The M3-Muscarinic Cholinoceptor Subtype in Rat Prostate and Its Down Regulation by Aging.
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概要
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Muscarinic cholinoceptor subtypes in the rat prostatic membrane were characterized by using [<SUP>3</SUP>H]-methyl-quinuclidinyl benzilate (QNB)in ligand binding studies. [<SUP>3</SUP>H]-Methyl-QNB saturation experiments showed the existence of a homogeneous population of binding sites with a high affinity (K<SUB>D</SUB> value)of 0.24 ± 0.04 nM and a maximum binding site number (B<SUB>max</SUB>)of 219 ± 65 fmol/mg protein. Inhibition of [<SUP>3</SUP>H]-methyl-QNB binding by nonlabelled compounds was in the following order of effectiveness in rat prostate: atropine > 4-diphenylacetoxy-<I>N</I>-methylpiperidine methiodide (4-DAMP)> hexahydro-sila-difenidol hydrochloride, <I>p</I>-fluoroanalog (p-F-HHSiD)> pirenzepine > methoctramine > [1 l-((2-((dimethylamino)methyl)-1-piperidinyl)acetyl)-5, 11-dihydro-6<I>H</I>-pyrido(2, 3-<I>b</I>)(1, 4)benzodiazepine-6-one] (AF-DX 116). This ranking order was similar to that for the salivary gland (M<SUB>3</SUB> subtype), but not for the brain (M<SUB>1</SUB> subtype)or the heart (M<SUB>2</SUB> subtype). These results indicate that the muscarinic cholinoceptors in the rat prostate belong mainly to the M<SUB>3</SUB> subtype. Furthermore, B<SUB>max</SUB> values for muscarinic cholinoceptors in the aged rat prostate (approximately 1-year-old)were smaller than those in the young rat prostate (6 to 8-week-old)(87 ± 13 vs. 183 ± 32 fmol/mg protein). However, K<SUB>D</SUB> values for muscarinic cholinoceptors, and B<SUB>max</SUB> and K<SUB>D</SUB> values for β-adrenoceptors showed no change. These results suggest that the number of prostatic muscarinic cholinoceptors decreases with aging.
- 公益社団法人 日本薬理学会の論文