Increases in arterial o2 content induced by splenic contraction reduce the requirement for coronary blood flow in response to sympathomimetic amines in conscious dogs. Sato, Naoki, M. D., You-Tang Shen, M. D., Kaname Kiuchi, M. D., Richard P. Shannon, M. D. and Stephen F. Vatner, M. D. Departments of Medicine, Harvard Medical School, Brigham & Woman's Hospital, Boston, MA 02115 and the New England Regional Primate Research Center, Southborough, MA 01772
APStracts 2:0044H, 1995.
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. Bood hemoglobin (Hb) and Cao2 increased by 16+/-2% and 18+/-2% respectively during norepinephrine (NE)(0.8 Ng/kg/min, i.v.) in the intact, conscious state following splenic contraction. Phenylephrine 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 either ganglionic, or [alpha], or 1/ 2-adrenergic blockade. Direct infusions of NE and PE into the splenic artery decreased splenic thickness and increased Hb and Cao2, while ISO had no effect. After splenectomy, NE, i.v., did not increase Cao2, but coronary blood flow 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 stimulation. The consequent increase in hemoglobin and Cao2 allows for equivalent increases in MVo2, but at a smaller increase in coronary blood flow. 

Received 2 September 1994; accepted in final form 27 January
1995.
APS Manuscript Number H794-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.