Recently, Miyamoto et al and King et al, independently isolated chicken LH-RH and determined its chemical structure as [Gln8] LH-RH. In this report, the in vivo effect of synthetic chicken LH-RH on the release of LH and FSH and ovulation in rats was investigated. A single i.v. injection of chicken LH-RH, as well as mammalian LH-RH, induced a significant increase of plasma LH levels at 15 min after injection in adult male rats. Plasma LH levels then declined at 30 min to 60 min and returned to basal levels at 120 min. The biological potency of chicken LH-RH estimated from plasma LH levels at 15 min after injection in adult male rats by parallel line assay was 4.1% of that of mammalian LH-RH. It was likely that the activity of chicken LH was shorter in duration on the LH secretion as compared with that of mammalian LH-RH because of quickly decreased plasma LH levels. Plasma FSH levels were also increased, but the increment of FSH was not so obvious as compared with that of LH. Plasma FSH levels reached a plateau at 15 min and did not return to basal levels at 120 min in either the chicken LH-RH injection groups or the mammalian LH-RH injection groups. The chicken LH-RH was able to induce an increase of plasma LH and FSH and ovulation in pentobarbital-blocked, proestrous female rats. The biological potency of chicken LH-RH estimated from plasma LH levels at 15 min after injection in pentobarbital-blocked, proestrous female rats was 2.2% that of mammalian LH-RH. The ovulation-inducing potency of chicken LH-RH estimated from ED50 was about 2.1% of that of mammalian LH-RH. It is noteworthy that chicken LH-RH has a LH and FSH releasing and ovulation inducing-activity on rats in vivo, but its biological potency is weaker and of shorter duration compared with that of mammalian LH-RH, although the chemical structure of chicken LH-RH is different from that of mammalian LH-RH.
