AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 3 599-R604, Copyright © 1996 by American Physiological Society
Nervous control of the spleen in the red-blooded Antarctic fish, Pagothenia borchgrevinki
S. Nilsson, M. E. Forster, W. Davison and M. Axelsson
Department of Zoology, University of Canterbury, Christchurch, New Zealand.
The mechanisms of splenic control in the Antarctic fish, Pagothenia
borchgrevinki, were investigated using isolated spleen and mesenteric
artery strips in vitro and perfused spleen preparations in situ.
Splenosomatic index (SSI) [100 x (spleen wt/body wt)] and hematocrit were
determined in animals treated with atropine and phentolamine. Atropine
injection increased the SSI from 0.60 +/- 0.06 to 0.89 +/- 0.04, whereas
phentolamine decreased SSI to 0.45 +/- 0.03. In atropine-injected fish,
hematocrit was 18.6 +/- 1.4 before and 6.6 +/- 0.8% 3 h after injection.
Electrical stimulation of the splenic nerves produced biphasic flow
responses. In 11 of 12 tested preparations, atropine (3 x 10(-7) to 10(-6)
M) abolished the response, suggesting a major cholinergic component in the
splenic innervation. Isolated spleen strip preparations contracted in
response to carbachol, a response that was antagonized by atropine. The
response to acetylcholine was markedly enhanced by the specific
cholinesterase inhibitor BW-284c51. Catecholamine effects were somewhat
irregular, and maximal contraction force with epinephrine and
norepinephrine was 41 and 56%, respectively, of the carbachol response. The
results suggest a mainly, if not solely, cholinergic autonomic control of
the borch spleen, and a major function of the cholinergic innervation in
the control of hematocrit in this species.
