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Biomedical subjects

H Kather

Publications and source records attributed to H Kather.

At least 37 records · Page 2Linked to original sources
PubMed1988

Restricted alpha- and beta-adrenoceptor affinity of sulfoconjugated catecholamines in human mononuclear leukocytes, platelets, and fat cells and reduction of the postreceptor mechanisms.

The physiologic significance of the racemic 3-O-sulfate esters of epinephrine (EPI-3-O-S) and norepinephrine (NE-3-O-S) as well as 4-O-sulfoconjugated dopamine (DA-4-O-S) was evaluated. For this purpose these conjugated catecholamines (CA) were synthesized and investigated with respect to their alpha 2- and beta 2-adrenoceptor affinities and their biological activity in three different human cell systems: in mononuclear leukocytes (MNL), platelets, and fat cells. The unequivocal identification and the minimal degree of contamination of the synthesized sulfoconjugates with free CA was proved by 1H-NMR and by high-performance liquid chromatography with amperometric detection (HPLCA) respectively. In isolated human MNL, beta-adrenoceptor affinities of these conjugated CA were determined in competition experiments with the lipophilic nonspecific radioligand (-) 125I-cyanopindolol (ICYP) and, in addition, with the hydrophilic ligand 3H-CGP12177. With both ligands the affinity constants (KD) of the sulfoconjugated CA under investigation were about 100- to 1000-fold higher when compared with the respective free amines. Moreover, these sulfoconjugated CA per se induced no intracellular production of cyclic adenosine monophosphate (cAMP) in MNL. In comparison with the free amines, metanephrine (MN) and normetanephrine (NMN) showed a highly reduced competitive potency on the MNL beta-adrenoceptors labelled with 3H-CGP or ICYP. The KD values for MN and NMN in competition studies with ICYP were 10- and 5-fold higher than in those with 3H-CGP respectively, indicating a restricted access of MN and NMN to intracellular receptors. The adenylate cyclase system was not stimulated at all by MN or by NMN. In human platelets EPI-3-O-S and NE-3-O-S neither competed with the specific alpha 2-adrenoceptor antagonist 3H-yohimbine nor elicited any aggregation response at all. MN and NMN exhibited an about 40-fold reduced affinity for alpha 2-adrenoceptors in platelets when compared with the respective free amines and elicited no aggregation response at all. However, in the presence of MN and NMN the EPI- and NE-induced platelet aggregation was dose-dependently attenuated. These findings reveal an alpha 2-adrenoceptor antagonistic potency of MN and NMN. In human adipocytes EPI-3-O-S and NE-3-O-S were 100- to 1000-fold less potent to inhibit lipid mobilization via alpha 2-adrenoceptors as well as to stimulate the beta-adrenoceptor mediated lipolysis when compared with free CA.

Adipose Tissue↗
PubMed1988

Adrenergic regulation of human fat-cell lipolysis.

The actual effects of adrenaline and noradrenaline on human fat cell lipolysis are the result of a balance of opposing signals which are mediated by alpha2- and beta-adrenergic receptors coupled to adenylate cyclase via stimulatory (beta-receptors) and inhibitory (alpha2-receptors) guanine nucleotide regulatory proteins. The signals transmitted by both hormones are therefore ambiguous. The physiological meaning of this ambiguity in signal transmission has not been satisfactorily explained. This report demonstrates that lipolysis first needs to be inhibited before it can be stimulated, indicating that current concepts on the role of lipolytic agents require re-evaluation. In the light of these findings it is concluded that a dual regulation of single metabolic pathways, i.e. lipolysis, by a single class of hormones, e.g. catecholamines, (1) prevents excessive activation of lipolysis and cyclic AMP accumulation which may lead to a depletion of cellular adenine nucleotides via an increased release of inosine and hypoxanthine which can not be re-utilized, and (2) adds a further degree of flexibility in regulation by restricting the stimulatory effects of both hormones to a narrow range of concentrations which is easily modified by inhibiting ligands.

Adenosine Deaminase↗
PubMed1987

Chemiluminescent determination of adenosine, inosine, and hypoxanthine/xanthine.

A fully automatic method for analysis of adenosine, inosine, and hypoxanthine/xanthine which combines the specificity of enzymatic catalysis and sensitivity of chemiluminescence is presented. The hydrogen peroxide formed by sequential catabolism of purines to uric acid is detected by the oxidation of luminol in the presence of peroxidase. The method takes advantage of the fact that light output in the H2O2/luminol system is transient. By adopting a two-step procedure this feature enables selective determination of adenosine, inosine, and hypoxanthine/xanthine. In step 1 any purines lower in the catabolic sequence than the analyte under study are converted to uric acid. Light emission is allowed to decay to baseline levels. During step 2 the analyte is selectively degraded. The H2O2 formed leads to a new light emission which is proportional to the square of analyte concentration. The method can be performed with commercially available reagents and enzymes and requires minimal processing of biological samples. Excellent agreement has been obtained with HPLC analysis. Sensitivity is in the range of 5-10 nmol/liter in as little as 0.1 ml. More than 200 samples per day can be analyzed by a single operator.

Adenosine↗
PubMed1987

Mitigation of alimentary lipemia by postprandial exercise--phenomena and mechanisms.

The effects of a single bout of exercise at 40% of maximum aerobic capacity with regard to alimentary lipemia and postprandial lipoproteins was studied in a cross-over design in 12 young healthy male volunteers. In addition to lipids and lipoproteins, lipoprotein lipase, free glycerol, free fatty acids, plasma insulin, and C-peptide concentrations were quantitated. Postprandial exercise reduced alimentary lipemia by 34% while lipoprotein lipase activity rose by 42%. The postprandial fall of high-density lipoprotein (HDL)3 was abolished and the rise of HDL2 accentuated. Free glycerol and free fatty acid concentrations were higher following the meal plus exercise regimen compared to the meal alone. It is concluded that at least part of the chronic effect of exercise may come from additive effects such as observed from individual bouts of muscular activity.

Adult↗
PubMed1987

Role of "local" hormones in regulation of lipolysis.

Lipid mobilization from adipose tissue can be activated by two distinct mechanisms, i.e. relief of inhibitory influences or reversal of a preexisting inhibition by lipolytic hormones. Adenosine and prostaglandins which are produced within adipose tissue may serve to maintain a functional state that is susceptible for stimulation and adjust non-stimulated lipolysis to the energetic demands of the organism.

Adenosine↗
PubMed1987

Effects of different phosphodiesterase inhibitors on the antilipolytic action of insulin in human adipocytes.

The effects of two phosphodiesterase inhibitors, e.g. theophylline and D-4-(3-butoxy-4 methoxybenzyl)-2-imidazolidinone (RO-20-1724) on the antilipolytic action of insulin in human adipocytes were investigated. At a concentration of 1 mmol/l (theophylline) and 0.1 mmol/l (RO-20-1724) both inhibitors increased cyclic AMP to a similar extent. However, their effects on insulin action were different. Whereas addition of theophylline abolished the ability of insulin to inhibit lipolysis, insulin was fully functional in depressing glycerol release in the presence of RO-20-1724. The results suggest that the insulin-sensitive phosphodiesterase of human adipocytes may be relatively resistant to RO-20-1724 as has been shown for the enzyme system of 3T3-L1 adipocytes.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1987

Influences of variation in total energy intake and dietary composition on regulation of fat cell lipolysis in ideal-weight subjects.

Weight-maintaining fat-rich, "prudent," carbohydrate-rich, as well as energy-restricted diets (300 kcal/d) were fed in succession for 7 d to 12 healthy males of ideal body weight under metabolic ward conditions. At the end of each period isolated fat cells were prepared from subcutaneous abdominal adipose tissue and incubated in vitro in the absence or presence of adenosine deaminase, either alone or in combination with various lipolytic or antilipolytic hormones and agents. Variations in total energy intake and dietary composition had characteristic and specific effects on fat cell lipolysis in vitro. High carbohydrate and prudent diets resulted in low rates of nonstimulated glycerol release and impaired insulin action in the presence of adenosine deaminase (320 mU/ml). High-fat and energy restricted diets were characterized by high rates of nonstimulated glycerol release. Sensitivity of antilipolysis to insulin and prostaglandin E2 was 10 to 200 times lower respectively on energy-restricted than on fat-rich diets. The effects of alpha 2- and beta-adrenergic catecholamines and of N6-phenylisopropyladenosine were not affected by the preceding diets.

Adenosine↗
PubMed1987

Antilipolytic action of insulin in abdominal adipocytes of obese subjects before and during energy restriction. Influence of adenosine deaminase.

The influence of prolonged energy restriction (1250 kJ for 4 weeks) on insulin's antilipolytic action was investigated in abdominal adipocytes of obese subjects. An attempt was made to discriminate between dietary influences per se and indirect influences caused by changes in the concentration or action of adenosine. Prolonged energy restriction resulted in about a 3.5-fold increase in basal lipolytic rate which was associated with a corresponding increase in maximal response to insulin. Both these effects could be mimicked by adenosine deaminase (1.6 micrograms/ml) which increased glycerol release of adipocytes from fed donors to levels normally seen during starvation suggesting that the improvement of lipolytic responsiveness to insulin during energy restriction was an apparent one only, due to the fact that glycerol release was increased. To identify dietary influences that selectively affect insulin action the effects of insulin were compared with those of other antilipolytic agents in the presence of adenosine deaminase. Maximally effective concentrations of prostaglandin E2, clonidine and N6-phenylisopropyladenosine almost completely suppressed glycerol release before and during starvation. The extent of inhibition produced by these latter compounds was therefore related to basal activity by the same linear relationship in all experimental settings. By contrast insulin only partially depressed glycerol release and the relationships between basal activity and response to maximal concentrations of insulin were significantly different before and during starvation (P less than or equal to 0.01) in the presence of adenosine deaminase indicating that starvation selectively influences insulin action via mechanisms that are unrelated to the effects of other antilipolytic compounds. It is concluded that the main effect of energy restriction on insulin's antilipolytic action is an apparent one which is secondary increased lipolytic activity. Direct dietary effects on insulin action became apparent upon removal of endogenous adenosine. These tend to limit the maximal response to insulin and may be due to changes at the post-binding level but could also reflect an intrinsic property of insulin's antilipolytic action.

Abdomen↗
PubMed1986

Automatic bioluminescent glucose determination using commercially available reagent kits coupled to the bacterial NAD(P)H-linked luciferase system.

A sensitive and specific automatic bioluminescent method is described for glucose determination in serum samples using commercially available reagent-kits. The Boehringer Gluco-quant kit, originally designed for spectrophotometric measurement, was successfully coupled to the bacterial luciferase NAD(P)H-linked system. The method's validity was proven by comparison with a spectrophotometric method. Correlation was excellent (r = 0.98, n = 50). Precision attained by 30 assays was good (CV 1.19%). The assay was verified by determining the glucose concentrations of more than 1000 serum samples. Using a microcomputer-controlled automatic luminescence analyser (Berthold LB 950 T) and reagent kits for luminometry (Boehringer Mannheim, LKB Wallac, Lumac/3M), the complete assay can be performed fully automatically with commercially available reagent kits. More than 200 samples can be assayed by one individual per day. The bioluminescence method is at least 100 times more sensitive than spectrophotometric measurements. Other reagent kits tested (Behring, Merck, Sigma) are also suitable for coupling to the NAD(P)H-linked luciferase system.

Blood Glucose↗
PubMed1985

Antilipolytic effects of N6-phenylisopropyladenosine and prostaglandin E2 in fat-cells of obese volunteers before and during energy restriction.

The antilipolytic effects of N6-phenylisopropyladenosine and of prostaglandin E2 were studied with adipocytes of obese volunteers before and after 4 weeks of severe energy restriction [1250 kJ (300 cal)/day] in the presence and absence of adenosine deaminase (1.6 micrograms/ml, corresponding to 320 m-units/ml). The studies were undertaken to define more clearly the role that local modulators might play in adaptation of lipid mobilization to starvation in humans. Starvation was associated with an approx. 3-fold increase in non-stimulated lipolysis. Removal of endogenous adenosine resulted in a similar increase in basal glycerol release under both conditions, averaging 2 and 2.2 mumol/180 min per 10(6) cells respectively. The sensitivity of the cells to N6-phenylisopropyladenosine and to prostaglandin E2 was not changed by starvation in the presence of adenosine deaminase. These results are discussed in terms of the possible role that local regulators might play during dietary adaption in human fat-cells in vitro.

Adenosine↗
PubMed1985

Adrenergic regulation of lipolysis in abdominal adipocytes of obese subjects during caloric restriction: reversal of catecholamine action caused by relief of endogenous inhibition.

The effects of adrenaline, noradrenaline, and of the alpha 2- and beta-selective agonists clonidine and isoproterenol were studied in fifteen obese subjects before and after 4 weeks of caloric restriction (300 cal day-1). Basal glycerol release averaged 1.4 mumol (10(6) cells)-1 (180 min)-1 before starvation and 2.8 mumol (10(6) cells)-1 (180 min)-1 during starvation (P less than or equal to 0.1). Before starvation adrenaline and noradrenaline caused a 2-3-fold increase of glycerol release. This lipolytic effect disappeared during starvation. An inhibitory effect of adrenaline was observed instead which was maximal at an adrenaline concentration of 1 mumol 1(-1) (P less than or equal to 0.05). The dose-response relationships of the alpha 2- and beta-selective agents clonidine and isoproterenol were not appreciably changed by caloric restriction. The increase of basal lipolytic rate and the reversal of adrenaline action seen during caloric restriction could be mimicked by removal of endogenous adenosine using adenosine deaminase (1.6 microgram ml-1). In addition, inclusion of N6-phenylisopropyladenosine (1 mumol 1(-1)) into the medium reverted the adrenaline-induced inhibition seen during caloric restriction. The results suggest that local modulators such as adenosine are of primary importance for the apparent change of responsiveness to adrenaline and noradrenaline seen during starvation of human fat cells in vitro.

Adenosine↗
PubMed1985

Human fat cell lipolysis is primarily regulated by inhibitory modulators acting through distinct mechanisms.

The effects of adenosine deaminase and of pertussis toxin on hormonal regulation of lipolysis were investigated in isolated human fat cells. Adenosine deaminase (1.6 micrograms/ml) caused a two-to threefold increase in cyclic AMP, which was associated with an increase in glycerol release averaging 150-200% above basal levels. Clonidine, N6-phenylisopropyladenosine, prostaglandin E2, and insulin caused a dose-dependent inhibition of glycerol release in the presence of adenosine deaminase. Pretreatment of adipocytes with pertussis toxin (5 micrograms/ml) for 180 min resulted in a five- to sevenfold increase in cyclic AMP. Glycerol release was almost maximal and isoproterenol caused either no further increase or only a marginal additional increase of lipolysis after pretreatment with pertussis toxin, whereas cyclic AMP levels were 500 times higher than in controls. The effects of antilipolytic agents known to affect lipolysis by inhibition of adenylate cyclase activity, i.e., clonidine, N6-phenylisopropyladenosine, and prostaglandin E2, were impaired. In contrast, the antilipolytic action of insulin was preserved in adipocytes pretreated with pertussis toxin. As in controls, the peptide hormone had no detectable effect on cyclic AMP after pertussis toxin treatment. The findings support the view that the antilipolytic effect of insulin does not require adenylate cyclase or phosphodiesterase action. In addition, the results demonstrate that, upon relief of endogenous inhibition, human fat cell lipolysis proceeds at considerable (adenosine deaminase) or almost maximal (pertussis toxin) rates. A certain degree of inhibition, therefore, appears to be necessary for human fat cell lipolysis to be susceptible for hormonal activation.

Adenosine Deaminase↗
PubMed1985

Semiautomatic bioluminescence determination of glycerol using a computer controlled luminescence analyser (Berthold LB 950 T).

A semiautomatic determination of glycerol is described, in which luminescence produced by bacterial NADH-linked luciferase is measured by an automatic luminescence analyser (Berthold LB 950 T). The glycerol determination is based on the enzymatic conversion of glycerol to 3-phosphoglycerate, made irreversible by the presence of arsenate. NADH, formed in the glycerol-3-phosphate and glyceraldehyde-3-phosphate dehydrogenase reactions, is subsequently determined by the bacterial luciferase system. Stable kinetics of light emission were obtained by reducing the catalytic concentration of NAD(P)H: FMN oxidoreductase from 85 U/1 to 8.5 U/1. This method was applied to serum samples and validated by comparison with an enzymatic fluorimetric method. The new method is approximately 10 times more sensitive than the fluorimetric one. Moreover, it is simpler, more convenient, less time consuming and also less expensive than spectrophotometric, fluorimetric or radiochemical methods used for glycerol determination.

Computers↗
PubMed1984

Bioluminescent determination of free fatty acids.

A simple, highly specific, and sensitive bioluminescent method for determination of free fatty acids in unextracted plasma or serum has been developed. The method is based on the activation of free fatty acids by acyl-CoA synthetase (EC 6.2.1.3). The pyrophosphate formed is used to phosphorylate fructose 6-phosphate in a reaction catalyzed by the enzyme pyrophosphate-fructose-6-phosphate phosphotransferase (EC 4.1.2.13). The triosephosphates produced from fructose 1,6-bisphosphate by aldolase are oxidized by NAD in the presence of arsenate to 3-phosphoglycerate. The NADH is detected via the bacterial NADH-linked luciferase system. Excellent agreement has been obtained by comparison with accepted methods. In addition, for the determination of serum free fatty acids, the method is particularly applicable for following lipolysis of isolated adipocytes.

Adipose Tissue↗
PubMed1984

[Hypertensive therapy with prazosin. Concomitant cardiovascular, metabolic and respiratory diseases. Proven facts and potential aspects].

Prazosin sinks the pathologically increased blood pressure, reduces pre- and afterload in myovascular insufficiency and has an interesting influence on plasma lipid fractions with regard to the coronary risk. Prazosin thus intervenes in the three cardiovascular disease processes, which often exist simultaneously, which are mutually caused. Studies which have taken place in the meantime demonstrate the possibilities of Prazosin as a treatment for Raynaud's disease and gangrene. The relatively long bio-availability of the preparation led constantly to the discovery of additional ranges of application, but did not deliver any new findings which would have made restrictions of the original application necessary. On the contrary, Prazosin proved to be especially favourable and capable of being universally applied in the illnesses which frequently accompany hypertension and cardiac insufficiency.

Adolescent↗
PubMed1984

Comparison of in vitro and in vivo effects of prazosin on lipid metabolism.

The results of an in vitro study indicate that only nonselective and alpha 2-blocking agents are capable of increasing adrenergic-stimulated lipolysis in human adipose tissue. Concentrations in vivo of total triglycerides, total cholesterol, and low-density lipoprotein and very low-density lipoprotein cholesterol did not change with prazosin treatment. It is suggested that the low affinity of prazosin for the cyclase-coupled alpha 2 receptors in human adipose tissue explains the lack of effect of prazosin on lipid mobilization from tissue to blood and the absence of a change in low-density lipoprotein and very low-density lipoprotein cholesterol in vivo. However, there was a significant increase in high-density lipoprotein cholesterol. The prazosin-related increase in the cholesterol ratio in vivo has been interpreted as a beneficial modification of this risk factor, but is not explained by our in vitro observations.

Adenylyl Cyclases↗