Vol. 274, Issue 3, R672-R676, March 1998
Opioid peptides mediate heat stress-induced immunosuppression
during pregnancy
Hiroyuki
Nakamura1,
Hirofumi
Nagase1,
Masami
Yoshida1,
Keiki
Ogino1,
Toshio
Seto2,
Kotaro
Hatta3, and
Ichiyo
Matsuzaki4
1 Department of Public Health,
Kanazawa University School of Medicine, Kanazawa
920; 2 Department of Public
Health, Kanazawa Medical University, Uchinada
920-02; 3 Department of
Psychiatry, Tokyo Metropolitan Bokuto Hospital, Tokyo 130; and
4 Institute of Community Medicine,
University of Tsukuba, Tsukuba, Ibaraki 305, Japan
To clarify the involvement of the opioid
system in enhanced immunosuppression induced by heat stress during
pregnancy, we examined the effects of heat exposure and
intraperitoneal administration of opioid receptor
antagonist naloxone on 
-endorphin (-EP) in blood, pituitary
lobes, and placenta as well as splenic natural killer cell activity
(NKCA) and placental steroids in pregnant rats at 15-16 days
gestation. Two-way analysis of variance revealed significant increases
in blood -EP induced by heat and naloxone and a significant
interaction between heat and naloxone on blood -EP and progesterone
(P). Whereas heat reduced NKCA, intraperitoneal administration of
naloxone reversed it. Significant increases in blood and placental
-EP induced by both heat and naloxone administration and a
significant interaction on blood and placental -EP was
observed. These results suggest that immunosuppression produced by heat stress during pregnancy is mediated by the opioid system. A positive correlation between -EP in blood and placenta during heat and naloxone administration suggests that increased placental -EP during heat results in hypersecretion of -EP into blood. P increased by heat during pregnancy may be involved in the
immunosuppression.
-endorphin; natural killer cell activity; pituitary; placenta; progesterone
