Kenji Tasaka

Presence of non-selective type of endothelin receptor on vascular endothelium and its linkage to vasodilation

We studied the role of non‐selective type (ET14) of endothelin (ET) receptor in the vasculature, using a ligand specific to the ET14 receptor, [Glu9]‐sarafotoxin S6b ([Glu9]SRTb). Endothelium‐containing rat thoracic aorta possessed specific binding sites for 125I‐[Glu9]SRTb, which were almost eliminated by removal of the endothelium, while ET‐3‐specific binding sites were not detected in the endothelium‐intact rat aorta. Only ET14 receptor was detected in the membranes from the endothelium of porcine thoracic aorta. [Glu9]SRTb exerted only vasodilation in rat aortic ring. These findings indicate that ET14 receptors are located on vascular endothelium and linked to vasodilation.

Influence of histamine depletion on learning and memory recollection in rats

To clarify the role of endogenous histamine in learning and memory, the effect of α-fluoromethylhistidine on active avoidance response in rats was studied. α-Fluoromethylhistidine (20–100 mg/kg or 10–50 µg) significantly (P<0.05 orP<0.01) prolonged the response latency in active avoidance response when administered by either intraperitoneal or intracerebroventricular injection. These effects were dose-related and long lasting. A prolongation of the response latency induced by an intraperitoneal injection of α-fluoromethylhistidine (100 mg/kg) was antagonized by intracerebroventricular injection of histamine (10 and 20 ng) in a dose-dependent manner. In addition, the acquisition of this response was retarded by a consecutive intracerebroventricular injection of α-fluoromethylhistidine (50 µg), whereas histamine (100 ng) facilitated the response acquisition when administered by the same route. Both intraperitoneal (100 mg/kg) and intracerebroventricular injection of α-fluoromethylhistidine (50 µg) significantly (P<0.05 orP<0.01) decreased the brain histamine content, especially in the hippocampus and hypothalamus. When α-fluoromethylhistidine (50 µg) was injected intracerebroventricularly, there is a high correlation between a prolongation of the response latency and a decrease in histamine content of these brain areas. Based on these findings, it was concluded that an intimate relation may exist between a prolongation of response latency in the active avoidance response and a decrease in the brain histamine content; endogenous histamine may play an important role in learning and memory recollection in rats.

Influence of certain H1-blockers on the step-through active avoidance response in rats.

The inhibitory effects of some newly developed H1-blockers on the step-through active avoidance response in rats were studied in comparison with those of classical H1-blockers. Single administration of diphenhydramine, pyrilamine, promethazine and chlorpheniramine caused dose-related depressant effects on the active avoidance response. Ketotifen and azelastine caused less potent inhibition than the classical H1-blockers, while the effects of astemizole and oxatomide were almost negligible in suppressing the response. Following chronic administration of pyrilamine and promethazine, the acquisition of active avoidance response was significantly retarded compared with the control group, where-as new H1-blockers caused a somewhat but not significantly slower acquisition than the control group. Chronic administration of astemizole and oxatomide caused only transient suppression of the response. However, classical H1-blockers such as pyrilamine and promethazine caused sustained inhibition for as long as drug administration was continued.

Analgesic effect of histamine induced by intracerebral injection into mice.

Three methods were used to study the analgesic effect of intracerebral injection of histamine (Hi) on mice: the writhing test (acetic acid and phenylquinone), the electrical stimulation of the tail and the hot plate test. At doses higher than 2 μg, Hi inhibited the writhing syndrome significantly, and at doses of 10 μg or higher, Hi displayed a marked analgesic effect during both the electrical stimulation and hot plate methods. The saline injection produced only a negligible effect.Simultaneous application of Hi and 10 μg of diphenhydramine, pyrilamine or promethazine, apparently causing no analgesic effect from a single administration, caused a parallel shift of the dose-response curve of Hi to the right. ED50 of Hi was increased approximately 2, 2.8 and 3.8 times, respectively. However, cimetidine did not reveal any antagonistic effect on Hi-induced analgesia. Subcutaneously administered, 3 mg/kg of morphine augmented the analgesic effect of Hi. In accordance with this, pretreatment of naloxone (0.005 mg/kg) antagonized the analgesic action of Hi almost completely. When 5 mg/kg of leucine-enkephalin, less than the minimum effective dose, was given prior to Hi injection, the analgesic effect of Hi was enhanced. In addition, 10 and 20 μg of Hi increased the morphine analgesia markedly and parallel shifted the dose-response curve of morphine to the left.

The influence of histamine on precursors of granulocytic leukocytes in murine bone marrow

The effect of histamine on granulocytic progenitor cells in murine bone marrow was studied in vitro. When bone marrow cells were cultured for three days with the drug, 10(-8) M to 10(-5) M of histamine stimulated differentiation and proliferation of myeloid precursor cells. Subsequently, the number of descendant cells, such as metamyelocytes and neutrophils, increased dose-dependently. Co-existence of equimolar H2 blockers such as cimetidine and ranitidine completely suppressed this effect of histamine, though this was not the case with an H1 blocker/histamine combination. Significant increase in 3H-thymidine incorporation was observed almost exclusively in myeloblasts, promyelocytes and myelocytes after exposure to histamine at concentrations higher than 10(-8) M. Also, selective incorporation of 3H-histamine into bone marrow cells was observed in myeloblasts and promyelocytes, but histamine incorporation was not influenced by the presence of either of histamine agonists or antagonists. While histamine, via H2 receptors, selectively increased the number of granulocytic colony forming units in culture (CFU-C), it had no such effect on macrophage colonies. Considering these findings, it was concluded that histamine promotes proliferation and differentiation of granulocytic myeloid cells via 1) H2 receptors in the CFU-C stage and 2) histamine receptors which are neither H1 nor H2 in the stages of myeloblast and promyelocyte differentiation.

Analysis of the mechanism of histamine release induced by substance P

Substance P causes release of histamine from rat peritoneal mast cells; the structure-activity relationship shows that N-terminal residue is essential and the hydrophobic region of C-terminal plays an important role. Electrical conductivity of black lipid membrane containing phosphatidic acid was augmented by substance P. In this case, N-terminal residues and C-terminal hydrophobicity were also unavoidable. The partitioning of substance P into the organic phase increased in the presence of phosphatidic acid. The CD spectrum of substance P was changed from the unordered form to beta-form by coexistence of phosphatidic acid/PC liposomes in the medium. The addition of calcium or magnesium in the test solution is effective to prevent either of these phenomena. These findings indicate that substance P probably binds to negatively charged sites of membrane lipids, and subsequent penetration of C-terminal into the hydrophobic core of lipid bilayer may induce an increase of membrane permeability and the following histamine release.

Excitatory effect of histamine on the arousal system and its inhibition by H1 blockers.

To clarify whether the sedative effect of H1 blockers is exerted in relation to H1 receptors in the brain, EEG activity recorded from the cortex and thalamus of rats was studied by power spectral analysis. EEG processing was performed by the FFT method and displayed as compressed spectral arrays. When a train of low frequency electrical stimulation was applied to the midbrain reticular formation of conscious rats, there was an increase in spectral power recorded at the cortex and thalamus, especially in the low frequency bands (0-6 Hz). The intraventricular administration of histamine suppressed the increase in power; this inhibition was antagonized by simultaneous administration of pyrilamine or diphenhydramine, though not in in combination with cimetidine or ranitidine. As in the case of histamine, the administration of 2-methylhistamine decreased power in the slow wave region, while administration of 4-methylhistamine did not. It was assumed that the arousal effect of histamine is exerted via H1 and not related to H2 receptors. Adverse effects of H1 blockers, such as drowsiness, may be caused by their inhibition of histamines arousal effect.

Anti-allergic constituents in the culture medium of Ganoderma lucidum. (I) Inhibitory effect of oleic acid on histamine release

The chloroform extract fromGanoderma lucidum broth markedly inhibited histamine release from rat peritoneal mast cells. From the active fractions, palmitic acid, stearic acid, oleic acid and linoleic acid were isolated. Oleic acid dose-dependently inhibited the histamine release and45Ca uptake into mast cells induced by compound 48/80 and A-23187 at concentrations of 5 to 50 μM and 0.5 to 5 μM, respectively. Saturated fatty acids, however, had only a weak inhibitory effect on histamine release. Although linoleic acid and linolenic acid effectively prevented this release, these two compounds caused marked release at concentrations higher than 10 μM and 20 μM, respectively. Oleic acid induces membrane-stabilization in model membrane systems. It was concluded that one of the effective constituents obtainable from the chloroform extract ofG. lucidum-cultured broth is oleic acid.

Inhibitory effects of oxatomide on intracellular Ca mobilization, Ca uptake and histamine release, using rat peritoneal mast cells

Oxatomide at concentrations of 0.01-10 microM inhibited not only an increase in 45Ca uptake but also the intracellular Ca2+ release induced by compound 48/80 in rat peritoneal mast cells. At higher concentrations, ketotifen or other calcium antagonists caused similar inhibitory effects. However, the inhibitory effect of oxatomide on the 45Ca uptake into rat neonatal heart cells was much weaker than that of verapamil. Through image processing of quin 2-stained mast cells, it was revealed that oxatomide inhibited Ca2+ release from the intracellular store. Although oxatomide alone did not affect cAMP and cGMP contents in sensitized guinea pig lung samples, the drug effectively prevented changes in the nucleotide contents evoked by antigen challenge. These results suggest that the inhibitory effect of oxatomide on histamine release may be caused by a combination of prevention of Ca uptake, which is highly selective toward mast cells; inhibition of Ca2+ release from the intracellular Ca store, and elevation of the cAMP content in mast cells.

Antiallergic Effects of Terfenadine on Immediate Type Hypersensitivity Reactions

Terfenadine dose-dependently inhibited rat homologous PCA (2.5-10 mg/kg, p.o.) and experimentally-induced asthma in guinea pigs (0.5-5 mg/kg, p.o.). Similarly, metabolites I and II dose-dependently inhibited experimentally-induced asthma but their respective potencies were approximately 1/2 and 1/15th that of terfenadine. These results suggest that the metabolites contribute to the antiallergic effects of terfenadine. In ex vivo, terfenadine (5-20 mg/kg, p.o.) also inhibited the release of both antigen-induced histamine and SRS-A from sensitized guinea pig lung samples and that of histamine from rat peritoneal mast cells. Terfenadine dose-dependently increased the cAMP content in rat mast cells and in the lungs; in the latter, the augmented cAMP is associated with an increase in adenylate cyclase activity, but not with the inhibition of phosphodiesterase activity. The above evidence indicates that the inhibitory effects of terfenadine on mediator release from mast cells are in some way related to its antiallergic effects, and that an elevated cAMP content may be effective to enhance mediator release inhibition.