Effects of the enkephalin analog (D-Met2,Pro5)-enkephalinamide on alpha-melanocyte-stimulating hormone secretion.
We used the met-enkephalin analog (D-Met2,Pro5)-enkephalinamide (DMPEA) to investigate enkephalinergic control of alpha-melanocyte-stimulating hormone (alpha-MSH) secretion. Systemic (s.c.) administration of DMPEA elevated plasma titers of alpha-MSH in a dose- and time-related manner. Pretreatment with the opiate antagonist naltrexone had no effect on basal plasma levels of alpha-MSH but blocked DMPEA-induced alpha-MSH release. Treatment with a dose of naltrexone sufficient to block DMPEA-induced secretion of alpha-MSH had no effect on stress-induced secretion of alpha-MSH. Although pretreatment with the dopamine receptor agonist apomorphine prevented DMPEA-induced alpha-MSH secretion, DMPEA had no effect on the synthetic activity of tuberohypophysial dopamine neurons as gauged by measuring the accumulation of 3,4-dihydroxyphenylalanine in the neurointermediate lobe (NIL) following administration of NSD-1015. In vitro treatment of isolated NILs with DMPEA resulted in a significant increase in alpha-MSH release. Naltrexone completely blocked the stimulatory effects of DMPEA on alpha-MSH release in vitro. Our results indicate that DMPEA stimulates alpha-MSH secretion by acting directly through opiate receptors at the level of the NIL.
Carr
J A
JA
Department of Biological Sciences, Texas Tech University, Lubbock 79409-3131.
Saland
L C
LC
Samora
A
A
Tejeda
D
D
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D000521:alpha-MSH / Q000097:blood / Q000378:metabolism*
D000521:alpha-MSH; D004744:Enkephalin, Methionine; D009271:Naltrexone; C021717:enkephalin, Met(2)-ProNH2(5)-