Biomedical subjects

C Sumners

Publications and source records attributed to C Sumners.

At least 127 records · Page 7Linked to original sources

PubMed1986

Sodium increases angiotensin II receptors in neuronal cultures from brains of normotensive and hypertensive rats.

Neuronal cultures from one-day-old brains of Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats were used to determine the effect of sodium ions on angiotensin II (Ang II) receptors in order to understand the mechanism of action of sodium at the cellular level. Incubation with sodium chloride of neuronal cultures from WKY rats caused a rapid and dose-dependent increase in the specific binding of 125I-Ang II to its receptors. A 260% increase in the binding was observed with 150 mM NaCl. Neuronal cultures from SH rat brains showed a similar sodium-stimulated increase in Ang II binding; however this increase was 150% greater than that observed in neuronal cultures from WKY rat brain. Kinetic studies of the effects of sodium ions on both WKY and SH neuronal cultures showed an increase in the dissociation of 125I-Ang II from its receptors in the presence of sodium ions. In addition, Scatchard analysis revealed that the increase in binding caused by sodium was due to an increase in the number of Ang II receptors. These observations indicate that sodium ions increase the number of Ang II specific receptors in intact neuronal cells and that this stimulation was more pronounced in neuronal cells from SH rat brains compared with WKY controls.

Angiotensin II↗

PubMed1986

Alpha 1-adrenergic receptor-mediated downregulation of angiotensin II receptors in neuronal cultures.

Previous evidence has suggested that brain catecholamine levels are important in the regulation of central angiotensin II receptors. In the present study, the effects of norepinephrine and 3,4-dihydroxyphenylethylamine (dopamine) on angiotensin II receptor regulation in neuronal cultures from rat hypothalamus and brainstem have been examined. Both catecholamines elicit significant decreases in [125I]angiotensin II-specific binding to neuronal cultures prepared from normotensive rats, effects that are dose dependent and that are maximal within 4-8 h of preincubation. Saturation and Scatchard analyses revealed that the norepinephrine-induced decrease in the binding is due to a decrease in the number of angiotensin II receptors in neuronal cultures, with little effect on the receptor affinity. Norepinephrine has no significant actions on [125I]angiotensin II binding in cultures prepared from spontaneously hypertensive rats. The downregulation of angiotensin II receptors by norepinephrine or dopamine is blocked by alpha 1-adrenergic and not by other adrenergic antagonists, a result suggesting that this effect is initiated at the cell surface involving alpha 1-adrenergic receptors. This is further supported by our data indicating a parallel downregulation of specific alpha 1-adrenergic receptors elicited by norepinephrine. In summary, these results show that norepinephrine and dopamine are able to alter the regulation of neuronal angiotensin II receptors by acting at alpha 1-adrenergic receptors, which is a novel finding.

Angiotensin II↗

PubMed1986

Alpha 1-adrenergic receptors in neuronal cultures from rat brain: increased expression in the spontaneously hypertensive rat.

Neuronal cells in primary culture from 1-day-old brains of normotensive, Wistar-Kyoto strain (WKY) and spontaneously hypertensive (SH) rats have been utilized to study the expression of alpha 1-adrenergic receptors. Binding of a selective alpha 1 antagonist, [125I]2-[beta-(4-hydroxy-3-iodophenyl)-ethylaminomethyl]-tetralone ([125I]HEAT) to neuronal membranes prepared from primary brain cultures of WKY and SH rats was 75-80% specific, rapid, and time-dependent although the binding was 1.5-2 times higher in neuronal membranes from SH rat brain cultures. Kinetic analysis of the association and dissociation data demonstrated no significant differences between rat strains. Competition-inhibition experiments provided IC50 values for various antagonists and agonists in the following order: prazosin less than phentolamine less than yohimbine less than phenylephrine less than norepinephrine less than propranolol, suggesting that [125I]HEAT bound selectively to alpha 1-adrenergic receptors. Scatchard analysis of the binding data provided straight lines for both strains of rats, indicating the presence of a homogeneous population of binding sites. It also showed that the increase in the binding in neuronal cells from SH rat brains over those from normotensive WKY controls was a result of an increase in the number of alpha 1-adrenergic receptors. Incubation of neuronal cultures from both strains of rats with phenylephrine, an alpha 1-adrenergic agonist, caused a time- and dose-dependent decrease in the binding of [125I]HEAT. This decrease was due to a decrease in the number of alpha 1-adrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Characteristics of the beta-adrenoreceptor from neuronal and glial cells in primary cultures of rat brain.

The cellular characteristics of the beta-adrenoreceptor in glial and neuronal cells from the newborn rat brain were determined by (-)-[125I]iodocyanopindolol binding. In membranes from both cell types, the binding was saturable and from competition assays the potency series of (-)-isoproterenol greater than (-)-epinephrine = (-)-norepinephrine greater than (+)-isoproterenol was observed. 5'-Guanylyl-imidodiphosphate reduced the affinity of (-)-isoproterenol for the beta-adrenoreceptor from glial cells but had no effect on agonist affinity in neuronal cells. Chronic treatment of both cell types with (-)-isoproterenol reduced the receptor content and the capacity of the agonist to increase the cellular cyclic AMP content. However, the receptor recovery after chronic agonist treatment was faster in glial cells (72 h) than neuronal cells (120 h) and was blocked by cycloheximide. Treatment of both types with the irreversible beta-blocker bromoacetylalprenololmentane (2 microM) reduced the receptor content by 78% but no receptor recovery was observed for 120 h after the initial receptor loss. The data indicated that the majority of beta-adrenoreceptors in both cell types are the beta-1 subtype, but show some differences in receptor-agonist interactions. Furthermore, these CNS cells may be useful models for regulatory studies on the beta-adrenoreceptor.

Adrenergic beta-Agonists↗

PubMed1986

Angiotensin II stimulates norepinephrine uptake in hypothalamus-brain stem neuronal cultures.

In this study we have characterized the uptake of [3H]norepinephrine (NE) into neuronal co-cultures of rat hypothalamus and brain stem and have examined the effects of angiotensin II (ANG II) on this uptake. Neuronal co-cultures prepared from the brains of 1-day-old Sprague-Dawley (SD) or Wistar-Kyoto (WKY) rats exhibited sodium-dependent and sodium-independent portions of the total [3H]NE uptake. The sodium-dependent uptake was abolished by blockers such as maprotiline, desmethylimipramine, and xylamine (0.1-100 microM) and is presumably neuronal uptake. The sodium-independent uptake was unaffected by these drugs and is presumably non-neuronal, since nonneuronal co-cultures from SD rats exhibited no significant sodium-dependent or blocker-sensitive uptake. In SD or WKY neuronal co-cultures, ANG II (0.1 nM-10 microM) caused increased [3H]NE uptake during short-term incubations (1-5 min). This stimulatory effect of ANG II was on neuronal NE uptake. Furthermore, it was inhibited by preincubation with saralasin (1-10 microM). Construction of saturation curves and kinetic analyses revealed that ANG II caused an increase in the maximal velocity of uptake of neuronal [3H]NE, but the affinity of the transporter for NE was not altered. With longer-term incubations (15-30 min), ANG II caused a reduction in neuronal [3H]NE uptake. This effect was also blocked by saralasin. However, reliable kinetic analysis was not possible with the longer-term incubations, and it is likely that the inhibitory action of the peptide represents a stimulation of NE release. Therefore, using neuronal co-cultures, we have identified a previously unseen stimulatory action of ANG II on neuronal [3H]NE uptake, which precedes the already documented inhibitory actions.

Angiotensin II↗

PubMed1986

Decreased alpha 1-adrenergic receptor-mediated inositide hydrolysis in neurons from hypertensive rat brain.

The expression of alpha 1-adrenergic receptors and norepinephrine (NE)-stimulated hydrolysis of inositol phospholipid has been studied in neuronal cultures from the brains of normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SH) rats. Binding of 125I-2-[beta-(4-hydroxyphenyl)-ethyl-aminomethyl] tetralone (HEAT) to neuronal membranes was 68-85% specific and was rapid. Competition-inhibition experiments with various agonists and antagonists suggested that 125I-HEAT bound selectively to alpha 1-adrenergic receptors. Specific binding of 125I-HEAT to neuronal membranes from SH rat brain cultures was 30-45% higher compared with binding in WKY normotensive controls. This increase was attributed to an increase in the number of alpha 1-adrenergic receptors on SH rat brain neurons. Incubation of neuronal cultures of rat brain from both strains with NE resulted in a concentration-dependent stimulation of release of inositol phosphates, although neurons from SH rat brains were 40% less responsive compared with WKY controls. The decrease in responsiveness of SH rat brain neurons to NE, even though the alpha 1-adrenergic receptors are increased, does not appear to be due to a general defect in membrane receptors and postreceptor signal transduction mechanisms. This is because neither the number of muscarinic-cholinergic receptors nor the carbachol-stimulated release of inositol phosphates is different in neuronal cultures from the brains of SH rats compared with neuronal cultures from the brains of WKY rats. These observations suggest that the increased expression of alpha 1-adrenergic receptors does not parallel the receptor-mediated inositol phosphate hydrolysis in neuronal cultures from SH rat brain.

Adrenergic alpha-Antagonists↗

PubMed1985

Reduced dipsogenic responsiveness to intracerebroventricularly administered angiotensin II in estrogen-treated rats.

Chronic administration of two doses of estradiol benzoate (30 and 46 micrograms/kg/day) reduced the drinking response to acute administration of either isoproterenol (25 micrograms/kg, s.c.), the beta-adrenergic agonist, or angiotensin II (Ang II) (200 micrograms/kg, s.c.). The drinking response to intracerebroventricular administration of Ang II (40 ng/kg), but not carbachol (800 ng/kg), was also attenuated in estrogen-treated rats. An assessment of the Ang II binding in a diencephalic block of tissue from estrogen-treated rats revealed a significant reduction compared to untreated controls. The results suggest, but do not prove, that the reduced drinking response observed in estrogen-treated rats may be related to a reduction in the number of Ang II receptors in the brain.

Angiotensin II↗

PubMed1985

Altered norepinephrine uptake in neuronal cultures from spontaneously hypertensive rat brain.

Uptake of [3H]norepinephrine (NE) has been characterized and compared in neuronal cultures prepared from the brains of 1-day-old normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SH) rats. In cultures from both strains total [3H]NE uptake consisted of a sodium-dependent portion and a sodium-independent portion. The sodium-dependent [3H]NE uptake was inhibited by NE uptake blockers such as maprotiline or desmethylimipramine (both at 0.5-100 microM). This sodium-dependent, NE uptake blocker-sensitive portion of the uptake was also stereospecific, preferring the l-isomer of NE. In contrast, the sodium-independent uptake was not sensitive to maprotiline or desmethylimipramine. Autoradiograms of cultures incubated with [3H]NE showed label concentrated in certain, but not all, neurites and in a few neuronal cell bodies. Cultures incubated with label in sodium-free buffer did not show any such localization of grains but instead showed a diffuse pattern. Incubation of neuronal WKY or SH brain cultures with various concentrations of l-[3H]NE and unlabeled l-NE in the presence or absence of sodium enabled the construction of saturation curves for sodium-dependent uptake in each culture type. In WKY cultures, Km and maximal velocity of uptake (Vmax) values of 0.37-0.45 microM and 0.58-0.69 pmol X mg protein-1 X min-1, respectively, were obtained for sodium-dependent uptake. In contrast, the Km and Vmax values for [3H]NE uptake in SH neuronal cultures were 1.4 microM and 1.31 pmol X mg protein-1 X min-1, respectively. Kinetic analyses of the results show that in SH neuronal cultures the [3H]NE uptake sites are of lower affinity but higher capacity compared with those in WKY neuronal cultures.

Animals↗

PubMed1985

Effects of catecholamines on lactic acid output during progressive working contractions.

Epinephrine and norepinephrine together (E + NE) and epinephrine (E) alone were infused intravenously in stepwise increasing doses during progressive isotonic tetanic contractions. The goal was to mimic, for in situ dog skeletal muscle, the concentrations of these catecholamines in the blood and the contractions during progressive exercise. The concentrations of lactate and O2 in arterial and muscle venous blood, the arterial plasma concentration of E and NE, PO2 in arterial and muscle venous blood, and the venous outflow were measured. The infusions caused a rise in plasma E and NE like those seen in progressive exercise. Compared with no-infusion controls, the E + NE infusions and the E alone infusion resulted in significant increases in maximal lactic acid output by the muscles during the contractions from 0.24 mumol X g-1 X min-1 in the controls to 0.44 and 0.54 mumol X g-1 X min-1 during E + NE and E alone infusions, respectively. The venous O2 concentrations and partial pressures were not reduced by the infusions. Both infusions resulted in a rise of arterial lactate concentration that could not be accounted for by the lactic acid output of the contracting muscles. The E alone infusions were associated with a rise in maximal O2 uptake during the contractions. Since the effects of the E + NE and E alone infusions were similar, it was suggested that E is more active than NE. It was suggested that E also increased lactic acid production in tissues other than the working muscles.

Animals↗

PubMed1984

Catecholamine-angiotensin II receptor interaction in primary cultures of rat brain.

Neuron-enriched primary cultures from 1-day-old rat brains have been used to study the influence of catecholamines on angiotension II receptors. Treatment of cultures with alpha-methyl-p-tyrosine caused a time- and concentration-dependent increase in the specific binding of 125I-angiotensin II and a decrease in neuronal norepinephrine and dopamine contents. A maximum increase of 75% in the binding and a decrease of 67% in catecholamine content was observed with 400 microM alpha-methyl-p-tyrosine. Removal of alpha-methyl-p-tyrosine from cultures resulted in the recovery of catecholamine levels and decrease in 125I-angiotensin II binding to control levels. In contrast, treatment of cultures with pargyline caused decreases in the binding of 125I-angiotensin II and increases in catecholamine levels in neuronal cultures. Scatchard analysis demonstrated that an increase in 125I-angiotensin II binding by alpha-methyl-p-tyrosine was due to an increase in the affinity of receptors for angiotensin II without changes in the number of angiotensin II binding sites. The results obtained here indicate that angiotensin II binding to neuron-enriched cultures is reciprocally related to the levels of neuronal catecholamines.

Angiotensin II↗

PubMed1984

Angiotensin II in neuronal cultures from brains of normotensive and hypertensive rats.

Primary neuronal cultures from 1-day-old rat brains, which contain angiotensin II (ANG II) immunoreactivity within the neurons and are capable of de novo synthesis of this immunoreactivity, have been used in this study to determine the nature of this immunoreactivity by high-performance liquid chromatography (HPLC). Neuronal cultures from the brains of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats were found to contain ANG II immunoreactivity, which co-migrated with authentic ANG II on HPLC. The angiotensin detected in brain cultures was not derived from the growth medium, and its level was significantly decreased by incubating the cultures with captopril. A 71% decrease in the levels of ANG II was observed in neuronal cultures of SH rat brains compared with those from WKY controls. These observations show that differences in brain angiotensin between SH and WKY are present before differences in blood pressure are manifested.

Angiotensin II↗

PubMed1984

Increased angiotensin II receptors in neuronal cultures from hypertensive rat brain.

Binding of 125I-angiotensin II (ANG II) to neuronal cultures made from the brains of 1-day-old normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SH) rats was time dependent, saturable, reversible, and 90-95% specific. Neuronal cultures from SH rats bound 50-70% more 125I-ANG II compared with their WKY controls. Scatchard analysis revealed that the increase in the specific binding of ANG II to SH rat neuronal cultures was due to an increase in the number of binding sites per cell rather than change in the affinity of receptors for ANG II. Light-microscopic autoradiographic analysis showed that ANG II specific binding sites were located on neuronal cell bodies and neurites. Treatment of neuronal cultures from both strains of rats with alpha-methyl-p-tyrosine caused a 50-60% decrease in the endogenous levels of norepinephrine (NE) and dopamine (DA). This decrease was associated with increases in the specific binding of 125I-ANG II in neuronal cultures from WKY rat brain. In contrast, ANG II binding in neuronal cultures from SH rat brain failed to respond to changes in NE and DA levels. These observations suggest that ANG II specific receptors are increased and that they are not under a negative-feedback control by catecholamines in SH rat brain neuronal cultures.

Angiotensin II↗

PubMed1984

Plasma catecholamines and their effect on blood lactate and muscle lactate output.

This study was designed to test the hypothesis that epinephrine (E) and norepinephrine (NE) increase net muscle lactate output (L) of in situ gastrocnemius-plantaris muscle group during contractions. Plasma [E] and [NE] were measured before and after the surgical isolation of the muscle and at 10-min intervals during the 60-min experiments. Plasma [E] and [NE] were increased threefold by intravenous infusions of E (n = 3) or NE (n = 3) at a rate of 1.5 micrograms X kg body wt-1 X min-1. Arterial and muscle venous blood samples for O2 and lactate concentrations were also obtained. The infusions began at min 11 and repetitive isometric contractions (4 tw/s) began at min 31. The presurgery plasma [E] and [NE] averaged 0.34 and 0.52 ng/ml, respectively, and rose to 1.12 and 1.19 ng/ml 10 min after surgery. Arterial and venous lactate concentrations (CaL and CvL) increased continuously during E infusion but remained constant during NE infusion. Maximal L during the first 10 min of contractions was significantly increased compared with an identical earlier study without infusions. O2 uptake was not changed by the infusions. It is concluded that E causes CaL to rise and that both E and NE increase maximal net lactate output during contractions.

Animals↗

PubMed1983

Angiotensin II stimulates changes in the norepinephrine content of primary cultures of rat brain.

Interactions between norepinephrine and angiotensin II were investigated in neuron-enriched primary brain cell cultures, which have been demonstrated to contain catecholamines, angiotensin II-like immunoreactivity and specific receptors for angiotensin II. Angiotensin II (7.5 and 15.0 micrograms/ml) caused significant increases in both neuronal and growth media norepinephrine levels, which were inhibited by saralasin. These observations suggest that angiotensin acts at its specific receptors to alter neuronal norepinephrine levels.

Angiotensin II↗

PubMed1983

Rat brain cells in primary culture: visualization and measurement of catecholamines.

Catecholamines have been visualized and quantified in primary cultures of whole rat brain. Twenty-one-day old cultures treated with glyoxylic acid and viewed under a fluorescence microscope revealed neurons stained specifically with blue-green catecholamine fluorescence. Brightly stained multipolar cell bodies were seen, along with stained neurites and varicosities, and there was no staining associated with the non-neuronal portion of the culture. Twenty-one-day-old non-neuron-enriched cultures contained 10-20 times less norepinephrine and dopamine than cytosine arabinoside-treated neuron-enriched cultures. The latter cultures contained 10-12 times more norepinephrine than 1-day-old rat brains, demonstrating maturation and differentiation of the cultured neurons. Norepinephrine levels of neuron-enriched cultures were, however, 3 times less than those in 21-day-old rat brains. The cultured neurons had the ability to synthesize catecholamines since levels were decreased with alpha-methyl-p-tryosine. On the other hand, the growth medium contained significant amounts of norepinephrine, but did not have the ability to synthesize catecholamines. It may be concluded that the cellular catecholamines are not derived from the medium in any great amounts. This study provides the basis of a system in which to examine catecholaminergic neurotransmission and peptide catecholamine interactions at the cellular level under semi-defined conditions.

Animals↗

PubMed1983

A comparison of the potencies of various dopamine receptor agonists in models for pre- and postsynaptic receptor activity.

Several dopamine (DA) receptor agonists, notably N,N-dipropyl-2-aminotetralin analogues differing in the number and position of phenolic hydroxyl groups, were evaluated in model systems for pre- and postsynaptic dopaminergic activity. Apomorphine, piribedil and pergolide were included for comparison. All compounds inhibited the gamma-butyrolactone (GBL)-induced increase in DA concentrations in the rat striatum and olfactory tubercle, although a dose-dependency could not be demonstrated for one of the compounds, i.e. N,N-dipropyl-2-amino-5,6-dihydroxy-tetralin. In addition to the reversal of the DA-increase all compounds decreased the HVA and DOPAC levels in a dose-dependent manner, in much the same way as in normal, non GBL-pretreated rats. The potencies of the drugs to decrease HVA in normal rats and to inhibit the DA-increase and to decrease HVA in GBL-pretreated rats, both in the striatum and the olfactory tubercle were compared with each other and with the potencies to induce stereotyped behaviour. It may be concluded that (1) N,N-dipropyl-2-amino-7-hydroxytetralin shows the largest difference in activity in the biochemical and the behavioural models, suggesting a selective presynaptic activity. This was corroborated by the appearance of a marked hypomotility after low doses of this compound; (2) The potencies to decrease striatal HVA concentrations are generally somewhat different from the potencies to inhibit GBL-induced DA-increases, but appear to be comparable to the potencies to inhibit GBL-induced dihydroxyphenylalanine (DOPA)-increases; (3) There is no indication that the DA agonists in general are more potent at presynaptic receptors in the tubercle than in the striatum.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1983

Central injection of angiotensin II alters catecholamine activity in rat brain.

Centrally injected angiotensin II (ANG II) produces a pressor response. The effect of ANG II injected intracerebroventricularly on catecholamine utilization in specific rat brain regions was examined. A pressor dose of ANG II stimulated an increase in norepinephrine (NE) utilization in the locus coeruleus, raphe magnus and AI regions of the brain stem, and in the hypothalamus. These increases in NE utilization were selective, and dopamine utilization was not altered in the same regions. Also, the changes in NE utilization were direct and not due to the rise in blood pressure caused by ANG II, since a similar pressor effect caused by intravenously injected hypertonic saline did not alter NE utilization in any of the above regions. Areas such as the subfornical organ and organum vasculosum of the lamina terminalis that contain both catecholamines and ANG II receptors did not show a substantial change in catecholamine utilization after intracerebroventricularly injected ANG II. This study demonstrates that specific brain NE rich regions are activated by intracerebroventricular injection of ANG II. Some of these regions correlate with known blood pressure control centers and the data points to brain catecholaminergic regions which are involved in the central ANG II pressor response.

Angiotensin II↗

PubMed1981

Involvement of both dopaminergic and alpha-adrenergic receptors in the hypomotility induced by dibenzoyl-6,7-ADTN.

The dopaminergic prodrug dibenzoyl-6,7-ADTN (DB-6,7-ADTN) can enter the brain following intraperitoneal injection and be hydrolysed to produce low concentrations of the dopamine agonist 6,7-ADTN. Intraperitoneal injections of DB-6,7-ADTN produce a decrease in motor activity and in the present study this response has been characterised, and the underlying mechanisms examined. Doses of 10-100 mumol/kg DB-6,7-ADTN elicit a strong hypomotive response, which is dose dependent. Treated animals are significantly less active than controls. DB-6,7-ADTN hypomotility was significantly attenuated by the non-sedative dopamine receptor antagonist sulpiride (62 mumol/kg, i.p.), but haloperidol (0.3 mumol/kg, i.p.) and cis-flupenthixol (0.45 mumol/kg, i.p.) were without effect. The hypomotility due to DB-6,7-ADTN was also antagonised by yohimbine (13 mumol/kg, i.p.) and piperoxane (21 mumol/kg i.p.), drugs which act mainly by blocking presynaptic (alpha 2) adrenergic receptors. Prazosin (1.5 mumol/kg, i.p.), drugs which act mainly by blocking presynaptic (alpha 2) adrenergic receptors. Prazosin (1.5 mumol/kg, i.p.), a postsynaptic (alpha 1) adrenergic blocker, did not affect the hypomotility, and nor did a range of other neurotransmitter antagonists. DB-6,7-ADTN (50 mumol/kg, i.p.) was also found to antagonise the alpha-methyltyrosine (alpha-MT, 1.02 mmol/kg, i.p.) induced fall in noradrenaline and dopamine levels in brain and spinal cord. Inhibition of the effects of DB-6,7-ADTN on noradrenaline and dopamine turnover by yohimbine and sulpiride, respectively, suggests that 6,7-ADTN (derived from the prodrug) has alpha adrenergic as well as dopaminergic activity. The results are discussed in connection with the hypomotive effects of other dopamine agonists.

Adrenergic alpha-Antagonists↗