We. Hurford et al., SPLENIC CONTRACTION, CATECHOLAMINE RELEASE, AND BLOOD-VOLUME REDISTRIBUTION DURING DIVING IN THE WEDDELL SEAL, Journal of applied physiology, 80(1), 1996, pp. 298-306
The spleen of the Weddell seal (Leptonychotes weddelli) may contract a
nd inject red blood cells (RBCs) into the peripheral circulation durin
g diving, but evidence for this hypothesis is indirect. Accordingly, w
e measured splenic dimensions by ultrasonography, plasma catecholamine
concentrations, hemoglobin concentration, and hematocrit in five Wedd
ell seals before and after intravenous epinephrine during halothane an
esthesia and while awake at the surface after voluntary dives. Spleen
size was reduced immediately after epinephrine injection or after the
seal surfaced. Within the first 2 min after the seal surfaced, cephalo
caudal splenic length was 71 +/- 2% (mean +/- SD; P < 0.05) and spleni
c thickness was 71 +/- 4% (P < 0.05) of the maximal resting values. Sp
lenic size increased (halftime = 6-9 min) after the seal surfaced and
was inversely correlated with plasma epinephrine and norepinephrine co
ncentrations. Hemoglobin concentration increased from 17.5 +/- 5.3 g/d
l (measured during general anesthesia) to 21.9 +/- 3.7 g/dl (measured
in the first 2 min after surfacing). At these same times, the hematocr
it increased from 44 +/- 12 to 55 +/- 8%. These values decreased (half
-time = 12-16 min) after the seal surfaced. We estimate 20.1 liters of
RBCs were sequestered at rest, presumably in the spleen, and released
either on epinephrine injection or during diving. Catecholamine relea
se and splenic contraction appear to be an integral part of the volunt
ary diving response of Weddell seals.