Response of serum LH, FSH and prolactin to injection of synthetic LH-RH into rat anterior pituitary.

Changes in serum LH, FSH and prolactin were measured by radioimmunoassay following injection of synthetic LH-RH into the anterior pituitary and median eminence of rats. The time course of serum levels of LH and FSH after injection of synthetic LH-RH into the pituitary showed a peak at 15 min. The synthetic LH-RH had a more marked releasing effect on LH than on FSH. After injection of 20 ng into the pituitary, the serum LH rose to about 10.7 times the control level but the serum FSH only to about 1.8 times. A significant rise of serum LH over the control level was noted after injection of more than 0.2 ng of synthetic LH-RH, while that of serum FSH was after injection of more than 2 ng. An injection of 2 ng of synthetic LH-RH into the pituitary following 0.1 mug of estradiol benzoate resulted in a fall of serum LH and FSH levels, and a rise of serum prolactin level. An injection of 2 ng of synthetic LH-RH into the median eminence resulted in a tendency towards slight decrease in serum LH and FSH. No significant response of serum prolactin to synthetic LH-RH was noted.