S. Garciabelenguer et al., FACILITATION AND FEEDBACK IN THE HYPOTHALAMO-PITUITARY-ADRENAL AXIS DURING FOOD RESTRICTION IN RATS, Journal of neuroendocrinology, 5(6), 1993, pp. 663-668
After 4 weeks of food restriction to 50% of ad libitum intake in rats,
plasma corticosterone levels were increased, without any change in ad
renal weight, and with no evidence of sympathetic nervous system activ
ation (as measured by Tyrosine Hydroxylase and Phenylethanolamine N-Me
thyl Transferase activities in the adrenal gland). Plasma corticostero
ne levels were normalized with the addition of 35% of the calories as
sugar. The adrenocortical axis activity was therefore investigated in
more detail (nycthemeral cycle of corticosterone levels, ACTH and cort
icosterone response to a CRF challenge) in ad libitum fed rats and in
animals fed 85% or 50% of the intake of the control animals, just befo
re switching the lights off in order to maintain the diurnal rhythm of
food intake. Food restriction to 85% did not change mean plasma corti
costerone levels but sharpened the peak of corticosterone measured in
the evening, indicating that the adrenocortical axis is more sensitive
to the endogenous signals responsible for its diurnal cycle of activi
ty. Indeed, the ACTH response to CRF was also increased. A 50% food re
striction regimen increased mean corticosterone levels and attenuated
the day/night difference, with high corticosterone levels maintained t
hroughout the day. However, the ACTH response to CRF was not different
from that measured in ad libitum fed rats, but the corticosterone res
ponse was lower, confirming that the adrenal gland is hyposensitive to
ACTH. The results are discussed in terms of the balance between inhib
iting/activating mechanisms and endocrine/neural influences at each le
vel of the hypothalamo-hypophyso-adrenal axis, depending on the level
of food deprivation.