Synthesis and activities of neurotensin, and its acid and amide analogs: possible natural occurrence of [Gln4]-neurotensin.

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Abstract
It was considered, a priori, that the isolation of the tridecapeptide, neurotensin, might have inadvertently allowed the hydrolysis of either the [Gln4]- or the [Leu13-NH2]-moieties. Neurotensin and its 3 acid and amide analogs, i.e., [Gln4]-neurotensin, neurotensin-NH2 and [Gln4]-neurotensin-NH2 were synthesized. Neurotensin and [Gln4]-neurotensin were indistinguishable by the [rat] hypotensive assay, hyperglycemic assay [in rats], contraction of [guinea pig] ileum and radioimmunoassay. Neurotensin-NH2 and [Gln4]-neurotensin-NH2 showed less than 1% of these neurotensin activities. Present information does not elucidate whether the glutamic acid residue in position 4 of neurotensin in situ is present as Glu4 or as Gln4. At high levels, neurotensin released the luteinizing hormone [LH] follicle stimulating hormone [FSH] and thyrotropin; [Gln4]-neurotensin-NH2 released thyrotropin, and [Gln4]-neurotensin released LH and FSH, but these activities do not appear biologically significant.