Search PubMed⌕ Search

Biomedical subjects

K Iwatsuki

Publications and source records attributed to K Iwatsuki.

At least 271 records · Page 15Linked to original sources
PubMed1975

Effect of apomorphine on the canine SA node.

A constant pressure perfusion of the sinus node artery was performed in 10 in situ and in 3 isolated SA node preparations. The selective administration of apomorphine caused a negative chronotropic effect which was not blocked by treatment with atropine. The sinus deceleration was usually produced by apomorphine, 10-300 mug, while sinus irregularity and finally atrioventricular nodal rhythm in the in situ preparation or sinus arrest in the isolated one resulted from doses above 1 mg. In the in situ preparation at a higher dose from 300 mug to 1 mg, a slight sinus acceleration was occasionally induced following sinus deceleration; In this time, a fall in blood pressure was usually observed; This acceleration response to apomorphine was inhibited by propranolol. From these results, it is concluded that apomorphine induces direct depressive action on the SA node and, in extremely high doses, a slight sinus acceleration may be induced by reflex mechanism.

Animals↗
PubMed1975

Effects of change in frequency of stimulation on myocardial depression produced by thiamylal and halothane.

The effects of change in the frequency of stimulation on the myocardial contractility depressed by thiamylal and halothane were studied in isolated dog heart muscle. An increase in the frequency of stimulation from 0.1 to 0.6 cps resulted in a progressive in increase in net-shortening (delta1) and maximum velocity of shortening at 0.4 g preload (V'max), namely a positive staircase. The myocardium previously depressed to a similar degree by thiamylal or halothane still showed a positive staircase. This result indicates that the mechanism to produce the myocardial depression by thiamylal or halothane is not a complete inhibition of Ca++ influx across the cell membrane. The time to reach a steady state of contraction following an increase in the frequency of stimulation was longer in the presence than in the absence of these anesthetics. The degree of recovery from the myocardial depression by increasing the frequency of stimulation was much higher in the presence of thiamylal than in the presence of halothane. This fact suggests that the mechanism to produce the myocardial depression may be different in there two anesthetics.

Animals↗
PubMed1975

Effect of morphine on PHA-stimulated human lymphocyte transformation.

The effect of morphine on lymphocyte blastoid transformation induced by PHA was studied in vitro by observing the uptake of 3H-thymidine into nucleic acid of the lymphocytes. Morphine at the estimated clinical blood concentrations did not inhibit lymphocyte blastoid transformation.

Humans↗
PubMed1975

Neuromuscular blocking properties of some antibiotics in man.

Neuromuscular blocking properties of ribostamycin (1 gm), dibecacin (100 mg) and tobramycin (60 mg) were studied in a man during anesthesia and surgery by observing the effects of these antibiotics on muscle twitch tension. These drugs alone did not show any neuromuscular blocking action in those therapeutic doses. However, during the recovery phase of d-tubocurarine block the intravenous administration of 1 gm of ribostamycin caused a fairly rapid decrease in twitch tension. Tobramycin 60 mg did not show any remarkable effect, but dibecacin 100 mg produced a slight potentiating effect on the action of d-tubocurarine. The enhancement of the action of d-tubocurarine was antagonized promptly by edrophonium and more slowly by calcium.

Anti-Bacterial Agents↗
PubMed1975

Direct effects of acryl bone cement monomer on isolated heart muscle.

Experiments were carried out in isolated dog heart muscle to determine the direct effect of acryl bone cement monomer on the myocardial contractility. The monomer caused a dose-dependent decrease in the maximum velocity of shortening (Vmax) and the maximum force development (Fm), consequently resulting in a leftward shift of the force-velocity relation curves. There was also a concomitant decrease in work, power, the maximum rate of force development (max dF/dt) and time to peak force (TPF) from the onset of force development. These results indicate that acryl bone cement monomer exerts a direct negative inotropic effect on the myocardium and that the myocardial depression due to free monomer absorbed from the mixed bone cement into the systemic circulation during operation seems to be one of the major causes of the cardiovascular complications associated with the clinical application of bone cement.

Animals↗
PubMed1974

Modification by drugs of the secretagogue effect of dopamine on the pancrease.

1 The specific stimulating action of dopamine and L-DOPA on exocrine pancreatic secretion was further investigated in the isolated blood-perfused canine pancreas.2 6-Hydroxydopamine (100 mug, i.a.) stimulated the secretion but was far less potent than dopamine. Epinine (0.3-1 mg. i.a.), alpha-methyldopamine (10-300 mug, i.a.) and octopamine (10-300 mug, i.a.) were ineffective.3 alpha-Methyldopa (30 mg, i.a.) inhibited the stimulating effect of L-DOPA (1-3 mg) on pancreatic secretion.4 Apomorphine (1 mg, i.a.) attenuated dopamine-induced (1-30 mug) pancreatic secretion but did not antagonize secretin-induced (0.03-0.3 units) or pancreozymin-induced (0.3-1 units) secretion.5 These observations suggest that L-DOPA is probably converted to dopamine to stimulate the exocrine pancreas, and that dopamine interacts with the specific receptors.6 The noradrenaline and dopamine content of the canine pancreas was estimated in controls and in dogs treated with secretin, reserpine, L-DOPA or alpha-methyldopa. The values for dopamine and noradrenaline in controls were 139 +/- 6 and 375 +/- 40 ng/g tissue (n=13), respectively. Reserpine reduced the noradrenaline content of the pancreatic tissue without affecting the dopamine content. L-DOPA or secretin caused a significant increase in the dopamine, but not in the noradrenaline content. It is suggested that dopamine has a physiological function in the pancreas which is independent of that of the noradrenaline-containing nerve fibres.

Animals↗
PubMed1974

Effects of phentolamine on the SA node of the dog heart in situ.

Direct perfusion of the sinus node artery at constant pressure of 100 mmHg was arranged in 6 canine hearts in situ. The injection of phentolamine into the sinus node artery usually induced dose-dependent positive chronotropic effect. However, at a larger dose of 300 mug, phentolamine frequently induced a biphasic chronotropic response, i.e., sinus deceleration followed by sinus acceleration. Phentolamine at a large dose of 1 mg usually induced a negative chronotropic effect. The threshold dose for inducing sinus acceleration was about 1 to 10 mug. The positive chronotropic response to phentolamine was blocked either by propranolol or by tetrodoxin. That to norepinephrine was blocked by propranolol but not suppressed by tetrodotoxin. These results suggest that the phentolamine-induced sinus acceleration is due to catecholamine which is released by excitation of local adrenergic fibers. The sinus deceleration to higher doses of phentolamine was not blocked either by atropine or by tetrodotoxin. It suggests that phentolamine has a direct depressive effect on the SA node at extremely high dose levels.

Animals↗