Biomedical subjects

C Sumners

Publications and source records attributed to C Sumners.

At least 109 records · Page 6Linked to original sources

PubMed1988

Increased expression of alpha 1-adrenergic receptors in the hypothalamus of spontaneously hypertensive rats.

The specificity and molecular weights of alpha 1-adrenergic receptors in various tissues of spontaneously hypertensive (SH) rat were compared with normotensive controls (Wistar-Kyoto; WKY) with the use of [125I]HEAT and [125I]azidoprazosin, specific alpha 1-adrenergic receptor antagonists. Binding of [125I]HEAT to membranes prepared from SH rat brain hypothalamus was significantly higher, due to a 75% increase in the Bmax, than the WKY control. In contrast, the Bmax and Kd of [125I]HEAT binding to brainstem and liver membranes from SH rats were not significantly different from those of WKY controls. Competition-inhibition data suggested similar pharmacological specificity with potencies in the order of prazosin greater than yohimbine greater than propranolol for both WKY and SH rat membranes prepared from liver, hypothalamus, brainstem and neuronal cultures. Photoaffinity labeling of alpha 1-adrenergic receptors from hypothalamus, brainstem and neuronal cultures using [125I]azidoprazosin followed by SDS-PAGE and autoradiography showed the presence of one major band with a molecular weight (MW) of 105,000 Da for both WKY and SH rats. In contrast, labeling of liver alpha 1-adrenergic receptors revealed one major band with a MW of 60,000 Da. Quantitation of the 105,000-Da band from SH rat hypothalamic membranes demonstrated a 52% higher intensity compared with WKY controls. Neuronal cultures prepared from 1-day-old SH rats showed a similarly greater intensity of the 105,000-Da band compared with WKY controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Receptors for phorbol esters are primarily localized in neurons: comparison of neuronal and glial cultures.

Binding of [3H]PDB has been measured in the present study to determine the levels of protein kinase C in the neuronal and astrocytic glial cells in culture from rat brain. Binding of [3H]PDB to homogenates of cultured neuronal cells from the brains of normotensive and hypertensive rats was time-dependent and specific. The relative potency for competition by various phorbol esters to [3H]PDB binding was TPA greater than beta-PDD greater than POE greater than alpha-PDD greater than or equal to 4 alpha phorbol. Scatchard analysis showed that neuronal cultures from normotensive rat brains contained 2-3 fold more phorbol ester receptors compared with the glial cultures from the same brains. No differences in the Kd and Bmax were observed between neuronal cultures from normotensive and spontaneously hypertensive rat brains. These studies suggest that the phorbol ester receptors are primarily localized in neuronal cells.

Animals↗

PubMed1988

Effects of increased circulating angiotensin II (AII) on fluid exchange and binding of AII in the brain.

Previous studies have shown that elevated levels of circulating angiotensin II (AII) can influence the binding capacity of this peptide for its receptors in peripheral tissues, but the effect of increased circulating levels of AII on its receptors in the brain has not been well-defined. In the present study, the effect of chronic subcutaneous infusions of AII on: (1) the binding of AII to neuronal membranes from the diencephalon (hypothalamus, thalamus and septum) (HTS) of the brain; (b) water intake and urine output, (c) blood pressure, and (d) their interrelationships was evaluated in rats. Significant increases in daily water intake and urine output accompanied chronic infusions of AII at a rate of 125 ng/kg/min. Both blood pressure and the concentration of aldosterone in plasma were also elevated in these rats. The acute dipsogenic response to either central (10 ng) or peripheral (100 micrograms/kg, SC) administration of AII was also tested both in controls and in rats receiving chronic infusions of AII at a rate of either 40 or 125 ng/kg/min, and no differences were observed. Analysis of the HTS region of the brain revealed a significant increase in the specific binding of AII in AII-infused rats compared to controls. Scatchard analysis of the specific binding of AII to its receptors in the HTS of rats treated with 40 ng AII/kg/min for 6 days revealed a significant increase in the number of binding sites for AII compared to controls (Bmax 12.13 vs. 8.79 fmol/mg protein), but no change in binding affinity (Kd).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1988

Phorbol ester-induced upregulation of angiotensin II receptors in neuronal cultures is potentiated by a calcium ionophore.

Previous studies have suggested that protein kinase C is important in the regulation of angiotensin II receptors in neuronal cultures, because the C-kinase agonists, phorbol esters, are able to increase the number of these receptors. In the present study, we have further investigated the role of protein kinase C in angiotensin II receptor regulation. This enzyme is calcium dependent, and so we investigated the effects of A23187, a calcium ionophore, on phorbol ester-stimulated and basal angiotensin II receptor regulation. A23187, at concentrations that increased 45Ca2+ influx, caused a dose-dependent potentiation of phorbol-12-myristate-13-acetate (TPA)-stimulated upregulation of angiotensin II receptors. This potentiation by A23187 was a further increase in angiotensin II receptor number and was abolished in calcium-free medium. In the absence of TPA, A23187 caused a decrease in angiotensin II receptor number, an effect not observed in calcium-free medium. The results suggest at least two pathways for angiotensin II receptor regulation in neuronal cells: (a) by calcium-dependent protein kinase C and (b) via an influx of calcium into the cell.

Angiotensin II↗

PubMed1988

Irreversible binding and recovery of the norepinephrine uptake system using an alkylating derivative of norepinephrine.

The effects of bromoacetylaminomenthylnorepinephrine (BAAN) on the sodium-dependent, high-affinity norepinephrine (NE) uptake system in rat brain synaptosomes and CNS neuronal cultures were investigated. BAAN inhibited [3H]NE uptake into synaptosomes in a dose- and time-dependent manner (IC50, 6.5 microM). Pretreatment of cortical synaptosomes or neuronal cells with BAAN alone, followed by washing to remove free drug, reduced the Vmax but did not alter the Km value for [3H]NE uptake. The BAAN-induced reduction in Vmax was attenuated by concurrent pretreatment with desipramine and blocked by the reaction of BAAN with dithiothreitol or cysteine. In contrast, BAAN was 19-fold less potent at inhibiting [3H]dopamine uptake in striatal synaptosomes, and no change in the Vmax or Km value for [3H]dopamine uptake was observed after a pretreatment with BAAN followed by washing. Furthermore, the irreversible beta-antagonist, bromoacetylalprenololmentane, was equipotent to BAAN for inhibiting [3H]NE uptake into cortical synaptosomes, but did not alter the Vmax or Km for [3H]NE after pretreatment. In neuronal cultures, BAAN inhibited sodium-dependent uptake of [3H]NE (IC50, 5.6 microM) with no effect on sodium-independent uptake. After pretreatment of cultures with 30 microM BAAN followed by washing, there was a 74% decrease in the Vmax for [3H]NE uptake. Following a 24-h lag period, uptake recovered to the control level within 48 h; however, recovery was completely blocked by cycloheximide. The data indicate that BAAN irreversibly binds to the [3H]NE uptake system in both CNS synaptosomes and neuronal cultures and may be a useful probe for studying the turnover of the [3H]NE uptake system.

Adrenergic beta-Antagonists↗

PubMed1988

Immunocytochemical and biochemical characterization of angiotensin I and II in cultured neuronal and glial cells from rat brain.

Neuronal and glial cells cultured from neonatal rat brains showed staining for both angiotensin I and II using the peroxidase-antiperoxidase method. In glial cell extracts of normotensive Wistar-Kyoto rats, the concentrations of angiotensin I and II were 12.47 +/- 2.71 (n = 4) and 66.73 +/- 13.28 fmol/mg protein (n = 4). Angiotensin I and II found in neuronal cell extracts of normotensive Wistar-Kyoto rats were 11.29 +/- 2.99 (n = 4) and 60.25 +/- 12.77 fmol/mg protein (n = 4). No significant difference was found in the concentration of angiotensin I and II in both cell types from the same rat strain. Angiotensin I concentrations of 16.83 +/- 3.43 fmol/mg protein (n = 5) determined in neuronal cell extracts derived from spontaneously hypertensive rats did not differ significantly from those found in neuronal cell extracts of Wistar-Kyoto rats. However, neuronal cell extracts from spontaneously hypertensive rats revealed values of 25.19 +/- 4.31 fmol angiotensin II/mg protein (n = 4). This was significantly different (p less than 0.05) and represented a 58% reduction in the angiotensin II levels in neuronal cells from spontaneously hypertensive rats compared to Wistar-Kyoto rat cultures. Angiotensin I and II measured in the growth medium containing 10% plasma-derived horse serum was below the detection limit of both radioimmunoassays. No difference in the angiotensin I and II levels was found in cells kept in serum-free medium. The angiotensin I and II immunoreactive material determined in the cell extracts could be characterized on reversed-phase high pressure liquid chromatography as (Ile5)-angiotensin I and II. (Ile5)-angiotensin III was not detectable.

Angiotensin I↗

PubMed1988

Alpha 1-adrenergic receptor stimulated responses.

alpha 1 Receptors have been investigated using a variety of experimental approaches. alpha 1-Receptor stimulation of phosphoinositide (PI) hydrolysis shows differences in agonist efficacy. The potency series and antagonists clearly suggest that alpha 1 receptors are coupled to phosphoinositide hydrolysis. This coupling appears to be mediated by a guanine nucleotide protein coupling the agonist-receptor complex to the phosphoinositide phosphodiesterase. However, certain alpha 1-agonists stimulate phosphoinositide hydrolysis only at very high concentrations that are not sensitive to prazosin antagonism. Other studies on alpha 1-receptor desensitization note discrepancies in coupling to phosphoinositide hydrolysis that are also found when comparing hypertensive (SHR) and normotensive (WKY) rats. Furthermore, molecular studies indicate that the apparent molecular weight of the alpha 1 receptors varies among tissues. These studies suggest heterogeneity in alpha 1 receptors and alpha 1-receptor-mediated responses. This heterogeneity is supported by studies on alpha 1-adrenergic-receptor-mediated decreases in angiotensin II receptors. The response to alpha 1 stimulation is opposite to that found with phorbol esters, which mimic the second messenger response to PI hydrolysis. Thus, these studies suggest that alpha 1-adrenergic receptors are coupled to multiple second messenger responses, one of which is phosphoinositide hydrolysis.

Animals↗

PubMed1987

Presence of renin in primary neuronal and glial cells from rat brain.

Immunocytochemical and biochemical techniques have been utilized in the present study to characterize renin in brain cell cultures. With the use of renin-specific antibody, positive renin staining was seen in neuronal and in astrocytic glial cells using the peroxidase-antiperoxidase method. Renin concentration was pH-dependent with highest concentrations at 5.5, decreasing from pH 6.0 to 6.5. At pH 7.4 no renin was detectable in either glial or neuronal cells. The contribution of cathepsin D to the measured renin was about 10% at pH 5.5; 7% at pH 6.0 and 3% at pH 6.5. Comparison of glial with neuronal cells from WKY rats revealed significantly elevated renin at pH 5.5 in glial cells. No difference was seen between glial and neuronal renin levels in WKY rats at pH 6.0 and 6.5. At pH 5.5 and 6.0 renin was significantly increased in neuronal cells of SHR compared to WKY, whereas at pH 6.5 no difference was observed. The renin concentration in cells kept for 2 days in serum-free medium did not differ from those measured in cells kept in serum-containing medium. The generated peptide was identified as [Ile5]Angiotensin I on reversed-phase HPLC.

Angiotensin I↗

PubMed1987

Dipeptidyl peptidase-II activity in cultured astroglial cells from neonatal rat brain.

Astrocytic glial cells in primary culture from neonatal rat brain possess prominent dipeptidyl peptidase-II activity. This enzyme has been previously isolated and purified from whole brain tissue. The glial enzyme characteristically hydrolyzed glycyl-proline-p-nitroanilide (GPN) substrate to release glycyl-proline dipeptide plus p-nitroaniline products. At the enzyme's optimal pH of 5.4, the activities of other tested amino exopeptidases were virtually zero. At pH greater than 8, activity was less than 2% of the activity at pH 5.4, which suggested a paucity of the related enzyme, dipeptidyl peptidase-IV. No competitive inhibition was observed for glycine, proline nor their permuted dipeptides. Glial dipeptidyl peptidase-II activity was strongly inhibited by Hg2+, while other redox sulfhydryl agents were ineffective. Tested cations did not affect activity, except K+ which was mildly inhibitory. Chelating agents were not inhibitory. Of the peptidase inhibitors tested, only phenylmethylsulfonyl fluoride and puromycin were partially inhibitory. We suggest that dipeptidyl peptidase-II may play a role in glial processing of brain peptides which possess an N-terminal penultimate proline residue.

Animals↗

PubMed1987

Angiotensin II inhibits the K+-evoked release of [3H]norepinephrine from hypothalamic synaptosomes of the spontaneously hypertensive rat.

The effect of angiotensin II on the basal and K+-evoked release of [3H]norepinephrine was examined in hypothalamic and brainstem synaptosomes from adult male normotensive (Wistar-Kyoto, WKY, and Sprague-Dawley, SD), and spontaneously hypertensive (SH) rats. Angiotensin II attenuated the [3H]norepinephrine release caused by maximal depolarizing concentrations of K+ (75 mM) in hypothalamic synaptosomes of the SH rat, but had no effect on basal [3H]norepinephrine release. Angiotensin II had no effect on either the basal or K+-evoked release of [3H]norepinephrine in brain synaptosomes prepared from either WKY or SD adult male rats. The results suggest a distinct role of angiotensin II in the modulation of catecholamine release in the SH rat.

Angiotensin II↗

PubMed1987

Distinct angiotensin II receptor in primary cultures of glial cells from rat brain.

Angiotensin II (Ang-II) has profound effects on the brain. Receptors for Ang-II have been demonstrated on neurons, but no relationship between glial cells and Ang-II has been established. Glial cells (from the hypothalamus and brain stem of 1-day-old rat brains) in primary culture have been used to demonstrate the presence of specific Ang-II receptors. Binding of 125I-Ang-II to glial cultures was rapid, reversible, saturable, and specific for Ang-II. The rank order of potency of 125I-Ang-II binding was as follows: Ang-II = [sarcosine1,Ala8]Ang-II greater than [sarcosine1,Ile8]Ang-II much greater than Ang-III greater than Ang-I. Scatchard analysis revealed a homogeneous population of high-affinity (Kd = 1.1 nM) binding sites with a Bmax of 110 fmol/mg of protein. Light-microscopic autoradiography of 125I-Ang-II binding supported the kinetic data, documenting specific Ang-II receptors on the glial cells. Ang-II stimulated a dose-dependent hydrolysis of phosphatidylinositols in glial cells, an effect mediated by Ang-II receptors. However, Ang-II failed to influence [3H]norepinephrine uptake, and catecholamines failed to regulate Ang-II receptors, effects that occur in neurons. These observations demonstrate the presence of specific Ang-II receptors on the glial cells in primary cultures derived from normotensive rat brain. The receptors are kinetically similar to, but functionally distinct from, the neuronal Ang-II receptors.

Angiotensin II↗

PubMed1987

Chronic treatment with L-5-hydroxytryptophan prevents the development of DOCA-salt-induced hypertension in rats.

Chronic subcutaneous (s.c.) infusion (osmotic minipump) of L-5-hydroxytryptophan (L-5-HTP, 4.2 to 12.6 mg/day) to uninephrectomized, deoxycorticosterone acetate-salt-treated (DOCA) rats (1.36 mg/kg per day via s.c. silastic implants) reduced their exaggerated intake of isotonic saline significantly (12.6 mg/day), prevented the elevation of blood pressure (4.2 to 12.6 mg/day), prevented cardiac hypertrophy (12.6 mg/day), and provided modest protection against reduction of urinary concentrating ability, characteristic of DOCA-treated rats during a 24-h dehydration. The exaggerated dipsogenic response of DOCA-treated rats to administration of angiotensin II (AII, 50 and 100 micrograms/kg, s.c.) was also reduced by treatment with L-5-HTP (4.2 and 8.4 mg/day). The specific binding of AII to its receptors in membranes from the diencephalon of the brain was increased significantly above control level by chronic treatment with DOCA, but was returned to control level by concomitant treatment with L-5-HTP. Daily urinary excretion of dopamine, increased by treatment with DOCA, was unaffected by treatment with L-5-HTP (6.3 mg/day). Daily urinary excretion of epinephrine was increased by treatment with L-5-HTP (6.3 and 12.6 mg/day). These results suggest that chronic administration of L-5-HTP provides significant protection against the development of DOCA-induced hypertension, polydipsia, polyuria, and cardiac hypertrophy in rats. The mechanism by which L-5-HTP protects is unclear and remains to be established.

5-Hydroxytryptophan↗

PubMed1987

Protein kinase C agonists increase the expression of angiotensin II receptors in neuronal cultures.

Previous studies have shown that norepinephrine is important in the regulation of central angiotensin II receptors, an effect mediated by alpha 1-adrenergic receptors. Because alpha 1-adrenergic stimulation leads to inositol phospholipid hydrolysis and activation of protein kinase C, we have examined a possible role of this enzyme in the regulation of central angiotensin II (Ang II) receptors. In the present study, we have examined the effects of protein kinase C activators, phorbol esters, on the expression of Ang II receptors in neuronal cultures prepared from 1-day-old rat brains. The active phorbol ester phorbol-12-myristate-13-acetate (TPA) caused time- and concentration-dependent increases in the specific binding of [125I]Ang II to its receptors in neuronal cultures of normotensive and spontaneously hypertensive rat brains. The stimulatory effect of TPA on Ang II receptors was apparent within 15 min and reached a maximum between 1 and 2 h. Ang II specific binding had returned to control levels by 24 h. Various phorbol esters increased [125I]Ang II binding in accordance with their order of potency in stimulating protein kinase C activity. Saturation and Scatchard analysis revealed that the phorbol ester-induced increase in [125I]Ang II binding was due to an increase in the number of Ang II receptors. These observations indicate that activation of protein kinase C results in an increased expression of Ang II receptors in neuronal cultures from both normotensive and spontaneously hypertensive rat brains. The results suggest a possible role of phosphorylation in Ang II receptor expression in neuronal cultures.

Angiotensin II↗

PubMed1987

Chronic dietary administration of tryptophan prevents the development of deoxycorticosterone acetate salt induced hypertension in rats.

Hypertension developed within 3 to 5 weeks in uninephrectomized rats administered deoxycorticosterone acetate (DOCA) at a dose of 850 micrograms X kg-1 X day-1 via Silastic tubes and given isotonic saline to drink. Chronic dietary administration of tryptophan (25 and 50 g/kg of food) to DOCA-treated rats reduced their exaggerated intake of NaCl solution and attenuated the elevation of blood pressure induced by treatment with DOCA alone. Treatment with tryptophan also protected against the reduction in urinary concentrating ability during a 24-h dehydration that is characteristic of DOCA-treated rats. Other tests assessed the responsiveness to the beta-adrenergic agonist, isoproterenol. These included measurement of drinking and heart rate following acute administration of isoproterenol. The characteristically depressed drinking and chronotropic responses of DOCA-treated rats to acute administration of isoproterenol were unaffected by tryptophan. Responsiveness to angiotensin II (AII) was also tested by assessment of dipsogenic and metabolic responses to acute administration of AII. The increased drinking and tail skin temperature responses to administration of AII, characteristic of DOCA-treated rats, were reduced in a graded fashion by treatment with graded doses of tryptophan. The specific binding of AII to its receptors in membranes form the diencephalon of the brain was increased by treatment with DOCA but was returned to control level by concomitant treatment with tryptophan. The content of serotonin in the mesencephalon of the brain was not changed significantly by treatment with tryptophan, but the content of 5-hydroxyindole acetic acid in the same region increased significantly, suggesting that turnover of serotonin was increased by chronic treatment with tryptophan. The cardiac hypertrophy characteristic of treatment with DOCA was attenuated significantly by chronic treatment with tryptophan, while the low, resting plasma renin activity of the DOCA-treated group was unchanged. These results suggest that tryptophan provides significant protection against the development of DOCA-induced hypertension, polydipsia, polyuria, and cardiac hypertrophy in rats. It also reduces the hyperresponsiveness to treatment with AII, possibly by decreasing the specific binding of AII to its receptors. It also appears to increase the turnover of serotonin in the brain. Whether either one or all of these is responsible for the antihypertensive effect of tryptophan remains for further study.

Angiotensin II↗

PubMed1987

Norepinephrine metabolism in neuronal cultures is increased by angiotensin II.

In this study we have examined the actions of angiotensin II (ANG II) on catecholamine metabolism in neuronal brain cell cultures prepared from the hypothalamus and brain stem. Neuronal cultures prepared from the brains of 1-day-old Sprague-Dawley rats exhibit specific neuronal uptake mechanisms for both norepinephrine (NE) and dopamine (DA), and also monoamine oxidase (MAO) and catechol O-methyltransferase (COMT) activity. Separate neuronal uptake sites for NE and DA were identified by using specific neuronal uptake inhibitors for each amine. In previous studies, we determined that ANG II (10 nM-1 microM) stimulates increased neuronal [3H]NE uptake by acting at specific receptors. We have confirmed these results here and in addition have shown that ANG II (1 nM-10 microM, 10-120 min) has no significant effects on neuronal [3H]DA uptake. These results suggest that the actions of ANG II are restricted to the NE transporter in neuronal cultures. It is possible that ANG II stimulates the intraneuronal metabolism of at least part of the NE that is taken up, because the peptide stimulates MAO activity, an effect mediated by specific ANG II receptors. ANG II had no effect on COMT activity in neuronal cultures. Therefore, the use of neuronal cultures of hypothalamus and brain stem we have determined that ANG II can specifically alter NE metabolism in these areas, while apparently not altering DA metabolism.

Angiotensin II↗

PubMed1987

Effects of adrenergic agonists and antagonists on muscle O2 uptake and lactate metabolism.

To investigate adrenergic receptor-mediated responses in dog gastrocnemius-plantaris muscle, several catecholamine agonists, isoproterenol, epinephrine, norepinephrine, and phenylephrine, and two antagonists, propranolol and phenoxybenzamine, were given during repetitive, isotonic, tetanic contractions. The response variables that were measured were muscle blood flow, shortening during constant load contractions, and arterial and venous O2 and lactate concentrations. The calculated variables were O2 uptake (VO2), net lactic acid output (L), and power output. In the control experiments, the contractions increased VO2 to approximately 50 times rest by 2 min. Thereafter, shortening, work, and VO2 declined together by 17% at 30 min, indicating muscle fatigue. L increased rapidly to nearly 0.8 mumol X g-1 X min-1 by 2 min, declined to 0.3-0.4 mumol X g-1 X min-1 by 7 min, and was like rest at 15, 22.5, and 30 min. The arterial lactate concentration rose steadily from rest to 30 min of contractions. Epinephrine infusion stopped the decline of VO2 during the contractions, but this effect was not observed with the other agonists. Propranolol decreased VO2 compared with controls at 22.5 and 30 min of contractions. Phenoxybenzamine decreased VO2 compared with controls at all times during contraction, and the decline with time was present. Coinfusion of epinephrine with propranolol reduced the decline in VO2 observed with propranolol alone. Both epinephrine and isoproterenol increased L compared with controls. This epinephrine response was antagonized by propranolol but enhanced by phenoxybenzamine. Both isoproterenol and epinephrine infusions increased arterial lactate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic Agonists↗

PubMed1987

Norepinephrine regulation of alpha-1 receptors and alpha-1-stimulated phosphoinositide hydrolysis in primary neuronal cultures.

Alpha-1 receptor density and alpha-1 receptor-stimulated phosphoinositide hydrolysis in neuronal primary cultures are regulated by exposure of the cells to the alpha-1 agonist norepinephrine (NE). Pretreatment of neuronal cultures with 10 microM NE caused a time- and concentration-dependent decrease in NE-stimulated accumulation of [3H]inositol phosphates. The maximal NE-stimulated inositide hydrolysis was decreased by approximately 80% after 2 hr of pretreatment with NE, and this loss of responsiveness was reversible over a period of 12 hr. NE pretreatment of neuronal cultures did not affect the muscarinic receptor stimulation of inositide hydrolysis. Neither the number of alpha-1 receptor recognition sites, assessed by measuring the specific binding of DL-[125I]-alpha-(3-iodohydroxyphenyl)-ethyl-aminomethyl tetralone ([125I]HEAT), nor the Ki for NE inhibition of [125I]HEAT binding were changed appreciably after treating neurons with NE for 2 hr. A time- and concentration-dependent decrease in alpha-1 receptor recognition sites occurred with longer periods of NE pretreatment. The maximal loss of 50 to 60% [125I]HEAT binding sites was seen after 14 hr of pretreatment with NE. The number of [125I]HEAT binding sites returned to control levels within 24 hr in parallel with the recovery of alpha-1-stimulated inositide hydrolysis after being down-regulated by a 24-hr exposure to NE. Cycloheximide (3.5 microM) blocked both the recovery of alpha-1 receptors and the recovery of alpha-1-stimulated inositide hydrolysis after 24 hr of NE pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Mineralocorticoids modulate central angiotensin II receptors in rats.

The effect of chronic administration of deoxycorticosterone acetate (DOCA) on the regulation of angiotensin II (AII) receptors in the brains of adult rats was compared with their drinking and pressor responsiveness to both peripheral and central administration of AII. Analysis of AII receptor binding in a block of tissue containing the hypothalamus, thalamus and septum (HTS) after treatment for 8 weeks with DOCA-salt (240 micrograms/kg/day) revealed a significant increase in the number of AII-binding sites compared to salt-loaded controls (Bmax 9.65 vs 6.80 fmol/mg protein) and no change in binding affinity (Kd). Significant increases in the drinking responses to peripheral (200 micrograms/kg) and central (10 ng) administration of AII were observed in these rats. Additional studies indicated that the pressor responses to either centrally (25 ng) or peripherally (20 micrograms/kg, s.c.) administered AII were augmented in DOCA-treated rats. The effect of mineralocorticoids on AII-binding sites was also investigated in primary neuronal cultures from the brains of one-day-old rats. Pretreatment of these cultures with either DOCA or aldosterone (ALDO) induced a time- and concentration-dependent increase in the specific binding of [125I]AII. Maximal increases in AII binding of 53 and 62% above control values were observed when cultures were treated with 500 pg of either ALDO or DOCA per milliliter of culture medium. Scatchard analysis of specific binding of [125I]AII in neuronal cultures treated with DOCA revealed a significant increase in Bmax but no change in Kd. Thus, mineralocorticoid hormones induce an increase in the number of AII-receptor binding sites in the HTS of rats which parallels physiological responses to both central and peripheral administration of AII. This relationship may be independent of the concentration of AII in the blood, since an increase in the number of AII binding sites was also observed in neurons cultured from the brains of one-day-old rats which had been treated with mineralocorticoid hormones.

Aldosterone↗