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Biomedical subjects

S Ikegami

Publications and source records attributed to S Ikegami.

At least 145 records · Page 8Linked to original sources
PubMed1979

Novel epimerization of steroidal allylic alcohols.

Epimerization of 4-pregnene-3 beta,20 alpha-diol into 4-pregnene-3 alpha,20 alpha-diol was achieved under the mild condition of an acidic medium at room temperature. This reaction was favorable for synthesis of 4-pregnene-3 alpha,20 alpha-diol in better yield, after chemical reduction of 20 alpha-hydroxy-4-pregnen-3-one with metal hydrides, which resulted in predominant production of 4-pregnene-3 beta,20 alpha-diol. The by-product which was formed more by raising the temperature was identified as 3,5-pregnadien-20 alpha-ol. This method was also applicable for epimerization of other delta 4-3 beta-hydroxysteroids.

Chemical Phenomena↗
PubMed1979

The mode of inhibitory action by aphidicolin on eukaryotic DNA polymerase alpha.

The mode of action by aphidicolin on DNA polymerase alpha from the nuclear fraction of sea-urchin blastulae was studied. The inhibition of DNA polymerase alpha by aphidicolin was uncompetive with activated DNA and competitive with the four deoxynucleoside triphosphates using activated DNA as a template-primer. For truncated (residual or limited) DNA synthesis with only three deoxynucleoside triphosphates, aphidicolin inhibited the residual synthesis more strongly in the absence of dCTP than in the absence of each of the other three deoxynucleoside triphosphates. The inhibition was reversed with excess dCTP but not with the other three deoxynucleoside triphosphates. That is, aphidicolin inhibited DNA polymerase alpha by competing with dCTP with a Ki value of 0.5 microgram/ml and by not competing with the other three deoxynucleoside triphosphates. dTMP incorporation with the activated DNA was more sensitive to aphidicolin than dGMP or dTMP incorporation with poly(dC). (dG)12-18 or poly(dA) . (dT)12-18. Similar results were obtained for DNA polymerase alpha (B form) from mouse myeloma MOPC 104E.

Animals↗
PubMed1978

Vasodilation produced by prostacyclin (PGI2) and 9(O)-thiaprostacyclin (PGI2-S) in the canine femoral circulation.

The action of 9(0)-thiaprostacyclin (PGI2-S) was compared with that of prostacyclin (PGI2) and papaverine in the femoral circulation of dogs. PGI2-S, injected into the dog femoral artery in a dose of 0.1 microgram or higher, produced marked vasodilation in the femoral artery without any change in blood pressure. The potentcy of PGI2-S was one tenth that of PGI2, and was a hundred times that of papaverine. The stability of PGI2-S in neutral solution was forty times that of PGI2.

Animals↗
PubMed1977

Operant discriminative conditioning of vertical eye movements in the midpontine pretrigeminal cat.

In the acute midpontine pretrigeminal cat, either upward or downward eye movements above a certain preset amplitude were reinforced by electrical stimulation of the lateral hypothalamic (LHT) reward area, which did not induce a significant eye movement by itself. During the course of the reinforcement procedure, eye movements greatly increased. In a yoked control test where LHT stimulation was delivered to a cat, independently of its own eye movements, no significant enhancement of the eye movements was observed. However, when reinforcement was given contingently on each large eye movement, eye movement rate became much higher. When cats were trained for an operant discrimination between an S+ (light-off or light-on) and an S- (light-on or light-off), 5 cats acquired clearly differential responses to the S + and S-. They also learned a discrimination reversal. Furthermore, removal of the visual cue eliminated differential responses during the reinforcement and nonreinforcement periods. These data strongly suggest that, in its preparation, a real learning process in the form of a visual discrimination is maintained and an operant conditioning of eye movements with hypothalamic stimulation was achieved without feedback from the peripheral nerve or caudal central nervous system.

Animals↗
PubMed1975

Effect of dietary protein on proteolytic activities in the pancreatic tissue and contents of the small intestine in rats.

The time-courses of proteolytic activities in pancreatic tissue and the contents of the small intestine (the intestinal contents) were determined in rats maintained on a diet containing 30% of various proteins after a switchover from a diet containing 12% casein. 1. The proteolytic activity of the pancreatic tissue quickly responded to change of dietary proteins--within 1 to 6 days--with respect to organ weight, nitrogen content and proteolytic activity, in rats receiving diets containing 30% casein, ovalbumin, lactalbumin, gluten, gelatin or zein. 2. However, the proteolytic activity in the intestinal contents did not necessarily coincide with the pancreatic digestive function; an approximately threefold increase of enzyme activity was demonstrated on the fifth day of feeding in rats receiving gluten. 3. The proteolytic activity in the intestinal contents returned to the initial level on the eighth day in the gluten-fed rats, but those rats maintained on a lysine-supplemented gluten diet exhibited no such elevation of proteolytic activity. 4. No significant difference in pancreatic composition was shown up to the eighth day between the group receiving gluten alone in diet and that receiving the same diet but supplemented with lysine, under the condition of equally restricted food intake. Intestinal trypsin and chymotrypsin levels, however, were higher in the gluten-fed rats, suggesting that the depressed rate of enzyme inactivation in the small intestine might be the principal cause of the finding described under (2) above.

Animals↗