Substance P stimulates gonadotropin-releasing hormone release from rat hypothalamus in vitro with involvement of oestrogen

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Abstract
The effects of substance P on the release of LH and GnRH were examined in a sequential double-chamber perifusion system by perifusing the mediobasal hypothalamus and or pituitary excised from normal female rats in dioestrus or ovariectomized rats. When the medio-basal hypothalamus and pituitary from normal rats were perifused in series with substance P (120-6 mol/l), the concentration of LH in the efflux was significantly (P < 0.05) increased by 70-120% compared with that before the injection, but substance P had no effect on LH release from the pituitary perifused alone. This LH release by substance P increased in a dose-dependent manner and was blocked by substance P antagonist. Administration of 10-6 mol/l substance P induced a significant release (40-80% increase, P < 0.05) of GnRH from the mediobasal hypothalamus. Infusion of 10-6 mol/l substance P induced significant release (50-100% increase, P < 0.05) of LH and GnRH in ovariectomized rats with an implanted oestradiol capsule, but caused no significant increase in LH release in ovariectomized rats without an oestradiol capsule. Progresterone injection to both ovariectomized rats and ovariectomized rats with an implanted oestradiol capsule had no significant effect on the response of LH to substance P. These findings suggest that substance P induces GnRH release from the medio-basal hypothalamus, resulting in LH release from the pituitary, and that oestrogen may be involved in these processes.