The relationship between opiate concentration and cellular activity in the pars distalis and neurointermediate lobe of the eel pituitary

Abstract

Both the pars distalis (PD) and neurointermediate lobe (NIL) of the eel pituitary were found to contain substantial levels of opiate activity when measured by the mouse vas deferens bioassay. Opiate bioactivity in the two lobes was measured either after injection of metopirone or following adaptation to black or white backgrounds. Metopirone did not significantly alter opiate activity of either lobe, but a wide variation between eels made interpretation of this result difficult. Three days after transfer from a black to a white background, MSH bioactivity of the NIL was increased threefold, whereas opiate bioactivity was unaffected. Opiate bioactivity in the NIL was reduced after 2 weeks adaptation to a white background.