Key result
Splenectomy abolished the norepinephrine-induced increase in arterial O2 content, resulting in a greater required increase in coronary blood flow (73% vs 49%) to meet myocardial O2 demands.
Absolute Event Rate: 73% vs 49%
Sympathomimetic amine-induced splenic contraction increases arterial oxygen content, allowing for equivalent increases in myocardial oxygen consumption with smaller increases in coronary blood flow.
May support splenic contraction limiting coronary flow needs during sympathetic stress in animals; leaves open relevance to human physiology.
We investigated the extent to which sympathomimetic amines induced splenic contraction and associated increases in arterial O2 content (CaO2) and how these mechanisms affected control of the coronary circulation by sympathomimetic amines in conscious dogs. Blood hemoglobin (Hb) and CaO2 increased by 16 +/- 2 and 18 +/- 2%, respectively, during norepinephrine (NE, 0.8 micrograms.kg-1.min-1 iv) in the intact, conscious state after splenic contraction. Phenylephrine (PE) induced similar effects. After either alpha 1-adrenergic-receptor blockade or splenectomy, these effects were abolished. Isoproterenol (Iso) also decreased splenic thickness, which was abolished after ganglionic, alpha-, or beta 1/beta 2-adrenergic-receptor blockade. Direct infusions of NE and PE into the splenic artery decreased splenic thickness and increased Hb and CaO2, whereas Iso had no effect. After splenectomy, NE did not increase CaO2, but coronary blood flow (CBF) increased more (73 +/- 6%) vs. before splenectomy (49 +/- 7%) without any differences before and after splenectomy in the responses of pressures, contractility, and myocardial O2 consumption (MVO2). In contrast, renal, mesenteric, and iliac artery blood flows were not significantly different in response to sympathomimetic amines before and after splenectomy. These data indicate that sympathomimetic amines induced splenic contraction either directly or reflexly via alpha-adrenergic-receptor stimulation. The consequent increase in Hb and CaO2 allows for equivalent increases in MVO2, but at a smaller increase in CBF.
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Sato et al. (1995) studied this question. Splenectomy vs. Intact state (before splenectomy) was evaluated on Increase in coronary blood flow (CBF) during norepinephrine infusion. Splenectomy abolished the norepinephrine-induced increase in arterial O2 content, resulting in a greater required increase in coronary blood flow (73% vs 49%) to meet myocardial O2 demands.
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