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Biomedical subjects

F H Schmidt

Publications and source records attributed to F H Schmidt.

At least 19 recordsLinked to original sources
PubMed1992

Fully enzymatic inulin determination in small volume samples without deproteinization.

A fully enzymatic method for the determination of inulin in serum or plasma without deproteinization is described. The assay is carried out by means of a fructose determination after hydrolysis of inulin via inulinase and simultaneous oxidation of the native glucose using glucose oxidase and H2O2. This time-saving procedure of high specificity, sensitivity and accuracy requires only small sample volumes. The usefulness of the method is shown by analysis of blood levels in humans and rabbits after an intravenous administration of Inutest.

Animals↗
PubMed1990

Blood-glucose-lowering activity of 2-(3-phenylpropoxyimido)-butyrate (BM 13.677).

A single oral or intraperitoneal application of 2-(3-phenylpropoxyimido)-butyrate (BM 13.677) resulted in a dose-dependent blood-glucose-lowering effect in fasted guinea-pigs. The threshold dose and the EC50 were estimated as 25 mg/kg and 63 mg/kg, respectively, which is between that of the biguanides phenformin and metformin. A rise in blood lactate concentrations was observed only at high doses of BM 13.677, but was not related to an irreversible metabolic inhibition. Among several rodent species studied the potency of the drug decreased in the order guinea-pig much greater than mouse greater than rat = rabbit. Inhibition of hepatic gluconeogenesis by the drug was demonstrated in the perfused liver or hepatocytes of guinea-pigs. Inhibition of glucose production by the perfused liver in the presence of 0.1 mM BM 13.677 was dependent on the substrate and decreased in the order: lactate greater than pyruvate greater than alanine much greater than propionate greater than glycerol = fructose. This suggests a specific interaction of the drug with a mitochondrial key reaction of gluconeogenesis. Stimulation of glucose oxidation in rat diaphragm by the compound (EC50 = 0.85 mM) suggests that besides inhibition of gluconeogenesis also extrahepatic effects contribute to the blood-glucose-lowering effects of the drug.

Animals↗
PubMed1990

Reduction of BM 15.766-induced 7-dehydrocholesterol accumulation by bezafibrate and mevinolin in rats. A non-isotopic in vivo test system for compounds reducing cholesterol synthesis.

The effects of mevinolin, a 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitor and bezafibrate, a modulator of lipoprotein metabolism, were measured on BM 15.766-induced 7-dehydrocholesterol (7-DHC) accumulation in liver and serum of rats. BM 15.766, an inhibitor of delta 7 sterol reductase, leads to an accumulation of 7-DHC, which can be used as a measure of cholesterol (CH) synthesis de novo. The investigations were carried out to evaluate the usefulness of this new non-isotopic in vivo method for testing compounds that affect directly and indirectly the CH-biosynthetic pathway. Mevinolin showed a dose-dependent reduction of BM 15.766-induced 7-DHC accumulation after a single oral dose. The dose range for reduction of 7-DHC in the liver of rats was comparable with that for serum CH-lowering in humans. Bezafibrate reduced the BM 15.766-induced 7-DHC accumulation in liver in a dose- and time-dependent manner. These findings agree with the reported reduced activity of HMG-CoA reductase and support the view, that bezafibrate reduces CH biosynthesis by modulation of lipoprotein metabolism. The 7-DHC levels in serum do not reflect those in the liver and cannot be used as a measure of CH biosynthesis. The investigations show that BM 15.766-induced 7-DHC accumulation in liver of rats is an appropriate measure for CH de novo synthesis and can be used for testing compounds that interfere directly and indirectly with the CH-biosynthetic pathway. In contrast to previously described methods, no radiolabelled precursors are necessary.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Modeling glucose distribution in the cornea.

The central cornea obtains its glucose by diffusion through the cornea from the aqueous humor to the epithelium. The diffusion of glucose in the cornea is analogous to the flow of current in an electrical resistance network. The cellular consumption of glucose can be compared to shunting a portion of the charge to electrical ground. An electrical analog model of the cornea was developed to predict the availability of glucose to the epithelium and the distribution of glucose in the stroma. The glucose constant concentration lines in the normal stroma are parallel to the corneal surface and have decreasing values from 880 to 580 micrograms/ml. The effects on epithelial glucose concentration by implanting an intracorneal lens (ICL) of varying diameter, depth, permeability and thickness can be modeled. Glucose permeability through the intracorneal lens has the most significant effect on glucose availability. The ICL profile i.e. power, can also be an important fact in determining glucose availability. A minus power design requires a thin central lens zone with a thick peripheral zone. The design results in relatively more glucose flux through the optical zone of the lens and thus improves central epithelial glucose availability.

Cornea↗
PubMed1990

Effects of drugs affecting cholesterol biosynthesis pathway on BM 15.766-induced 7-dehydrocholesterol accumulation in rats. An animal model for testing compounds reducing cholesterol synthesis.

7-Dehydrocholesterol (7DHC), an intermediate of cholesterol, accumulates in animals after administration of BM 15.766 and can be measured in addition to cholesterol photometrically. The effect of compounds acting at different points in the cholesterol biosynthetic pathway on BM 15.766-induced 7DHC accumulation was investigated in rats to evaluate its usefulness as in vivo test system for cholesterol lowering agents. 7DHC in liver of rats proved to be an appropriate measure for cholesterol de novo synthesis. In contrast to previously described methods no radiolabelled precursors are necessary. The extraction of 7DHC and its photometric determination is, in comparison with separation and measurement of radioactive cholesterol, a simple analytical procedure.

Animals↗
PubMed1990

A computer program for modeling the kinetics of gene expression.

Enzyme induction may be modeled on the basis of four, quantifiable processes that control the rates at which specific gene products accumulate and decay. These processes include synthesis of functional mRNA, translation and degradation of mRNA, and degradation of the protein product. We present a simple computer program that permits mathematical simulation of gene expression on the basis of experimentally determined rates of synthesis and degradation. The program was implemented as a spreadsheet using Microsoft Excel for Macintosh and MS-DOS operating systems and also was adapted for HyperCard on the Macintosh. It contains a formula to account for growth of tissue or cell populations. The program predicts amounts of individual mRNAs and proteins (or enzyme activities) in cells as a function of time after a stimulus alters their rates of synthesis or degradation.

Animals↗
PubMed1989

The role of mRNA and protein stability in gene expression.

How important is the stability of gene products in the process of gene expression? We use a dual-compartment mathematical model to demonstrate the effects that changing the rates of synthesis and degradation of hypothetical mRNAs and proteins would have on the final concentration of protein. The model predicts that the concentration of protein at steady state equals the product of the rate constants for synthesis of mRNA and protein (ks1 and ks2) divided by the product of the rate constants for degradation (kd1 and kd2) and that the rate at which protein concentration changes depends on the rate constants for degradation of both the mRNA and the protein. This permits great flexibility in controlling induction kinetics for particular gene products, since their synthesis, translation, and degradation may be regulated coordinately to permit induction to be stable or transient or to amplify the final yield of protein. We suggest single exons may encode structural features that cause both mRNAs and proteins to be labile, thereby ensuring that modal stabilities of highly regulated macromolecules are similar.

Animals↗
PubMed1989

Glucose consumption in cultured corneal cells.

The rate of glucose consumption in cultured epithelium, endothelium, and keratocytes was measured; and the effect of reduced glucose availability on the consumption rate of these three cell lines was delineated. All three cell types exhibited an asymptotic decrease of glucose over time while being incubated in Krebs-Ringers solutions of varying glucose concentrations. At a concentration resembling that of the aqueous, epithelium (EPI), endothelium (ENDO), and keratocytes (K) consumed 6.7, 7.4, and 9.0 micrograms/cm2/hr respectively. Each cell type consumed glucose at a rate that was related to the amount of available glucose. As glucose concentration was reduced from 90 to 30 mg%, which was a 66% reduction in available glucose, the consumption of EPI, ENDO, and K dropped 74%, 61%, and 44% respectively.

Animals↗
PubMed1988

The induction of liver peroxisomal proliferation by beta,beta'-methyl-substituted hexadecanedioic acid (MEDICA 16).

Treatment of rats by beta,beta'-methyl-substituted hexadecanedioic acid (MEDICA 16) resulted in a dose- and time-dependent increase in liver peroxisomal enoyl-CoA hydratase and cyanide-insensitive palmitoyl-CoA oxidation with a concomitant increase in the volume density of peroxisomes as determined by morphometry. The induced peroxisomal proliferation was sustained as long as treatment was maintained and was accompanied by an increase in liver weight. Incubation of cultured rat hepatocytes in the presence of MEDICA 16 added to the culture medium resulted in a dose-dependent increase in peroxisomal beta-oxidation activities with a concomitant elevation of the volume density of peroxisomes. The induction of peroxisomal proliferation by MEDICA 16 in culture could be prevented in the presence of carnitine palmitoyltransferase inhibitors added to the culture medium, e.g. 2-bromopalmitate, 2-tetradecylglycidic acid or 2-[5-(4-chlorophenyl)-pentyl]oxirane-2-carboxylate. The induction of liver peroxisomes by MEDICA 16 conforms to the previously defined requirement for an amphipathic carboxylate in initiating peroxisomal proliferation. The prevention of peroxisomal proliferation by carnitine acyltransferase inhibitors may implicate the involvement of this acyltransferase in the induction of peroxisomal proliferation by xenobiotic or native amphipathic carboxylates.

Animals↗
PubMed1988

Morphometric analysis of the endocrine pancreas in streptozotocin-diabetic rats kept on different dietary regimens.

The effects of different diets on the endocrine pancreas of streptozotocin-diabetic rats were investigated by morphometry. Three dietary regimens were used over a period of 43 weeks: standard diet (SD), low carbohydrate-high protein diet (LC-HP), and low carbohydrate-high fat diet (LC-HF). Nondiabetic controls received standard diet. Volume density of the total endocrine tissue was significantly reduced in streptozotocin-diabetic rats kept on standard diet as compared to control rats. This reduction of endocrine tissue was significantly less in rats kept on LC-HP diet, whereas diabetic rats kept on LC-HF did not differ from diabetic rats on standard diet. In streptozotocin-diabetic rats volume density of B cells was drastically reduced, whereas volume densities of A, D and PP cells did not differ from nondiabetic controls. This decrease of B cells was partially prevented by LC-HP diet, but not by LC-HF diet. In nondiabetic control rats as in diabetic rats on standard diet most of the islets of Langerhans sized 500-6000 microns2. In contrast, diabetic rats on LC-HP diet revealed more endocrine tissue sized from 50 to 560 microns2 consisting of two to four endocrine cells, single cells, and small islets. The results suggest that LC-HP diet may initiate reparation processes in the endocrine pancreas of streptozotocin-diabetic rats.

Animals↗
PubMed1988

Effect of bezafibrate on serum lipids in normo- and spontaneously hyperlipidemic rats.

Rats, due to their availability and ease of handling, are a frequently used animal model for studying the effects of drugs on lipid metabolism. Hypolipidemic effects showed great variations in different studies. We investigated the effect of bezafibrate on serum concentrations of cholesterol and triglycerides in different strains of rats from several breeders. Under these conditions Lewis rats seemed to be the most suitable strain to investigate drug effects on cholesterol in serum. A hypercholesterolemic male Lewis rat found in a screening program was mated with normolipidemic female Lewis rats. The hyperlipidemia was found in some of the male and female offspring. Cholesterol and triglycerides were dramatically elevated in older animals. Bezafibrate (75 mg/kg/d) produced a marked reduction of lipids in serum in normo- and hyperlipidemic male rats but only in hyperlipidemic female rats, which is in agreement with former findings. These spontaneously hyperlipidemic rats could be a useful tool for investigation of drug effects on disturbed lipid metabolism and its pathophysiology. Therefore, we tried to establish a hyperlipidemic strain of rats.

Animals↗
PubMed1987

Tyramine neurotoxicity and first-pass brain technetium-99m-diethylenetriamine penta-acetic acid.

Tyramine induces coma in phenelzine-treated dogs with liver disease. The objective of the present investigation was to examine the influence of tyramine in these monoamine oxidase-inhibited dogs on the kinetics of Tc-99m-diethylenetriamine penta-acetic acid (Tc-99m-DTPA) during its first passage through the brain by nuclear imaging techniques. The study began with anesthetized mongrel dogs (n = 10) in a supine position over the camera detector. Data acquisition was started simultaneously after the rapid intracarotid injection of Tc-99m-DTPA (5 mCi) and 60 0.5-sec images of the brain were taken. Tyramine induced increased uptake with a concomitant impairment in the elimination of Tc-99m-DTPA from the brain of these phenelzine-treated animals with hepatic injury (n = 5) as compared to pretreated animals serving as a control group or phenelzine-treated animals without liver disease. This was accompanied by an appreciable reduction in hemispheric cerebral blood flow (50.5 +/- 19.3 vs. 110 +/- 16 ml/100 g/min), respectively. Increased cerebrovascular permeability of Tc-99m-DTPA and decreased cerebral blood flow occurred concomitantly with increased cerebrospinal fluid pressure and elevation in cerebrospinal fluid catecholamines of monoamine oxidase-inhibited animals with hepatic injury.

Animals↗
PubMed1987

Proliferation of peroxisomes in pericentral hepatocytes of rat liver after administration of a new hypocholesterolemic agent (BM 15766). Sex-dependent ultrastructural differences.

The effects of a new piperazine derivative BM 15766, which inhibits the biosynthesis of cholesterol at the 7-dehydrocholesterol-delta 7-reductase step, upon the ultrastructure of rat liver and the serum lipids, have been investigated. Treated animals showed a marked reduction in total sterol content in serum with simultaneous reduction of triglycerides. The catalase activity in liver homogenates was unchanged, carnitine acetyltransferase increased only slightly, and the 3-hydroxy-3-methylglutaryl-coenzyme A reductase was augmented by a factor of 2. In sections stained with alkaline 3,3'-diaminobenzidine for catalase, distinct proliferation of peroxisomes (PO) in perivenous regions of the hepatic lobules was noted in rats of both sexes. In male animals many PO showed loop-like extensions and invaginations of their limiting membranes into the matrix. Such alterations were seen less frequently in female animals; instead, females exhibited in the same regions of the hepatic lobules, large aggregates of PO, smooth endoplasmic reticulum, and mitochondria with longitudinal cristae. Close contacts of PO and fenestrated segments of smooth endoplasmic reticulum were noted in both sexes. These observations demonstrate the marked adaptive response of rat hepatocyte organelles to severe hypocholesterolemia induced by BM 15766. The alterations of PO may reflect attempts to increase their surface membrane, which plays a crucial role in the exchange of substrates between the cytoplasm and the peroxisomal matrix. Moreover, the close association of PO and smooth endoplasmic reticulum could facilitate the shuttle of lipid intermediates between these two intracellular compartments involved in the biosynthesis of complex lipids.

Animals↗
PubMed1986

[Mechanism of action of combined administration of glibenclamide and insulin in type II diabetics with secondary failure of oral treatment].

In a double-blind placebo-controlled cross-over study eight type II diabetics (three men, five women), of whom six were at the point of late failure to oral treatment, were given an insulin infusion of 22 U human insulin/patient for 45 min (approximately 7 microU/kg X min); 30 min before infusion either glibenclamide (1 tablet Euglucon N) or placebo was administered. Glucose in venous blood, C-peptide, insulin, and glibenclamide concentrations in the blood plasma were simultaneously determined over a period of 210 min. The monitoring of glucose was handled using a Biostator. The insulin level reached a mean maximum of 400 to 500 microU/ml and was in a behavior of 100 microU/ml for 60 min. The areas under the concentration-time curves (AUCs) were practically identical in the two regimes. The blood glucose fell (in mean) from 260 mg/dl to 135 mg/dl and at the end of the experiment was in the range of 155 mg/dl. The glibenclamide concentrations reached maximal concentrations of 185 ng/ml 90 min after administration. The C-peptide concentrations fell in the placebo phase by more than 40%. In contrast, in the glibenclamide period there was at first a slight rise and later a slight marginal fall (initial, 2.0 ng/ml vs 1.9 ng/ml; 60 min, 1.3 ng/ml vs 1.8 ng/ml; 180 min, 1.2 ng/ml vs 1.8 ng/ml). Values after 90, 120, and 180 min were statistically different. The AUCs (0-180 min) were different (329 ng X min/ml vs 251 ng X min/ml). The inhibition of insulin secretion (measured by C-peptide) caused by exogenous insulin administration is largely abolished by glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1986

The effects of BM 15.766, an inhibitor of 7-dehydrocholesterol delta 7-reductase, on cholesterol biosynthesis in primary rat hepatocytes.

The effect of the piperazine derivative BM 15.766 (4-(2-[1-(4-chlorocinnamyl)piperazin-4-yl]ethyl]-benzoic acid) on the biosynthesis of sterols was investigated in adult rat hepatocytes in primary monolayer culture. The substance led to a dose-dependent reduction of cholesterol in the serum of various species of animals such as rat, dog and marmoset. BM 15.766 showed a dose-dependent action on the incorporation of 14C-acetate in neutral, nonsaponifiable lipids. The inhibition of the overall incorporation was 10-12% (10(-5) M). No inhibition was observed in the hepatocytes over the entire dose range of 10(-8) M to 2 X 10(-5) M, while the release of the neutral lipids from the hepatocytes into the culture medium was reduced by up to 40%. The biosynthesis of cholesterol could be reduced by more than 90%. Simultaneously, 7-dehydrocholesterol levels rose in the cells and, to a less marked extent, in the medium. This can be interpreted as an indication that 7-dehydrocholesterol is incorporated into the cell membrane, which results in a lower release of 7-dehydrocholesterol into the medium in comparison with controls. The site of attack is the inhibition of the delta 5.7-sterol delta 7-reductase. The formation of desmosterol and cholestatrienol as well as other 7-dehydrocholesterol precursors could also be demonstrated. After longer incubation, there was an additional accumulation of squalene and lanosterol with simultaneous reduction of 7-dehydrocholesterol by BM 15.766, whereas the total 14C-acetate incorporation in neutral lipids was increased.

Acetates↗
PubMed1985

[Combined treatment of type-2 diabetics with insulin and glibenclamide after secondary drug failure. Double-blind, insulin-placebo-controlled crossover study].

A double-blind, placebo-controlled, crossover-therapy study was carried out using intraindividual comparisons on 18 type II diabetics. All patients were secondary drug failure patients and had been on insulin-glibenclamide combination therapy for periods of 1-14 months. On the last day of each of the 2-week-treatment periods (insulin-glibenclamide [verum phase] versus insulin-placebo [placebo phase]) the patients received a standard breakfast equivalent to 100 g glucose. Medication was given 30 minutes before the standard breakfast. The blood glucose level during insulin-glibenclamide therapy was 35-45 mg/dl below that during insulin-placebo treatment at all time points investigated. Correspondingly, the glucose excretion was reduced by about 40% during the verum phase. beta-Hydroxybutyrate in serum and urine and glycosylated haemoglobin (HbA1) measurements made during the verum phase were also significantly lower. As expected, the insulin level in serum showed no change. In contrast, C peptide concentrations were significantly raised by 15-40% during the verum phase. Combination therapy with insulin and glibenclamide produced therefore a marked improvement in the metabolic status of C peptide-positive patients classified as secondary drug failure patients to oral therapy.

Aged↗
PubMed1985

A new inhibitor of the long-chain fatty acid transfer across the mitochondrial membrane: 2-(3-methylcinnamylhydrazono)-propionate (BM 42.304).

Using two different assay systems to distinguish between overt and inner forms of carnitine palmitoyl transferase (CPT, EC 2.3.1.21) of intact guinea-pig liver mitochondria, we have shown that the hypoglycemic agent 2-(3-methylcinnamylhydrazono)-propionate (BM 42.304) inhibits the activity of carnitine-acylcarnitine translocase of liver mitochondria. The results offer an explanation for the inhibitory effect of the compound on ketogenesis with oleate but not with octanoate in the perfused guinea-pig liver, previously reported by us (Biochem. Pharmacol. 32, 3405-3412, 1983).

Acyltransferases↗