Central pharmacological activities and opiate receptor binding studies of some dermorphin analogs

A series of dermorphin-like compounds were injected intracerebroventricularly in the rat to assess in vivo their effects on intestinal motility and analgesia. In vitro they were tested by binding assay using 3H-naloxone as radioligand or by guinea pig ileum bioassay. The synthetic peptides were less potent than dermorphin in inhibiting intestinal transit and in producing analgesia, or even inactive up to doses 30 times the dermorphin ED50. This reduction in pharmacological activity was coupled with a decrease in binding potency. The 3H-naloxone binding studies in the absence or presence of Na+ indicated that Na+ reduced the interaction of dermorphin and its analogs with brain opiate receptors. Only the dibenzyl derivative was slightly affected by sodium, suggesting a dual action for this peptide, as confirmed by preliminary data from guinea pig ileum bioassay.