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Splenic contraction-induced increases in arterial O2 reduce requirement for CBF in conscious dogs
Ist Teil von
American journal of physiology. Heart and circulatory physiology, 1995-08, Vol.269 (2), p.H491-H503
Ort / Verlag
United States
Erscheinungsjahr
1995
Quelle
MEDLINE
Beschreibungen/Notizen
N. Sato, Y. T. Shen, K. Kiuchi, R. P. Shannon and S. F. Vatner
Department of Medicine, Harvard Medical School, Boston 02115, USA.
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.