Response of substance P-immunoreactive nerve fibres in the anterior pituitary to plasma oestrogen levels in the rat.

The mammalian anterior pituitary has recently been shown to be innervated by substantial amounts of peptidergic nerve fibres. It has also been found that adrenalectomy increases the amount of calcitonin gene-related peptide-like immunoreactive nerve fibres in the anterior pituitary of the rat, and that stimulation of the nerve fibres in vitro can enhance release of ACTH. In the present study, the density of substance P-like immunoreactive nerve fibres in the anterior pituitary of the rat were examined in relation to variations in plasma oestrogen status. The amount of substance P-like immunoreactive nerve fibres increased significantly (P < 0.001) after ovariectomy, and decreased significantly (P < 0.01) under oestrogen replacement, in a dose-dependent manner. The results suggest the possibility of the direct neural involvement of oestrogen secretion in anterior pituitary regulation, which further substantiates the hypothesis of neural-humoral dual regulation of the mammalian anterior pituitary.