The frequency and responsiveness to the TUNEL assay were used to compare th
e DNA fragmentation associated with programmed cell death in erythrocytes o
f the circulating blood from chickens, pigeons, bullfrogs and tortoise spec
ies in which the life span and/or metabolic activities of these cells vary
considerably. While most avian and adult bullfrog erythrocytes gave a posit
ive response in this test, only 31% of the tortoise erythrocytes showed a p
ositive TUNEL response, which was generally weak. The strongest positive re
sponse was seen in bullfrog erythrocytes. The positive results for avian er
ythrocytes may possibly be associated with their higher metabolic rate and
body temperature while the lower response for tortoise erythrocytes may ref
lect the very long life span and lower metabolic rate of these cells. Based
on previous literature reports, the results for the bullfrog are unlikely
to be associated with the animal metabolic rate and do not necessarily indi
cate genomic inertness. Together with literature data showing divergent pat
hways for programmed cell death in erythrocytes, the differences in DNA fra
gmentation reported here indicate that further studies on vertebrate nuclea
te erythrocytes are required for a better understanding of cell death in th
ese cells.