Wang C, Martyn J A
Department of Anesthesiology, Harvard Medical School, Boston, MA, USA.
Crit Care Med. 1996 Jan;24(1):118-24. doi: 10.1097/00003246-199601000-00020.
The molecular pharmacologic bases for the attenuated cardiovascular and metabolic responses to catecholamines, after burn injury, have not been elucidated. In the present study, myocardial tissues were used as a model of beta-adrenergic receptors to study burn injury-induced alterations in receptors and in signal transduction.
Prospective study, randomized to treatment and control groups.
University-hospital research laboratory.
Male Sprague-Dawley rats (180 to 210 g).
A 50% body surface area burn or sham-burn was administered to the rats.
Myocardial membranes were isolated at 24 hrs, 7 days and 14 days after 50% body surface area scald or sham injury. (-)125I-iodocyanopindolol was used to assess maximal binding capacity and affinity of the beta-adrenergic receptor. Basal and stimulated concentrations of second messenger, cyclic adenosine monophosphate (cAMP), were also assessed. Production of cAMP during isoproterenol stimulation tested the integrity of the beta-adrenergic receptor-mediated signal transduction. Forskolin, which stimulates adenylate cyclase enzyme directly (bypassing the receptor and G protein) to produce cAMP, tested the efficacy of the enzyme itself. Maximal binding capacity was unaltered between the experimental and control groups, but the affinity (mean +/- SEM) was significantly decreased in burned animals at 7 days (125.4 +/- 15.5 picomoles [pmol]; p = .01) and at 14 days (216.7 +/- 50.7 pmol; p = .001) compared with controls (75.5 +/- 8.4 pmol). In different set experimental and control groups, basal concentrations of cAMP in myocardial membranes were significantly decreased in burned animals at 7 days (control 38.6 +/- 4.2 vs. 5.8 +/- 0.9 pmol/mg of protein/min; p = .003) and at 14 days (control 47.4 +/- 3.2 vs 28.3 +/- 6.6 pmol/mg of protein/min; p = .002). The forskolin (direct)-stimulated synthesis of cAMP was decreased in burned animals at 24 hrs (control 339.0 +/- 40.5 vs. 214.4 +/- 16.6 pmol/mg of protein/min; p = .01), at 7 days (control 289.0 +/- 34.4 vs. 32 +/- 13.0 pmol/mg of protein/min; p = .01), and at 14 days (control 322.9 +/- 28.6 vs. 137.0 +/- 46.1 pmol/mg of protein/min; p = .01). The isoproterenol or receptor-mediated stimulation of cAMP production was also significantly (p < .001) impaired in burned animals compared with controls at 24 hrs (control 134.7 +/- 11.9 vs. 83.1 +/- 13.3 pmol/mg of protein/min), and at 14 days (control 128.2 +/- 7.2 vs. 92.8 +/- 17.7 pmol/mg of protein/min).
The etiology of the decreased responses in the myocardium to exogenous and endogenous beta-adrenergic receptor agonists after burn injury may be attributed to decreased affinity for ligands, and also to impaired receptor-mediated signal transduction and to decreased adenylate cyclase enzyme activity, resulting in decreased basal and stimulated second messenger (cAMP) production.
烧伤后机体对儿茶酚胺的心血管及代谢反应减弱的分子药理学基础尚未阐明。在本研究中，以心肌组织作为β-肾上腺素能受体模型，研究烧伤诱导的受体及信号转导变化。
前瞻性研究，随机分为治疗组和对照组。
大学医院研究实验室。
雄性Sprague-Dawley大鼠（180至210克）。
对大鼠进行50%体表面积烧伤或假烧伤。
在50%体表面积烫伤或假伤后24小时、7天和14天分离心肌膜。用（-）125I-碘氰吲哚洛尔评估β-肾上腺素能受体的最大结合能力和亲和力。还评估了第二信使环磷酸腺苷（cAMP）的基础浓度和刺激浓度。异丙肾上腺素刺激期间cAMP的产生测试了β-肾上腺素能受体介导的信号转导的完整性。福斯可林直接刺激腺苷酸环化酶（绕过受体和G蛋白）产生cAMP，测试了该酶本身的效能。实验组与对照组之间最大结合能力未改变，但与对照组（75.5±8.4皮摩尔[pmol]）相比，烧伤动物在7天（125.4±15.5皮摩尔；p = 0.01）和14天（216.7±50.7皮摩尔；p = 0.001）时亲和力显著降低。在不同的实验组和对照组中，烧伤动物在7天（对照组38.6±4.2 vs. 5.8±0.9皮摩尔/毫克蛋白/分钟；p = 0.003）和14天（对照组47.4±3.2 vs 28.3±6.6皮摩尔/毫克蛋白/分钟；p = 0.002）时心肌膜中cAMP的基础浓度显著降低。烧伤动物在24小时（对照组339.0±40.5 vs. 214.4±16.6皮摩尔/毫克蛋白/分钟；p = 0.01）、7天（对照组289.0±34.4 vs. 32±13.0皮摩尔/毫克蛋白/分钟；p = 0.01）和14天（对照组322.9±28.6 vs. 137.0±46.1皮摩尔/毫克蛋白/分钟；p = 0.01）时福斯可林（直接）刺激的cAMP合成减少。与对照组相比，烧伤动物在24小时（对照组134.7±11.9 vs. 83.1±13.3皮摩尔/毫克蛋白/分钟）和14天（对照组128.2±7.2 vs. 92.8±17.7皮摩尔/毫克蛋白/分钟）时异丙肾上腺素或受体介导的cAMP产生刺激也显著受损（p < 0.001）。
烧伤后心肌对外源性和内源性β-肾上腺素能受体激动剂反应降低的病因可能归因于对配体的亲和力降低，以及受体介导的信号转导受损和腺苷酸环化酶活性降低，导致基础和刺激的第二信使（cAMP）产生减少。
