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Biomedical subjects

I Hanbauer

Publications and source records attributed to I Hanbauer.

At least 73 records · Page 4Linked to original sources
PubMed1978

Heat-stable low molecular weight form of phosphodiesterases from bovine pineal gland.

The 105,000 X g supernatant fraction of bovine pineal gland contains a phosphodiesterase activity that hydrolyzes both cyclic AMP and cyclic GMP. The rate of hydrolysis is 4-5 times greater with cyclic GMP as substrate than with cyclic AMP. Chromatography of supernatant fraction on Sephadex G-150 resolves phosphodiesterase activity into two fractions designated PDE I and PDE II. These are distinguishable on the basis of their molecular size, substrate specificity, and kinetic parameters. PDE I hydrolyzes cyclic GMP at a faster rate than cyclic AMP and has a molecular weight of 163,000. PDE II appears to be a smaller protein with a molecular weight of 24,400 and is specific for cyclic AMP. PDE I has apparent Km values of 83 and 53 micron for cyclic AMP and cyclic GMP, respectively, whereas PDE II exhibits an apparent Km value of 330 micron for cyclic AMP. With subsaturating concentrations of cyclic AMP as substrate, the phosphodiesterase activity of PDE I is inhibited by the addition of cyclic GMP. However, PDE II activity remains unaffected by cyclic GMP even at concentrations up to 125 micron. PDE II appears to be thermostable, losing only 20% of its activity on heating at 80 degrees for 2 min. Similar treatment completely abolishes the enzyme activity of PDE I.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

The regulation of dopamine and noradrenaline in the rat carotid body and its modification by denervation and by hypoxia.

1. The mechanism whereby hypoxia lasting 20 min elicits a decrease in the dopamine content of rat carotid bodies was studied. 2. The concentrations of dopamine, noradrenaline, dihydroxyphenylacetic acid and homovanillic acid in carotid body were measured by a mass-fragmentographic procedure. The turnover rate of dopamine was determined by measuring the elimination rate of dihydroxyphenylacetic acid immediately after inhibition of monoamine oxidase by injection of pargyline. The turnover rate of noradrenaline was derived from measurements of the rate of decline of noradrenaline content after injection of L-methyl-p-tyrosine. 3. The results indicate that hypoxia increases the rate of dopamine release without changing its turnover rate thereby accounting for the decrease in dopamine content. The content and turnover rate of noradrenaline remained unchanged during exposure to hypoxia. 4. Neither the carotid sinus nerve nor the sympathetic innervation appeared to participate in the regulation of dopamine content or turnover rate in carotid bodies of rats either before or during hypoxia. 5. Since transection of the carotid sinus nerve or/and ganglionectomy failed to prevent the decrease of dopamine content caused by hypoxia, it is inferred that low arterial PO2 depletes dopamine stores independently of the above mentioned innervation.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1976

Long-term regulatory mechanisms for tyrosine hydroxylase in sympathetic ganglia and carotid body.

The delayed activation of TH elicited by hypoxia in carotid body indirectly suggests that the release of dopamine is part of the responses elicited by hypoxia. The TH activation appears to be independent from nicotinic receptor stimulation and can be abolished by dopaminergic receptor stimulation. Dexamethasone also increases the activity of TH. Since both hypoxia and dexamethasone fail to change the kinetic constants, the long-term increase of TH could be viewed as an expression of new synthesis of enzyme molecules. This assumption is supported by the evidence presented on the prompt kinetic change in PDE, which according to the model proposed by Uzunov et al. (42) expresses the participation of a prompt and sustained response of the second messenger in postsynaptic cells. It remains to be ascertained whether the change in the catalytic activity of PDE which metabolizes the second messenger can be suppressed by dopamine-receptor blockers. Immediate changes of PDE coupled with the delayed increase in TH activity may contribute to a better understanding of the neuronal mechanisms controlling the chemoreceptor function. It is hoped that the continuation of these studies will help to define the function of type I cells in the carotid body.

Adrenal Medulla↗
PubMed1975

Further evidence for a cAMP dependent regulation of tyrosine-3-monoxygenase induction in adrenal medulla: effect of denervation.

Unilateral adrenal denervation caused a gradual decrease of adenylate cyclase activity in rat adrenal medulla. The extent of the increase in adrenal medullary 3',5'-cyclic adenosine monophosphate (cAMP) content elicited by injections of carbamylcholine declined gradually folling adrenal denervation. Three or nine days after denervation carbamylcholine caused rise of cAMP and a delayed increase of tyrosine-3-mono-oxygenase (TH) activity of similar magnitude in intact and denervated adrenal medullae. However, after an interval of 15 days or longer following denervation the increase in TH activity elicited by carbamylcholine was greatly reduced. These results support previous proposals that cAMP is involved as a second messenger in the trans-synaptic induction of TH.

Adenylyl Cyclases↗
PubMed1975

ATP, cyclic AMP, and magnesium increase the affinity of rat striatal tyrosine hydroxylase for its cofactor.

Treatment of rat striatal tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] with conditions optimal for protein phosphorylation results in the reduction of the tyrosine hydroxylase Km for the cofactor 6-methyltetrahydropterin from 0.50 mM to 0.16 mM. This reaction is dependent upon ATP, 3':5'-cAMP, and Mg++ and causes a marked decrease in the sensitivity to end-product inhibition. Other brain regions and the adrenal gland show a similar response.

Adenosine Triphosphate↗
PubMed1975

Induction of tyrosine hydroxylase elicited by beta adrenergic receptor agonists in normal and decentralized sympathetic ganglia: role of cyclic 3',5' - adenosine monophosphate.

A subcutaneous injection of an oil suspension of l-epinephrine (270 mumol/kg), dopamine (270 mumol/kg) or l-norepinephrine (270 mumol/kg), when administered with phenoxybenzamine (32 mumol/kg i.p.) to blocl alpha adrenergic effects, increases the cyclic 3', 5'-adenosine monophosphate (cAMP) content in superior cervical ganglia (SCG) of rats. The increase is highest after l-epinephrine and dopamine and is barely detectable after l-norepinephrine; it lasts longer than 2 hours after l-epinephrine, about 30 minutes after dopamine and is fleeting after l-norepinephrine. The duration of the increase in cAMP elicited by l-epinephrine in SCG of rats is dose-related. Furthermore, when the cAMP increase lasts longer than 90 minutes, 48 hours later the tyrosine hydroxylase (TH) activity in SCG is increased. l0Epinephrine (150 mol/kg s.c.) induces TH in decentralized ganglia. One injection of l-isoproterenol (77 mol/kg i.p.) increases cAMP concentrations in intact and decentralized SCG. This increase lasts only 30 minutes and fails to induce TH 48 hours later. However, if the increase of cAMP concentration is prolonged by four successive injections of l-isoproterenol (15 30-minute intervals) the TH activity of intact and decentralized SCG is increased 48 hours later.l-Isoproterenol (four injections of 77 mumol/kg, each) and l-epinephrine (270 mumol/kg) fail to induce TH in the adrenal medulla. dl-Propranolol (125 mumol/kg i.p.) injected 30 minutes before l-isoproterenol blocks the increase of cAMP content and the delayed induction of TH activity in SCG. The elevation of TH activity elicited in SCG by beta adrenergic receptor agonists is always preceded by an increase of cAMP concentration lasting 90 minutes or longer. However, the induction of TH elicited by cold exposure or by reserpine administration can occur without an apparent increase in ganglionic cAMP concentration.

Adrenal Medulla↗