Search PubMed⌕ Search

Biomedical subjects

O E Brodde

Publications and source records attributed to O E Brodde.

At least 199 records · Page 11Linked to original sources
PubMed1980

[3H]-Spiroperidol labels dopamine receptors in membranes from rabbit mesenteric artery.

The potent dopamine receptor antagonist [3H]-spiroperidol was used to label binding sites in a membrane fraction derived from rabbit mesenteric artery which had characteristics expected for dopamine receptors. The binding was of high affinity with an equilibrium dissociation constant (KD) of 13.1 nM; it was saturable with 110 fmol of [3H]-spiroperidol bound/mg protein at maximal occupancy of the sites. Binding at 37 degrees C was rapid and readily reversible with rate constants of 0.0154nM-1 min-1 and 0.114min-1 for forward and reverse reaction, respectively. Dopamine receptor antagonists were about 100--200 times more potent than alpha-adrenolytic drugs in competing for the [3H]-spiroperidol binding sites and dopamine was much more potent than (-)-noradrenaline, (-)-isoprenaline, clonidine or serotonin. It is concluded that in a membrane fraction of the rabbit mesenteric artery there exist binding sites for [eH]-spiroperidol indistinguishable from dopamine receptors. Thus the present results support the view that in vascular smooth muscle there exist specific dopamine receptors.

Animals↗
PubMed1980

Effects of thyroid hormone deficiency on pre- and postsynaptic noradrenergic mechanisms in the rat cerebral cortex.

Thyroid hormones are known to influence the noradrenergic neurotransmission in several peripheral organs. In order to find out whether similar changes exist in the central nervous system, we investigated adrenoceptor-mediated responses in the rat brain cortex during propylthiouracil-induced hypothyroidism. In contrast to unchanged basal cAMP levels, the cAMP accumulation following (-)noradrenaline incubation (3 X 10(-6)--3 X 10(-5) M) was significantly reduced in brain slices from hypothyroid animals. The difference between controls and propylthiouracil-fed rats became more pronounced when (-) isoprenaline (3 X 10(-6)--3 X 10(-5) M) was used for selective stimulation of beta-adrenoceptors. Since the cAMP increase mediated via alpha-adrenoceptors was not affected, it may be concluded that thyroid hormone deficiency only impairs the beta-adrenergic transmission. Phosphodiesterase activity remained unaltered suggesting that thyroid hormones influence the beta-adrenoceptors or the adenylate cyclase coupled to it. The sensitivity of presynaptic alpha-adrenoceptors modulating the release of noradrenaline was evaluated using occipital cortical slices preincubated in 3H-noradrenaline. Clonidine inhibited whereas phentolamine enhanced the 3H-overflow induced by electrical stimulation in a dose-dependent manner. No differences could be detected between control- and propylthiouracil-treated animals. Thus presynaptic alpha-adrenoceptors are not affected by hypothyroidism.

Animals↗
PubMed1979

Demonstration of alpha-adrenoceptors in the rabbit heart by [3H]-dihydroergocryptine binding.

For direct identification of alpha-adrenoceptors in a membrane fraction of the rabbit heart the potent alpha-adrenoceptor antagonist [3H]-dihydroergocryptine ([3H]-DHE) was used. 1. The binding of [3H]-DHE was saturable with 80 fmol of [3H]-DHE bound/mg protein and of high affinity with an equilibrium dissociation constant (KD) of 11.5 nM. Binding of [3H]-DHE (6 nM) was rapid (t 1/2 = 2 min) and readily reversible. From the ratio of the rate constants for forward (K1 = 1.97 X 10(7) M-1 min-1) and reverse (K2 = 0.206 min-1) reactions a KD-value of 10 nM was calculated, which is in good agreement with that obtained by equilibrium studies. 2. Adrenergic agonists compete for [3H]-DHE binding in an order to potency: (-)adrenaline greater than (-)phenyleprine greater than (-)isoprenaline and adrenergic antagonists in the order: phentolamine greater than yohimbine greater than (-)propranolol. Binding is stereospecific as indicated by the greater potency of (-)adrenaline than (+/-)adrenaline in displacing [3H]-DHE from the binding sites. 3. For comparison the binding of the potent beta-adrenoceptor antagonist (-)[3H]-dihydroalprenolol ((-)[3H]-DHA) was measured in the same membrane fraction. The number and affinity of beta-adrenoceptors amounted to 115 fmol of (-)[3H]-DHA bound/mg protein at saturation and KD = 7.9 nM. Adrenergic agonists compete for (-)[3H]-DHA binding in an order of potency: (-)isoprenaline greater than (-)adrenaline greater than (-)phenylephrine; and adrenergic antagonists in the order: (-)prapranolol greater than phentolamine. 4. It is concluded that in a membrane fraction of the rabbit heart there exist binding sites for [3H]-DHE which have characteristics indistinguishable from alpha-adrenoceptors. Thus the present results are in agreement with previously reported data on the existence of cardiac alpha-adrenoceptors in the rabbit heart (Schümann et al., 1974; Endoh et al., 1976b).

Adrenergic alpha-Agonists↗
PubMed1978

The role of cyclic AMP in temperature-dependent changes of contractile force and sensitivity ot isoprenaline and papaverine in guinea-pig atria.

Right and left guinea-pig atria responded to decreasing temperatures (42-27 degrees C) with elevation for force of contraction and concomitant increases in cAMP. When atria were rapidly cooled from 42 to 27 degrees C the increase in cAMP occurred prior to the onset of the inotropic responses. Papaverine (3 X 10(-5) M) potentiated the effects of temperature on cAMP and force of contraction on left atria driven at 0.5 Hz. On right atria beating spontaneously at frequencies above 2 Hz papaverine only potentiated the effect of decreasing temperatures on the response of cAMP but not on that of force of contraction. Time course studies of the effects of isoprenaline (3 X 10(-8) M) on right atria at 27 degrees C showed large inotropic responses to isoprenaline which were accompanied by increases in cAMP. At 42 degrees C the responses of force of contraction and cAMP to isoprenaline occurred faster and were only short-lasting. As with the time courses for isoprenaline, dose-response curves for the effect of isoprenaline and papaverine on cAMP content and force of contraction also appeared to be shifted towards higher levels at hypothemia. However, pD2 values reflected increases in affinity for inotropic, but not for the cAMP responses to isoprenaline and papaverine at hypothermia. These results show that cyclic AMP is involved in the inotropic responses to hypothermia, but not in the supersensitivity of heart to isoprenaline and papaverine as observed at low temperatures.

Animals↗
PubMed1978

No evidence for involvement of dopaminergic receptors in the positive inotropic action of dopamine on the isolated rabbit papillary muscle.

Experiments were carried out on the isolated rabbit papillary muscle driven at 0.5 Hz in order to further elucidate the mechanism of the positive inotropic effect evoked by dopamine. The dose-response curve for dopamine was not affected by the antagonists pimozide (10(-6) M), yohimbine (10(-5) M) pindolol (3 x 10(-8) M) and phentolamine (10(-6) M) when these agents were given separately. Only the simultaneous administration of yohimbine plus pindolol and phentolamine plus pindolol, respectively, shifted the entire curve to the right. This shift was not further influenced by pimozide. Dopamine (10(-4) M) increased the cyclic AMP content of the papillary muscle by about 50%; this increase was not affected by pimozide, but was markedly elevated by yohimbine and completely depressed by pindolol. From the present results it is concluded, that dopamine produces its positive inotropic effect through stimulation of myocardial alpha-as well as beta-adrenoceptors to about the same degree; stimulation of specific dopaminergic receptors, however, is not involved. The stimulation of beta-adrenoceptors is accompanied by an increase of the cyclic AMP level, while that of alpha-adrenoceptors is not.

Animals↗
PubMed1977

H1 - and H2-receptor mediated responses to histamine on contractility and cyclic AMP of atrial and papillary muscles from guinea-pig hearts.

On guinea-pig heart we investigated whether cyclic AMP serves as a messenger for H1 - and/or H2-mediated responses to histamine. (1) On papillary muscle histamine elicited positive inotropic responses which were antagonized by burimamide but not by promethazine. The stimulation of H2-receptors was not only associated with an increase in contractility but also with an increase in cAMP. As shown by the time course of effects for 10(-5) M histamine, the maximal increase in cAMP preceded the maximum in contractility. The mechanical and biochemical responses to histamine were potentiated by the phosphodiesterase inhibitor papaverine, but antagonized by burimamide. (2) On the left guinea-pig atrium containing H1-receptors the inotropic response to histamine (10(-5) M) was not accompanied by increases in cAMP at stimulation frequencies of 0.5 and 2 Hz, respectively. In addition, in the presence of papaverine (3 X 10 (-5) M) no change in the cyclic AMP level occurred after application of histamine. Papaverine by itself, however, concomitantly increased contractility and cyclic AMP at a stimulation frequency of 0.5 Hz. In contrast, at 2 Hz papaverine increased only cAMP leaving the contractility unchanged. At this frequency the well-known Ca2+-antagonistic effect comes into prominence, thus masking the positive inotropic effect attributable to the inhibition of the phosphodiesterase. (3) On the right guinea-pig atrium the mediation of the positive chronotropic response to histamine by H2-receptors which is partly involved in the inotropic effect via the frequency-force relationship does not lead to a concomitant increase in cAMP. Also, in the presence of papaverine, histamine had no influence on the cAMP. However, papaverine potentiated the cardioacceleration produced by histamine. Although it is very likely that the cAMP in the sinus node rises, we were not able to detect an increase in cAMP in the whole atrial tissue. From the present results the conclusion can be drawn that the mediation of the inotropic effect due to stimulation of H2-receptors by histamine is associated with an increase of cyclic AMP, whereas that of H1-receptors is not. The view that cAMP may be the second messenger in the chronotropic action of histamine needs further elucidation by experiments on sino-atrial cells.

Animals↗
PubMed1977

Mechanism of inhibition of dopamine beta-hydroxylase evoked by FLA-63. An in vitro study.

Bis-(4-methyl-1-homopiperazinylthiocarbonyl)-disulphide (FLA-63) inhibits in vitro purified bovine adrenal medullary dopamine beta-hydroxylase (BDH) concentration-dependently; 50% inhibition is produced by 2 x 10(-6)M FLA-63. Spectrophotometric experiments show that FLA-63 is reduced by ascorbate very likely to the corresponding dithiocarbamate-derivative, which acts as a Cu++-chelator. Cu++-ions are able to completely abolish the inhibition of the DBH caused by FLA-63 in concentrations up to 2.5 x 10(-6)M. It is concluded that FLA-63 inhibits the DBH mainly in its reduced form via the formation of a chelate-complex with copper ions derived from the DBH.

Adrenal Medulla↗
PubMed1976

The role of lactic acid in retinal neovascularization.

In order to gain information on the possible role of lactate in the development of neovascularization following retinal malperfusion, the lactate content in vitreous-retina-choroid specimens of 02-treated kittens and streptozotocin-diabetic rats was determined. In both experiments there was no significant difference of lactate content between the diseased eyes and healthy controls.

Animals↗
PubMed1976

Lack of epinine formation in adrenal medulla and brain of rats during cold exposure and inhibition of dopamine beta-hydroxylase.

Cold exposure of rats for 4 h and simultaneous inhibition of dopamine beta-hydroxylase by FLA-63 (25mg/kg) led to a reduction of the catecholamine content of the adrenal medulla by 46% and of the brain by 68%. Additional injections of 5 mg/kg FLA-63 4 and 9 h after beginning of the experiments, respectively, kept the catecholamine content on this low level (brain) or decreased it further (adrenal medulla). Administration of 5 mg/kg (-)DOPA together with the mono-amine oxidase inhibitor pargyline (50 mg/kg) 24 h after the first injection of FLA-63 stimulated the resynthesis. It amounted for the adrenal medulla to 20 mug/kg body weight/8 h and for the brain to 45ng/g tissue wet weight/8 h. Paper chromatographic analyses of the extracts of adrenal medulla and brain, respectively, performed at each time of the different injections, clearly identified adrenaline, noradrenaline and dopamine (in traces) in the adrenal medulla as well as noradrenaline and dopamine in the brain; epinine on the contray could not be demonstrated, not even in traces. Since at least 25 ng of epinine can be detected with certainty by our method, it can be concluded that epinine is not formed in amounts greater than 75 ng/pair adrenal glands or 37.5 ng/brain. The present results support the view that the main pathway of adrenaline biosynthesis in the suprarenal medulla and the brain proceeds via noradrenaline and not via epinine.

Adrenal Medulla↗
PubMed1976

Relationship between the level of cAMP and the contractile force under stimulation of alpha- and beta-adrenoceptors by phenylephrine in the isolated rabbit papillary muscle.

The time course of changes of the level of 3',5'-cyclic AMP (cAMP) and of the tension developed under stimulation of alpha- and beta-adrenoceptors by phenylephrine was investigated in the isolated rabbit papillary muscle. Furthermore the dose-response relationships for increases of cAMP and of developed tension elicited by phenylephrine were determined. 1. A submaximally effective concentration of phenylephrine (10(-5) M) increased significantly the level of cAMP of the papillary muscle at 15 and 30 s by 45 and 36% respectively; the level of cAMP returned to the control value at 60 s after the administration. The developed tension increased significantly not before 45 s and reached its maximal level at 180 s. 2. When alpha-adrenoceptors were blocked by phentolamine (10(-6) M), the positive inotropic effect of phenylephrine was decreased significantly but the increase of cAMP induced by phenylephrine was not reduced. In the presence of phentolamine the increase of cAMP induced by phenylephrine lasted longer than in the control experiments. 3. The effects of phenylephrine (10(-5) M) both on the level of cAMP and the developed tension mediated via stimulation of beta-adrenoceptors in the presence of phentolamine were enhanced by the phosphodiesterase inhibitor papaverine throughout the course of responses. 4. Phenylephrine produced an increase in developed tension as well as in cAMP. The corresponding dose-response curves run parallel to each other but differed by about 1.5 log units whereby the developed tension was evoked by lower concentrations. Phentolamine (10(-6) M) shifted the curve for the positive inotropic action by about 1.5 log units but did not affect that for increase in cAMP. Therefore, in the presence of the alpha-adrenolytic drug phentolamine the difference between both curves became smaller so that both curves were superimposed. Papaverine (10(-5) M) shifted the whole curve for cAMP upwards and enhanced the maximal contractile response to phenylephrine mediated by stimulation of beta-adrenoceptors. 5. The present results indicate that the positive inotropic action of phenylephrine in lower concentrations (less than 10(-5) M) induced by stimulation of alpha-adrenoceptors is independent of the level of cAMP. The positive inotropic action of the higher concentrations of phenylephrine induced via stimulation of beta-adrenoceptors was preceded by an accumulation of cAMP; the inhibition of the cAMP phosphodiesterase activity by papaverine enhanced the actions of phenylephrine both on the level of cAMP and on the contractile force.

3',5'-Cyclic-AMP Phosphodiesterases↗