ABSTRACT
Luteinizing hormone-releasing hormone (LH-RH) is known to be inactivated by peptidases in the rat hypothalamus with consequent loss of LH-releasing ability. To make a further study of the peptidases' action on the decapeptide, synthetic LH-RH and its [1–9NH2] analogue were incubated with the supernatant hypothalamic fraction containing the enzyme activity. Using an assay system measuring gonadotrophin release in ovariectomized/steroid-primed rats, both LH-RH and the [1–9NH2] analogue were found to be inactivated to different extents after incubation with the fraction, the analogue completely losing both LH- and FSH-releasing activity, and the releasing hormone almost completely losing its LH- and totally losing its FSH-releasing activity. The findings extend the initial studies by showing that the peptidases can remove both the decapeptide's intrinsic LH- and FSH-releasing activity and that these enzymes act on LH-RH at a site other than the C-terminal glycinamide, since they are able to inactivate the [1–9NH2] analogue lacking this residue.
Acetylcholine, melatonin, and potassium depolarization stimulate release of luteinizing hormone-releasing hormone from rat hypothalamus in vitro.
