PubMed Health⌕ Search

Biomedical subjects

M Samejima

Publications and source records attributed to M Samejima.

At least 55 records · Page 3Linked to original sources
PubMed1988

Bioavailability and pharmacokinetics of oral dopamine in dogs.

The bioavailability and pharmacokinetics of oral dopamine (DA) were studied in dogs. Plasma concentrations of DA and its main metabolites, such as dopamine-3-O-sulfate (DA-SO4) and 3,4-dihydroxyphenyl acetic acid (DOPAC) were determined after intravenous or oral administration of DA using high-performance liquid chromatography with electrochemical detector (HPLC-ECD). Following the intravenous administration, plasma DA-SO4 and DOPAC concentrations were lower than the plasma DA concentration. On the other hand, following the oral administration, plasma DA-SO4 and DOPAC concentrations were much higher than the plasma DA concentration. The absolute bioavailability of DA after oral administration was calculated to be approximately 3%. Intraduodenal and mesenteric venous administration of DA revealed that DA-SO4 was mainly produced in the intestine and DOPAC was produced in the intestine and liver. On the basis of these observations, the bioavailability and pharmacokinetics of oral DA are discussed in connection with the metabolic inactivation due to first-pass metabolism.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1988

External sodium ions are required for the light response in pineal photoreceptors.

Photoreceptor cells of the pineal organ of river lamprey, Lampetra japonica, showed hyperpolarizing light responses associated with a decrease in membrane resistance. Effects of external ion concentrations (Na+, K+, Li+, Cl-) on the light response and the resting membrane potentials were investigated. The average resting membrane potential in the standard solution was -29.7 +/- 7.3 mV (mean +/- SD, n = 125) and the amplitude of the response to white light (1 sec, 1.4 X 10(-8) W/cm2) was -20.4 +/- 6.3 mV (n = 125). The amplitude depended largely on external Na+ concentration. The change was 18 mV/10-fold increase of Na+ concentration, and the external Na+ was essential for generation of the response.

Animals↗
PubMed1988

Photosynthetic characteristics of an amphibious plant, Eleocharis vivipara: Expression of C(4) and C(3) modes in contrasting environments.

Eleocharis vivipara Link, a freshwater amphibious leafless plant belonging to the Cyperaceae can grow in both terrestrial and submersed aquatic conditions. Two forms of E. vivipara obtained from these contrasting environments were examined for the characteristics associated with C(4) and C(3) photosynthesis. In the terrestrial form (delta (13)C values = -13.5 to -15.4 per thousand, where per thousand is parts per thousand), the culms, which are photosynthetic organs, possess a Kranz-type anatomy typical of C(4) plants, and well-developed bundle-sheath cells contain numerous large chloroplasts. In the submersed form (delta (13)C value = -25.9 per thousand), the culms possess anatomical features characteristic of submersed aquatic plants, and the reduced bundle-sheath cells contain only a few small chloroplasts. (14)C pulse-(12)C chase experiments showed that the terrestrial form and the submersed form fix carbon by way of the C(4) pathway, with aspartate (40%) and malate (35%) as the main primary products, and by way of the C(3) pathway, with 3-phosphoglyceric acid (53%) and sugar phosphates (14%) as the main primary products, respectively. The terrestrial form showed photosynthetic enzyme activities typical of the NAD-malic enzyme-C(4) subtype, whereas the submersed form showed decreased activities of key C(4) enzymes and an increased ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) activity. These data suggest that this species can differentiate into the C(4) mode under terrestrial conditions and into the C(3) mode under submersed conditions.

Journal Article↗
PubMed1987

Pharmacokinetic analysis of concentration data of drugs with irregular absorption profiles using multi-fraction absorption models.

Nonlinear regression analysis of plasma drug concentration data with irregular or stepwise absorption profiles was studied using multi-fraction absorption models in which drugs in the gastrointestinal tract were assumed to be divided into several fractions each with its respective lag time and absorption rate constant. Plasma allopurinol concentration data, with two-phase absorption profiles in dogs after oral administration, were found to be satisfactorily fitted using a two-fraction absorption model. Plasma sulfisoxazole concentration data in humans were also successfully analyzed using a two-fraction absorption model. Plasma and urinary concentrations of pindolol in humans after oral administration of sustained-release preparations were fitted to two- or three-fraction absorption models. The pharmacokinetic absorption behavior of a sustained-release preparation of diltiazem hydrochloride was studied using a multi-fraction absorption model. Pharmacokinetic parameters derived from these models and those from the discontinuous absorption model were compared.

Allopurinol↗
PubMed1984

Intracellular dynamic response characteristics of pineal photoreceptors.

The dynamic properties of single pineal photoreceptors of Lampetra japonica were measured intracellularly by sinusoidal modulated light stimuli. According to the Bode plots the response amplitude and phase characteristic of pineal photoreceptors could be simulated by a linear model with 4th-order transfer function. A similarity to the receptor response of the vertebrate lateral eye was observed.

Animals↗
PubMed1982

Simultaneous bilateral renal artery reconstruction and intraoperative renal protection. A case report.

A 22-year-old Japanese man with bilateral renal artery stenosis associated with hypertension underwent successful surgery of simultaneous bilateral renal artery reconstruction under conditions of intraoperative renal perfusion with St. Thomas Hospital solution which is used for cardioplegia in open heart surgery. Circulation in the left kidney was interrupted for 58 minutes and that of the right kidney for 35 minutes. The patient fully recovered with no serious impairment of renal function. In addition to these stenotic lesions of the renal artery, there were medial necrosis of the aorta and fibromuscular dysplasia of the superior mesenteric artery. Administration of SQ14,225, an angiotensin I converting enzyme inhibitor, was effective in controlling hypertension during the preoperative period.

Adult↗