Delta sleep-inducing peptide (DSIP) stimulates growth hormone (GH) release in the rat by hypothalamic and pituitary actions.

To evaluate possible effects of delta sleep-inducing peptide on GH release, the peptide was micro-injected into conscious animals with third ventricular cannulae and blood samples were drawn from indwelling external jugular vein cannulae. Ovariectomized animals were used in order to eliminate gonadal steroid feedback. In the initial experiment, intraventricular injection of 5 micrograms of the peptide induced an elevation of GH which became significant by 30 min and persisted for the 120 min duration of the experiment after the injection. Diluent-injected animals showed a slight initial drop in GH and then no increase. The increase in plasma GH induced by the peptide was dose-related with a minimal effective dose of 0.1 microgram and a linear log-dose increase to a dose of 10 micrograms. This effect is presumably mediated hypothalamically via a dopaminergic mechanism since it could be blocked by pre-treatment of the animals with pimozide, a dopamine receptor blocker. Dispersed overnight, cultured pituitary cells from ovariectomized rats exhibited a dose-related increase in GH release in static incubations with DSIP. A response occurred with the lowest dose tested (10(-12) M) which increased to a maximum at 10(-10) M DSIP. The responses then declined at higher doses such that they were no longer significant at doses of 10(-7) and 10(-5) M. The increase even at the most effective dose was approximately 50% above the basal values. The results are consistent with the hypothesis that DSIP may be involved in GH release via a dopaminergic mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)