Dissociation of nitric oxide synthase immunoreactivity and NADPH-diaphorase enzyme activity in rat pituitary

The relationship between nitric oxide synthase (NOS) immunocytochemistry and NADPH-diaphorase (NADPH-d) histochemistry was investigated in the anterior and posterior pituitary of ovariectomized rats. NADPH-d activity was present throughout the posterior pituitary but could not be detected in the anterior pituitary. By contrast, an antibody raised against whole recombinant rat neuronal NOS revealed strongly NOS-immunoreactive gonadotrophs and folliculo-stellate cells scattered throughout the anterior pituitary in addition to immunoreactive fibres in the posterior pituitary. The study demonstrates that NADPH-d histochemistry is not always coincident with NOS and provides evidence for an as yet uncharacterized subtype of NOS in the rat anterior pituitary.