Effects of chronic and acute oestrogen treatment on the developing noradrenaline-containing nerves of the rat uterus.

The developing noradrenaline-containing (NA-C) sympathetic nerves of the rat uterus were analyzed following acute and chronic treatment with oestrogen. Histochemical methods were used in association with nerve density measurements and biochemical assays. For comparative purposes, noradrenaline (NA) levels were measured in the urinary bladder and right auricle following chronic oestrogen treatment. Acute treatment was performed by s.c. administration of a single dose of 40 micrograms oestradiol cypionate on the 25th day of age. Chronic treatment consisted of four doses of 10 micrograms oestradiol on days 10, 15, 20 and 25 of postnatal development. Both acute- and chronic-treated animals were killed at 28 days of age. The main biochemical findings were the following: (a) both acute and chronic oestrogen treatment increased the weight of the uterine horn, parametrial tissue and uterine cervix; (b) in the uterine horn, the total content of NA was reduced following both oestrogen treatments. However, the degree of reduction was greater after chronic treatment; (c) in the parametrial tissue, the NA levels were reduced only after chronic treatment; (d) in the cervix, the NA total content was increased after both treatments; (e) in the urinary bladder, there was a parallel increase between organ growth and NA content following chronic oestrogen treatment; (e) in the auricle neither the tissue weight nor the total content of NA were changed by chronic estrogen treatment. Histochemical studies showed that: (a) acute treatment with one single dose of oestradiol, provoked a marked reduction in the density of NA-C nerves associated with the myometrial and parametrial smooth muscle, without affecting the innervation of blood vessels; (b) following chronic treatment, the only fibers we were able to recognize were those associated with blood vessels. These fibers were thinner and less intensely fluorescent than in controls. Results are interpreted considering the differential sensitivity of uterine nerves to sex hormones. A possible involvement of oestrogen in changes of noradrenergic innervation of the uterus following puberty is discussed.