neuromedin-n and ubenimex

The purpose of this study was to examine the possible role of endogenous peptidases in the inhibition of intracranial self-stimulation (ICSS) produced by injections of neurotensin (NT) and neuromedin N (NN) into the medial prefrontal cortex (MPC) of the rat. We studied the effects on ICSS of the MPC of the administration of thiorphan and bestatin, two specific inhibitors of the peptidases that inactivate NT and NN respectively. Microinjections into MPC of thiorphan (10 micrograms) and bestatin (25 micrograms) potentiated in inhibition of ICSS produced by the intracortical administration of NT (10 nmol) and NN (20 nmol) respectively. This potentiation affected both the amplitude and the duration of the inhibition of ICSS produced by the neuropeptides. Our data indicate that endogenous peptidases are involved in the inactivation of NT and NN in the prefrontal cortex.

Topics: Animals; Conditioning, Operant; Leucine; Male; Microinjections; Neurotensin; Peptide Fragments; Prefrontal Cortex; Protease Inhibitors; Rats; Rats, Wistar; Self Stimulation; Thiorphan

Neuromedin N (NN) induced a concentration-dependent contraction (ED50 = 2.3 +/- 0.2 microM) of the isolated longitudinal smooth muscle from guinea pig ileum. This effect was drastically enhanced (ED50 = 0.06 microM) by the aminopeptidases M and B inhibitor bestatin (10 microM), which elicited a 40-fold increase in NN potency. HPLC analysis indicated that the main NN catabolite generated by membranes from guinea pig longitudinal smooth muscle homogenate corresponded to des-Lys1-NN, which results from removal of the N-terminal lysyl residue of NN. The fact that the formation of des-Lys1-NN was fully prevented by bestatin (10 microM) further supports the involvement of aminopeptidases in NN degradation. We examined the catabolic fate of NN in vivo in the vascularly perfused dog ileum. Bolus administration or continuous infusion of the peptide led to rapid disappearance of NN. This was prevented by prior treatment of ileal segments with bestatin (10 microM) but not with arphamenine B (0.5 microM), which indicated that aminopeptidase M but not aminopeptidase B participated in NN proteolysis in vivo. We showed that 1 and 10 nmol NN trigger the release of 28 +/- 5 and 59 +/- 1 pmol, respectively, of endogenous vasoactive intestinal polypeptide-like immunoreactivity after infusion in the vascularly perfused dog ileum. This release was virtually doubled by prior treatment with 10 microM bestatin but not with 0.5 microM arphamenine B. Altogether, our data indicate that aminopeptidase M is largely responsible for NN degradation in vitro and in vivo in the gastrointestinal tract and could be considered the physiological inactivator of NN in the gut.

Topics: Amino Acid Sequence; Aminopeptidases; Animals; Dogs; Female; Guinea Pigs; Ileum; In Vitro Techniques; Leucine; Male; Methionyl Aminopeptidases; Molecular Sequence Data; Muscle Contraction; Muscle, Smooth; Neurotensin; Peptide Fragments; Protease Inhibitors; Vasoactive Intestinal Peptide

The effects of the endopeptidase 24.11 ('enkephalinase') inhibitor thiorphan, the aminopeptidase inhibitor bestatin and a novel metallopeptidase inhibitor JMV 390-1 on the K(+)-evoked release of immunoreactive neurotensin and neuromedin N (iNT and iNN) from mouse hypothalamic slices were examined. (JMV 390-1 inhibits several metallopeptidases including endopeptidases 24.11, 24.15 and 24.16, and aminopeptidase N equipotently with Ki values around 50 nM.) Thiorphan increased the recovery of released iNT nearly 2-fold and had no effect on iNN. Bestatin produced a 4-fold increase in iNN recovery and was inactive on iNT. Finally, iNT and iNN recoveries were increased up to 4- and 5-fold, respectively, by JMV 390-1. These results show that in the mouse hypothalamus endopeptidase 24.11 participates with other metalloendopeptidases to the degradation of endogenously released NT while endogenously released NN is principally degraded by aminopeptidase(s).

Topics: Amino Acid Sequence; Aminopeptidases; Animals; Hypothalamus; In Vitro Techniques; Leucine; Metalloendopeptidases; Mice; Molecular Sequence Data; Neprilysin; Neurotensin; Oligopeptides; Peptide Fragments; Potassium; Thiorphan