During pregnancy there are dramatic changes in the endocrine and metab
olic status of the mother: growth hormone (GH) is an important regulat
or of growth and development. A proportion of CH is bound by specific
GH binding proteins (GHBP) that closely resemble the GH receptor (GHR)
. In the rodent both GHBP and the GHR are considered to be GH dependen
t, and consequently during pregnancy the increase in serum GH is assoc
iated with an increase in GHBP. To examine whether an increase in mate
rnal GH is obligatory for elevation of maternal GHBP or GHR during pre
gnancy, we used a unique GH-deficient (GHD) strain of rats, to avoid t
he methodological complications of hypophysectomy and assessed serum G
H, GHBP and hepatic GHR binding during the course of pregnancy. In GH
normal rats, serum GH concentrations increased twofold and GHBP levels
increased threefold; there was no change in hepatic GHR binding. In C
HD rats, serum GH concentrations were low and did not increase during
pregnancy. Nonetheless, levels of both serum GHBP and hepatic GHR bind
ing increased to that measured in normal rats. Thus, an increase in ma
ternal GH concentration is not required for the gestational upregulati
on of maternal GHBP or hepatic GHR binding, suggesting that other horm
ones may be essential in modulating the GH axis during pregnancy.