Human studies on the mu opiate receptor agonist fentanyl: neuroendocrine and behavioral responses

The neuroendocrine and behavioral responses to the potent mu opiate receptor agonist Fentanyl (FE) have been systematically investigated in healthy male volunteers. These volunteers received, according to a randomized block design, different doses of FE: 0.1 mg/70 kg (n = 11), 0.2 mg/70 kg (n = 11), 0.25 mg/70 kg (n = 8), and saline (n = 11). FE induced a pronounced dose-dependent increase of plasma prolactin concentrations, which was significant at the lowest dose. In contrast, growth hormone was significantly stimulated by the highest FE dose only. Moreover, FE induced a maximum reduction of plasma cortisol concentrations at the lowest dose (0.1 mg/70 kg). In parallel, marked euphoric responses were also observed at this lowest FE dose. These results suggest a mu specific influence on all neuroendocrine and behavioral parameters investigated. Different responses of these parameters to different doses of FE, however, suggest a differential modulation of these parameters by the mu receptor agonist FE.