In rats, a tiny dose of DSIP (0.1 mg/kg) made them colder when they were in a chilly room, but the same dose made them warmer in a normal‑temperature room. Higher doses didn’t change temperature much. When combined with d‑amphetamine, DSIP’s effect depended on the room temperature: it didn’t change the cold‑induced drop in body heat, but in a warm room it flipped amphetamine’s usual heat‑raising effect into a cooling one. DSIP also altered how much the rats moved and even made some of them look like they were sleeping when given both DSIP and amphetamine at normal temperature.

A low dose (0.1 mg/kg) of peripherally administered delta sleep-inducing peptide (DSIP) caused hypothermia in rats maintained at 4 degrees C but larger doses (1.0 or 3.0 mg/kg) did not. At 22 degrees C all 3 doses of DSIP caused hyperthermia. The interaction of d-amphetamine with DSIP was dependent on ambient temperature; at 4 degrees C DSIP had no effect on d-amphetamine-induced hypothermia, but at 22 degrees C DSIP reversed the usual d-amphetamine-induced effect of hyperthermia to hypothermia. At 4 degrees C, DSIP also potentiated the hypermotility effects of d-amphetamine but blocked it at 22 degrees C. Many rats receiving DSIP (0.1 mg/kg) and d-amphetamine (15.0 mg/kg) at 22 degrees C paradoxically exhibited what appeared to be sleep. This sleep-like effect was not found after several other doses of DSIP and d-amphetamine, chlorpromazine, or at a cold ambient temperature. Sodium methohexital caused apparent sleep in animals treated with DSIP alone or with DSIP and d-amphetamine, but was unable to induce this effect in rats receiving d-amphetamine alone. The results suggest that the effects of peripherally injected DSIP on body temperature are independent from its effects on locomotion and that both effects are dependent upon ambient temperature.