Abstract
The effects of synthetic LH-RH and its analogues on cyclic AMP formation, LH and FSH release in anterior pituitary of Wister rat were investigated.
LH and FSH in the incubation medium and tissue were determined with radioimmunoassay by using rat LH and FSH assay system of NIH. Cyclic AMP of the pituitary was assayed by using cyclic AMP specific binding protein purified from rat liver.
Synthetic LH-RH increased significantly cyclic AMP formation of rat anterior pituitary within 1 min. incubation and, LH and FSH release into the incubation medium within 15 min. incubation.
The minimum effective dose of synthetic LH-RH stimulation cyclic AMP formation and LH release was 100ng/ml. and 10ng/ml., in vitro respectively. A larger dose of synthetic LH-RH (100μg/ml. or more) showed a smaller effect on cyclic AMP formation and LH release than that obtained by a smaller dose of synthetic LH-RH.
Several analogues of LH-RH were synthetized by a step-by-step method and their effects on cyclic AMP and LH release were tested.
A nonapeptide (H-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) in which N-terminal pyro-glutamic acid of LH-RH was removed had no effect on cyclic AMP formation and LH release, and a decapeptide in which position 8 (arginine) was changed for position 9 (proline) of LH-RH had no effect.
Only one of the LH-RH analogues examined (pyro-Glu-His-Pro-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) had some effect on cyclic AMP formation and LH release both in vitro and in vivo, but its effect was 1/100 to 1/200 lower in comparison with that of synthetic LH-RH.
In summary, these results show that synthetic LH-RH acts through adenyl cyclase-cyclic AMP system in anterior pituitary, and N-terminal amino acid of synthetic LH-RH may be biologically the most important structure of LH-RH.
