The influence of hypoxia on uterine and maternal placental blood flow, and the effect of α-adrenergic blockade

Abstract

The peripheral blood flow in all species is widely to the placenta was reduced from about 60 to redistributed during hypoxia. Dependent upon about 32 per cent during hypoxia. the species and the respiratoryresponsealowering In a study using the macroaggregate distribution of the arterial P Oa gives an increase in c rdiac technique POWER et al. [ISjfoundthatthedistribuoutput and in heart f requency, or a decrease in the tion in the placenta became more uniform, when same parameters [11]. The general pattern of the animal was hypoxic, giving a less variable response is a reduction of blood flow to most local relation between the maternal and fetal flow. organs, but preservation or even an increase of This indicates a placental vasodilatation. blood flow to vital organs -the brain and the The present experiments were performed to myocardium. In pregnancy a special Situation is investigate whether hypoxic vasoconstriction established since the placenta is a non-vital organ takes place in the uterus-placental circulation in for the mother but a vital organ for the fetus. the pregnant rabbit, and if so, what the mechanism The question arises, whether the Uterus-for vasoconstriction might be. placenta circuit will take part in the general peripheral vasoconstriction during maternal . _,, . . Έ ^, , ϊ . * i^ t ui j Λ ·ιι t-* Material and Methods hypoxia, or whether the blood flow will be preserved.The material consisted of 14 pregnant rabbits Great difficulties have earlier been encountered with dated gestations from 25 to 30 days. The when studying the uterine circulation. The posi-pregnant term for rabbits is 31 ± 2 days. The tion of the organ, with several vessels both on the mean body weight was 4.39 kg i 0.16 (SD). inflow and outflow side, has complicated the study Anesthesia was induced with pentothal (25 mg/ of circulation of this special organ. Information on kg) through a catheter in a lateral ear-vein, and the uterine circulation in pregnancy during hypo-maintained with additional small amounts of xia is conflicting. Thus ASSALI et al.[2] found a pentothal. The rabbit was placed on a warm table progressive increase in blood flow to the Uterus and the trachea cannulated. The animal was in pregnant ewes, when these were breathing artificially ventilated with known gas mixtures 10 per cent oxygen, while DUNCAN et al.[5] using a small animal Ideal Pump (volume/ found a reduction in the total uterine blood flow, f requency = 22 ml/36 rpm). probably because of local vasoconstriction during Arterial blood pressure and heart frequency were hypoxia. The latter authors performed their in-registered through a catheter in the right brachial vestigations on rabbits with the microsphere artery. The Signals were monitored by a STATHAM technique and found, apart from the reduction P 23 AC transducer, atnplified and recorded on a of uterine blood flow, a redistribution of the total GRASS model 7 polygraph. Samples for blood flow within the organ, so that the fraction going gas determinations were taken through the same

The uterine and maternal placental blood flow during hyperoxia

“…The maternal Pco 2 > PO Z an d pH during control Situation (inhalation of 30 per cent oxygen) were within the ranges previously observed [7]. The arterial P Oa rose from an average of 96 mm Hg to an average of 471 mm Hg when the inspired oxygen was increased from 30 to 100 per cent.…”

“…The injection chamber was carefully agitated before and during the injection by a high frequency mechanical whirlmixer, and the chamber was afterwards flushed with 6-10 ml of 6 per cent Dextran. Further particulars about the methods used for counting are given in an accompanying paper [7]. This paper also contains results suggesting that the spheres were homogeneously mixed in the cardiac Output and that the sampling time of two minutes for the reference blood sample was adequate.…”

Acute effect of an antihypertensive drug, labetalol, on uteroplacental blood flow

“…1 Y 70) or by hypoxia (Karlsson 1974) the addition of a n a adrenoceptor antagonist will abolish this decrease. so that it is theoretically sound to use such a n antagonist a s labetalol in the treatment 01' hypertension in pregnancy.…”