Radiotracers, tritium labelling of neuropeptides

Tritium labelled endomorphins (Tyr-Pro-Trp-Phe-NH2, EM1, Tyr-Pro-Phe-Phe-NH2, EM2) and their analogs, Angiotensin-IV (Val-Tyr-Ile-His-Pro-Phe) and its analogs, Neuromedin N (Lys-Ile-Pro-Tyr-Ile-Leu) and a new nociceptin analog (Phe-Phe-Gly-pFPhe-Thr-Gly-Aib-Arg-Lys-Ser-Ala-Arg-Lys-Arg-Lys-Asn-Gln-NH2) and Substance P analogs (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Nle-NH2, Arg-Pro-Lys-Pro-Gln-Gln-Phe) were synthesized by catalytic dehalogenation or saturation of the precursor peptides with tritium gas. The specific radioactivity of the neuropeptides is high, ranging from 0.6 TBq/mmol to 2.8 TBq/mmol. The labelled peptides were characterized by radioreceptor binding assays and used in mapping their metabolic pathway using rat brain membrane preparation.