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Biomedical subjects

K Mikami

Publications and source records attributed to K Mikami.

At least 163 records · Page 9Linked to original sources
PubMed1979

Internuclear control of DNA synthesis in exconjugant cells of Paramecium caudatum.

An exconjugant cell of Paramecium caudatum has two kinds of macronuclei, fragmented prezygotic macronuclei and postzygotic new macronuclei (anlagen). Although the DNA synthesis in the fragmented prezygotic macronucleus continues until the third cell cycle after conjugation, selective suppression of the DNA synthesis in the prezygotic macronucleus takes place at the fourth cell cycle. The inhibition of DNA synthesis in prezygotic fragmented macronuclei is due to the presence of a postzygotic macronucleus (anlage) in the same cytoplasm because the inhibition does not occur when the postzygotic macronucleus (anlage) is removed by micromanipulation during the third or fourth cell cycle. Well-developed postzygotic macronuclei (anlagen) with full ability to divide have the ability to depress the DNA synthesis of prezygotic macronuclear fragments. The suppression of DNA synthesis in prezygotic macronuclear fragments seems to be irreversible. Competition for the limited amount of DNA precursors also plays an important role in the onset of the selective suppression of the DNA synthesis.

Animals↗
PubMed1979

Stomatogenesis during sexual and asexual reproduction in an amicronucleate strain of Paramecium caudatum.

Amicronucleate cells of Paramecium caudatum, whose micronuclei have been artifically removed by micropipetting, are characterized by the appearance of a deciliated area at the posterior part of the buccal opening. These cells form food vacuoles at a slightly lower rate than micronucleate cells. Their mean interfission time is longer than that in micronucleates. The exconjugants of amicronucleate cells can not form food vacuoles and eventually die witout fission, though conjugation proceeds normally in them as well as in their micronucleate mate. The oral apparatus of amicronucleate exconjugants seems to be shallower than that of micronucleates. The membranellar cilia, therefore, can be seen through the buccal overture by scanning electron microscope. The results obtained from the cross of micronucleate and amicronucleate strains and from the induction of autogamy in amicronucleate strains suggest that the micronucleus has a primary role in developing the normal oral apparatus after nuclear reorganization.

Animals↗
PubMed1979

Induction of autogamy by treatment with trypsin in Paramecium caudatum.

Firmly united conjugant pairs of P. caudatum were easily separated by treatment with trypsin, 0.025--1.0 mg/ml in 2 mM phosphate buffer at pH 7.2. Cytological observations showed that pairs separated by this means undergo normal meiosis and subsequent prezygotic divisions. Microspectrophotometric comparisons of G1 micronuclei in the parent with those in clones derived from prematurely separated conjugants indicate usually the same DNA content in both. The stock dm -13, heterozygous for mating type gene loci, showed the definite ratio of segregation to 2 mating types in clones derived from prematurely separated conjugants. Those results suggest that the prematurely separated cells usually undergo autogamy.

Animals↗
PubMed1979

Comparative study of cyclic AMP-generation system, steroid biosynthesis and lipid metabolism in vitro in ACTH responsive and unresponsive adrenal tumors.

The responses of the cyclic AMP-generation system and corticosteroids biosynthesis to ACTH and angiotensin II and cholesterol and other lipid contents in adrenal tissues were estimated in the in vitro experiments in 3 cases of Cushing's syndrome due to ACTH-responsive and unresponsive adenomas, one case of Cushing's disease (diffuse hyperplasia), one case of primary aldosteronism and one normal subject. The responses of cAMP accumulation and corticosteroids production to ACTH in in vitro studies were quite in good agreement with the in vivo responses of plasma cortisol by ACTH infusion test. The adenylate cyclase activity decreased and the phosphodiesterase activity increased in the case of hyperplasia and in one case of ACTH-responsive adenoma, whereas the basal cyclic AMP content was slightly more in ACTH-responsive adenoma and maximal in hyperplasia compared with that of the normal adrenal tissue. The characteristic features observed in ACTH-unresponsive adenoma were the largest amount of the basal corticosteroids production and esterified cholesterol content, and the lowest content cAMP. These results indicate that there was not always the consistent correlation between the cAMP-generation system, corticosteroids and aldosterone production, and conversion of cholesterol to pregnenolone by the stimulation of ACTH and angiotensin II in adrenal tumors.

Adenoma↗
PubMed1978

Adrenal steroidogenesis and hepatic corticosteroid metabolism in hypertensive rats.

In vitro metabolism of progesterone and cholesterol by the adrenal glands and hepatic delta 4-reductase activity of SHR and ARH were investigated to clarify the possible hyperactivity of the pituitary-adrenal axis and abnormal steroid metabolism in SHR. The increased conversion rate of progesterone to 11 beta-hydroxyprogesterone, corticosterone and 18-hydroxy-deoxycorticosterone and the increased biosynthesis of pregnenolone from cholesterol were noted in ARH, which were similar to those seen with chronic ACTH administration. On the other hand, adrenal steroidogenesis in SHR showed no difference from that of control. Therefore the apparently normal adrenal steroidogenesis in SHR may suggest that the adrenal gland is not involved in the spontaneous hypertension of rats. The markedly decreased hepatic delta 4-reductase activity in ARH and SHR was observed in this investigation.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1978

Quantitative and qualitative estimation of urinary kallikrein in a patient with Bartter's syndrome.

Urinary kallikrein in a patient with Bartter's syndrome was remarkably higher than normal. Indomethacin treatments increased serum potassium concentration and urinary Na/K ratio, and improved the response of blood pressure to angiotensin II infusion, while it decreased plasma renin activity, plasma aldosterone and urinary kallikrein. The purified urinary kallikrein had one component of the iso-electric point 4.3 by isoelectric focusing using Ampholine system, and its molecular weight was 4.2 x 10(4), which was greater than those of three components of normal human urinary kallikreins (normal HUK). Also Km values with TAME and BAME of urinary kallikrein in our patient with Bartter's syndrome did not correspond to those of normal HUK. Thus it can be said that urinary kallikrein in our patient with Bartter's syndrome was qualitatively different from normal HUK. The present observation might be a reflection of renal tubular dysfunction in this patient with Bartter's syndrome.

Angiotensin II↗