The effect of labetalol on maternal haemodynamics and placental perfusion in awake near term guinea pigs.
The effect of labetalol (20 micrograms/kg/min) on maternal haemodynamics in general, and absolute placental perfusion in particular, was studied in eight chronically instrumented hypertensive guinea pigs near term. One day before drug testing, all experimental animals were subjected to haemoconcentration (haematocrit was gradually raised from 35.9 +/- 2.9 to 49.4 +/- 5.6 vol%, mean +/- S.D.) to establish a prolonged and stable state of hypertension. This procedure increased mean arterial pressure from 59.7 +/- 7.2 to 70.3 +/- 8.6 mmHg, and was paralleled by mild foreseeable systemic haemodynamic effects (redistribution of cardiac output away from intestines and brain), without consistent changes in the maternal placental blood flow. The hypotensive effect of labetalol was paralleled by a selective reduction in placental perfusion as reflected by a consistent fall in weight-specific cardiac output fraction (from 55.5 +/- 26.6 to 40.9 +/- 12.5%/100 g, P < 0.05) and blood flow (from 155 +/- 76 to 112 +/- 44 ml/min/100 g, P < 0.05) to the placentas. The concomitant placental resistance had increased consistently from 0.55 +/- 0.26 to 0.62 +/- 0.32 mmHg.min.100 g/ml, P < 0.05. We conclude that in awake late-pregnant hypertensive guinea pigs, labetalol reduces uteroplacental blood flow selectively. We speculate that the latter selective effect is secondary to the fall in blood pressure.
Verkeste
C M
CM
Department of Gynaecology and Obstetrics, University of Limburg, Maastricht, The Netherlands.
Peeters
L L
LL
D000818:Animals; D005260:Female; D005865:Gestational Age; D006168:Guinea Pigs; D006439:Hemodynamics / Q000187:drug effects; D007741:Labetalol / Q000494:pharmacology*; D010920:Placenta / Q000187:drug effects* / Q000502:physiology; D011247:Pregnancy; D012039:Regional Blood Flow / Q000187:drug effects; D013997:Time Factors
D007741:Labetalol