Endomorphin synthesis in rat brain from intracerebroventricularly injected [(3)H]-Tyr-Pro: A possible biosynthetic route for endomorphins
by
Ronai AZ, Szemenyei E, Kato E, Kocsis L, Orosz G, Al-Khrasani M, Toth G.
Department of Pharmacology and Pharmacotherapy,
Semmelweis University, Faculty of Medicine,
NET Bldg. 412, P.O.B. 370,
H-1445 Budapest, Hungary.
Regul Pept. 2006 Feb 4;

ABSTRACT

In spite of concentrated efforts, the biosynthetic route of mu-opioid receptor agonist brain tetrapeptide endomorphins (Tyr-Pro-Trp-Phe-NH(2) and Tyr-Pro-Phe-Phe-NH(2)), discovered in 1997, is still obscure. We report presently that 30 min after intracerebroventricular injection of 20 or 200 muCi [(3)H]Tyr-Pro (49.9 Ci mmol(-1)) the incorporated radioactivity was found in endomorphin-related tetra- and tripeptides in rat brain extracts. As detected by the combination of HPLC with radiodetection, a peak corresponding to endomorphin-2-OH could be identified in two of four extracts of "20 muCi" series. Radioactive peaks in position of Tyr, Tyr-Pro, Tyr-Pro-Phe or Tyr-Pro-Trp appeared regularly in both series and also in the "tetrapeptide cluster" constituted by endomorphins and their free carboxylic forms. In one of the four extracts in the "200 muCi" series a robust active peak in the position of endomorphin 2 could be detected. Intracerebroventricularly injected 100 nmol, but not 10 or 1000 nmol cold Tyr-Pro (devoid of opioid activity in vitro), caused a naloxone-reversible prolongation of tail-flick latency in rats, peaking between 15 and 30 min. We suggest that Tyr-Pro may serve as a biosynthetic precursor to endomorphin synthesis.

Analogs
Endomorphins 1 and 2
Endomorphins and the mouse
The rewards of endomorphin 1
Endomorphins and rodent brains
Adenylyl cyclase superactivation
The degradation of endomorphins
Endomorphins and the mu-opioid receptor
Morphine: a mood-brightening smart-drug?
Opioids, depression and learned helplessness
How to increase blood-brain barrier penetration of endomorphin 1
A peripherally administered endomorphin-1 analogue offers pain relief

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