Previous studies have shown that chronic administration of oestrogen during postnatal rat development
dramatically reduces the total content of noradrenaline in the uterine horn, abolishes myometrial
noradrenergic innervation and reduces noradrenaline-fluorescence intensity of intrauterine perivascular nerve
fibres. In the present study we analysed if this response is due to a direct and selective effect of oestrogen on
the uterine noradrenaline-containing sympathetic nerves, using the in oculo transplantation method. Small
pieces of myometrium from prepubertal rats were transplanted into the anterior eye chamber of adult
ovariectomised host rats. The effect of systemic chronic oestrogen treatment on the reinnervation of the
transplants by noradrenaline-containing sympathetic fibres from the superior cervical ganglion was analysed
on cryostat tissue sections processed by the glyoxylic acid technique. In addition, the innervation of the host
iris was assessed histochemically and biochemically. The histology of the transplants and irises was examined
in toluidine blue-stained semithin sections. These studies showed that after 5 wk in oculo, the overall size of
the oestrogen-treated transplants was substantially larger than controls, and histology showed that this
change was related to an increase in the size and number of smooth muscle cells within the transplant.
Chronic oestrogen treatment did not provoke trophic changes in the irideal muscle. Histochemistry showed
that control transplants had a rich noradrenergic innervation, associated with both myometrium and blood
vessels. Conversely, in oestrogen-treated transplants only occasional fibres were recognised, showing a
reduced NA fluorescence intensity. No changes in the pattern and density of innervation or in the total
content of noradrenaline of the host irises were detected after chronic exposure to oestrogen. We interpreted
these results to indicate that the effects of oestrogen on uterine noradrenaline-containing sympathetic nerves
are neither selective or direct, but result from an interaction between sympathetic nerve fibres with the
oestradiol-primed uterine tissue. A potential effect of oestrogen on the neurotrophic capacity of the uterus is
discussed.