Immunoreactive neurotensin in gonadotrophs and thyrotrophs is regulated bysex steroid hormones in the female rat

In addition to regulating anterior pituitary function by being released fro m the median eminence, mammalian neurotensin (NT) may also exert an autocri ne or a paracrine action within the anterior pituitary, In this study, usin g double immunostaining with elution restaining, we identified the specific anterior pituitary cells which express NT immunoreactivity (NT-IR) during the rat oestrous cycle. In the normal cycling rat, NT-IR was present in bot h gonadotrophs and thyrotrophs and displayed plastic changes along the oest rous cycle. Both the number of TSH-NI positive cells and the intensity of i mmunological reaction were elevated during dioestrus, and decreased through prooestrus and early oestrus, NT-IR was also high in both follicle stimula ting hormone (FSH)- or luteinizing hormone (LH)-positive cells during early pro-oestrus, and decreased during late prooestrus, Treatment of intact rat s with either the anti-oestrogens Tamoxifen or LY117018, or the anti-proges tagen RU486 prevented the normal expression of NT-IR in thyroid-stimulating hormone (TSH)-, FSH-, and LH-positive cells during pro-oestrus, Bilateral ovariectomy induced a dramatic reduction in the number of NI-IR cells. This effect was completely prevented by treatment of ovariectomized rats with o estradiol and progesterone, and was unaffected by the concurrent administra tion of a GnRH antagonist. Furthermore, administration of an anti-oestrogen together with an anti-progestagen to ovariectomized-oestrogen, progesteron e-treated rats, blocked the stimulatory effect of ovarian hormones on NT-IR in anterior pituitary cells. These findings demonstrate that, in female ra ts, NT is specifically localized in gonadotrophs or thyrotrophs, In additio n, they strongly suggest that changes in circulating concentrations of ovar ian steroids may control both NT synthesis in, and release from, these cell s.