AJP - Endocrinology and Metabolism, Vol 258, Issue 1 E98-102, Copyright © 1990 by American Physiological Society
Growth-promoting properties of the internal milieu of pregnant and lactating rats
M. Chiang, S. M. Russell and C. S. Nicoll
Department of Integrative Biology, University of California, Berkeley 94720.
The growth-promoting properties of the internal milieu of pregnant and
lactating rats were investigated using transplanted whole rat embryos or
fetal paws. When placed under the kidney capsule of intact nonpregnant
hosts and incubated for 12 days, such transplants grow rapidly, and tissues
differentiate normally. Thus they provide an accurate means of assessing
the growth-promoting properties of the internal environment of host animals
in different physiological states. Transplant growth during days 0-11 of
pregnancy was similar to that observed in age-matched virgin control hosts
during an equivalent 12-day period. However, growth of transplants was
decreased by 40% in hosts during days 10-22 of pregnancy and by
approximately 30% in hosts during days 1-13 or days 11-23 of lactation.
Increase in tail length, which was used as an index of maternal skeletal
growth, was reduced by 50% during the second half of pregnancy and the
early and late periods of lactation compared with age-matched virgin
females. No such inhibition was recorded during the first half of
pregnancy. Compared with virgins, serum insulin-like growth factor I
(IGF-I) levels were reduced by approximately 20% on days 6 and 10 of
pregnancy, and by 63-66% during the second half of gestation. Serum IGF-I
levels rose during lactation to reach prepregnancy levels by day 12, but a
second decline occurred by day 18 postpartum.(ABSTRACT TRUNCATED AT 250
WORDS)
