In-vivo inhibition of the preovulatory LH surge by substance P and in-vitro modulation of gonadotrophin-releasing hormone-induced LH release by substance P, oestradiol and progesterone in the female rat.

The effects of substance P (SP) on the preovulatory surge of LH and on the inhibitory and stimulatory effects of oestradiol-17 beta and progesterone on gonadotrophin-releasing hormone (GnRH)-induced LH release were investigated in vivo and in vitro in the rat. A single s.c. injection of 100 micrograms SP at 12.00 h on the day of pro-oestrus significantly decreased the preovulatory surge of LH. In vitro, the inhibitory effect of oestradiol-17 beta on GnRH-induced LH release was not modified by treatment with SP. The stimulatory effect of progesterone on GnRH-induced LH release was reduced by treatment with SP. It is concluded that SP may play a modulatory role in the neuroendocrine control of the preovulatory LH surge.