Changes in extracellular LHRH and β-endorphin-like immunoreactivity in the nucleus infundibularis-median eminence of anestrous ewes under stress condition

To clarify the effect of beta-endorphin released under stress condition on LHRH secretion, the concentration of LHRH and beta-endorphin-like-immunoreactivity (beta-END-LI) were analysed in perfusates from the nucleus infundibularis-median eminence of anestrous ewes subjected to footshocks stimulation. The dynamics of LHRH and beta-END-LI release during timecourse of footshocks stimuli was altered. A brief facilitatory influence of stress on LHRH and beta-END-LI release was observed at the beginning of the stimulation on the first and third day; however the peaks of beta-END-LI were delayed about half an hour in relation to LHRH. Than on the first day of the stimulation LHRH returned to the control value but on the third day it declined below the control levels. Prolonged stress had stimulatory effect on beta-END-LI secretion during first and third day. The presented results indicate that: 1) short stress activates LHRH and (beta-END-LI release, 2) prolonged stress has stimulatory effect on beta-END-LI release but leads to suppression of LHRH release. It is suggested that stress-induced (beta-endorphin release may be one of the factors responsible for suppression of LHRH activity.