Sympathetic nerves to the enlarged fetus-containing region of the
uterus undergo degenerative changes
during late pregnancy and show slow regrowth after parturition. It is not
known whether this unusual
response of sympathetic nerves to smooth muscle hypertrophy is due to the
sensitivity of short adrenergic
neurons to hormonal changes, or whether the nerves respond to changes in
the neurotrophic capacity of the
target. We have investigated this question using in oculo transplantation.
Small pieces of myometrium from
the uterine horn of virgin guinea pigs, or from the region previously occupied
by the placenta and fetus in
postpartum guinea pigs, were transplanted into the anterior eye chamber.
After 3 wk in oculo, the pattern of
reinnervation of the transplants was assessed on whole mount stretch preparations
stained for tyrosine
hydroxylase. The histology of the transplants was examined in toluidine
blue-stained semithin sections.
Myometrial transplants from virgin donors and uterine artery transplants
from both virgin and postpartum
donors became organotypically reinnervated by sympathetic fibres from the
host iris. In contrast,
sympathetic nerves did not reinnervate myometrial transplants from postpartum
donors, although they
approached the transplants and became distributed in the surrounding connective
tissue. All transplanted
tissues showed a normal histological appearance. Both the myometrium and
uterine artery from postpartum
donors retained a hypertrophic appearance after 3 wk in oculo. We interpret
these results to indicate that
the degeneration of sympathetic nerves in late pregnancy, as well as their
slow regrowth to the uterus after
delivery, may be due to changes in uterine smooth muscle rather than a
particular sensitivity of short
adrenergic neurons to hormonal changes.