Experimental study of endogenous opioid peptides participating in the fetal distress

Dian HU; Hang GU; Xinru HONG; Yihong LI; Chenghai WANG; Liping CAO; Ping LI

ABSTRACT

BACKGROUND:

Endogenous opioid peptides are mainly mediated by μ receptor and produce inhibitory effect on breathing and heartbeat, and because of this, fetal distress happens and develops. Therefore, μ receptor mediation is the most important way that endogenous opioid peptides participate in the fetal distress and the pathological process of suffocation. Β-FNA (β-Funaltrexamine, μ-receptor antagonist) and ICI174864(δ-receptor antagonist) are helpful to reduce the happening of fetal distress.

OBJECTIVE:

To explore the roles of μ and δ receptors in the fetal distress based on the point of view that opioid peptides are involved.

DESIGN:

Completely randomized allocation and randomized and controlled trial using experimental animals as the subjects.MATERIALS Twenty healthy white New Zealand purebred rabbits were randomly divided into 5 groups, and among them 16 rabbits were pregnant for 30 days and were put to death with the method of suffocation. The fetal rabbits were taken out immediately after cesarean section, with 6 - 8 fetal rabbits in each den. The fetal rabbits were classified into the following groups untreated fetal distress group, (fetal distress group, 29 fetal rabbits), normal saline rabbits group(Normal saline group, 25 rabbits), rabbit distress β-FNA group(β-Funaltrexamine ) (FNA group, 28 rabbits), fetal rabbits ICI174864 treatment group(ICI174864 group, 31 rabbits).

INTERVENTIONS:

Pregnant rabbits in the saline group, FNA group , ICI group were intravenously given a bolus of normal saline or the opiate antagonist β-FNA or ICI174864 and were then asphyxiated. Another 4 rabbits that were pregnant for 30 days were put to death with the cut on the neck, and 28 fetal rabbits were taken out as the control group. After being delivered by cesarean section, all rabbit fetuses in the above five groups were assessed by Apgar scoring for respiration, heartbeat, skin color, muscle tension, and response to stimulation at 1, 5, 10, 15 and 30 minutes of age.MAIN OUTCOME

MEASURES:

Apgar scoring for respiration, heartbeat,skin color, muscle tension, and response to stimulation at 1, 5, 10, 15 and 30 minutes of age was made.

RESULTS:

The total Apgar score for respiration, heartbeat, skin color, muscle tension in the control group was the highest (8. 8 ± 1.1 ). And that of FNA group was 6. 8 ± 1.7, obviously higherthan that of the fetal distress group (2.1 ±1.0) and the saline-treated pups(2.5±1. 1) and(t=2.832 and 2. 795, P < 0.01 ). That of group ICI was 4.9 ± 0.7, markedly higher than that of the saline-treated pups and the fetal distress group( t = 2. 232 and 2. 195, P < 0.05) . There was no marked difference between the saline group and the distress group ( P > 0.05 ) and between the FNA group and the control group(P < 0.05) . The total Apgar scores of the ICI group,saline group, and distress group were significantly lower than that of the control group ( t = 2.913,2. 893, P < 0.01 and t = 2. 174, P < 0.05).

CONCLUSION:

Endogenous opioid peptides participates in the process of the happening and development of fetal rabbit distress that is mediated by opioid peptides receptor, the effect of μ receptor was much more than that of δ receptor. This study provides a basis for the evaluation of fetal distress and intervening at an earlier stage to enhance prognostic function.