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A. M. Contijoch, A. L. Johnson, J. P. Advis, Norepinephrine-Stimulated in Vitro Release of Luteinizing Hormone-Releasing Hormone (LHRH) from Median Eminence Tissue is Facilitated by Inhibition of LHRH-Degrading Activity in Hens, Biology of Reproduction, Volume 42, Issue 2, February 1990, Pages 222–230, https://doi.org/10.1095/biolreprod42.2.222
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Abstract
We and others have previously reported the existence of hypothalamic and anterior pituitary (AP) enzymes that degrade luteinizing hormone (LH)-releasing hormone (LHRH). We have further characterized these LHRH-degrading activities (LHRH-DA) and in addition assessed the role of LHRH-DA in LHRH release from median eminence (ME) tissue in vitro.
Major LHRH-DA components were separated and their molecular weights were estimated by gel filtration chromatography. The role of LHRH-DA in LHRH release was determined by release studies from isolated ME, in the presence and absence of N-tosyl L-phenylalanine chloromethyl ketone (TPCK) and/or norepinephrine (NEpi). Degradation and in vitro release studies were performed by using LHRH analogs with amino acid substitutions at their 5–6 bond. Biological activity of these analogs was assessed by measuring in vitro LH release from dispersed anterior pituitary cells. LHRH-DA was determined by high-performance liquid chromatography; LH and LHRH were measured by radioimmunoassay.
Separation of LHRH-DA by gel filtration chromatography yielded two major enzymatic activities: a Tyr5-Gly6 cleaving endopeptidase and a post-proline cleaving enzyme. Although LHRH-DA from AP and ME produced identical degradation fragments, the former had 3-fold greater specific activity than the latter. LHRH moieties with a Tyr5-Gly6 bond substitution were more resistant to enzymatic degradation and had greater biological activity than LHRH moieties with a Tyr5-Gly6 bond. TPCK decreased LHRH-DA and increased NEpi-stimulated in vitro release of LHRH from isolated ME.
Although these results are consistent with a modulatory role for LHRH-DA on median eminence release of LHRJI,further degradation studies are needed during reproductive states in which LHRH release is known to be altered.
Author notes
Supported by USDA 87-CRCR-I-2558 to LP.A.
