"Robert J. Bradbury" wrote:
> On Sun, 29 Aug 1999, Brian Manning Delaney wrote:
>> Hi Greg. I've followed White's research a
>> bit, and I believe this is indeed an
>> accurate report on the state of his research.
> I think White gave a presentation at A4M
> a couple of years ago.
>> Stem cell research will soon obviate any
>> need for whole part/organ replacement, I'm
>> guessing -- at least in many cases.
> I'm of the opinion that one of the major
> problems is the cell division rate. How long
> does it take you to grow a 5 kg (?) liver from a
> single cell with a 24 hour doubling time?
Yes, this is definitely a problem. Most organs would take over a month to grow. For emergencies, this won't help.
I guess we actually have three options here: 1) Whole organs grown naturally as replacement parts (what we have now); 2) Whole organs grown "unnaturally" as replacement parts (2a: using stem cells; 2b: using other means -- 2b we essentially have, or will very shortly, at this point in various forms: xenotransplantation, for example); 3) Replacement of dysfunctional organs via infusion of stem cells.
Once (3) becomes possible, I'm guessing we won't need (2), since (1) will easily be able to provide the need for organs in emergencies, and (3) will be able to provide the non-emergency organs (via infusion into an organ that has enough good cells left to allow integration of the new cells -- what's being done now with hearts partially damaged by blood-loss during a heart attack).
> The question comes down to how much you can "push"
> mammalian growth (e.g. with hyperoxygenation/glucose
> levels, hormones, etc.). What is the fastest
> growing mammal? And would this result in an
> organ that was "prematurely" aged? [Pushing
> division rates=pushing mutations, pushing oxygen
> levels=pushing free radical damage, pushing
> glucose= pushing protein glycosylation, etc.]
Yes, exactly (though if we could learn the tricks that birds' cells use, we could push it without problems -- we could also radically slow aging! )
>> It's in the case of the brain, above all, that I
>> think stem cell infusion could be extremely
>> beneficial. The newer cells could just take up
>> the connections currently maintained by older
>> cells (which taking up might require, though, "rehearsing
>> the thought" that the old cells are maintaining).
> I've thought about this as well. I think there
> are going to be three very interesting avenues; (a)
> hormones to promote axonal hypergrowth; (b)
> hormones to promote stem cell multiplication and
> (c) stem cell injections, perhaps followed by (a)
> or (b).
> I think (a) gets you back to the childhood
> state of hyperlearning, perhaps sacrificing some of
> your "known" knowledge.
Yes, although, after a certain degree of neuronal loss, the learning might be difficult to make hyper- (though I think we can lose a lot without much functional loss -- I wonder about creativity, though).
> I agree that rehearsing would repattern old
> memories on new cells, I suspect however that
> without such rehearsing (and I'm sure you can't
> rehearse "everything"), that much of the old
> information will fade away.
Yes -- fading happens, and may even be good in many ways.
>> In fact, it seems that we pretty much have the
>> science for this to take place -- certainly in
>> many organs -- just not, for the most part, the
>> technology (though even that we partly have, in
>> a not thoroughly tested form).
> People will die and be lost forever while we
> wait for the tests...
Correct. I'd happily have some stem cells (if they were my own) injected into my brain (well, CAREFULLY injected...).
Birds as animal models for the comparative biology of aging: a prospectus. Holmes DJ, Austad SN
J Gerontol A Biol Sci Med Sci 1995 Mar;50(2):B59-66 http://www.ncbi.nlm.nih.gov/cgi-bin/Entrez/referer?/htbin-post/Entrez/query%3fdb=m&form=6&uid=7874580&Dopt=r