Masayori Ozaki

Radioprotective effects of (-)-epigallocatechin 3-0-gallate (green-tea tannin) in mice

Long-term administration of (-)-epigallocatechin 3-O-gallate (EGCG) to mice through drinking water prevented radiation-induced increase of lipid peroxides in liver and significantly prolonged life span after lethal whole-body X-irradiation. The result indicates validity of this green-tea component as an orally active radio-protector of very low toxicity.

Atrial natriuretic peptide modulates amiloride-sensitive Na+ transport across the blood−brain barrier

Abstract: We obtained evidence that amiloride specifically potentiates 125I‐labeled α‐rat atrial natriuretic peptide (1‐28) [atrial natriuretic peptide (ANP)‐(99‐126); rANP] binding to cerebral capillaries isolated from the rat cerebral cortex. The binding parameters, KD of 173 pM and Bmax of 159 fmol/ mg of protein, became 33 pM and 88 fmol/mg of protein, respectively, when 10−4M amiloride was added to the incubation medium. When the effect of rANP was investigated on in vitro 22Na+ uptake into isolated cerebral capillaries, 10−7M rANP significantly inhibited the uptake in the presence of 1.0 mM ouabain, 1.0 mM furosemide, and 2.0 mM LiCI in the uptake buffer, a finding suggesting a specific inhibitory effect of rANP on amiloride‐sensitive Na+ transport. Thus, the possibility that ANPs control amiloride‐sensitive Na4+ transport at the blood‐brain barrier by interacting with specific receptors has to be considered

Atrial natriuretic polypeptides elevate the level of cyclic GMP in the rat choroid plexus

We studied the effect of synthetic rat alpha-atrial natriuretic polypeptide (1-28) (ANF-(99-126)) and related atrial natriuretic polypeptides on the accumulation of cyclic GMP (cGMP) in isolated rat choroid plexus in vitro, the objective being to determine whether ANF-(99-126) binding sites are physiologically active receptors. One microM of ANF-(99-126) increased the level of cGMP within 30 s and the accumulation reached the maximum level 5 min after adding of ANF-(99-126) to the incubation media. Significant increase in the level of cGMP depended on concentrations of the ANF-(99-126), ANF-(101-126) and ANF-(103-125), with a range of 10.0 nM to 10.0 microM. These data indicate that binding sites for ANF-(99-126) in the rat choroid plexus may be physiologically active receptors, possibly linked to the production of cerebrospinal fluid.

Receptor autoradiographic analysis of insulin-like growth factor-I (IGF-I) binding sites in rat forebrain and pituitary gland

Summary1.Specific125I-labeled insulin-like growth factor-I ([125I] IGF-I) binding sites in the rat forebrain and pituitary gland were investigated using quantitative receptor autoradiography.2.High densities of [125I]IGF-I binding sites were present in the olfactory nerve layer, olfactory glomerular layer, choroid plexus, CA3 and CA4 of the hippocampus, basolateral amygdaloid nucleus, and endopiriform nucleus. Moderate to high binding densities were found in the cerebral cortex (II, VI), bed nucleus stria terminalis, accumbens nucleus, lateral septum, median preoptic nucleus, supraoptic nucleus, paraventricular hypothalamic nucleus, and ventroposterior thalamic nucleus. In the circumventricular organs, subfornical organ, vascular organ of the lamina terminalis, and median eminence, the binding sites were numerous. High densities of [125I]IGF-I binding sites were also observed in the anterior pituitary gland.3.In kinetic experiments, [125I]IGF-I binding sites in the olfactory glomerular layer, choroid plexus, median eminence, and anterior pituitary gland were found to be single and of a high affinity.4.Noteworthy was the difference in the potency of insulin in inhibiting the binding among the areas examined, a finding which suggests heterogeneity of IGF-I receptors.5.The possibility that IGF-I plays the role of a neurotransmitter and/or neuromodulator in the central nervous system warrants further investigation.

α-Atrial natriuretic peptide binding sites in the rat choroid plexus are increased in the presence of hydrocephalus

Specific alpha-rat atrial natriuretic peptide(1-28) [ANF-(99-126)] (rANP) binding sites in the choroid plexus of rats with kaolin-induced hydrocephalus were analyzed following incubation of related tissue sections with 125I-rANP, then using autoradiography and an image analysis coupled with computer-assisted micro-densitometry. The number of 125I-rANP binding sites in the choroid plexus of these rats was significantly higher, as compared to findings in the control rats, whereas no differences in the binding affinity were observed, 3 days and 3 weeks after the intracisternal injection of kaolin. The possibility that atrial natriuretic peptide may play a significant role in the function of cerebrospinal fluid production by interacting with specific, high affinity receptors in the rat choroid plexus has to be considered.

Specific [125I]Bolton-Hunter substance P binding sites in human and rat skin

[125I]Bolton-Hunter substance P [( 125I]BH-SP) binding sites in rat and human skin were investigated, using quantitative receptor autoradiographic and emulsion autoradiographic methods. [125I]BH-SP binding sites were discretely localized in skin areas anatomically corresponding to dermal papillae, sweat glands, and hair follicles. The highest density of the binding sites was in the dermal papilla of the finger, followed by the sweat gland. [125I]BH-SP binding to the dermal papillae of the human finger pad skin and rat paw pad skin was displaced by unlabeled SP, with a high affinity, and Kd values were calculated to be 744 pM and 297 pM, respectively. The existence of [125I]BH-SP binding sites supports the idea of the neurotransmitter role of substance P in skin dermal papilla.

Receptor autoradiographic evidence of specific brain natriuretic peptide binding sites in the porcine subfornical organ

Specific binding sites of brain natriuretic peptide (BNP), a newly discovered peptide in the subfornical organ (SFO) of porcine brain were investigated, following incubation of related tissue sections with 125I-BNP, then using autoradiography and an image analysis coupled with computer-assisted microdensitometry. Specific 125I-BNP binding sites were found to be localized in the SFO, an area densely labeled by 125I-alpha-rat atrial natriuretic peptide and 125I-(Sar1,Ile8)-angiotensin II. Specific 125I-BNP binding to the SFO was displaced by unlabeled BNP, with a high affinity, and was calculated to be Ka = 0.385 x 10(-9) M and Bmax = 40.1 fmol/mg using a LIGAND computer program. Acquisition of these present findings enhances our knowledge of the physiology of BNP, atrial natriuretic peptides and angiotensin II system in the SFO.

β-Adrenoceptor blocking agents release catecholamines from rat adrenal medulla

Abstract When small doses of pindolol and propranolol (0.1 mg/kg and 5 mg/kg, respectively) were administered intraperitoneally to conscious normotensive Kyoto Wistar rats, acute hypotension occured. However, these hypotensive effects diminished when the doses were increased to 5 mg/kg and 20 mg/kg, respectively. Unilateral adrenalectomy had no effect on these hypotensive effects but they were suppressed by bilateral adrenalectomy. Subsequently, marked and lasting hypotensive effects (20–35 mm Hg) were observed. In urethane-anaesthetized rats, intravenous infusions of the blocking agents produced a rise in blood pressure and an increase in the content of epinephrine, norepinephrine and dopamine in adrenal venous blood. These hypertensive actions were not seen in adrenalectomized rats. When rats were given 6-hydroxydopamine (2 μg/μl) bilaterally at the C 4 level of the spinal cord 7 days before or 5,7-dihydroxytryptamine (2 μg/μl, after desmethylimipramine, 25 mg/kg i.p.), the catecholamine content of adrenal venous blood and the catecholamine releasing actions of these blocking agents decreased, but were not completely abolished. These results suggest that the lack of hypotensive effects with higher doses of β-adrenoceptor blocking agents may have been due partly to the direct release of catecholamines from the adrenal medulla and partly to central noradrenergic or serotonergic nerve action.

Specific 125I-endothelin-1 binding sites in the atrioventricular node of the porcine heart

The quantitative receptor autoradiographic method we used revealed that specific 125I-endothelin-1 binding sites are highly concentrated in the atrioventricular node of the porcine heart. 125I-Endothelin-1 binding to the atrioventricular node, interatrial and interventricular septa was displaced by unlabeled endothelin-1 with Kd values of 53 pM, 2.03 nM and 3.48 nM, respectively. Knowledge of the existence of specific 125I-endothelin-1 binding sites in the porcine heart helps with understanding the physiology of endothelin, a possible endogenous Ca2+ channel agonist.

Specific 125I-Endothelin-1 Binding Sites in the Central Nervous System

The quantitative receptor autoradiographic method we used revealed that specific 125I-endothelin-1 (125I-ET-1) binding sites are highly concentrated in the choroid plexus (ChP), subfornical organ (SFO), lacunosum molecular layer of the hippocampus (LMol) and granular layer of the cerebellum (GC) of the rat brain. High densities of the binding sites were also observed in the laminae I-III and intermediolateral nucleus of the porcine spinal cord. 125I-ET-1 bound to the rat ChP and LMol with a high-affinity and to the SFO and GC with a low-affinity. The possibility that ET-1 acts as a neuropeptide within the central nervous system by interacting with specific receptors would have to be considered.