Long term beta-adrenoceptor-mediated up-regulation of Gi alpha and G(o) alpha mRNA levels and pertussis toxin-sensitive guanine nucleotide-binding proteins in rat heart.
Chronic stimulation of beta-adrenoceptors leads to increased mRNA and protein levels of pertussis toxin (PTX)-sensitive guanine nucleotide-binding proteins (G proteins) in the heart. In the present study the time course is reported of the effect of isoprenaline infusions on myocardial mRNA levels of Gi alpha-2, Gi alpha-3, G(o) alpha, Gs alpha, and G beta and myocardial levels of PTX-sensitive G proteins. Rats were treated by subcutaneous infusions, with osmotic minipumps, of 0.9% NaCl, isoprenaline (2.4 mg/kg/day), propranolol (9.9 mg/kg/day), or a combination thereof for 1, 2, 3, 4, or 8 days, and two groups were treated with NaCl or isoprenaline for 13 or 26 days. Additional groups of rats were treated with 0.24 or 0.07 mg/kg/day for 4 days to determine the dose dependency of the effects of isoprenaline. mRNA concentrations were determined by standardized slot blotting with 32P-labeled cDNA or cRNA probes. In isoprenaline-treated rats, mRNA levels of all members of the Gi alpha/G(o) alpha family increased gradually in parallel. The increase in Gi alpha-2, Gi alpha-3, and G(o) alpha mRNA levels reached significance on days 2-3, reached maximal values on days 3-4, and remained stable over the total time of treatment of up to 26 days. Compared with NaCl, maximal increases were 77% (Gi alpha-2; 16.4 versus 9.3 pg/micrograms), 58% (Gi alpha-3; 4.65 versus 2.95 pg/micrograms), and 78% (G(o) alpha; 0.40 versus 0.22 pg/microgram). Gs alpha mRNA levels (about 30 pg/micrograms) and G beta mRNA levels remained unchanged. In isoprenaline-treated rats myocardial levels of PTX-sensitive G proteins increased by maximally 54%, compared with control. The time course differed slightly from the time course of mRNA up-regulation in the first 3 days of treatment and paralleled the increase in mRNA levels from day 4 on. Propranolol had no effect on G alpha mRNA or protein levels when given alone but abolished all effects of isoprenaline when given in combination. Isoprenaline at a dose of 0.24 mg/kg/day still induced an increase in Gi alpha-2 mRNA levels of 24%, without any effects on histopathology of the myocardium.(ABSTRACT TRUNCATED AT 400 WORDS)
Eschenhagen
T
T
Abteilung Allgemeine Pharmakologie, Universitäts-Krankenhaus Eppendorf, Hamburg, FRG.
Mende
U
U
Diederich
M
M
Nose
M
M
Schmitz
W
W
Scholz
H
H
Schulte am Esch
J
J
Warnholtz
A
A
Schäfer
H
H
D000818:Animals; D015152:Blotting, Northern; D002395:Catecholamines / Q000097:blood; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D037342:Pertussis Toxin; D010957:Plasmids; D011433:Propranolol / Q000494:pharmacology; D015347:RNA Probes; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D015854:Up-Regulation; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D002395:Catecholamines; D015347:RNA Probes; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D010566:Virulence Factors, Bordetella; D012965:Sodium Chloride; D011433:Propranolol; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D007545:Isoproterenol