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Naloxone does not Affect the Luteinizing Hormone‐Releasing Hormone‐Induced Inhibition of Luteinizing Hormone Secretion in Sheep
Author(s) -
Naylor A. M.,
Porter D. W. F.,
Lincoln D. W.
Publication year - 1989
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.1989.tb00107.x
Subject(s) - luteinizing hormone , endocrinology , medicine , (+) naloxone , hormone , naloxone hydrochloride , gonadotropin releasing hormone , chemistry , opioid , receptor
Injection of luteinizing hormone‐releasing hormone (21 pmol) into the third cerebral ventricle of long‐term ovariectomized ewes caused a marked inhibition of luteinizing hormone secretion. Mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly when compared with the control responses to saline (50 μl). A notable characteristic of the response was the delayed and sustained nature of the luteinizing hormone‐releasing hormone‐induced inhibition. In the presence of the opioid antagonist naloxone (4 ± 25 mg iv), the central administration of luteinizing hormone‐releasing hormone still produced a marked inhibition of luteinizing hormone secretion. Again, mean luteinizing hormone levels and luteinizing hormone pulse frequency were reduced significantly. When naloxone was injected iv, there was a significant rise in mean luteinizing hormone levels as a consequence of an increase in pulse frequency (in four out of five ewes) and a significant increase in luteinizing hormone pulse amplitude. In conclusion, these data suggest that central opioid pathways sensitive to blockade by naloxone are not involved in the luteinizing hormone‐releasing hormone‐induced inhibition of luteinizing hormone release. Furthermore, in the long‐term ovariectomized ewe, endogenous opioid peptides exert a tonic inhibitory influence on luteinizing hormone‐releasing hormone/luteinizing hormone secretion.