Biochemical medicine最新文献

Effect of depot medroxyprogesterone acetate on the hepatic drug-metabolizing enzymes was studied in female protein-deficient and normal pair-fed rats. Treatment with this drug did not cause any change in organ weight, microsomal protein, and soluble protein yield per gram of tissue in both groups. MPA administration resulted in significant increases in the content of cytochrome P-450 and b₅, and activities of benzo[a]pyrene hydroxylase, UDP-glucuronosyltransferase, and NADPH-Cyt c reductase in both pair-fed control and protein-deficient rats. However, the content of glutathione and activity of glutathione-S-transferase were not affected appreciably. The present study suggests that MPA treatment induces drug-metabolizing enzymes in liver to almost the same extent in both protein-deficient and normal pair-fed rats.

Seventy-one pyrimidine analogs have been tested as possible inhibitors of human spleen mitochondrial dihydroorotate dehydrogenase. Of these nine were demonstrated to be effective inhibitors of the enzymic activity. Two compounds, dihydro-5-azaorotate and 6-thiobarbiturate appeared to be specific inhibitors of the DHO-DHase. In addition, three compounds, 5-azaorotate, 5-bromoorotate, and barbiturate were also inhibitory against the two subsequent enzymes of the pathway, orotate phosphoribosyltransferase and orotidylate decarboxylase, so that they could act against three enzymes of the mammalian pyrimidine de novo biosynthetic pathway.

Submitochondrial particles prepared from liver and skeletal muscle of control and iron-deficient rats were examined for cytochrome content and for both energy-independent and energy-conserving functions. Liver submitochondrial particles appear quite resistant to iron deficiency with cytochrome content and electron-transferring or energy-conserving functions maintained at a level of 85% or better of normal. Iron-deficient skeletal muscle submitochondrial particles, in contrast, have decreased cytochrome content and only 15–20% of the normal capacity for oxidation through either complex I (NADH dehydrogenase) or complex II (succinate dehydrogenase). Energy-linked reactions which involve substrate oxidation/reduction (succinate → NAD⁺ reversed electron flow and succinate-driven energy-dependent transhydrogenation) are likewise markedly decreased, while ATP-driven energy-dependent transhydrogenation and mitochondrial ATPase are normal. Our data support the concept that iron deficiency leads to decreased electroncarrying capacity of iron-containing mitochondrial enzymes, with skeletal muscle being much more susceptible than liver, but that the mitochondria are otherwise normal with regard to energy conservation.

Several drugs/chemicals were allowed to interact with the cytochrome P-450 dependent mixed function oxidase system in the postmitochrondrial supernatant fractions of Ficoll-Hypaque-separated granulocytes from human normal subjects and patients with chronic myeloid leukemia. The substrate-induced spectral changes were followed by recording the difference spectra. Compounds conventionally classified as type I and type II substrates, on addition to S₁ fractions of both normal and leukemic granulocytes, caused spectral changes that were reverse to those reported for the rat liver microsomes. Aminopyrine, phenobarbital, and Tween 80 evoked a reverse type I spectral change with a peak at 420–430 nm and a trough at 380–400 nm, whereas aniline and pyridine induced a modified type I (a reverse type II) spectral change characterized by a peak at 408 nm and a trough at 421 nm. These changes were found to be quantitatively proportional to the amounts of substrate added. However, the magnitude of the peaks and troughs was considerably less in the S₁ fraction of the leukemic granulocytes. Correspondingly, total heme content was significantly decreased in S₁ fractions of CML granulocytes as compared to similar fractions of normal granulocytes.

Nicotinamide nucleotides play an important role in cellular metabolism. Sander et al. (1) have described a procedure for the extraction of pyridine nucleotides from erythrocytes which circumvents most of the difficulties reported by others (2–4). For NAD assay simple recycling methods involving a single enzyme were employed by some authors (5–8), but the NAD extraction procedures adopted by them were essentially similar to the earlier methods. In the present study, an attempt was made to develop a simplified procedure for NAD estimation in human erythrocytes based on the existing improved methods of NAD extraction (1) and assay (6,7,9). During the experimentation, it became apparent that the erythrocyte extracts contained an interfering substance which accelerated the NAD cycling rate in the assay resulting in overestimation of the NAD content.

We investigated the catecholamine-stimulated lipolytic response of perirenal adipocytes isolated from spontaneously hypertensive (SHR) and normotensive (C) rats of the Sprague-Dawley (SD) and Wistar-Kyoto (WKY) strain. Younger rats (10–17 weeks) were matched with respect to age and body weight. Age-matched SHR rats were smaller than their C counterparts, had equal-size adipocytes, and demonstrated lipolytic responses equal to C cells. Weight-matched SHR rats were older than normotensive controls, had larger adipocytes, and showed depressed norepinephrine (NE)-stimulated responses with a rightward shift in the doseresponse curve. Rates of lipolysis of SHR and C cells were not different in the simultaneous presence of norepinephrine and theophylline. Nine- to ten-month-old rats were of comparable body weight and adipocyte size regardless of blood pressure status; however, SHR cells still showed a significantly blunted response to catecholamine stimulation. We conclude that (1) the NE-stimulated lipolytic response of adipocytes of SHR rats is significantly less than that elicited from C cells; (2) this function difference seems unrelated to a size difference between cells of younger, SHR and C rats, thus implicating the adrenergic system; and (3) whole body growth (as reflected by body weight) and perirenal adipocyte growth do not proceed in parallel in actively growing SHR rats.

Liver mitochondria from octanoate-treated rabbits showed an impaired ability to synthesize citrulline. Two methods were used to evaluate citrulline synthesis in rat liver mitochondria. Under these conditions octanoate inhibited citrulline synthesis by over 50%. When ATP was included in the assay medium the inhibitory effect of ocatanoate was prevented. In the absence of ATP in the suspending medium, octanoate did not significantly lower total adenine nucleotides in rat liver mitochondria. However, under these conditions octanoate caused a change in the adenine nucleotide profile such that ATP content was decreased and AMP content was increased. When ATP was present in the assay medium, octanoate caused a similar increase in AMP content. However, ATP decreased only slightly. The alterations in mitochondrial adenine nucleotide profile by octanoate and the reversal of the effect by exogenous ATP suggests that octanoate inhibits citrulline synthesis via reduced intramitochondrial ATP levels. The ability of octanoate to lower mitochondrial ATP and elevate mitochondrial AMP may be related to its intramitochondrial activation by the medium chain fatty acid activating enzyme.

The mechanism of antiarrhythmic action of phosphocreatine on ischemic myocardium was studied by analyses of electrograms from normal and ischemic tissues. Ischemia induced significant changes in amplitude, duration, and conduction time of the electrograms, thereby showing depolarization of membranes and retarded conduction of excitation. Phosphocreatine administered in a single dose, 300 mg/kg iv, completely eliminated ventricular fibrillations in the ischemic hearts and significantly diminished the electrical instability occurring during reperfusion. The effects of phosphocreatine were completely reproduced by its structural analog phosphocreatinine which is inactive in the creatine kinase reaction. It is concluded that the antiarrhythmic effect of both compounds is related to their specific chemical structure and that their specific effect is likely to be mediated via interaction with a sarcolemma site.

This study has measured plasma lipoprotein lipid levels and the in vitro rate of cholesterol synthesis from [2⁻¹⁴C]acetate by mononuclear leukocytes in blood from normolipidemic subjects and two patients with Tangier disease. The rate of cholesterol synthesis in blood was related inversely to plasma levels of HDL cholesterol in the normolipidemic subjects. This relationship was mainly due to a similar correlation in the women. The rate of blood cholesterol synthesis was raised in a woman with Tangier disease, which is consistent with the above correlation, but not in a man with this disease. We suggest that this correlation reflects an association between plasma HDL cholesterol levels and whole-body sterol synthesis.

Platelet interaction with plasma lipoproteins was studied using gel-filtered platelets free of plasma constituents and purified lipoproteins. On incubation of gel-filtered platelets with plasma lipoproteins at 30°C for 30 min, 100 μg of protein/ml of very-low as well as low-density lipoprotein caused 10% increment in platelet aggregation and [¹⁴C]serotonin release in parallel to elevation of around 15% of malondialdehyde and thromboxane B₂ production. High-density lipoprotein showed the opposite effect and reduced platelet aggregation as well as thromboxane B₂ synthesis by 17 and 32%, respectively. Lipoprotein-deficient plasma enhanced platelet function. Preincubation of the platelet suspension with prostacyclin did not prevent the effect of the lipoproteins on the in vitro platelet response as well as on the platelet prostaglandin pathway. Our results suggest that the formation of thromboxane B₂ and malondialdlehyde is influenced by plasma lipoproteins and that these, in turn, affect platelet aggregation and the release reaction. The possible significance of these results to platelet function in hyperlipidemic patients is discussed.