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Multiple Factors Influencing the In Vitro Release of [Met 5 ]‐Enkephalin from Rat Hypothalamic Slices
Author(s) -
Nikolarakis K. E.,
Almeida O. F. X.,
Herz A.
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb09138.x
Subject(s) - medicine , endocrinology , enkephalin , (+) naloxone , tetrodotoxin , hypothalamus , castration , antagonist , basal (medicine) , chemistry , met enkephalin , opioid peptide , in vitro , hormone , receptor , opioid , biology , biochemistry , insulin
This study examined several in vivo and in vitro factors which influence the release of [Met 5 ]‐enkephalin (Met‐ENK) from male rat hypothalamic slices superfused in vitro. Met‐ENK release was significantly stimulated by corticotropin‐releasing hormone (CRH; 10 −12 –10 −8 M ), an effect which was abolished in the presence of the CRH‐receptor antagonist, α‐helical CRF 9–41 (10 −6 M ). The amount of Met‐ENK release diminished with time in experiments in which the slices were continuously exposed to CRH. The opioid receptor antagonist naloxone (10 −6 M ) stimulated Met‐ENK release, even in the presence of the Na + ‐channel blocker tetrodotoxin (10 −6 M ), a result indicating presynaptic opioid feedback inhibition of Met‐ENK release. The role of gonadal steroids in the control of Met‐ENK release in vitro was also examined. It was found that the basal and CRH‐induced release of Met‐ENK was not changed 1 week after castration. However, a significant increase in the basal release of this peptide was observed 4 weeks after gonadectomy, and the Met‐ENK–releasing efficacy of CRH was found to be reduced. The Met‐ENK content of hypothalami from 1‐week castrates was not significantly changed from control levels, but was significantly reduced in those from 4‐week castrates. These long‐term effects of castration could be overcome by the subcutaneous implantation of testosterone‐containing capsules at the time of castration.