X-Message-Number: 30008
Date: Thu, 8 Nov 2007 21:31:36 -0800 (PST)
From: 
Subject: inducing hypometabolism is tricky

[H2S is a dud in sheep, and almost certainly also in humans.]

Respir Physiol Neurobiol. 2007 Sep 14; [Epub ahead of print]
H(2)S induced hypometabolism in mice is missing in sedated sheep.
    Haouzi P, Notet V, Chenuel B, Chalon B, Sponne I, Ogier V, Bihain B.
Penn State Heart & Vascular Institute, Pennsylvania State University College
of Medicine, Hershey, Pennsylvania, United States.
    On the basis of studies performed in mice that showed H(2)S inhalation
decreasing dramatically the metabolic rate, H(2)S was proposed as a means of
protecting vital organs from traumatic or ischemic episodes in humans.
Hypoxia has in fact also long been shown to induce hypometabolism. However,
this effect is observed solely in small-sized animals with high [Formula:
see text] , and not in large mammals. Thus, extrapolating the hypometabolic
effect of H(2)S to large mammals is questionable and could be potentially
dangerous. We measured metabolism in conscious mice (24g) exposed to H(2)S
(60ppm) at an ambient temperature of 23-24 degrees C. H(2)S caused a rapid
and large (50%) drop in gas exchange rate, which occurred independently of
the change in body temperature. The metabolic response occurred within less
than 3min. In contrast, sheep, sedated with ketamine and weighing 74kg did
not exhibit any decrease in metabolic rate during a similar challenge at an
ambient temperature of 22 degrees C. While a part of H(2)S induced
hypometabolism in the mice is related to the reduction in activity, we
speculate that the difference between sheep and mice may rely on the nature
and the characteristics of the relationship between basal metabolic rate and
body weight thus on the different mechanisms controlling resting metabolic
rate according to body mass. Therefore, the proposed use of H(2)S
administration as a way of protecting vital organs should be reconsidered in
view of the lack of hypometabolic effect in a large sedated mammal and of
H(2)S established toxicity.
PMID: 17980679

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