(−)Doxazosin is a necessary component for the hypotensive effect of (±)doxazosin during long-term administration in conscious rats
Abstract
Jing ZHAO#, De-zhi KONG#, Qing LI, Ya-qin ZHEN, Miao WANG, Yan ZHAO, Dong-kai WANG, Lei-ming REN*
Institute of Chinese Integrative Medicine, Hebei Medical University, Shijiazhuang 050017, China
Aim: Doxazosin is a racemic mixture of (–)doxazosin and (+)doxazosin that is currently used as an add-on therapy for hypertension. In this study we investigated the contribution of each enantiomer to the hypotensive action of long-term administration of (±)doxazosin in conscious rats.
Methods: Blood pressure of conscious SD rats was measured using a volume pressure recording system. The rats were orally administered (–)doxazosin, (+)doxazosin, or (±)doxazosin (8 mg·kg-1·d-1) for 12 weeks. Plasma concentrations of the agents were analyzed with HPLC. The effect of the agents on α1-adrenoceptor was examined in isolated rat caudal artery preparations.
Results: Treatment of conscious rats with a single dose of (±)doxazosin (8 mg/kg) did not affected DBP and MBP, but significantly decreased SBP by 11.9% 4 h after the administration. Long-term treatment of conscious rats with (±)doxazosin significantly decreased SBP, DBP and MBP with a maximal decrease of SBP by 29.3% 8 h after the last administration. The rank order of the hypotensive actions caused by long-term treatment in conscious rats was (±)doxazosin>(+)doxazosin>>(–)doxazosin. However, the pKB values for inhibiting NA-induced contraction of isolated rat caudal artery were (+)doxazosin (8.995)>(±)doxazosin (8.694)>(–)doxazosin (8.032). The plasma concentrations of (–)doxazosin, (+)doxazosin, and (±)doxazosin were 18.26±3.55, 177.11±20.66, and 113.18±13.21 ng/mL, respectively, 8 h after the last administration of these agents.
Conclusion: Long-term treatment with (±)doxazosin produces potent hypotensive action in conscious rats that seems to result from synergic interaction of the two enantiomers.
Keywords: doxazosin; enantiomer; blood pressure; hypotension; plasma drug concentration; α1-adrenoceptor; noradrenaline; tail artery; conscious rat
This work was supported by grants from the National Science & Technology Major Project “Key New Drug Creation and Manufacturing Program” of China (No 2011ZX 09102-011-04) and the National Program on Key Basic Research Project of China (973 Program) (No 2012CB518601).
# These authors contribute equally to this work.
* To whom correspondence should be addressed.
E-mail ren-leiming@263.net
Received 2013-07-30 Accepted 2013-09-23
Keywords:
Institute of Chinese Integrative Medicine, Hebei Medical University, Shijiazhuang 050017, China
Aim: Doxazosin is a racemic mixture of (–)doxazosin and (+)doxazosin that is currently used as an add-on therapy for hypertension. In this study we investigated the contribution of each enantiomer to the hypotensive action of long-term administration of (±)doxazosin in conscious rats.
Methods: Blood pressure of conscious SD rats was measured using a volume pressure recording system. The rats were orally administered (–)doxazosin, (+)doxazosin, or (±)doxazosin (8 mg·kg-1·d-1) for 12 weeks. Plasma concentrations of the agents were analyzed with HPLC. The effect of the agents on α1-adrenoceptor was examined in isolated rat caudal artery preparations.
Results: Treatment of conscious rats with a single dose of (±)doxazosin (8 mg/kg) did not affected DBP and MBP, but significantly decreased SBP by 11.9% 4 h after the administration. Long-term treatment of conscious rats with (±)doxazosin significantly decreased SBP, DBP and MBP with a maximal decrease of SBP by 29.3% 8 h after the last administration. The rank order of the hypotensive actions caused by long-term treatment in conscious rats was (±)doxazosin>(+)doxazosin>>(–)doxazosin. However, the pKB values for inhibiting NA-induced contraction of isolated rat caudal artery were (+)doxazosin (8.995)>(±)doxazosin (8.694)>(–)doxazosin (8.032). The plasma concentrations of (–)doxazosin, (+)doxazosin, and (±)doxazosin were 18.26±3.55, 177.11±20.66, and 113.18±13.21 ng/mL, respectively, 8 h after the last administration of these agents.
Conclusion: Long-term treatment with (±)doxazosin produces potent hypotensive action in conscious rats that seems to result from synergic interaction of the two enantiomers.
Keywords: doxazosin; enantiomer; blood pressure; hypotension; plasma drug concentration; α1-adrenoceptor; noradrenaline; tail artery; conscious rat
This work was supported by grants from the National Science & Technology Major Project “Key New Drug Creation and Manufacturing Program” of China (No 2011ZX 09102-011-04) and the National Program on Key Basic Research Project of China (973 Program) (No 2012CB518601).
# These authors contribute equally to this work.
* To whom correspondence should be addressed.
E-mail ren-leiming@263.net
Received 2013-07-30 Accepted 2013-09-23