APStracts 2:0104R, 1995.

Lack of relationship between opioid-induced changes in fetal breathing and plasma glucose levels. Szeto, Hazel H., Peter Y. Cheng, Yi Soong, and Dun-Li Wu. Department of Pharmacology, Cornell University Medical College, 1300 York Avenue, New York, N.Y. 10021

APStracts 2:0104R, 1995.

The mechanisms by which opioids increase or decrease fetal breathing remain unclear. Fetal plasma glucose is known to modulate breathing activity, and opioids have been reported to alter glucose regulation in the adult. In this study, we investigated whether alterations in fetal breathing by opioids may be explained by changes in plasma glucose levels. We compared the effects of morphine (non-selective), DAMGO ([D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin, [mu]-selective) and DPDPE ([D-Pen2,D-Pen5]-enkephalin, [delta]-selective) on fetal breathing and plasma glucose in unanesthetized fetal sheep. While both 1.2 and 5.0 mg/h (iv) of morphine resulted in an increase in breath number (P < 0.01), plasma glucose was decreased after 1.2 mg/h (P = 0.006), but increased after 5.0 mg/h (P = 0.008). DAMGO (100 [mu]g/h, icv) resulted in an increase in plasma glucose (P = 0.001) but a reduction in fetal breathing (P < 0.001). In contrast, DPDPE (30 [mu]g/h, icv) increased fetal breathing (P = 0.026), but had no effect on plasma glucose concentration. These data demonstrate that the actions of opioids on fetal glucose regulation and breathing are dependent on dose and receptor- selectivity. However, there is no relationship between the effects of opioids on fetal breathing and plasma glucose concentration.

Received 25 April 1994; accepted in final form 13 April 1995.
APS Manuscript Number R220-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.