Plasma oxytocin concentrations in man after different routes of administration of synthetic oxytocin.

Plasma oxytocin was determined by RIA in three male subjects under basal conditions and following administration of synthetic oxytocin. As compared to basal levels (below 10 pg/ml), plasma oxytocin was found to be elevated markedly (36 to 85 pg/ml) in response to application by nasal spray (total dose: 65 to 100 micrograms). Intramuscular injection (25 micrograms) resulted in very high oxytocin levels (360 to 480 pg/ml), whereas buccal administration (70 micrograms) was proved to be ineffective (levels below 10 pg/ml plasma). In each case, plasma vasopressin remained unchanged.