May act as a paracrine/endocrine mediator in the neurohypophysis. Inhibits the effects of both endogenous and exogenous opiates - H.-Y. T. Yang et al., PNAS 82, 7757 (1985); S. Labrouche et al., Endocrin. 132, 2191 (1993); M. Allourd et al., International Narcotic Research Conference (INRC), Skovde, Sweden, July 10-15, 1993.