Radioimmunoassay of DSIP-like material in rat brain.

Antibodies generated in a rabbit by immunization with synthetic delta-sleep inducing peptide (DSIP) showed no cross-reactivity with 19 naturally-occurring peptides or analogues and were used to establish a radioimmunoassay. Since DSIP is not readily iodinated by conventional methods, N-Tyr-DSIP was synthesized to prepare the tracer; the dose-response curve for N-Tyr-DSIP was exactly parallel to that for DSIP. With this assay, DSIP-like immunoreactivity was detected in the brain of rats. The highest brain values were found in the thalamus (11.9 +/- 1.3 pg/mg). The widespread presence of DSIP-like material throughout the body as well as the shared amino acid sequences of DSIP with other proteins suggest caution in defining the material being measured by this new assay. Nevertheless, the demonstration of DSIP-like activity in brain tissue and elsewhere warrants consideration of functions in addition to a possible role in sleep.