Objectives:To determine whether physiological increases in fetal plasma arginine vasopressin (AVP) concentration alter blood flow rates to the ovine chorion, amnion or placenta, and to determine whether these AVP-induced changes in flow are dependent on gestational age.
Methods:Colored microspheres (15.10 ± 0.02 μm (standard deviation)) were infused into the superior vena cava before and at 30, 75, and 125 minutes of an intravenous AVP infusion (3 ng/min/kg) in 9 chronically catheterized fetal sheep between 103 to 141 days gestation (term = 147 days). Chorion, amnion, and placental cotyledons were removed, and microspheres were counted to determine blood flow rates.
Results:Fetal arterial pressure (FAP) increased (analysis of variance, P < .0001) and heart rate (FHR) decreased (P < .0001) during the infusion, with responses greater in older (> 125 days) compared to younger (<125 days) fetuses (P < .001). Chorionic blood floow rate increased by 19 ± 7% at 30 min of the AVP infusion, and declined by 18 ± 6% at 75 min, and 32 ± 5% at 125 min (P < .0001). Similarly, fetal placental blood flow rate increased by 20 ± 7% at 30 min of infusion, and declined, in parallel with chorionic blood flow rates, by 6 ± 4% at 75 min, and 17 ± 4% at 125 min (P < .0001). Amniotic blood flow rate did not change significantly during the infusion. The membranous and placental blood flow rate responses to AVP infusion did not depend upon gestational age.
Conclusions:Physiologic increases in plasma AVP concentration induce an early increase in chorionic blood flow followed by a gradual decrease which parallels similar changes in placental blood flow rate. Unlike FAP and FHR, these blood flow changes are not gestational age-dependent. AVP-induced blood flow changes could play an important role in determining abnormalities amniotic fluid volume observed clinically in some stressed fetuses.
1. Alexander DP, Bashore RA, Britton HG, Forsling ML. Maternal and fetal arginine vasopressin in the chronically catheterized sheep. Biol Neonate1974;25:242-248.
2.
2. Rurak DW. Plasma vasopressin levels during hypoxaemia and the cardiovascular effects of exogenous vasopressin in the foetal and adult sheep. J Physiol1978;277:341-357.
3.
3. Daniel SS, Husian MK, Milliez J, Stark RI, Yeh MN, James LS. Renal response of fetal lamb to complete occlusion of umbilical cord. Am J Obstet Gynecol1978;131:514-519.
4.
4. Wintour EM, Congiu M, Hardy KJ, Hennessy DP. Regulation of urine osmolality in fetal sheep. Q J Exp Physiol1982;67:427-435.
5.
5. Tomita H, Brace RA, Cheung CY, Longo LD. Vasopressin dose-response effects on fetal vascular pressures, heart rate and blood volume. Am J Physiol1985;249:H974-H980.
6.
6. Gilbert WM, Cheung CY, Brace RA. Rapid intramembranous absorption into the fetal circulation of arginine vasopressin injected intraamniotically. Am J Gynecol1991;164:1013-1020.
7.
7. Stark RI, Daniel SS, Husain MK, Sanocka UM, Zybrow AB, James LS. Vasopressin in amniotic fluid as an index of fetal hypoxia: mechanism of release in sheep. Pediatr Res1984;18:835-841.
8.
8. Brace RA. Progress toward understanding the regulation of amniotic fluid volume: water and solute fluxejs in and through the fetal extraplacental membranes. Placenta1995;16:1-18.
9.
9. Brace RA, Gilbert WM, Thornburg KL. Vascularization of the ovine amnion and chorion: A morphometric characterization of the surface area of the intramembranous pathway. Am J Obstet Gynecol1992;167:1747-1755.
10.
10. Hedriana HL, Brace RA, Gilbert WM. Changes in blood flow to the ovine chorion and amnion across gestation. J Soc Gynecol Invest1995;2:727-734.
11.
11. Makowski EL, Meschia G, Droegemueller W, Battaglia FC. Measurement of umbilical arterial blood flow to the sheep placenta and fetus in utero: Distribution to cotyledons and intercotyledonary chorion. Circ Res1968;23:623-631.
12.
12. Lumbers ER, Kingsford NM, Menzies RI, Stevens AD. Acute effects of captopril, an angiotensin-converting enzyme inhibitor, on the pregnant ewe and fetus. Am J Physiol1992;262:R754-R760.
13.
13. Gibson KJ, Lumbers ER. The roles of arginine vasopressin in fetal sodium balance and as a mediator of the effects of fetal “stress.”J Dev Physiol1993;19:125-136.
14.
14. Lumbers ER, Smith FG, Stevens AD. Measurement of net transplacental transfer of fluid to the fetal sheep. J Physiol1985;364:289-299.
15.
15. Iwamoto HS, Rudolph AM, Keil LC, Heyman MA. Hemodynamic responses of the sheep fetus to vasopressin infusion. Circ Res1979;44:430-436.
16.
16. Paulick RP, Meyers RL, Rudolph CD, Rudolph AM. Umbilical and hepatic venous responses to circulating vasoconstrictive hormones in fetal lamb. Am J Physiol1991;260:H1205-H1213.
17.
17. Irion GL, Mack CE, Clark KE. Fetal hemodynamic and fetoplacental vascular response to exogenous arginine vasopressin. Am J Obstet Gynecol1990;62:1115-1120.
18.
18. Wiriyathian S, Porter JC, Nader RP, Rosenfeld CR. Cardiovascular effects and clearance of arginine vasopressin in the fetal lamb. Am J Physiol1983;245:E24-E31.
19.
19. Gibson KJ, Lumbers ER. Ovine fetal cardiovascular, renal, and fluid balance responses to 3 days of high arginine vasopressin levels. Am J Physiol1997;272:R1069-R1076.
20.
20. Dawes GS. Fetal and neonatal physiology: A comparative study of the changes at birth. Chicago: Year Book Medical Publishers, Inc., 1968.
21.
21. Zhang S, Hirano Y, Hiraoka M. Arginine vasopressin-induced potentiation of unitary L-type Ca2+ channel current in guinea pig ventricular myocytes. Circ Res1995;76:592-599.
