Christ G J, Dunlap C E, Blizard D A
Department of Physiology and Pharmacology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27103.
Biochem Pharmacol. 1988 Apr 1;37(7):1281-6. doi: 10.1016/0006-2952(88)90783-6.
Regulation of beta-adrenoceptor-agonist function in the Maudsley Reactive (MR/Har) and the Maudsley Non-Reactive (MNRA/Har) rat strains was assessed by comparison of isoproterenol competition for [125I]iodocyanopindolol (ICYP) binding sites in crude left ventricular homogenate preparations. Non-linear, least-squares analysis of isoproterenol competition for ICYP binding in the absence of guanine nucleotide revealed different proportions of high- and low-affinity receptors in the two strains; MR/Har rats (59 +/- 3.3%) had a significantly greater proportion of receptors in the high-affinity state than the MNRA/Har rats (41 +/- 4.5%). Addition of the non-hydrolyzable guanine nucleotide analog guanylylimidodiphosphate (Gpp(NH)p) converted receptors to the low-affinity state. Analysis of Gpp(NH)p concentration-response curves in left ventricular homogenates of the two strains revealed that the MR/Har strain had a significantly (P less than 0.02) lower EC50 for guanyl nucleotide inhibition of isoproterenol competition for ICYP binding than the MNRA/Har. Confirming previous experimental results, a significantly (P less than 0.04) greater density of ventricular beta-receptors was found in MR/Har rats (13.16 +/- 0.92 fmol/mg protein) than in MNRA/Har rats (10.81 +/- 0.63 fmol/mg protein). Left ventricular catecholamine levels were found to be correlated inversely with beta-adrenoceptor density in the two strains; norepinephrine (NE) and epinephrine (EPI) concentrations (ng/mg protein) in left ventricle were 12.19 +/- 0.94 for NE and 0.165 +/- 0.038 for EPI in MNRA/Har, and 8.73 +/- 0.95 and 0.018 +/- 0.018, respectively, in MR/Har. All other parameters of agonist interactions with the cardiac beta-adrenoceptor for the MR/Har and MNRA/Har rat strains were similar [the IC50 for displacement of ICYP binding by isoproterenol, the accompanying Hill coefficients in the Gpp(NH)p present and absent condition, the Kd of the high- and low-affinity states in the absence of Gpp(NH)p, and the Kd of the uniform low-affinity state in the presence of Gpp(NH)p]. We hypothesize that the strain-dependent differences in high-affinity state formation reported here may account for some of the in vivo differences in cardiovascular function previously demonstrated in the Maudsley rats.
通过比较异丙肾上腺素对粗制左心室匀浆制剂中[125I]碘氰吲哚洛尔（ICYP）结合位点的竞争情况，评估了莫兹利反应性（MR/Har）和莫兹利非反应性（MNRA/Har）大鼠品系中β-肾上腺素能受体激动剂功能的调节。在不存在鸟嘌呤核苷酸的情况下，对异丙肾上腺素竞争ICYP结合进行非线性最小二乘法分析，结果显示两个品系中高亲和力和低亲和力受体的比例不同；MR/Har大鼠（59±3.3%）处于高亲和力状态的受体比例显著高于MNRA/Har大鼠（41±4.5%）。添加不可水解的鸟嘌呤核苷酸类似物鸟苷酰亚胺二磷酸（Gpp(NH)p）可将受体转变为低亲和力状态。对两个品系左心室匀浆中Gpp(NH)p浓度-反应曲线的分析表明，MR/Har品系对鸟苷核苷酸抑制异丙肾上腺素竞争ICYP结合的EC50显著低于MNRA/Har品系（P<0.02）。证实了先前的实验结果，MR/Har大鼠（13.16±0.92 fmol/mg蛋白）的心室β受体密度显著高于MNRA/Har大鼠（10.81±0.63 fmol/mg蛋白）（P<0.04）。发现两个品系左心室儿茶酚胺水平与β-肾上腺素能受体密度呈负相关；MNRA/Har大鼠左心室中去甲肾上腺素（NE）和肾上腺素（EPI）的浓度（ng/mg蛋白）分别为12.19±0.94和0.165±0.038，而MR/Har大鼠中分别为8.73±0.95和0.018±0.018。MR/Har和MNRA/Har大鼠品系中激动剂与心脏β-肾上腺素能受体相互作用的所有其他参数均相似[异丙肾上腺素取代ICYP结合的IC50、存在和不存在Gpp(NH)p时伴随的希尔系数、不存在Gpp(NH)p时高亲和力和低亲和力状态的Kd以及存在Gpp(NH)p时均匀低亲和力状态的Kd]。我们推测，此处报道的高亲和力状态形成的品系依赖性差异可能解释了先前在莫兹利大鼠中证明的心血管功能的一些体内差异。
