AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 4 537-R543, Copyright © 1983 by American Physiological Society
Weaning in the rat: a study of hormonal influences
H. H. Blake and S. J. Henning
The control of weaning was studied in rat pups aged 17-24 days. The
influence of two hormones, thyroxine (T4) and corticosterone, and the
effect of declining intestinal lactase activity were evaluated.
Hypothyroidism was induced by administration of n-propylthiouracil and
hyperthyroidism was induced by injection of T4. Hypothyroid pups failed to
begin nibbling chow while littermates injected with T4 weaned normally. Two
abnormalities resulting from hypothyroidism, hypothermia and stunted
incisors, were not responsible for the lack of weaning in hypothyroid pups.
Hyperthyroidism did not cause precocious weaning. Glucocorticoid levels
were manipulated by both adrenalectomy (ADX) and administration of
corticosterone. ADX pups exhibited a delayed pattern of weaning while both
ADX pups injected with corticosterone and sham-operated pups weaned
normally. Corticosterone injected before its normal developmental surge did
not cause precocious weaning. Lactase activity, measured throughout these
experiments, did not consistently reflect the degree of weaning
progression. We conclude that 1) the hormones, T4 and corticosterone, are
necessary for the onset of weaning, but neither is a sufficient stimulus to
initiate weaning, and 2) low lactase activity does not initiate weaning.
