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Biomedical subjects

S Sakurai

Publications and source records attributed to S Sakurai.

At least 289 records · Page 16Linked to original sources
PubMed1983

Inhibition by alpha 2-adrenoceptor agonists of the secretion of catecholamines from isolated adrenal medullary cells.

In adrenal medullary cells, carbachol evokes the secretion of catecholamines with simultaneous uptake of 45Ca. Highly selective agonists for alpha 2-adrenoceptors, clonidine, naphazoline, guanfacine, tramazoline and oxymetazoline inhibited carbachol evoked secretion of catecholamines in a dose-dependent manner. These alpha 2-agonists also inhibited the uptake of 45Ca evoked by carbachol with similar dose-response curve to inhibition of catecholamine secretion. On the contrary, highly selective agonists for alpha 1-adrenoceptors, phenylephrine and norfenefrine did not inhibit the secretion of catecholamines and cellular uptake of 45Ca. The inhibition by alpha 2-agonists was not restored either by the increase in carbachol or Ca concentrations, suggesting that the mode of inhibition was distinct from competition at cholinergic receptors or Ca-channels. It is likely that alpha 2-agonists inhibited the secretion of catecholamines via the inhibition of Ca uptake which was probably caused through the activation of alpha 2-adrenoceptors.

Adrenal Medulla↗
PubMed1983

Trifluoperazine inhibits 45Ca2+ uptake and catecholamine secretion and synthesis in adrenal medullary cells.

In isolated adrenal medullary cells, carbamylcholine and high K+ cause the calcium-dependent secretion of catecholamines with a simultaneous increase in the synthesis of 14C-catecholamines from [14C]tyrosine. In these cells, trifluoperazine, a selective antagonist of calmodulin, inhibited both the secretion and synthesis of catecholamines. The stimulatory effect of carbamylcholine was inhibited to a greater extent than that of high K+. The inhibitory effect of trifluoperazine on carbamylcholine-evoked secretion of catecholamines was not overcome by an increase in either carbamylcholine or calcium concentration, showing that inhibition by trifluoperazine occurs by a mechanism distinct from competitive antagonism at the cholinergic receptor and from direct inactivation of calcium channels. Doses of trifluoperazine that inhibited catecholamine secretion and synthesis also inhibited the uptake of radioactive calcium by the cells. These results suggest that trifluoperazine inhibits the secretion and synthesis of catecholamines mainly due to its inhibition of calcium uptake. Trifluoperazine seems to inhibit calcium uptake by uncoupling the linkage between calcium uptake by uncoupling the linkage between cholinergic receptor stimulation and calcium channel activation.

Adrenal Medulla↗
PubMed1983

A regurgitant jet and echocardiographic abnormalities in aortic regurgitation: an experimental study.

Acute aortic regurgitation was created experimentally in 21 mongrel dogs to examine the relationship of the regurgitant jet to observed echocardiographic findings. The direction of the regurgitant jet was studied by echo contrast injections in the aortic root. Diastolic fluttering of the anterior mitral leaflet (AML) was noted in all 21 dogs irrespective of direction of the jet. Diastolic fluttering of the interventricular septum (IVS) was noted in six of the seven dogs with a tear of the noncoronary cusp and in one of seven dogs with lesions in the left coronary cusp. In all seven dogs with echocardiographically demonstrated IVS fluttering, a regurgitant jet impinged on the anterior part of the IVS. Amplitude of the AML excursion was not significantly different from control when the lesions involved the noncoronary or the left coronary cusps. However, all seven dogs that had a lesion in the right coronary cusp demonstrated a significant reduction in the amplitude of the AML excursion. The regurgitant jet in these dogs impinged uniformly on the AML. We conclude that diastolic fluttering of the AML is uniformly observed and unrelated to the direction of the regurgitant jet, diastolic fluttering of the IVS is caused by the regurgitant jet impinging upon the IVS, and amplitude of the AML may be reduced as a result of a jet impingement of the AML.

Animals↗
PubMed1983

Reduction of maximum heart rate in acute, severe hypoxia.

By determining a ceiling for heart rate increase in a given exercise with increment of simulated altitude up to 7,000 m, a reduction of maximum heart rate (HR max) in acute hypoxia was experimentally ascertained. Such a reduction was similarly observed immediately after a high-altitude expedition. In addition, the reduction rate against altitude was close to that shown previously in chronic hypoxia, indicating that the reduction of HR max might be independent of altitude acclimatization.

Acute Disease↗
PubMed1982

alpha 2-Adrenergic receptors inhibit catecholamine secretion from bovine adrenal medulla.

Catecholamine secretion evoked by carbamylcholine from isolated bovine adrenal medullary cells was inhibited by alpha 2-agonist, clonidine, in a dose-dependent manner with IC50 value of 2.8 X 10(-5) M. [3H]Clonidine bound to adrenal medullary membranes with high affinity and saturable characteristics. These results suggest that alpha 2-adrenergic receptors which exist on adrenal medullary cells have inhibitory effect on the secretion of catecholamine from the cells.

Adrenal Medulla↗
PubMed1981

Laryngeal carcinoid tumor: light and electron microscopic studies.

A case of laryngeal carcinoid in a Japanese 76-year-old man is reported. This neoplasm is extremely rare in the larynx and the case is the fourth so far reported in the world medical literature. Light and electron microscopic studies revealed argyrophilia and the presence of neurosecretory granules that had not been demonstrated in the previous cases. A review of the medical literature showed that all laryngeal carcinoids were pathologically malignant. The relationship of carcinoid tumor to oat cell carcinoma of the larynx is discussed, and the suggestion is made that a similar relationship exists between them as between carcinoid tumors and oat cell carcinomas of the lung.

Aged↗
PubMed1981

Hemodynamic determinants of pulmonary valve motion during systole in experimental pulmonary hypertension.

To clarify the determinants of pulmonary valve (PV) motion in pulmonary hypertension, we examined the correlations among PV echo patterns, the pulmonary artery (PA) flow curve just above the PA orifice and the pulmonary artery-right ventricle (PA-RV) pressure gradient. By constricting the PA, we could produce a variety of PV echo patterns, including midsystolic semiclosure in open-chest dogs. Throughout the experiments, the PV echo pattern and PA flow curve were similar in pattern and timing. When the PV echo showed midsystolic semiclosure with reopening. The PA flow curve showed a transient decrease followed by a transient increase during midsystole. The PA-RV pressure gradient became transiently positive (PA pressure greater than RV pressure) and then negative in midsystole only when the PV echo showed midsystolic semiclosure with reopening. In conclusion, PV motion during systole may be instantaneously determined by PA flow change and the PA-RV pressure gradient during the cardiac cycle in experimental pulmonary hypertension.

Animals↗