AJP - Regulatory, Integrative and Comparative Physiology, Vol 259, Issue 1 157-R162, Copyright © 1990 by American Physiological Society
Feeding influences plasma cortisol levels during preweaning life in baboons
D. S. Lewis and E. M. Jackson
Department of Physiology and Medicine, Southwest Foundation for Biomedical Research, San Antonio, Texas 78228-0147.
The effect of feeding on plasma cortisol concentrations was examined in
neonate (preweaning), infant (postweaning), and adult baboons (Papio
cynocephalus). Neonates were bottle fed four times daily, infants twice
daily, and adults once daily. In neonates, plasma cortisol declined within
30 min after feeding. This decline in plasma cortisol was dependent on
ingestion of formula and was independent of the time of feeding. During the
day, cortisol fluctuations were synchronized with feeding times: peak
levels occurred before feeding and trough levels occurred 30-60 min after
feeding. Plasma adrenocorticotropic hormone (ACTH) declined within 30 min
after feeding but returned to prefeeding levels at 60 min after feeding and
did not exhibit significant variation associated with feeding times as did
cortisol. The decline in plasma cortisol after feeding in neonates was
delayed with increasing age. By 18 wk, the feed-related decline in plasma
cortisol was delayed until 60 min after feeding compared with 30 min at age
of 8 wk. After weaning, the decline in plasma cortisol after feeding was
delayed until 90 min, and there was no effect of feeding in the afternoon
on plasma cortisol. Finally, there was no significant decline at all in
adult baboons greater than 6 yr of age. These results demonstrate plasma
cortisol concentration is associated with feeding in neonates fed formula.
The cortisol-feeding rhythm changes before weaning, and after weaning it
begins to disappear, until it is completely absent in adults.
