Antiallergic mechanisms of beta-adrenergic stimulants in rats.

Antiallergic mechanisms of beta-adrenergic stimulants were investigated in rats. Isoproterenol administered intravenously inhibited IgE antibody-mediated homologous passive cutaneous anaphylaxis (PCA) and histamine-induced cutaneous reaction (HCR) elicited at the same time in the same rats significantly. The inhibition of PCA was more potent than that of HCR, suggesting that PCA is inhibited by at least 2 mechanisms. One is the inhibition of vascular permeability increase. In vivo histamine release in the rat peritoneal cavity caused by intravenous antigen was inhibited by the intravenous administration of isoproterenol or salbutamol dose-dependently. On the contrary, when the histamine release in the peritoneal cavity was caused by intraperitoneal antigen, isoproterenol or salbutamol administered simultaneously with antigen failed to inhibit the reaction. Furthermore, antigen-induced histamine release from sensitized peritoneal exudate cells in vitro was not inhibited by isoproterenol or salbutamol. These results indicate that the primary target of beta-adrenergic stimulants is the vascular endothelium, and that the direct inhibition of chemical mediator release from mast cells does not play an important role for the inhibition of PCA and in vivo histamine release in the peritoneal cavity in rats. Beta-adrenergic stimulants therefore may prevent intravenously administered antigen from activating sensitized mast cells through affecting endothelial cells.     

The micronucleus test using peripheral blood reticulocytes from methotrexate-treated mice.

The induction of micronuclei by methotrexate (MTX) was examined in two laboratories using mouse peripheral blood reticulocytes. MTX was a weak inducer in the micronucleus test using bone marrow cells and single treatments, and was one of the few chemicals showing a multiple-treatment effect (CSGMT/JEMS.MMS, 1990). In our preliminary experiments, the ratio of reticulocytes to total erythrocytes decreased greatly after a single treatment with MTX at 100 mg/kg, so lower dose levels of MTX were selected to carry out the micronucleus test in peripheral blood. Full-scale tests were performed at dose levels of 0, 10, 20, 40, and 80 mg/kg, with five sampling times of 0, 24, 48, 72, and 96 h. Frequencies of micronucleated reticulocytes (MNRETs) increased dose-dependently at 72 h, to a maximum of approximately 1%; some preparations obtained from the animals at higher doses could not be examined because the ratio of reticulocytes to total erythrocytes had decreased severely. At doses of 0.5-4.0 mg/kg, the effect of multiple treatments vs. single treatments was not clear, nor was the maximum level of response much different. Since MTX induced a clear positive response in peripheral blood reticulocytes after a single treatment, the reticulocytes in peripheral blood seem a more sensitive target.     

Fluorometric determination of plasma adenosine concentrations using high-performance liquid chromatography

Methods are described for the fluorometric determination of plasma adenosine concentrations, using HPLC. Plasma obtained from blood of dogs treated with erythro-(2-hydroxy-3-nonyl)adenine hydrochloride and dipyridamole was deproteinized with perchloric acid and the neutralized sample was put sequentially onto a SepPak C18 and boronic acid affinity column. Subsequently, adenosine in the final elution was converted to 1,N6-ethenoadenosine and was quantitated by HPLC with a fluorescence detector. The percentage recovery of adenosine added to the deproteinized plasma was nearly 100%. In the adenosine deaminase treated plasma, the increase in adenosine concentration of even 4 nM can be accurately determined. The control renal venous plasma concentrations of adenosine in anesthetized dogs were 19.9 +/- 1.9 nM, a significantly higher value than the corresponding arterial concentrations (12.7 +/- 1.1 nM), thereby suggesting the renal release of adenosine. This release was markedly enhanced following the removal of the renal arterial occlusion. Thus, taken together with the in vivo results, the present method is sensitive, hence most useful for the determination of plasma adenosine concentrations.     

Enhanced growth of the red algaPorphyra yezoensis Ueda in high CO2 concentrations

Leafy thalli of the red algaPorphyra yezoensis Ueda, initiated from conchospores released from free-living conchocelis, were cultured using aeration with high CO₂. It was found that the higher the CO₂ concentration, the faster the growth of the thalli. Aeration with elevated CO₂ lowered pH in dark, but raised pH remarkably in light with the thalli, because the photosynthetic conversion of HCO ₃ ^? to OH^? and CO₂ proceeded much faster than the dissociation of hydrated CO₂ releasing H⁺. Photosynthesis of the alga was found to be enhanced in the seawater of elevated dissolved inorganic carbon (DIC, CO₂ + HCO ₃ ^? + CO ₃ ^? ). It is concluded that the increased pH in the light resulted in the increase of DIC in the culture media, thus enhancing photosynthesis and growth. The relevance of the results to removal of atmospheric CO₂ by marine algae is discussed.     

Effect of bradykinin on airway neural responses in vitro.

We investigated the effects of bradykinin (BK) on airway excitatory nonadrenergic noncholinergic (e-NANC) and cholinergic nerves in vitro. Neural responses were elicited by electrical field stimulation in guinea pig airways in vitro before and after the addition of BK (10(-10)-10(-7) M). Captopril (10(-5) M) and phosphoramidon (10(-6) M) were added to prevent degradation of BK, and all neural responses were measured in the presence of indomethacin (10(-5) M) and propranolol (10(-6) M). BK potentiated e-NANC responses in bronchi in a concentration-dependent manner (10(-10)-10(-7) M) without changing concentration-response curves to exogenously applied substance P (10(-10)-10(-5) M). BK significantly potentiated e-NANC neural constrictor responses by 22 +/- 7% at 10(-8) M (mean +/- SE, n = 5, P < 0.05) and 32 +/- 7% at 10(-7) M (n = 8, P < 0.01), compared with changes in time-matched control tissues (7 +/- 2%, n = 8). The potentiation of e-NANC responses by BK was abolished by pretreatment with a specific B2-receptor antagonist, HOE 140 (10(-7) M). Cholinergic constrictor responses elicited to electrical field stimulation were not affected by the addition of BK (up to 10(-7) M). These results suggest that BK potentiates e-NANC bronchoconstrictor responses prejunctionally via a B2-receptor.     

Inhibitory NANC nerves in human tracheal smooth muscle: a quest for the neurotransmitter.

Inhibitory nonadrenergic noncholinergic (i-NANC) nerves are the only neural bronchodilator pathway in human airways. Possible candidates for the neurotransmitter include vasoactive intestinal peptide (VIP) and nitric oxide (NO) and purines such as ATP. We have investigated the potential role of these neurotransmitters. Phosphoramidon (10(-5) M) significantly potentiated relaxations to low doses of VIP with no effect on i-NANC responses. Relaxations induced by VIp were abolished with alpha-chymotrypsin (2 U/ml), but i-NANC responses were unaffected. Reactive blue 2 had no effect on i-NANC neural responses, indicating that endogenous ATP was not involved. The NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME, 10(-4) M) produced a concentration-dependent inhibition of the i-NANC response, producing almost complete inhibition at every frequency studied (0.5-40 Hz), whereas L-NG-monomethyl arginine was effective only at low stimulation frequencies. The inhibitory effect of L-NAME was partially reversed by L- but not D-arginine, and D-NAME was without effect. These results suggest that in human tracheal segments the neural bronchodilator response is mediated by NO, and there is no functional evidence for implicating VIP in this response.     

Estimation of the degree of self-fertilization in Porphyra yezoensis (Bangiales,Rhodophyta)

Crosses between genotypically distinct thalli of the monoecious species Porphyra yezoensis were carried out using immature thallus fragments from green- and red-type color mutants and also wild-type thalli. As the genes governing the mutants are monogenic, recessive to the wild-type, and belong to the same linkage group, the degree of self-fertilization could be estimated based on the pigmentation of the resultant diploid conchocelis. The degree of self-fertilization in the cross between the green-type and the wild-type was 48.5–55.0%, and in the cross between the red-type and the wild-type was 45.1–56.5%. In the cross between the green- and red-type mutants, the degree of self-fertilization was 46.0–54.5% when the green-type was the female parent, and was 44.8–55.6% when the red-type was the female parent.     

The effects of planktivorous fishes on the plankton community in a eutrophic lake

Stocking silver carp, a phytoplankton feeder, and bighead carp, an omnivorous plankton feeder, into an eutrophic lake at high densities caused a dramatic change in the lake ecosystem.Microcystis, which had been dominant in summer and a main food of the fishes decreased markedly, and green algae smaller than 10 μm then became dominant. Consequently, chlorophyll-a per unit area decreased slightly, while the rate of production was higher than that in the previous years. As the total density of the fishes increased (from 0.09 to 0.11 fish m⁻²), the growth of silver carp was retarded, while that of bighead carp increased.Microcystis, was unable to become dominant due to increased grazing pressure by the fishes, and small green algae became dominant. The lake conditions thus became more favourable for zooplankters which selectively consumed small green algae, and accordingly, the production of zooplankton rose. Bighead carp consumed more animal food, which they assimilate at a higher rate than plant food, and grew better in spite of the fact that the fish density increased. The feeding rate of silver carp was greatly reduced because the green algae were too small to ingest, and the fish therefore grew poorly. Results of a computer simulation of a model consisting of five compartments, representing the blue-green algae, green algae, zooplankton, silver and bighead carp, support the food-web change observed in the lake.