Chronic (-)-isoprenaline infusion down-regulates β1- and β2-adrenoceptors but does not transregulate muscarinic cholinoceptors in rat heart

Janine M. Matthews, Patrick H.J. Falckh, Peter Molenaar, Roger J. Summers

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Regulation of β-adrenoceptor (β-ar) subtypes and transregulation of muscarinic cholinoceptors (mAchr) was examined in regions of rat heart after chronic infusion of (-)-isoprenaline (450 μg/kg per hour) for 14 days. Following (-)-isoprenaline infusion systolic blood pressure was reduced for 10 days but then gradually returned to control levels, whereas heart rate was increased for 7 days before declining to a level significantly above control. Heart weight to body weight ratio was increased in (-)-isoprenaline treated rats, β-ar subtype densities were measured by quantitative autoradiography with [125I]-cyanopindolol (CYP) in sinoatrial node (SA), atrioventricular node (AV), bundle of His (BH), left (LB) and right (RB) bundle branches, interventricular (IVS) and interatrial (IAS) septa, right atria (RA), apex (AX) and mitral valve (MV). β1-ars were reduced by 59.1-74.2% in the AV conducting regions, 53.4% in the SA node and 43.3-53.4% in myocardial areas. β2-ars were markedly reduced in myocardial regions (93.2-98.5%) and in pacemaker and conducting regions (87.7-97.8%). No changes in mAchr densities measured using [3H]-N-methyl scopolamine (NMS) occurred in the AV node, BH, LB, RB, IVS and IAS following ( )-isoprenaline infusion. Densities of β1- and β2-ars and mAchrs were also measured in ventricular homogenates from control and (-)-isoprenaline treated animals. β-ar levels were significantly reduced (P < 0.05) in treated animals and the ratio of β1- to β2-ars increased after treatment. mAchr density in ventricular homogenates measured using either [3H]-NMS or [3H]-quinuclidinyl [phenyl-4-3H]benzilate (QNB) was unchanged. Homogenates of left and right ventricle also showed no change using [3H]-NMS. Organ bath studies were used to investigate the effect of (-)-isoprenaline infusion on negative inotropic and chronotropic effects of the non-selective muscarinic receptor agonist bethanechol in left and right atria, respectively. Lower concentrations of bethanechol (3 × 10-10 to 10-6 M) produced a negative inotropic response in isolated electrically driven left atria from (-)-isoprenaline treated rats, but not from control rats, with the slope of the curves being significantly different between groups (ANCOVA, P = 0.037). At concentrations of bethanechol from 10-6 to 3 × 10-4 M the negative inotropic response was not changed between (-)-isoprenaline treated and control animals. Bethanechol also produced a negative chronotropic response at lower concentrations (10-10 to 10-6 M) in (-)-isoprenaline treated rats, but not in controls. A second, steeper phase of the negative chronotropic response occurred at concentrations of bethanechol greater than 10-6 M and was also seen in control rats. Expression of M2 (cardiac) mAchrs (m2Achr) in left and right ventricular tissues measured using a quantitative non-competitive polymerase chain reaction (PCR) assay showed a significant (P = 0.001) 28.5% increase in expression in left ventricle and a significant (P = 0.003) 21.5% decrease in expression in right ventricle after (-)-isoprenaline treatment, compared to controls. There was no significant difference in total ventricular m2Achr expression between the two groups of rats. The results suggest that chronic β-ar stimulation down-regulates both β1- and β2-ars, and appears to differentially transregulate m2Achr expression, but not mAchr protein. Following (-)-isoprenaline infusion, muscarinic receptor mediated responses were sensitised, with no change in receptor densities, suggesting changes occur in the cell signalling system beyond the level of the receptor.

Original languageEnglish
Pages (from-to)213-225
Number of pages13
JournalNaunyn-Schmiedeberg's Archives of Pharmacology
Volume353
Issue number2
Publication statusPublished - 1 Dec 1996
Externally publishedYes

Keywords

  • β- and β-adrenoceptors
  • ( )-Isoprenaline
  • Autoradiography
  • Chronotropic response
  • Homogenate binding
  • Inotropic response
  • Muscarinic cholinoceptors
  • Rat heart

Cite this

@article{542ae60378b748b7a3f9942fab7dd38e,
title = "Chronic (-)-isoprenaline infusion down-regulates β1- and β2-adrenoceptors but does not transregulate muscarinic cholinoceptors in rat heart",
abstract = "Regulation of β-adrenoceptor (β-ar) subtypes and transregulation of muscarinic cholinoceptors (mAchr) was examined in regions of rat heart after chronic infusion of (-)-isoprenaline (450 μg/kg per hour) for 14 days. Following (-)-isoprenaline infusion systolic blood pressure was reduced for 10 days but then gradually returned to control levels, whereas heart rate was increased for 7 days before declining to a level significantly above control. Heart weight to body weight ratio was increased in (-)-isoprenaline treated rats, β-ar subtype densities were measured by quantitative autoradiography with [125I]-cyanopindolol (CYP) in sinoatrial node (SA), atrioventricular node (AV), bundle of His (BH), left (LB) and right (RB) bundle branches, interventricular (IVS) and interatrial (IAS) septa, right atria (RA), apex (AX) and mitral valve (MV). β1-ars were reduced by 59.1-74.2{\%} in the AV conducting regions, 53.4{\%} in the SA node and 43.3-53.4{\%} in myocardial areas. β2-ars were markedly reduced in myocardial regions (93.2-98.5{\%}) and in pacemaker and conducting regions (87.7-97.8{\%}). No changes in mAchr densities measured using [3H]-N-methyl scopolamine (NMS) occurred in the AV node, BH, LB, RB, IVS and IAS following ( )-isoprenaline infusion. Densities of β1- and β2-ars and mAchrs were also measured in ventricular homogenates from control and (-)-isoprenaline treated animals. β-ar levels were significantly reduced (P < 0.05) in treated animals and the ratio of β1- to β2-ars increased after treatment. mAchr density in ventricular homogenates measured using either [3H]-NMS or [3H]-quinuclidinyl [phenyl-4-3H]benzilate (QNB) was unchanged. Homogenates of left and right ventricle also showed no change using [3H]-NMS. Organ bath studies were used to investigate the effect of (-)-isoprenaline infusion on negative inotropic and chronotropic effects of the non-selective muscarinic receptor agonist bethanechol in left and right atria, respectively. Lower concentrations of bethanechol (3 × 10-10 to 10-6 M) produced a negative inotropic response in isolated electrically driven left atria from (-)-isoprenaline treated rats, but not from control rats, with the slope of the curves being significantly different between groups (ANCOVA, P = 0.037). At concentrations of bethanechol from 10-6 to 3 × 10-4 M the negative inotropic response was not changed between (-)-isoprenaline treated and control animals. Bethanechol also produced a negative chronotropic response at lower concentrations (10-10 to 10-6 M) in (-)-isoprenaline treated rats, but not in controls. A second, steeper phase of the negative chronotropic response occurred at concentrations of bethanechol greater than 10-6 M and was also seen in control rats. Expression of M2 (cardiac) mAchrs (m2Achr) in left and right ventricular tissues measured using a quantitative non-competitive polymerase chain reaction (PCR) assay showed a significant (P = 0.001) 28.5{\%} increase in expression in left ventricle and a significant (P = 0.003) 21.5{\%} decrease in expression in right ventricle after (-)-isoprenaline treatment, compared to controls. There was no significant difference in total ventricular m2Achr expression between the two groups of rats. The results suggest that chronic β-ar stimulation down-regulates both β1- and β2-ars, and appears to differentially transregulate m2Achr expression, but not mAchr protein. Following (-)-isoprenaline infusion, muscarinic receptor mediated responses were sensitised, with no change in receptor densities, suggesting changes occur in the cell signalling system beyond the level of the receptor.",
keywords = "β- and β-adrenoceptors, ( )-Isoprenaline, Autoradiography, Chronotropic response, Homogenate binding, Inotropic response, Muscarinic cholinoceptors, Rat heart",
author = "Matthews, {Janine M.} and Falckh, {Patrick H.J.} and Peter Molenaar and Summers, {Roger J.}",
year = "1996",
month = "12",
day = "1",
language = "English",
volume = "353",
pages = "213--225",
journal = "Naunyn-Schmiedeberg's Archives of Pharmacology",
issn = "0028-1298",
publisher = "Springer-Verlag London Ltd.",
number = "2",

}

Chronic (-)-isoprenaline infusion down-regulates β1- and β2-adrenoceptors but does not transregulate muscarinic cholinoceptors in rat heart. / Matthews, Janine M.; Falckh, Patrick H.J.; Molenaar, Peter; Summers, Roger J.

In: Naunyn-Schmiedeberg's Archives of Pharmacology, Vol. 353, No. 2, 01.12.1996, p. 213-225.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Chronic (-)-isoprenaline infusion down-regulates β1- and β2-adrenoceptors but does not transregulate muscarinic cholinoceptors in rat heart

AU - Matthews, Janine M.

AU - Falckh, Patrick H.J.

AU - Molenaar, Peter

AU - Summers, Roger J.

PY - 1996/12/1

Y1 - 1996/12/1

N2 - Regulation of β-adrenoceptor (β-ar) subtypes and transregulation of muscarinic cholinoceptors (mAchr) was examined in regions of rat heart after chronic infusion of (-)-isoprenaline (450 μg/kg per hour) for 14 days. Following (-)-isoprenaline infusion systolic blood pressure was reduced for 10 days but then gradually returned to control levels, whereas heart rate was increased for 7 days before declining to a level significantly above control. Heart weight to body weight ratio was increased in (-)-isoprenaline treated rats, β-ar subtype densities were measured by quantitative autoradiography with [125I]-cyanopindolol (CYP) in sinoatrial node (SA), atrioventricular node (AV), bundle of His (BH), left (LB) and right (RB) bundle branches, interventricular (IVS) and interatrial (IAS) septa, right atria (RA), apex (AX) and mitral valve (MV). β1-ars were reduced by 59.1-74.2% in the AV conducting regions, 53.4% in the SA node and 43.3-53.4% in myocardial areas. β2-ars were markedly reduced in myocardial regions (93.2-98.5%) and in pacemaker and conducting regions (87.7-97.8%). No changes in mAchr densities measured using [3H]-N-methyl scopolamine (NMS) occurred in the AV node, BH, LB, RB, IVS and IAS following ( )-isoprenaline infusion. Densities of β1- and β2-ars and mAchrs were also measured in ventricular homogenates from control and (-)-isoprenaline treated animals. β-ar levels were significantly reduced (P < 0.05) in treated animals and the ratio of β1- to β2-ars increased after treatment. mAchr density in ventricular homogenates measured using either [3H]-NMS or [3H]-quinuclidinyl [phenyl-4-3H]benzilate (QNB) was unchanged. Homogenates of left and right ventricle also showed no change using [3H]-NMS. Organ bath studies were used to investigate the effect of (-)-isoprenaline infusion on negative inotropic and chronotropic effects of the non-selective muscarinic receptor agonist bethanechol in left and right atria, respectively. Lower concentrations of bethanechol (3 × 10-10 to 10-6 M) produced a negative inotropic response in isolated electrically driven left atria from (-)-isoprenaline treated rats, but not from control rats, with the slope of the curves being significantly different between groups (ANCOVA, P = 0.037). At concentrations of bethanechol from 10-6 to 3 × 10-4 M the negative inotropic response was not changed between (-)-isoprenaline treated and control animals. Bethanechol also produced a negative chronotropic response at lower concentrations (10-10 to 10-6 M) in (-)-isoprenaline treated rats, but not in controls. A second, steeper phase of the negative chronotropic response occurred at concentrations of bethanechol greater than 10-6 M and was also seen in control rats. Expression of M2 (cardiac) mAchrs (m2Achr) in left and right ventricular tissues measured using a quantitative non-competitive polymerase chain reaction (PCR) assay showed a significant (P = 0.001) 28.5% increase in expression in left ventricle and a significant (P = 0.003) 21.5% decrease in expression in right ventricle after (-)-isoprenaline treatment, compared to controls. There was no significant difference in total ventricular m2Achr expression between the two groups of rats. The results suggest that chronic β-ar stimulation down-regulates both β1- and β2-ars, and appears to differentially transregulate m2Achr expression, but not mAchr protein. Following (-)-isoprenaline infusion, muscarinic receptor mediated responses were sensitised, with no change in receptor densities, suggesting changes occur in the cell signalling system beyond the level of the receptor.

AB - Regulation of β-adrenoceptor (β-ar) subtypes and transregulation of muscarinic cholinoceptors (mAchr) was examined in regions of rat heart after chronic infusion of (-)-isoprenaline (450 μg/kg per hour) for 14 days. Following (-)-isoprenaline infusion systolic blood pressure was reduced for 10 days but then gradually returned to control levels, whereas heart rate was increased for 7 days before declining to a level significantly above control. Heart weight to body weight ratio was increased in (-)-isoprenaline treated rats, β-ar subtype densities were measured by quantitative autoradiography with [125I]-cyanopindolol (CYP) in sinoatrial node (SA), atrioventricular node (AV), bundle of His (BH), left (LB) and right (RB) bundle branches, interventricular (IVS) and interatrial (IAS) septa, right atria (RA), apex (AX) and mitral valve (MV). β1-ars were reduced by 59.1-74.2% in the AV conducting regions, 53.4% in the SA node and 43.3-53.4% in myocardial areas. β2-ars were markedly reduced in myocardial regions (93.2-98.5%) and in pacemaker and conducting regions (87.7-97.8%). No changes in mAchr densities measured using [3H]-N-methyl scopolamine (NMS) occurred in the AV node, BH, LB, RB, IVS and IAS following ( )-isoprenaline infusion. Densities of β1- and β2-ars and mAchrs were also measured in ventricular homogenates from control and (-)-isoprenaline treated animals. β-ar levels were significantly reduced (P < 0.05) in treated animals and the ratio of β1- to β2-ars increased after treatment. mAchr density in ventricular homogenates measured using either [3H]-NMS or [3H]-quinuclidinyl [phenyl-4-3H]benzilate (QNB) was unchanged. Homogenates of left and right ventricle also showed no change using [3H]-NMS. Organ bath studies were used to investigate the effect of (-)-isoprenaline infusion on negative inotropic and chronotropic effects of the non-selective muscarinic receptor agonist bethanechol in left and right atria, respectively. Lower concentrations of bethanechol (3 × 10-10 to 10-6 M) produced a negative inotropic response in isolated electrically driven left atria from (-)-isoprenaline treated rats, but not from control rats, with the slope of the curves being significantly different between groups (ANCOVA, P = 0.037). At concentrations of bethanechol from 10-6 to 3 × 10-4 M the negative inotropic response was not changed between (-)-isoprenaline treated and control animals. Bethanechol also produced a negative chronotropic response at lower concentrations (10-10 to 10-6 M) in (-)-isoprenaline treated rats, but not in controls. A second, steeper phase of the negative chronotropic response occurred at concentrations of bethanechol greater than 10-6 M and was also seen in control rats. Expression of M2 (cardiac) mAchrs (m2Achr) in left and right ventricular tissues measured using a quantitative non-competitive polymerase chain reaction (PCR) assay showed a significant (P = 0.001) 28.5% increase in expression in left ventricle and a significant (P = 0.003) 21.5% decrease in expression in right ventricle after (-)-isoprenaline treatment, compared to controls. There was no significant difference in total ventricular m2Achr expression between the two groups of rats. The results suggest that chronic β-ar stimulation down-regulates both β1- and β2-ars, and appears to differentially transregulate m2Achr expression, but not mAchr protein. Following (-)-isoprenaline infusion, muscarinic receptor mediated responses were sensitised, with no change in receptor densities, suggesting changes occur in the cell signalling system beyond the level of the receptor.

KW - β- and β-adrenoceptors

KW - ( )-Isoprenaline

KW - Autoradiography

KW - Chronotropic response

KW - Homogenate binding

KW - Inotropic response

KW - Muscarinic cholinoceptors

KW - Rat heart

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M3 - Article

VL - 353

SP - 213

EP - 225

JO - Naunyn-Schmiedeberg's Archives of Pharmacology

JF - Naunyn-Schmiedeberg's Archives of Pharmacology

SN - 0028-1298

IS - 2

ER -