Central opioids: a possible role in parturition?
Pregnant rats were implanted with subcutaneous minipumps to deliver either naloxone or saline. The time-course of subsequent parturition was different between the two groups: the interval between successive births was significantly shorter for the naloxone-treated rats. This supports the hypothesis that the opioid innervation of the neurohypophysis, which is known to influence oxytocin release profoundly, has a physiological role in parturition. To test the further hypothesis that this role is particularly important in a stressful environment, pregnant rats, again implanted with minipumps, were regularly transferred, at 15-min intervals beginning with the birth of the first pup, between their normal cage and the unfamiliar environment of a glass observation chamber. No difference was noted between the time-courses of parturition for the naloxone- and saline-treated groups, although the time-courses were markedly altered from those observed in rats not subjected to an unfamiliar environment. We conclude that opioid modulation of oxytocin release may play a role in 'spacing' the delivery of successive births during normal parturition.
Leng
G
G
Mansfield
S
S
Bicknell
R J
RJ
Dean
A D
AD
Ingram
C D
CD
Marsh
M I
MI
Yates
J O
JO
Dyer
R G
RG
D000818:Animals; D004723:Endorphins / Q000494:pharmacology; D005260:Female; D007743:Labor, Obstetric / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology*; D049590:Postpartum Period; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D013312:Stress, Physiological; D013997:Time Factors; D014590:Uterine Contraction / Q000187:drug effects; D001615:beta-Endorphin
D004723:Endorphins; D009270:Naloxone; D001615:beta-Endorphin