Role of the alpha-adrenergic blocking effect in the acute hypotensive effect of beta-adrenergic blocking drugs with alpha-blocking activities in conscious SHR.
Acute hypotensive effects and the mechanisms of three beta-adrenergic blocking drugs with alpha-blocking activity were studied in comparison with those of prazosin, propranolol and hydralazine in the conscious spontaneously hypertensive rat (SHR). Prazosin lowered the blood pressure dose-dependently and inhibited the pressor response to phenylephrine. Three beta-adrenergic blocking drugs with alpha-blocking activity, labetalol (30 mg/kg), arotinolol (100 mg/kg) and nipradilol (100 mg/kg) also lowered the blood pressure to the same extent as prazosin (0.3 mg/kg), but the inhibition of the pressor response to phenylephrine produced by them was disproportionately slight. Propranolol (100 mg/kg) did not lower the blood pressure. These results suggest that the acute hypotensive effects of three beta-adrenergic blocking drugs with alpha-blocking activity were attributable only partially to the alpha-adrenergic blocking effect; a mechanism or mechanisms other than the alpha-adrenergic blocking effect must be invoked to explain the acute hypotensive effect produced by lower doses of these drugs in the conscious SHR.
Nakahara
H
H
Nakazawa
M
M
Takeda
K
K
Imai
S
S
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents; D001794:Blood Pressure / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006830:Hydralazine / Q000494:pharmacology; D007741:Labetalol / Q000494:pharmacology; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D013997:Time Factors
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D000959:Antihypertensive Agents; D011412:Propanolamines; D006830:Hydralazine; C024523:arotinolol; C036089:nipradilol; D007741:Labetalol; D011224:Prazosin