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Biomedical subjects

M Nagano

Publications and source records attributed to M Nagano.

At least 235 records · Page 13Linked to original sources
PubMed1990

Regulatory mechanisms of erythropoietin levels in dialysis patients.

We described a radioimmunoassay system for measuring blood erythropoietin (Epo) levels using recombinant human Epo and evaluated the regulatory mechanisms of Epo in dialysis patients. A satisfactory dose-response relationship for Epo levels was observed within the wide range of 3-250 mU/ml with a sensitivity of approximately 5 mU/ml. The Epo levels were found to be 16.1 +/- 8.6 mU/ml (m +/- SD) in 422 uremic patients on maintenance dialysis and 17.1 +/- 7.2 mU/ml in 86 normal subjects. The Epo levels were not statistically different between the two groups, although the hematocrit was significantly lower in the dialysis patients. No correlation was observed between the Epo levels and hematocrit in the dialysis patients. Patients with polycystic kidneys had higher hematocrits and Epo levels than patients with chronic nephritis. No changes in Epo levels were observed with age and with the period of dialysis. Diurnal variations in the Epo levels revealed a significant increase after hemodialysis, and an acute reduction in hematocrit following massive hemorrhage raised the Epo levels up to 3,180 mU/ml. These findings indicate that the Epo levels in dialysis patients are inappropriately low for the severity of anemia and suggest that a negative feedback mechanism of the hematocrit on the Epo secretion may exist in uremic patients as well as in normal subjects and that the threshold for Epo secretion might be 'reset' at a low hematocrit level.

Erythropoietin↗
PubMed1989

Endothelin inhibits presynaptic adrenergic neurotransmission in rat mesenteric artery.

The effect of endothelin(ET) on adrenergic neurotransmission was examined in isolated perfused rat mesenteric arteries. Porcine ET(10(-12) to 10(-10)M) attenuated the pressor response to sympathetic nerve stimulation (NS). It also stimulated the release of prostaglandin E2 (PGE2), but its inhibition of the pressor response to NS was not affected by indomethacin treatment. ET also caused dose-dependent inhibition of [3H]norepinephrine release during NS. Higher doses of ET rather enhanced the pressor response to NS. These results suggest that ET inhibits presynaptic adrenergic neurotransmission without mediation of PGE2, while it potentiates the responsiveness of the postsynaptic alpha-adrenergic receptor. Thus ET appears to act directly on the neuroeffector junction as well as on the peripheral vasculature.

Adrenergic Fibers↗
PubMed1989

Endothelin stimulates the release of prostacyclin from rat mesenteric arteries.

The effect of endothelin on the release of prostacyclin was examined in perfused rat mesenteric arteries with or without their pretreatment with indomethacin. Porcine endothelin at 10 pmol (a subpressor dose) and 40 pmol stimulated the release of 6-keto-PGF1 alpha, a stable metabolite of prostacyclin. Rat endothelin also stimulated its release, but less than porcine endothelin. Pretreatment with indomethacin completely inhibited this 6-keto-PGF1 alpha release. These results indicate that endothelin stimulates the release of prostacyclin from mesenteric arteries. This release may modulate the action of endothelin locally.

Animals↗
PubMed1989

Endothelin enhances adrenergic vasoconstriction in perfused rat mesenteric arteries.

The interaction of endothelin with alpha-adrenergic receptors was examined in isolated perfused rat mesenteric arteries. Infusion of porcine or rat endothelin increased the baseline perfusion pressure dose-dependently. Subpressor doses of both porcine (10(-11) and 10(-10)M) and rat (10(-10) and 10(-9)M) endothelin enhanced the pressor responses to norepinephrine. Nicardipine (10(-7)M), a calcium channel blocker, attenuated this potentiation. These results suggest that endothelin enhances the responsiveness of alpha-adrenergic receptors to catecholamines probably through the increase in calcium influx. Thus endothelin may interact with sympathetic nerve activity in addition to having a direct vasoconstrictor action in peripheral vascular tissue.

Animals↗
PubMed1989

Increase in the blood pressure and decrease in the norepinephrine release in the ventrolateral medulla during intraventricular administration of hypertonic NaCl.

Norepinephrine (NE) release in the ventrolateral medulla (VLM) was serially measured in anesthetized male Wistar rats during the rise in the blood pressure (BP) produced by acute intraventricular (ICV) administration of hypertonic (1.5 M) NaCl. Catecholamine release was determined by a brain microdialysis method using high performance liquid chromatography and electrochemical detector. The release of NE in the VLM was significantly decreased after ICV 1.5 M NaCl. In another set of rats, the pressor response to acute ICV 1.5 M NaCl was attenuated by selective administration of NE to the VLM using the microdialysis method. Chronic and continuous ICV infusion of 1.5 M NaCl to conscious rats caused an increase in BP on day 10 which was associated with a decrease in NE release in the VLM; concomitant ICV infusion of NE or of a synthetic NE precursor, L-threo-3,4-dihydroxyphenylserine (L-DOPS) prevented the rise in BP as well as the reduction in NE release. These results suggest that a decrease in the NE release of the VLM may contribute to the change in BP induced by ICV infusion of hypertonic saline.

Animals↗
PubMed1989

Effects of gammalinolenic acid on plasma lipoproteins and apolipoproteins.

Nineteen hypercholesterolemic patients (10 without and 9 with hypertriglyceridemia) were given evening primrose oil rich in gammalinolenic acid (GLA, 18: 3n - 6), in a placebo controlled cross-over design, over 16 weeks (8 + 8 weeks), with safflower oil as the placebo. During supplementation with evening primrose oil, dihomogammalinolenic acid (20: 3n - 6) increased in plasma lipids and red blood cells, and in subjects without hypertriglyceridemia there was a significant decrease in low density lipoprotein-cholesterol and plasma apolipoprotein B compared with the levels observed during safflower oil administration. Our results confirmed that evening primrose oil is effective in lowering low density lipoprotein in hypercholesterolemic patients.

Adult↗
PubMed1989

Actions of endothelin on adrenergic neuroeffector junction.

The effect of endothelin, a novel vasoconstrictor peptide, on the adrenergic neuroeffector junction was investigated in isolated perfused rat mesenteric arteries. The vasoconstrictor responses to periarterial nerve stimulation and exogenous noradrenaline were determined. Infusion of endothelin-1 (10(-14) to 10(-8) mol/l) increased the baseline perfusion pressure dose dependently. Subpressor doses of endothelin-1 (10(-11) and 10(-10) mol/l) enhanced the pressor response to noradrenaline, and 10(-12) to 10(-10) mol/l endothelin-1 attenuated the pressor response to periarterial nerve stimulation. Endothelin-1 also caused a dose-dependent inhibition of [3H]-noradrenaline release during the periarterial nerve stimulation. However, higher doses of endothelin-1 (3 x 10(-10) to 10(-8) mol/l) enhanced the pressor response to stimulation. These results suggest that endothelin potentiates adrenergic vasoconstriction postjunctionally while it inhibits adrenergic neurotransmission. Thus endothelin may have actions on the neuroeffector junction in addition to its direct vasoconstricting effect.

Animals↗
PubMed1989

[Effect of sevoflurane on respiratory impedance measured by the forced oscillation method with random noise input].

This study was performed to investigate the effect of sevoflurane, a new inhalation anesthetic, on the respiratory impedance measured by forced oscillation method with random noise input. Random noise (1 to approximately 25Hz) oscillated by a loudspeaker was imposed on the respiratory system of dogs through a tracheostomy and the oscillatory pressure wave and flow wave were monitored at the same point with a pressure transducer and a pneumotachograph. This procedure was repeated during inhalation of 100%-oxygen, 2.0%-then 4.0%-sevoflurane-oxygen mixture, respectively. Impedance was calculated with fast Fourier transform by spectrum analyzer and a personal computer. During inhalation of 4.0%-sevoflurane-oxygen mixture, respiratory impedance especially respiratory resistance decreased at the high frequency area (6to approximately 20Hz), but 2.0%-sevoflurane-oxygen mixture did not cause a significant change of respiratory impedance. This study suggests that inhalation of an anesthetic concentration of sevoflurane produces weak bronchodilation compared with halothane or enflurane.

Anesthetics↗
PubMed1989

[Partitioning and measurement of respiratory impedance into central and peripheral airways with catheter tip type transducer].

In this study, we have examined the availability of catheter tip type transducer for the partitioning of respiratory impedance. Total respiratory resistance and reactance from 1 to 20 Hz determined by forced oscillation method with random noise input in anesthetized dogs were partitioned by catheter tip type transducer into central airway resistance (Rc) and reactance (Xc) as well as peripheral resistance (Rp) and reactance (Xp). Intratracheal acetylcholine (0.1g) increased Rp at the wide frequency range (from about 1 to 20 Hz), although Rc did not change with it. The decreases of Rc at higher frequencies (over 12Hz) were produced by intratracheal salbutamol (10mg), whereas Rp did not change significantly. These results suggest that the predominant site of action of intratracheal acetylcholine and salbutamol is peripheral airway and central airway respectively. We have concluded that the respiratory impedance can be partitioned noninvasively with catheter tip type transducer without pneumothorax and hemorrhage caused with the retrograde catheter. This method can be applied clinically during general anesthesia or in intensive care.

Acetylcholine↗