According to this paper from Journal of Applied Physiology it can, at least in humans who are diving.

http://jap.physiology.org/content/92/5/2071.short

In the dog, splenic contraction during sudden athletic activity and hypoxic stress is very well recognized.

Apart from those examples, it also does in fish, see:

J Comp Physiol B. 2012 Dec;182(8):1057-67. doi: 10.1007/s00360-012-0678-3. Should I stay or should I go?: Physiological, metabolic and biochemical consequences of voluntary emersion upon aquatic hypoxia in the scaleless fish Galaxias maculatus.

Then, I do not see why I shouldn't play a major role in humans.

All the best,

The splenic activity whilst diving seems to provide evidence that the spleen is an erythrocyte resivoir, which is stimuated in that article via breath hold simluated dive. One could then say that splenic contraction and the human dive reflex are linked. However, during trauma or purely hypoxia without breathholding, does the spleen play a role, and if so, would it make a difference? The spleen contains about a volume of 165 cm3 (http://www.jultrasoundmed.org/content/18/3/231.short). Given that volume size, in acute hypovolemic shock, one would estimate that this plays no role in maintaining cardiac output. However, one would have to investigate this via ultrasound in simulated hypovolemic shock. The other question is, on what axis is the spleen stimulated, by sympathetic fibers acting on the myofibroblast laying on the outer cortex of the spleen, as there are no other nerve inputs to that organ.

I know that the contraction of the spleen plays a substantial role in providing extra blood supply in racing horses.

some other species -such as cats- have "reactive spleen" that reacts against certain medications and may alter the CBC results, significantly.

It probably does, according to our studies in different hypoxic situations in humans. I would assume it also could play a role in hypovolemia, and the volume of red cells can be larger than that stated above.

A couple questions remain though:

Is splenic contraction an acute response or rather more an adaptation mechansm which needs more time to activate, possibly through humoral factors as opposed to direct nerve stimulation?

If splenic contraction is sympathetically controlled, which neurotransmitter plays a role, norepinephrine (direct sympathetic nerve activation), or through epinephrine from the adrenal glands (humoral activation)?

What do you mean by "more time"? We did a study on long term effects on high altitude (recently accepted) and there are also long term effects. The acute effect is likely mediated by norepinephrine (older studies in animals).

The people that were examined in that study, had they been adequately accilimatisized to the high altitude? I would love to read the article to find more about your results. Thank you for the interesting feedback. We just completed a small LBNP study examining if splenic contraction occurred after exposition to simulated hypoxic and normoxic hypovolemia. The data analysis will commence shortly. Maybe we find something interesting.

From what I gather though is that through intense anaerobic movement in mammals such as horses and dogs, the spleen does contract, providing an extra surplus of erythrocytes. I would imagine that there is also an expulsion of blood volume as well. This is then triggered by noradrenaline released from the adrenal glands acting on sympathetic fibers acting on the myofibroblast in the splenic capsule. Would however ,there by a baroreceptor sympathetic mediated pathway to the spleen as well? When the baroreceptors in the aortic arch receive less stimulation ie shock, there is a system wide activation of endothel actvity (vasoconstriction). Is there also a stimulation of the nerve fibers surronding the spleen as well? This is what we hope to shed a little light on, hopefully.

Dear Michael,

There are a number of papers over the last 17 years on this in humans, and also other species (mammals: dogs, horses, rats, seals and fish). Erica Shagatay has earlier mentioned her work at altitude, showing that hypoxia per se rather than apnoea is an independent driver for this response.

1. Espersen et al in humans ( J Appl Physiol 92: 2071–2079, 2002)

2. Bakovic et al in humans (J Appl Physiol 95: 1460–1466, 2003 )

3. Panneton et al in rats ( J Appl Physiol 109: 1256–1269, 2010.)

4. Cabanac et al in seals ( J Appl Physiol 82: 1989–1994, 1997)

5. Thornton et al in seal ( Proc Natl Acad

Sci 98: 9413–9418, 2001.)

6. Urbina et al in Fish ( J Comp Physiol B. 2012 Dec;182(8):1057-67.)

Lindholm and Lundgren's review of the subject also gves the literature on splenic response to apnoea/ diving and hypoxia (J Appl Physiol 106: 284–292, 2009). See also arecent review : The Mammalian Diving Response: An Enigmatic Reflex to Preserve Life?

Physiology September 2013 28:(5) 284-297

Hope this helps.

Thanks alot!