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Biomedical subjects

S Németh

Publications and source records attributed to S Németh.

At least 19 recordsLinked to original sources
PubMed2003

CD spectrometric methods for the simultaneous determination of ethisterone and its delta5-isomer.

Quick and accurate direct and indirect circular dichroism (CD) spectrometric methods were developed for the simultaneous determination of ethisterone (17alpha-ethinyl-17-hydroxy-4-androstene-3-one) and its delta(5)-isomer (delta(5)-ethisterone). The direct method is based on the selective negative Cotton effect of the delta(4)-3-oxo group in ethisterone (negative maximum at 348 nm in dioxan) and measurement of the ellipticity at 296 nm (positive maximum of delta(5)-ethisterone), where the measured ellipticity is the sum of those of the two isomers. In the indirect procedure delta(5)-ethisterone is transformed to ethisterone by base-catalysed isomerization and the ellipticities are measured at 339 nm in ethanol before and after isomerization. Preliminary experiments show the usefulness of CD detector in the HPLC determination of the mixture of the isomers. A major advantage of the direct CD spectrometric and the HPLC/CD methods is that the delta(5)-isomer with extremely low UV activity can also be directly measured with high sensitivity.

Catalysis↗
PubMed1988

[Development and significance of estrogen-induced increase in the activity of several liver enzymes].

In experiments on adult, female rats, the author confirm the stimulatory effect of 50 micrograms kg-1 17-beta-estradiol daily, s.c., for more than 1 week on the activity of liver tyrosine aminotransferase and tryptophan pyrrolase and describe experiments suggesting an increased glucocorticoid sensitivity, as a consequence of the estrogen treatment. The study contributes to the information on potential side effects of hormonal contraception.

Animals↗
PubMed1988

Dose dependent reversal by i.v. glucose administration of the stimulation of rat liver glycogen phosphorylase by epinephrine infusion.

Infusion of 0.5 ml kg-1 min-1 20% glucose i.v. failed to suppress the stimulatory effect of 0.25 microgram kg-1 min-1 epinephrine dissolved in and infused together with the above glucose solution on the activity of liver glycogen phosphorylase in adult male rats. However, 40% glucose solution administered in the same way abolished the effect of the epinephrine infusion completely. An i.v. pulse of 1 g kg-1 glucose in the form of a 40% solution immediately before the infusion of the same dose of epinephrine in saline had only a temporary inhibitory effect on epinephrine induced increase of phosphorylase activity. Finally, i.p. administration of 10 mg kg-1 phentolamine 60 min before epinephrine infusion in saline completely blocked the increasing effect of the latter on both liver phosphorylase and serum glucose, while that of 4 mg propranolol 30 min before the hormone failed to exert any influence. This reconfirmed the well known mediation of the glycogenolytic effect of catecholamines in adult male rats by alpha type adrenergic receptors.

Animals↗
PubMed1988

The inhibition of stress induced increase of liver enzyme activity by progesterone occurs in rats of both sexes.

Adult rats of both sexes were injected an aqueous suspension of progesterone in a dose of 12.5 mg i.p. + 12.5 mg i.m. and 50% of the animals were subjected to immobilization stress for 150 minutes either immediately after the hormone administration or at various time intervals after that. Non injected rats served as controls. After decapitation the plasma corticosterone level and the activity of tyrosine aminotransferase and tryptophan pyrrolase in the liver was determined. It was found that in non immobilized animals all three parameters investigated were increased to a minor degree 3 hours after progesterone injection. In stressed rats the stimulatory effect of stress induced hypercorticosteronaemia on the activity of both enzymes was decreased at 14 and/or 20 hours after progesterone administration, no sex differences being observed. The potential usefulness of progesterone as inhibitor of exaggerated stress is underlined.

Animals↗
PubMed1988

Diminished growth hormone secretion in blind males after L-dopa stimulation.

Growth hormone secretion after L-dopa administration (1000 mg p.o.) was investigated in young adult normal and blind volunteers. The average increment of plasma growth hormone after L-dopa stimulation in the blind was below the criterion for a positive response (less than 5 ng ml-1). The control volunteers showed normal response. After L-dopa stimulation there was a significantly diminished growth hormone response in the young adult blind compared to control volunteers.

Administration, Oral↗
PubMed1987

Dual effect of exogenous progesterone on the activity of tyrosine aminotransferase in the liver of female rats.

An as yet undescribed biphasic response of liver tyrosine aminotransferase (TAT) activity to a single administration of a microcrystallic watery suspension of 25 mg of progesterone (Agolutin Depot, SPOFA Praha) is described in adult female rats subjected to immobilization stress for 150 min. Exaggeration of the stress induced increase of TAT activity 3 and 8 h after hormone administration and its suppression 20 h after it was observed. The stress induced serum corticosterone increase is not correlated with the described changes, however, in non-stressed animals an increased TAT activity at 3 and 8 h after progesterone injection tightly follows the increased plasma corticosterone values. No statistically significant changes were found with respect to liver tryptophan pyrrolase activity.

Animals↗
PubMed1987

Progressive weakening of the response of key enzymes of liver glycogen metabolism to permanently increased plasma epinephrine levels.

In adult male rats anaesthetized with pentobarbital the intravenous infusion of 0.5 micrograms.kg-1.min-1 of epinephrine increased liver phosphorylase a activity within 5 min, whereas later a weakening of the hormone effect was observed. After increasing the infusion rate to 1.0 micrograms.kg-1.min-1 and extending the study to more parameters, the diminishing effect on phosphorylase was confirmed and a similar response was established for liver cAMP. Concomitantly, a decrease and recovery of liver glycogen synthase a activity was observed. In rats with permanent catheters in one of their tail arteries for obtaining blood samples, the plasma epinephrine levels were shown to be permanently increased (from cca 1 pmol.ml-1 before infusion of 1.0 micrograms.kg-1.min-1 to more than 30 pmol.ml-1 during infusion) and remained at steady levels throughout the infusion. Therefore, the weakening of the epinephrine effect should be ascribed to changes at (or beyond) the catecholamine receptor level. A hitherto undescribed decrease of total glycogen synthase activity was observed during the infusions.

Animals↗
PubMed1987

Dose-dependent relationships between the effects of epinephrine and glucose on the activity of key enzymes of glycogen metabolism in the rat liver.

The interactions of the effects of i.v. injections of 1.00, 0.50 or 0.25 g kg-1 glucose with those of i.v. administration of 0.5 or 1.0 microgram kg-1 epinephrine applied 10 min after glucose on the activity of liver glycogen phosphorylase and glycogen synthase were studied one minute after the hormone injection in adult male rats which had fasted for 24 h. The administration of 0.5 microgram kg-1 epinephrine failed to influence the activity of either enzyme. After the dose of 1.0 microgram kg-1, however, phosphorylase activity increased, that of synthase decreased. This effect of epinephrine on the activity of both enzymes was counteracted by 1.00 and 0.50 g kg-1 of glucose, that of synthase even by 0.25 g kg-1 of glucose. A stimulatory effect of glucose on synthase a activity was confirmed. A similar effect on total synthase activity is being described both in fed rats and those which had fasted for 24 h. In fed animals a decreased sensitivity of synthase against physiological levels of catecholamines and the paradoxical rebound of the sensitivity after an i.v. glucose load of 1.00 g kg-1 were observed.

Animals↗
PubMed1987

Effect of epinephrine infusions imitating plasma epinephrine levels in immobilization stress and of fasting on the activity of key enzymes of liver glycogen metabolism.

In adult male rats anaesthetized with pentobarbital, intravenous infusion of 0.25 microgram kg-1 min-1 of epinephrine increased plasma epinephrine levels to more than 10 pmol ml-1 within 5 min, the values remaining constant during the next 20 min. On the other hand, a maximal increase of liver phosphorylase a was found after 5 min and this response was attenuated at 10 and 20 minutes in the fed rats. Fasting for 24 h extinguished the greatest part of this response. During infusion, a decrease of liver synthase a activity was observed in the fasted and of total synthase activity in both the fed and fasted animals. In fed rats an i.v. bolus of 0.50 microgram.kg-1 or doubling of the infusion rate for 5 min, both immediately after 20 min of infusion, led to maximal phosphorylase a activity again and to a decrease of synthase a activity. The levels of cAMP in the liver were increased by the infusion in one series and unchanged in another.

Animals↗
PubMed1985

Interaction of the effects of glucose and stress hormones on the activity of key enzymes of liver glycogen metabolism in rats.

Endogenous corticosterone released in protracted immobilization stress fails to increase the activity of liver glycogen synthase, perhaps because of the inhibition of synthase phosphatase by phosphorylase a. It was also found, that in rats subjected to acute immobilization stress the stimulation of the activity of both synthase a and total forms by glucose administered i.v. is depressed. Finally, in rats fasting for 24 h a paradoxical augmentation by glucose of the stimulatory effect of glycogenolytic hormones released in acute immobilization stress on phosphorylase a activity was observed.

Animals↗
PubMed1985

Are endogenous glucocorticoids involved in short-term regulation of hepatic glycogen metabolism?

The release of endogenous corticosterone was stimulated by intraperitoneal administration of ACTH to conscious rats. Corticosterone had no reproducible stimulatory effect either on the activation of synthase or inactivation of phosphorylase. On the other hand, an induction of the synthesis of total synthase enzyme protein was observed which could be blocked by actinomycin D. In Sephadex-filtered liver homogenates, a particularly impaired pattern of phosphorylase inactivation/synthase activation was observed during incubation at 20 degrees C in the ACTH-treated rats.

Adrenocorticotropic Hormone↗
PubMed1985

Intravenous thiobarbital anaesthesia for determination of liver glycogen phosphorylase activity in rats subjected to various forms of stress.

Glycogen phosphorylase activity was determined in rat livers obtained by laparotomy in thiobarbital (Inactin, PROMONTA) anaesthesia induced by injection of the drug via a polyethylene catheter into a jugular vein as described previously [Németh et al. 1983a]. Intact rats and animals exposed to open field stress without or after i.p. injection of the alpha blocker phentolamine (Regitine, CIBA; 20 mg kg-1, 90 min before stress) or the beta blocker propranolol (Inderal, ICI; 2 mg kg-1, 30 min before stress) were studied. In stressed animals a net increase of phosphorylase activity was observed. This response was abolished after alpha blockade, while after beta blockade it was potentiated. In a further series on animals subjected to the same type of anaesthesia, the activating effect of immobilization stress on phosphorylase activity was confirmed in both fed and fasted animals, the response of the latter issuing from a lower initial level but being of the same extent as in the fed rats.

Animals↗
PubMed1984

Interaction of glucocorticoids in stimulation of liver tyrosine aminotransferase and tryptophan pyrrolase by estrogen in female rats.

Bilateral adrenalectomy inhibited the increase in liver tyrosine aminotransferase and tryptophan pyrrolase activity after s.c. administration of cca 50 micrograms 17-beta-estradiol (Agofollin SPOFA, Praha) per 1 kg body weight daily for 14 days. Moreover, the authors describe the restitution of the estrogen effect by peroral dexamethasone intake via the drinking saline offered to the animals during the period of Agofollin treatment. In rats substituted in this way the resulting enzyme activities even exceeded those caused by dexamethasone alone.

Adrenal Glands↗
PubMed1983

[Hormonal activity control of liver glycogen phosphorylases with special reference to their significance within the scope of a stress reaction].

For the mechanism of glycogen metabolism in the liver hormonal action of epinephrine, norepinephrine, glucagon, vasopressin and angiotensin II is of importance. The potential importance of hormonal regulation for interpreting the changes in glycogen metabolism under conditions of stress is underlined. Own results show an acute increase of glycogen phosphorylase activity in stress within 1-2 minutes. 24 hours fasting decreases the sensibility of this enzyme towards the hormonal influence.

Angiotensin II↗
PubMed1983

Fasting reduces the response of liver glycogen phosphorylase to physiological levels of epinephrine in rats.

The effect of 24 h fasting on the response of rat liver glycogen phosphorylase activity to an i.v. bolus of 2.75, 5.50 or 22.00 nmol kg-1 of epinephrine was studied. Even the lowest dose increased activity of the a form of the enzyme in the liver of anesthetized, fed rats to approximately 70 - 80% of total enzyme activity two minutes after administration. Further increased epinephrine doses failed to potentiate the enzyme response significantly, but shortened the time necessary for attaining the response, and delayed the return of enzyme activity to control values. No activation of phosphorylase was demonstrable after 2.75 nmol kg-1 of the hormone injected to fasted rats, but after increasing the hormone dose to 5.50 nmol kg-1 the enzyme response was the same as in the corresponding fed group at 2 min, and after administering the highest dose both at 1 and 2 min. According to these results, an increased threshold to epinephrine should be added to the already described effects of fasting, i.e. decreased phosphorylase a and total enzyme activity and shortened response to catecholamines. The efficacy of the i.v. bolus of 5.50 nmol kg-1 of epinephrine in increasing plasma epinephrine level to the theoretical value of 27.5 pmol ml-1 was proven by measuring plasma epinephrine which increased during the first minute after hormone administration to 24.5 + 5.9 pmol ml-1, to decrease during an additional minute with a half life of cca 22.2 seconds.

Animals↗