Splenic contraction-induced increases in arterial O2 reduce requirement for CBF in conscious dogs
Sato, N.; Shen, Y.T.; Kiuchi, K.; Shannon, R.P.; Vatner, S.F.
American Journal of Physiology 269(2 Pt 2): H491-H503
1995
ISSN/ISBN: 0002-9513 PMID: 7653614 Document Number: 448120
We investigated the extent to which sympathomimetic amines induced splenic contraction and associated increases in arterial O-2 content (Ca-O-2) and how these mechanisms affected control of the coronary circulation by sympathomimetic amines in conscious dogs. Blood hemoglobin (Hb) and Ca-O-2 increased by 16 +- 2 and 18 +- 2%, respectively, during norepinephrine (NE, 0.8 mu-g cntdot kg-1 cntdot min-1 iv) in the intact, conscious state after splenic contraction. Phenylephrine (PE) induced similar effects. After either alpha-1adrenergic-receptor blockade or splenectomy, these effects were abolished. Isoproterenol (Iso) also decreased splenic thickness, which was abolished after ganglionic, alpha-, or B-1/beta-2-adrenergic-receptor blockade. Direct infusions of NE and PE into the splenic artery decreased splenic thickness and increased Hb and Ca-O2, whereas Iso had no effect. After splenectomy, NE did not increase Ca-O2, 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 O-2 consumption (M ovrhdot VO-2). 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 Ca-O2 allows for equivalent increases in M ovrhdot VO-2, but at a smaller increase in CBF.