Sw. Lindow et al., THE EFFECT OF MORPHINE AND NALOXONE ADMINISTRATION ON MATERNAL OXYTOCIN CONCENTRATION IN LATE PREGNANCY, Clinical endocrinology, 39(6), 1993, pp. 671-675
OBJECTIVE Modification of the inhibitory control of oxytocin secretion
by endogenous opiates in late pregnancy may be one of the factors inv
olved in the onset of labour. The interrelationships between exogenous
ly administered opioids and oxytocin may demonstrate activity of this
control mechanism. This study was undertaken to investigate the effect
of an opiate and an opiate antagonist on maternal oxytocin levels in
late pregnancy. DESIGN Patients were randomized to receive either morp
hine (5 mg), naloxone (2.4 mg) or sterile water (1 ml) intravenously.
PATIENTS Thirty women with singleton pregnancies greater than 36 weeks
gestation who were not in labour were studied. MEASUREMENTS Blood for
peripheral oxytocin levels was sampled every 2.5 minutes for 15 minut
es before and 15 minutes after administration of the assigned substanc
e. Oxytoxin was measured by radioimmunoassay. Peripheral beta-endorphi
n levels were measured at the beginning and end of the study. RESULTS
There was no significant change in the maternal oxytocin concentration
after administration of either morphine, naloxone or sterile water co
mpared to pretreatment levels. beta-Endorphin levels did not change si
gnificantly, either from the beginning to the end of the study, or bet
ween groups. CONCLUSION in tate pregnancy exogenous opiates and opiate
antagonists have no effect on maternal peripheral oxytocin levels.