L. Kehoe et al., OPIATE RECEPTOR SUBTYPE INVOLVEMENT IN THE STIMULATION OF PROLACTIN-RELEASE BY BETA-ENDORPHIN IN FEMALE RATS, Neuroendocrinology, 57(5), 1993, pp. 875-883
The prolactin secretory response to beta-endorphin and the involvement
of opiate receptor subtypes in this response was determined in both d
iestrous and postpartum, lactating female rats. The involvement of the
mu-, delta- and/or kappa-site was determined by administering specifi
c antagonists for each of these sites prior to beta-endorphin. Beta-Fu
naltrexamine (beta-FNA, 1 or 5 mug) was administered to block mu-sites
, ICI 154,129 (5, 10 or 25 mug) blocked delta-sites and nor-binaltorph
imine (norBNI, 8 mug) blocked kappa-sites. The ability of beta-FNA and
ICI 154, 129 to block prolactin secretion following morphine administ
ration was also determined. A dose response study for beta-endorphin i
ndicated that beta-endorphin, at doses as low as 25 ng, was a potent s
timulus for prolactin release producing an increase in prolactin that
mimicked the suckling-induced prolactin increase. In addition, all thr
ee antagonists were capable of antagonizing the stimulatory effect of
beta-endorphin in both diestrous and postpartum female rats. These res
ults indicate that beta-endorphin is a potent stimulus for prolactin s
ecretion and that these three opiate receptor subtypes interact to pro
duce its stimulatory effect on prolactin release.