Objective:The effects of magnesium sulfate on fetal heart rate (FHR) responses during acute hypoxemia in goats were investigated.
Methods:The FHR responses due to hypoxemia during magnesium sulfate infusion (Mg study) were compared with those during vehicle infusion (controls) in six chronically instrumented goat fetuses at 125-130 days' gestation.
Results:Four-hour infusions of magnesium sulfate significantly increased fetal plasma concentrations of magnesium from 2.3 to 6.5 mg/dL. During the hypoxemic period, the fetal arterial oxygen pressure was significantly decreased from 29.0 ± 2.5 to 14.6 ± 2.6 torr in the controls, and from 28.9 ± 3.9 to 13.7 ± 4.7 torr during the Mg study. Neither arterial carbon dioxide pressure nor pH was significantly altered. In the controls, FHR was significantly decreased by hypoxemia, accompanied by increases in variability. In the Mg study, FHR was not significantly decreased by hypoxemia. Acute hypoxemia also increased the FHR variability during magnesium infusion, which was significantly reduced compared with those in the control populationl.
Conclusion:Magnesium sulfate masks FHR-slowing responses during acute hypoxemia in fetal goats.
1. Freeman RK, Anderson G, Dorchester W. A prospective multiinstitutional study of antepartum fetal heart rate monitoring. I. Risk of perinatal mortality and morbidity according to antepartum fetal heart test results. Am J Obstet Gynecol1982;143:771-777.
2.
2. Kubli FW, Hon EH, Khazin AF, Takemura H. Observations on heart rate and pH in the human fetus during labor. Am J Obstet Gynecol1969;104:1190-1205.
3.
3. Paul RH, Suidan AK, Yeh SY, Schifrin BR, Hon EH. Clinical fetal monitoring. VII. The evaluation and significance of intrapartum baseline FHR variability. Am J Obstet Gynecol1975;123:206-209.
4.
4. Murata Y, Martin CB Jr, Ikenoue T, et al. Fetal heart rate accelerations and late decelerations during the course of intrauterine death in chronically catherized fetal monkeys. Am J Obstet Gynecol1982;144:218-223.
5.
5. Ikenoue T, Martin CB Jr, Murata Y, Ettinger BB, Lu PS. Effect of acute hypoxemia and respiratory acidosis on the fetal heart rate in monkeys. Am J Obstet Gynecol1981;141:797-806.
6.
6. Choi D. Ionic dependence of glutamate neurotoxicity. J Neurosci1987;7:369-373.
7.
7. Rothman SM, Olney JW. Glutamate and the pathophysiology of hypoxic-ischemic brain damage. Ann Neurol1986;19:105-111.
8.
8. Nelson KB, Grether JK. Can magnesium sulfate reduce the risk of cerebral palsy in very low birthweight infants?Pediatrics1995;95:263-269.
9.
9. McIntosh TK. Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: A review. J Neurotrauma1993;10:215-261.
10.
10. Martin CB Jr, de Haan J, van der Wildt B, Jongsma HW, Deleman A, Arts THM. Mechanisms of late decelerations in the fetal heart rate. A study with autonomic blocking agents in fetal lambs. Eur J Obstet Gynecol Reprod Biol1979;9:361-373.
11.
11. Walker AM, Cannata J, Dowling MH, Ritche B, Maloney JE. Sympathetic and parasympathetic control of heart rate in unanaesthetized fetal and newborn lambs. Biol Neonate1978;33:135-143.
12.
12. Hallak M, Berman RF, Irtenkauf SM, Cotton DB. Magnesium sulfate treatment decreases N-methyl-D-asparate (NMDA) receptor binding in the rat brain. Abstract no. S226, 40th SGI, 1993.
13.
13. Gleed RD, Poore ER, Figueroa JP, Nathanielsz PW. Modification of maternal and fetal oxygenation with the use of tracheal gas infusion. Am J Obstet Gynecol1986;155:429-435.
14.
14. Huey JR, Jr, Paul RH, Hadjiev AA, Jilek J, Hon EH. Fetal heart rate variability: An approach to automated assement. Am J Obstet Gynecol1979;134:691-695.
15.
15. Green KW, Key TC, Coen R, Resnik R. The effects of maternally administered magnesium sulfate on the neonate. Am J Obstet Gynecol1983;146:29-33.
16.
16. Nowak L, Bregestovski P, Archer P, et al. Magnesium gates glutamate-activated channels in mouse central neurons. Nature1984;307:462-465.
17.
17. Altura BT, Altura BM. The role of magnesium in the etiology of stokes and cerebrovasospasms. Magnesium1982;1:277-291.
18.
18. Altura BT, Altura BM, Gebrewold A, Ising H, Gunter T. Magnesium-deficient diets and microcirculatory changes in situ. Science1984;223:1315-1317.
19.
19. Cohn HE, Sacks EJ, Heymann MA, Rudolph AM. Cardiovascular responses to hypoxemia and acidemia in fetal lambs. Am J Obstet Gynecol1974;120:817-824.
20.
20. Mudge GH. Agents affecting volume and composition of body fluid. In: Gilman AG, Goodman LS, Gilman A, eds. The pharmacological basis of therapeutics. 6th ed.New York: Macmillan, 1980:879-883.
21.
21. Cech SY, Broaddus WC, Maguire ME. Adenylate cyclase: The role of magnesium and other divalent cations. Mol Cell Biochem1980;33:67-92.
22.
22. Petrie RH, Yeh SY, Murata Y, et al. The effect of drugs on fetal heart rate variability. Am J Obstet Gynecol1978;130:294-299.
23.
23. Stallworth JC, Yeh SY, Petrie RH. The effect of magnesium sulfate on fetal heart rate variability and uterine activity. Am J Obstet Gynecol1981;140:702-706.
24.
24. Zuspan FP. Problems encountered in the treatment of pregnancy-induced hypertension. A point of view. Am J Obstet Gynecol1978;131:591-597.
25.
25. Carlan SJ, O'Brien WF. The effect of magnesium sulfate on the biophysical profile of normal term fetuses. Obstet Gynecol1991;77:681-684.
