ANTI-LYMPHOPROLIFERATIVE ACTIVITY OF BROWN ADIPOSE-TISSUE OF HIBERNATING GROUND-SQUIRRELS IS MAINLY CAUSED BY AMP

A fraction with mol wt < 1 kDa was obtained from the brown fat of hibe rnating ground squirrels (Citellus undulatus) by means of delipidizati on, acid extraction, ultracentrifugation and ultrafiltration, This fra ction suppressed the proliferation of mouse lymph node cells under sta ndard mitogenic stimuli for T lymphocytes, In contrast, the fraction w ith mol wt < 1 kDa obtained from the brown fat of active ground squirr els in spring did not display such activity. Further HPLC purification of the biologically active fraction and chemical and structural analy sis of its most potent antilymphoproliferative component revealed that this is adenosine 5'-monophosphate (AMP). These data lend support to the notion that in hibernating mammals AMP originating, at least partl y, from the brown fat down-regulates the seasonally-dependent prolifer ation of the thymus.