  Intestinal apoptosis and expression of apoptosis inducers - the cytokines
TNFalpha, TGFbeta1 - and the intestinal transcription factor Cdx2, were studied
according to two different metabolic and hormonal phases which characterize
long-term fasting: the long period of protein sparing during which energy
expenditure is derived from lipid oxidation (phase II), and the later phase
characterized by a rise in body protein utilization and plasma corticosterone
(phase III). Apoptosis was further studied in 2, 6, and 24 h refed rats.
Morphological apoptotic events were observed by environmental and conventional
scanning electron microscopy and a TUNEL test was used to characterize the
final stages of apoptotic death. The gene and protein expressions of TNFalpha,
TGFbeta1, and Cdx2 were measured. Apoptotic events and TNFalpha, TGFbeta1, and
Cdx2 gene and protein expressions did not vary significantly during phase II as
compared to the normally fed animals. However, a phase III fasting induced a
delay in intestinal epithelial apoptosis, along with a 92, 58, and 25% decrease
in TNFalpha, TGFbeta1, and Cdx2 mRNAs, respectively. The amounts of TNFalpha,
TGFbeta1, and Cdx2 proteins decreased by 70, 36, and 25%, respectively.
Apoptosis was restored rapidly after a 2 h refeeding following the phase III,
accompanied by a significant increase in TNFalpha, TGFbeta1, and Cdx2 mRNA and
the protein levels, compared to the phase III fasting values. The concomitant
decreases in cytokines and Cdx2 and in apoptotic cells during phase III suggest
the preservation of enterocytes during this critical fasting period in order to
optimize nutrient absorption as soon as food is available and thus, to rapidly
restore body mass.

Populations and Evolution