The effects of long term treatment with nonselective β adrenoceptor(β AR) antagonist propranolol (70 mg·kg 1 ·d
1 , in drinking water for 8 weeks) on β AR subtypes in rat hearts and lymphocytes, and plasma concentration of
catecholamine were studied by radioligand binding assay, functional experiment of isolated perfused left atrias, reverse transcription polymerase chain reaction and high performance liquid chromatography methods. The results indicated that after long term propranolol treatment: (1) the density of total β AR in the hearts was up regulated from 41±9 pmol·g 1 protein in control group to 61±9 pmol·g 1 protein, the competitive inhibition curves of CGP20712A for < 125 I> pindolol showed that the numbers of β 1 and β 2 AR were up regulated to the same extent; (2) β 1 AR mRNA level was not changed, but β 2 AR mRNA level was increased significantly in hearts; (3) the positive inotropic response induced by activation of β AR and subtypes was markedly enhanced, functional alteration was more significant in β 2 AR than that in β 1 AR; (4) the numbers of β 2 AR in lymphocytes were increased from 19±8 pmol·g 1 protein in control group to 32±8 pmol·g 1 protein; (5) plasma concentration of norepinephrine was decreased obviously in propranolol group (0.21±0.12 μg·L 1 ) compared with control group (0.38±0.15 μg·L 1 ).