Teruhisa Umeda

Isolated rat hepatocytes as a model to study drug metabolism: dose-dependent metabolism of diphenylhydantoin.

Abstract The metabolism of diphenylhydantoin (DPH) was studied using isolated rat hepatocytes. The V max of DPH metabolism when calculated from the disappearance of DPH in the medium was 0.39 to 0.48 μmole/g cell/hr which is comparable to that in microsomal preparations. Disappearance rate of DPH was concentration-dependent but not of a simple Michaelis-Menten type. The formation of a DPH metabolite (glucuronide of hydroxylated DPH, HPPH-G) has an apparent V max of 0.29 to 0.32 μmole/g cell/hr. DPH binds extensively to hepatocytes and its distribution between the hepatocytes and the suspension medium was independent of DPH concentration.

Renal sodium handling and sodium transport inhibitor in salt-sensitive essential hypertension.

To investigate the mechanism whereby blood pressure rises with NaCl loading in salt-sensitive essential hypertension, salt-sensitivity index was determined along with sodium and lithium clearances, plasma Na+, K+-ATPase inhibitor and intra-erythrocyte sodium and potassium concentrations. Salt-sensitivity index was defined as the percentage of change in mean blood pressure when NaCl intake was changed from low (34 mmol/day) to high (342 mmol/day). Salt-sensitivity index was inversely correlated with fractional excretion of lithium both on the low and high NaCl diets (r = −0.721, P < 0.01 and r = −0.591, P < 0.02, respectively; n = 16), but not with fractional excretion of sodium. The change of plasma Na+, K+-ATPase inhibition with NaCl loading had a direct correlation with salt-sensitivity index (r = 0.704, P < 0.01; n = 16). Either intra-erythrocyte sodium and potassium concentrations or the ratio of these two values did not change significantly with an increase of dietary NaCl intake. These results suggest that an enhancement of proximal tubular sodium reabsorption stimulates secretion of plasma Na+, K+-ATPase inhibitor which may be involved in a rise in blood pressure with sodium loading. They also suggest that lithium clearance is a determinant which can predict salt sensitivity without actual NaCl loading.

Uptake and metabolism of diphenylhydantoin in the isolated perfused rat liver

Abstract The elimination of diphenylhydantoin (DPH) was studied in isolated perfused rat livers and the dose-dependent kinetics was confirmed. Kinetic analysis using a saturable two-compartmental analogue indicated that, with increasing doses, the V max remained constant but the elimination halflife (2.8–13 min) for the metabolic component and with it the Michaelis constant (2.9–37 μg/ml) increased progressively. Thus. at first sight, the data appeared to be consistent with the hypothesis of product inhibition. However, the rapid elimination of the metabolic product as well as quantitative results of computer simulations render inhibition unlikely as an explanation for the observed features of DPH elimination. The subcellular distribution of DPH and its metabolites in the liver indicated that DPH and its hydroxylated metabolite were localized mainly in the 600 g and microsomal fractions; the glucuronide was mainly in the cytosol. The results were compatible with the possibility of capacity-limiting DPH access to the drug-oxidizing enzyme system.

A sensitive radioimmunoassay of α human atrial natriuretic polypeptide using monoclonal antibody recognizing human form ring structure

A monoclonal antibody (C351) against alpha human atrial natriuretic polypeptide (alpha hANP) recognizing human form ring structure was established and applied to a radioimmunoassay of plasma alpha hANP. The minimum detectable amount in terms of 10% radioligand displacement relative to zero dose were 0.28 fmol/tube, corresponding to 0.7 fmol/ml in plasma after extraction using Sep-Pak C18 cartridges. When the mean plasma levels at recumbent position in fasted morning were compared in 10 young (less than 30 years) and 10 elderly (greater than or equal to 50 years) healthy subjects taking normal sodium diet, it was slightly higher in the latter (3.2 +/- 0.4 vs 4.7 +/- 0.5 fmol/ml, mean +/- SE, p less than 0.05). After i.v. infusion of hypertonic saline (2.5% NaCl) at a rate of 0.24 ml/kg/min for 20 min in 6 normal subjects (26 to 35 years), it was increased from 4.1 +/- 0.4 to 5.9 +/- 0.7 fmol/ml (p less than 0.01). In 6 patients with essential hypertension (34 to 57 years), it was elevated with high salt intake, i.e. 3.3 +/- 0.3, 3.9 +/- 1.03 and 7.6 +/- 1.5 fmol/ml under 34, 170 and 340 mEq NaCl/day for 7 days, respectively. From these results, the radioimmunoassay of plasma IR-alpha hANP using MAb C351 seems to be quite suitable to detect rather small changes at low plasma concentrations and to investigate a physiological importance of alpha hANP in man.

An aged SLE patient with rapidly progressing renal failure.

全身性エリテマトーデス (SLE) は, 20歳代をピークとし, 女性に多くみられる疾患である. 今回我々は, ネフローゼ症候群から比較的急速な経過をたどり腎不全となり, 薬物療法と, DFPPにより透析を離脱させ得た高齢者SLEの1症例を経験した. 高齢発症SLEは若年発症SLEと比べ特殊な病型を呈し早期診断が困難な例が多い. 本症例では, 関節炎, 漿膜炎に加え, 激しい腎障害を呈し高齢者SLEには珍しいことと考えられた. また血清学的検査では, 補体の著しい低下は認めなかったが, 血中免疫複合体値と腎障害度が相関すると考えられた. DFPPは免疫複合体量の多いSLE患者ならびに, 免疫抑制剤の副作用の出易い高齢患者では, 試みるべき治療法の一つとして考慮すべきと考える.