Ak. Karabulut et al., The mechanism of growth-promoting effects of prolactin in embryogenesis - Links to growth factors, CELLS T ORG, 164(1), 1999, pp. 2-13
The polypeptide hormone prolactin (PRL) has been implicated in the regulati
on of embryonic growth and development, but the control mechanisms involved
in the effects of the hormone are poorly understood. Several investigators
suggested that there may be a possible link between the effects of PRL and
insulin-like growth factors (IGFs). Recent studies have also shown that li
gand-induced activation of PRL receptors leads to tyrosine phosphorylation
of multiple intracellular proteins, and tyrosine kinase activation takes pl
ace in mediating the mitogenic action of PRL. In order to determine whether
IGFs are involved in mediating the growth-promoting effect of PRL, rat emb
ryos were culture in vitro for 48 h in whole rat serum and serum depleted o
f low molecular weight molecules (30 kD retenate) supplemented with rat PRL
in the presence and absence of antisera against rat PRL, IGF I and IGF II.
To investigate the effects of inhibiting the signal transduction of the PR
L receptors, the embryos were preincubated for 2 h in retenate in the prese
nce of tyrosine kinase inhibitors, tyrphostin 47 and genistein, then rat PR
L was added to the culture medium. Embryos cultured in retenate showed seve
re growth retardation, and the addition of rat PRL caused significant incre
ase in growth and development of the embryos suggesting that embryos may be
able to utilize maternally derived PRL during organogenesis. The presence
of antiserum against rat PRL abolished the PRL-induced increase in developm
ent and antibodies against IGF I and II had a similar effect,, suggesting t
hat IGFs may be involved in the effect of the hormone. The 2-hour preincuba
tion with genistein and tyrphostin also abolished the PRL-induced increase
in development. These results indicate that functional PRL receptors are pr
esent in rat embryos at this stage which may play an important role in the
control of growth and development and this may be linked to growth factors
and their receptors.