ISOLATION, PRIMARY STRUCTURE, AND EFFECTS ON ALPHA-MELANOCYTE-STIMULATING HORMONE-RELEASE OF FROM NEUROTENSIN

Neurotensin (NT) was isolated in pure form from the small intestine of the European green frog, Rana ridibunda, and its primary structure wa s established as u-Ala-His-Ile-Ser-Lys-Ala-Arg-Arg-Pro-Tyr-Ile-Leu. Th is sequence contains five amino acid substitutions (Leu(2)-->Ala, Tyr( 3)-->His, Glu(4)-->Ile, Asn(5)-->Ser, and Pro(7)-->Ala) compared with human NT. A peptide with identical chromatographic properties was iden tified in an extract of frog brain. Synthetic frog NT produced a conce ntration-dependent increase in (alpha MSH release from perifused frog pars intermedia cells, with an ED50 of 5 x 10(-9) M. A maximum respons e (276.3 +/- 45.5% above basal release) was produced by a 10(-8)-M con centration. Repeated administration of NT to melanotrope cells reveale d the occurrence of a rapid and pronounced desensitization mechanism. The data are consistent with a possible role for the peptide as a hypo physiotropic factor in amphibians.