Abstract
The effects of propranolol (PRO), a nonselective β-adrenergic receptor (β-AR) antagonist with membrane-stabilizing action on bone metabolism, were examined in spontaneously hypertensive rats (SHR) showing osteoporosis with hyperactivity of the sympathetic nervous system. Treatment of SHR with PRO at 1 and 5 mg/kg p.o. for 12 weeks increased bone mass of the lumbar vertebra and proximal tibia without affecting blood pressure, but PRO at 50 and 100 mg/kg with hypotensive action did not increase bone mass. Next, the effects of PRO at 0.1, 1, and 10 mg/kg on bone status were examined in more detail. Compared with the SHR control, not only bone mass but also biomechanical parameters of strength and toughness of the lumbar vertebrae were increased in SHR treated with PRO at 0.1 and 1 mg/kg, suggesting antiosteoporotic action. PRO at 1 mg/kg statistically increased histomorphometry indices of bone formation, whereas PRO at doses of 0.1, 1, and 10 mg/kg decreased those of bone resorption. Antiosteoporotic effect of PRO is attenuated at 10 mg/kg compared with 0.1 and 1 mg/kg. In addition, treatment with timolol, a nonselective β-AR antagonist without membrane-stabilizing action, or butoxamine, a selective β2-AR antagonist, at 1 mg/kg increased bone mass in SHR. These results suggested that treatment of SHR with β-blockers at low dose improved bone loss and bone fragility. This antiosteoporotic effect of β-blockers seems to be caused by the blocking action of β2-AR, regardless of the membrane-stabilizing action.
Footnotes
This work was partly supported by the Japan Society for the Promotion of Science [Grant 20592193] (to A.T.) and the Strategic Research AGU-Platform Formation [2008-2012].
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.167643.
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ABBREVIATIONS:
- PRO
- propranolol
- AR
- adrenergic receptor
- SHR
- spontaneously hypertensive rat
- WKY
- Wistar-Kyoto rat
- μCT
- microcomputed tomography
- BV
- bone volume
- TV
- tissue volume
- Tb.N
- trabecular number
- MAR
- mineral apposition rate
- BFR
- bone formation rate
- Oc.N
- osteoclast number
- Oc.S
- osteoclast surface
- BS
- bone surface
- TRAP
- tartrate-resistant acid phosphatase
- OVX
- ovariectomized
- ICI 118551
- 3-(isopropylamino)-1-[(7-methyl-4-indanyl)oxy]butan-2-ol.
- Received March 1, 2010.
- Accepted April 15, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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