Effect of beta-endorphin on fetal breathing movements in sheep.
It has been suggested that endogenous opioids, such as beta-endorphin (beta-EP), act to depress respiration in the fetus and newborn. We have investigated the effect of infusing beta-EP either intravenously or into a lateral cerebral ventricle on breathing movements and electrocortical activity in eight fetal lambs between 116 and 133 days gestation. Intravenous infusion of beta-EP (200 or 500 micrograms over 1 h) increased plasma beta-EP concentrations 2- to 230-fold and was associated with a small decrease in the percent time spent breathing, from 57.8 +/- 9.1 to 51.3 +/- 8.2%/h (n = 6 exp). There was no change in the amount of high- or low-voltage electrocortical activity. Intracerebroventricular beta-EP infusion (1 or 2 micrograms beta-EP/min for 120 min) was not associated with any change of breathing movements (n = 5 exp) during the period of the infusion. However, in four experiments, in the 6-h period after the end of the beta-EP infusion there were episodes of 2-4 h when the percent time per hour spent breathing exceeded 70%. Electrocortical activity increased in amplitude and distinct episodes of high- and low-voltage activity were sometimes lost in these experiments. We conclude that high concentrations of beta-EP in plasma or cerebrospinal fluid do not totally suppress fetal breathing directly in the fetal lamb.
D000818:Animals; D004569:Electroencephalography; D004723:Endorphins / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D005260:Female; D005333:Fetus / Q000187:drug effects* / Q000502:physiology; D007262:Infusions, Intravenous; D007276:Injections, Intraventricular; D011247:Pregnancy; D012119:Respiration / Q000187:drug effects*; D012756:Sheep; D001615:beta-Endorphin; D008083:beta-Lipotropin / Q000097:blood
D004723:Endorphins; D001615:beta-Endorphin; D008083:beta-Lipotropin