Regulation of formation and proposed structure of the factor inhibiting the release of melanocyte-stimulating hormone.
Microsomal preparations from the stalk median eminence of female rats are shown to contain an enzymic activity that is responsible for the formation of MSH-release-inhibiting factor (MSH-R-IF). The amount of this activity remains constant throughout the estrous cycle. The corresponding mitochondrial preparations from the stalk median eminence contain another enzymic principle, estrous cycle-dependent, which competes with the enzyme present in the microsomal preparation for the same "substrate", and can thereby prevent the formation of MSH-R-IF. Several neurohypophyseal hormones, analogs, and peptide intermediates have been tested for their intrinsic MSH-R-IF activity and for their ability to be transformed into MSH-R-IF by incubation with microsomal preparations of stalk median eminence from male rats; it is concluded that the enzyme responsible for the formation of MSH-R-IF is an exopeptidase and that the release-inhibiting factor itself is a tripeptide. Oxytocin is converted by the incubation to (L)-prolyl-(L)-leucylglycinamide; nanogram amounts of this tripeptide inhibit the release of MSH from the pituitary both in vivo and in vitro.
D000818:Animals; D010450:Endopeptidases; D004971:Estrus; D005260:Female; D005998:Glycine / Q000494:pharmacology; D007031:Hypothalamus / Q000166:cytology / Q000201:enzymology*; D007930:Leucine / Q000494:pharmacology; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology*; D008928:Mitochondria / Q000201:enzymology; D010121:Oxytocin / Q000378:metabolism / Q000494:pharmacology; D010452:Peptide Biosynthesis; D010455:Peptides / Q000494:pharmacology*; D010902:Pituitary Gland / Q000032:analysis / Q000187:drug effects* / Q000378:metabolism; D011247:Pregnancy; D011392:Proline / Q000494:pharmacology; D051381:Rats; D014667:Vasopressins / Q000494:pharmacology
D010455:Peptides; D014667:Vasopressins; D010121:Oxytocin; D009074:Melanocyte-Stimulating Hormones; D011392:Proline; D010450:Endopeptidases; D007930:Leucine; D005998:Glycine