Comparative Biochemistry and Physiology Part A 120 (1998) 277 – 281
Effects of adrenergic and cholinergic drugs on splenic arteries and
veins from hooded seals (Cystophora cristata )
A. Cabanac *, L.P. Folkow, A.S. Blix
Department of Arctic Biology and Institute of Medical Biology, Uniersity of Tromsø, Tromsø, Norway
Received 15 October 1997; received in revised form 13 January 1998; accepted 28 January 1998
Abstract
Isolated ring preparations of arteries and veins from hooded seal spleens were subjected in vitro to adrenaline (A),
noradrenaline (NA), isoprenaline (Iso), and acetylcholine (ACh), alone or in combination with the blockers phentolamine (Phe),
propranolol (Pro), and atropine (Atr). Both arteries and veins constricted in response to A (the estimated effective dose required
for half-maximal response (ED
50
) was 3.3 and 0.2 M, for arteries and veins, respectively) and NA (estimated ED
50
was 1.5 and
0.6 M, for arteries and veins, respectively), but these effects were abolished when the drugs were given in combination with the
-adrenoceptor blocker Phe. The responses of arteries and veins to ACh and the -adrenoceptor agonist Iso were minor and
inconsistent, and were completely abolished when combined with their respective blockers (Atr and Pro, respectively). The ED
50
for both A and NA are quite high in relation to normal plasma levels of A and NA in seals. This implies that these vessels (and,
hence, the supply of blood to the spleen) primarily are subjected to neurogenic, rather than humoral physiological control. © 1998
Elsevier Science Inc. All rights reserved.
Keywords: Pinnipeds; Diving; Spleen; Splenic vascular resistance; Vasomotor control; In vitro; Adrenaline; Noradrenaline;
Isoprenaline; Acetylcholine; Vasoconstriction; Vasodilation; Vessels
1. Introduction
A series of dramatic cardiovascular changes take
place in seals when they dive for extended periods of
time. These changes include a profound peripheral
vasoconstriction which is accompanied by intense
bradycardia [4]. The changes serve to reduce the rate of
utilization of endogenous oxygen stores, and thereby
extend the submersion period. Another change which
may be observed is a substantial increase in the number
of circulating red blood cells [9,27]. Several authors
[6,8,19,26,27,33] have suggested that the spleen is the
origin of the increased hematocrit during diving, and
that this mechanism probably is important for the
ability of these mammals to dive repeatedly and for
extended periods of time. The proposed function of
splenic contraction and release of (oxygenated) red
blood cells has been that this increases the available
blood oxygen store [32], or that it improves the oxygen-
carrying capacity and, hence, reduces surface time dur-
ing repeated diving [10].
Recently, Cabanac and coworkers [7] demonstrated
in vitro that the spleens of the hooded seal (Cystophora
cristata ) and the harp seal (Phoca groenlandica ) are
capable of active and forceful contraction under -
adrenergic stimulation. However, that study did not
include any examination of the vasomotor responses of
the splenic vasculature. Such responses are obviously
important since they are the means by which blood
supply to the spleen — which determines both splenic
filling and subsequent drainage — is controled.
The purpose of the present study, therefore, was to
investigate the physiological control of the splenic vas-
* Corresponding author. Present address: 263 route du fleuve,
Pointe-au-pe `re, Que ´bec G5M 1K7, Canada.
0742-8413/98/$19.00 © 1998 Elsevier Science Inc. All rights reserved.
PII S1095-6433(98)00029-4