Exposing Siberian hamsters (Phodopus sungorus) to shorter photoperiods (think winter) for about two months causes the animals to spontaneously undergo daily bouts of torpor during which time they decrease metabolic rate to conserve energy. New research published in the American Journal of Physiology - Regulatory, Integrative and Comparative Physiology was designed to examine whether decreases in growth hormone secretion was involved in stimulating these daily torpor episodes. By administering a chemical that inhibits growth hormone, pasireotide (SOM230), they discovered that inhibition of this pathway increased both the frequency and duration of torpor. Somatostatin is a hormone that naturally inhibits growth hormone release in the body. The findings from this study suggest that increased release of somatostatin may be a stimulus for triggering torpor in these animals.
Scherbarth F, Deidrich V, Dumbell RA, Schmid HA, Steinlechner S, Barrett P. Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal.
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If I understand this correctly: giving the hamsters doses of a drug that blocked a growth hormone, caused them to exhibit increased periods of torpor.
Question: Did the test group also show decreased growth (presumably in whole body size/mass) as an outcome?
I can't help but leap way beyond the conclusions to speculate that control of day/night cycles could have an effect on bodily growth. Is there any basis for that?, or is it just pointless speculation at this time?
yes, indeed, control of day/night cycles does have a strong impact on bodily growth - at least in these hamsters as we and several other groups have shown before (e.g. http://link.springer.com/article/10.1007/BF00376859). In contrast to large mammals these hamsters (and many other small mammals) loose weight during autumn. They have their lowest body weight in winter. This also somewhat answers your question: Because the test group already had their lowest body mass (which is one prerequisite for showing torpor), blocking of the growth hormone had no further effect on body mass.