Alpha-blockade and vasodilatation induced by nipradilol, arotinolol and labetalol in pithed rats.
In pithed rats two recently-introduced beta-blockers, nipradilol and arotinolol, as well as labetalol shifted the pressor dose-response curve for phenylephrine to the right. Labetalol and arotinolol did not modify the pressor dose-response curve for clonidine, while nipradilol induced a definite rightward shift. These results indicate that labetalol and arotinolol are selective alpha 1-blockers, while nipradilol is a non-selective one. In addition, all the three beta-blockers produced complex changes in the blood pressure in pithed rats. A fall of the diastolic blood pressure induced by labetalol and nipradilol was preceded by a slight rise, while arotinolol produced a fall at lower doses and a rise at higher ones. The hypotension by labetalol was abolished after propranolol, while the hypertension was suppressed by prazosin, indicating that labetalol has an intrinsic beta- and alpha 1-sympathomimetic effect. The hypertension and the hypotension produced by nipradilol and arotinolol persisted even in the presence of propranolol and prazosin or propranolol and yohimbine.
Nakagawa
Y
Y
Nakahara
H
H
Chin
W P
WP
Imai
S
S
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology; D003655:Decerebrate State; D007741:Labetalol / Q000494:pharmacology; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014664:Vasodilation / Q000187:drug effects*; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D010656:Phenylephrine; D015016:Yohimbine; C024523:arotinolol; C036089:nipradilol; D003000:Clonidine; D007741:Labetalol; D011224:Prazosin