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The pituitary peptide beta-lipotropin displays essentially no opoid activity in a preparation of guinea pig ileum or in the opiate receptor binding assay. However, a fragment, beta-lipotropin-(61-91), with the enkephalin sequence (Tyr-Gly-Gly-Phe-Met) at its NH2-terminus, has typical opioid effects in these two assays.
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Cox et al. (1976) studied this question.
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