AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 2 154-R159, Copyright © 1983 by American Physiological Society
Mechanisms of control of milk intake in suckling rats
C. P. Cramer and E. M. Blass
To reconcile reported differences in the development of internal controls
over milk intake via suckling, infant rats 5-20 days of age were allowed to
withdraw milk from anesthetized dams periodically induced to let down milk
by intravenous infusion of oxytocin. In experiment 1, milk supply was made
unlimited by providing pups with a series of milk-replete dams. Five- and
ten-day-old pups withdrew inappropriately large volumes of milk, whereas
15- and 20-day-old pups limited intake to moderate volumes. In experiment
2, intake of deprived and nondeprived pups was measured after only 10
oxytocin-induced milk letdowns, comparable to the normal nursing bout. When
milk availability was thus limited, pups of all ages consumed volumes of
milk dependent on their level of deprivation. Moreover intake of pups 10-20
days of age was highly correlated with incidence of nipple shifting. Thus
rats as young as 5 days of age can vary the rate at which milk is taken
from a limited source; however, not until 15 days are they able to control
the volume withdrawn from an unlimited source.
