction mechanisms by which indoleamines induce encystment of dinoflagellates. In particular, we explored the possible involvement of G proteins and cAMP in cyst formation. Both melatonin and 5-MOT promoted the encystment of Gonyaulax tamarensis and Crypthecodinium cohnii. Exposure of dinoflagellates to dibutyryl cAMP, which directly activates cAMP-dependent pathways, did not affect the ability of indoleamines to promote encystment. However, dibutyryl cAMP dose-dependently diminished the indoleamine-induced suppression of cell growth. Exposure of dinoflagellates to the bacterial toxins from Vibrio cholerae and Bordetella pertussis had no effect on the indoleamine-induced encystment response, indicating the lack of involvement of Gs or Gi-like proteins. Moreover, [32P]ADP ribosylation of dinoflagellate membranes by either toxin failed to identify substrate proteins. These results suggest that although the indoleamine-induced encystment of dinoflagellates may involve a G-protein-coupled signal transduction pathway, the identity of the G protein concerned may be distinct from those that regulate adenylyl cyclases in mammalian cells.

The effects of streptozotocin-induced diabetes on pituitary neuropeptides were studied. Substance P, dynorphin and beta-endorphin in both pituitary lobes and cholecystokinin and somatostatin in the neurointermediate lobe (NIL) were measured 4 weeks after streptozotocin treatment in adult male rats. There were significant decreases of substance P levels in both the anterior lobe (AL) and NIL, and of cholecystokinin, dynorphin and beta-endorphin in the NIL, whereas the dynorphin content in the AL increased, when values were expressed on a per-lobe basis. On a per-milligram-protein basis, however, only beta-endorphin in the NIL showed a significant decrease, while AL beta-endorphin and dynorphin were increased. Correlated with these changes were a drastic decrease in the serum insulin level and a marked increase in serum glucose and corticosterone levels. All these changes were reversible with insulin treatment. It is suggested that the decrease in NIL contents of neuropeptides demonstrated (except for beta-endorphin) might be due to mechanisms other than a change in synthesis.

The nephrotoxic action of anticancer drugs such as nitrogranulogen (NG), methotrexate (MTX), 5-fluorouracil (5-FU) and cyclophosphamide (CY) administered alone or in combination [MTX + 5-FU + CY (CMF)] was evaluated in experiments on Wistar rats. After drug administration, creatinine concentrations in the plasma and in the urine of the rats were determined, as well as creatinine clearance. Histopathologic evaluation of the kidneys was also performed. After MTX administration a significant increase (p = 0.0228) in the plasma creatinine concentration and a significant (p = 0.0001) decrease in creatinine clearance was noted compared to controls. After the administration of NG, 5-FU and CY neither a statistically significant increase in creatinine concentration nor an increase in creatinine clearance was observed compared to the group receiving no cytostatics. Following polytherapy according to the CMF regimen, a statistically significant decrease (p = 0.0343) in creatinine clearance was found, but creatinine concentration did not increase significantly compared to controls. CY caused hemorrhagic cystitis in 40% of rats, but it did not cause this complication when combined with 5-FU and MTX. Histologic changes were found in rat kidneys after administration of MTX, CY and NG, while no such change was observed after 5-FU and joint administration of MTX + 5-FU + CY compared to controls. Our studies indicate that nephrotoxicity of MTX + 5-FU + CY administered jointly is lower than in monotherapy.

Cooling is known to inhibit glucose-induced insulin secretion from pancreatic islets, but temperature-dependent processes in stimulus-secretion coupling remain unclear. In the present study, we examined the effects of cooling on the glucose-induced increase in cytoplasmic Ca2+ concentration ([Ca2+]i) and concomitant insulin secretion in rat pancreatic islets to analyze the temperature dependence of processes proximal and distal to the Ca2+ signal in stimulus-secretion coupling. Rat pancreatic islets were isolated and perifused. [Ca2+]i was measured using fura-2. Glucose (15 mM) caused a triphasic [Ca2+]i response in single islets at 35 degrees C: an initial decrease and a transient increase followed by a gradual increase, on which series of Ca2+ transients were frequently superimposed. Cooling to 30 and 25 degrees C caused slower and smaller [Ca2+]i responses with a Q10 (temperature coefficient) of 1.8. Glucose caused biphasic insulin secretion at 35 degrees C, which was inhibited by cooling, with a Q10 of 11.6. The ratio of glucose-induced insulin secretion to [Ca2+]i rise (IS/Ca) was calculated to represent the efficiency of Ca2+ to cause exocytosis. The Q10 value of the ratio of IS/Ca was 6.6. The Q10 values of the ratio of IS/Ca in the responses to high K+ (30 mM), carbamylcholine (100 microM) and glibenclamide (2 microM) were 5.6, 3.8, and 13.0, respectively. These values were greater than the Q10 values of corresponding [Ca2+]i responses: 1.2, 1.4, and 1.8, respectively. From these results, we conclude that cooling inhibits not only the glucose-induced [Ca2+]i rise but also Ca(2+)-activated exocytosis, and that the latter is much more sensitive to cooling than the former.

The hormone synthesized by the pineal gland, melatonin, has been shown to be a direct free radical scavenger both in vivo and in vitro. Thus, it potently protects cells from the damage induced by oxidative agents. In this study, we demonstrate that melatonin increases glutathione peroxidase activity in several tissues from chicks. This stimulation is time dependent and maximal increases are seen 90 min after melatonin injection (500 micrograms/kg intraperitoneally), although enzymatic activity is still elevated 135 min after its administration. No significant increases were detected 45 min after the injection. Glutathione peroxidase is generally considered to be an important antioxidative enzyme because it metabolizes hydrogen peroxide and other hydroperoxides. Thus, melatonin not only is a direct scavenger of toxic radicals but in an avian species, as in mammals, it stimulates the antioxidative enzyme glutathione peroxidase. The ability of melatonin to increase glutathione peroxidase activity is consistent with its general role as an antioxidant.

The formation and accumulation of reactive oxygen species within liver macrophages and their release into the medium were determined by lucigenin-enhanced chemiluminescence, the reduction of cytochrome c, the formation of formazan from nitroblue tetrazolium and the fluorescence of 5- (and 6)-carboxy-2',7'-dichlorodihydrofluorescein. Zymosan, phorbol ester and fluoride induced the formation and accumulation of oxygen radicals intra- and extracellularly, ionomycin and lipopolysaccharide led to an intracellular accumulation of oxygen radicals, while after arachidonic acid and tumor necrosis factor-alpha, no reactive oxygen species were formed. While zymosan and phorbol ester predominantly induced the formation and release of superoxide, hydroperoxide was the main form released by fluoride. These results indicate that agents of different biological potencies induce reactive oxygen species within and/or outside liver macrophages and that different techniques must be used to detect different oxygen species within and outside cells.

This study was conducted to investigate the effect of intracerebroventricular administration of adrenomedullin (13-52) [ADM(13-52)], a novel hypotensive peptide, on the hemodynamic parameters of anesthetized rats. ADM(13-52) was administered centrally in a dose of 0.4-3.2 nmol/kg. It provoked marked, prolonged and dose-dependent increases in mean arterial blood pressure, heart rate, stroke volume, cardiac index, left ventricular pressure, left ventricular dp/dtmax and dp/dtmin, but reduction in total peripheral resistance index. In addition, intracerebroventricular administration of ADM(13-52; 1.6 nmol/kg) provoked a marked increase in renal sympathetic nerve activity. Intracerebroventricular administration of artificial cerebrospinal fluid had no effect on the hemodynamic parameters and renal sympathetic nerve activity. The results indicate that ADM(13-52) exerts a central action on the cardiovascular system. The mechanisms of hemodynamic changes induced by central ADM(13-52) were preliminarily analyzed in this study. ADM might play a role in the central control of the cardiovascular system, although the confirmed mechanisms and the physiological implications are undetermined.

We have compared the pharmacological characteristics of 2-[125I]iodomelatonin binding to crude membrane preparations of the lung, spleen, brain and kidney of chicken. Saturation studies indicated significant differences (p < 0.05) in the equilibrium dissociation constant (Kd) and maximum number of binding site (Bmax) values among the four tissues studied. The descending order of affinities was lung = spleen > brain > kidney. Competition curves of 2-[125I]iodomelatonin binding to crude membrane preparations of all four chicken tissues by melatonin were studied simultaneously to reduce individual, physiological, age and interassay variations. Similar competition experiments were also performed on 2-phenylmelatonin, 2-iodomelatonin, 6-chloromelatonin, 6-hydroxymelatonin and N-acetylserotonin (NAS). Concentrations of indoles which inhibited 50% of specific 2-[125I]iodomelatonin binding (IC50) were calculated. The IC50 of 2-[125I]iodomelatonin inhibition curves by the indole compounds in different tissues showed the following descending orders of affinity: (1) melatonin: lung = spleen > brain > kidney, (2) 2-phenylmelatonin: lung = spleen = brain = kidney, (3) 2-iodomelatonin: lung = spleen = kidney > brain, (4) 6-chloromelatonin: lung = spleen = kidney > brain, (5) 6-hydroxymelatonin: kidney > lung = spleen = brain, and (6) NAS: kidney > lung = spleen > brain. The non-hydrolizable GTP analog, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), exhibited differential effects on the saturable binding of the four tissues. GTP gamma S increased the Kd of 2-[125I]iodomelatonin binding by 2- to 3-fold in the lung and spleen, 0.5-fold in the brain and 1-fold in the kidney. Based on our findings, we would like to suggest that the 2-[125I]iodomelatonin binding sites in these four tissues may belong to three different high affinity (picomolar) subtypes of melatonin receptor. We name them cML1A represented by the lung and spleen, cML1B by the brain and cML1C by the kidney.

Catecholamine secretion from carotid body glomus cells is hypothesized to cause the hypoxia-induced increase in nerve activity. To test aspects of this hypothesis, tissue catecholamine and single-fiber nerve activity was measured from rat carotid bodies in vitro. Hypoxia (1-min duration, 0 Torr at nadir) caused a rapid increase in catecholamine release and nerve activity, consistent with the hypothesis, but repetitive hypoxias interspersed with short rest periods resulted in a much greater decline in catecholamine release than nerve activity. Furthermore, pretreatment with reserpine (24 h) nearly abolished catecholamine release, but nerve response was not different than untreated controls. These results suggest that catecholamine secretion is not causal to the increase in nerve activity of rat carotid body.

Previous studies [Czyzyk-Krzeska et al.: J Neurochem 1992;58:1538] demonstrated the relationship between low O2 breathing and tyrosine hydroxylase (TH) gene expression in chemosensory type I cells of the carotid body. In the present study, we have exposed carotid bodies in vitro to hypoxic superfusion media, and subsequently used the reverse transcriptase-polymerase chain reaction technique to measure relative changes in the TH transcript in an effort to elucidate the cellular mechanisms which regulate TH gene expression. Carotid bodies and superior cervical ganglia (SCG) were exposed for 3 h to superfusion media equilibrated with either 10% O2 or 100% O2 and then rapidly frozen on dry ice prior to extraction of total RNA. Hypoxia elevated TH mRNA in the carotid body 3.63 +/- 0.84-fold (mean +/- SEM), while in contrast, these parameters were unchanged in SCG similarly exposed to hypoxic media. Incubation of carotid bodies in zero Ca2+ superfusates greatly attenuated the increase in TH mRNA evoked by hypoxia (1.39 +/- 0.34-fold increase; p < 0.025 compared to normal Ca2+ group). Likewise, exposure to the guanylate cyclase activator, atriopeptin III (100 nM), attenuated the TH mRNA hypoxic response (p < 0.005), while activation of adenylate cyclase with forskolin (10 microM) tended to elevate the response to low O2. Our data suggest that hypoxia, independent of circulating hormones, induces TH gene expression in the carotid body, and that multiple factors, including [Ca2+] and cyclic nucleotides, may be important components of the signal transduction pathway.