Endocrine Abstracts

The fetus may successfully respond to acute hypoxaemia, but little is known about what effects prevailing adverse intrauterine conditions might have on these responses. The fetal cardiovascular response to acute hypoxaemia involves increased plasma vasopressin, which aids the redistribution of blood flow away from the periphery towards the fetal brain (Perez et al. Am.J.Physiol. 256:1011-1018, 1989). We investigated the effects of prevailing, but independently-occurring, hypoxaemia, acidaemia or hypoglycaemia on plasma vasopressin during acute hypoxaemia in fetal sheep.

Thirty-three fetuses were instrumented (halothane) with catheters 7 days before study. Nineteen fetuses were designated as either spontaneously hypoxaemic (SpHPX, n=8), or acidaemic (SpAC, n=5) or hypoglycaemic (SpHG, n=6). The criteria for inclusion was determined as one parameter only being -2 S.D. below the normal range in pH, PO₂, or blood glucose. The remaining 14 fetuses were controls. Between 129-137 days, all fetuses underwent 1 h of hypoxaemia via maternal inhalational hypoxia. Arterial blood samples were taken for vasopressin (RIA) analysis.

In control fetuses, basal arterial pH, PO₂ and blood glucose were 7.35 ± 0.01, 23.7 ± 0.8 mmHg and 0.82 ± 0.04 mmol.L-1, respectively. In SpHPX fetuses basal PO₂ was 16.8 ± 0.9 mmHg, in SpAC fetuses basal pH was 7.25 ± 0.01, and in SpHG fetuses basal arterial glucose was 0.51± 0.04 mmol/L (P<0.05). Basal plasma vasopressin in controls was 3.0 ± 0.5 pg/ml and was similar in all other groups. During hypoxaemia (PO₂ to 12 ± 1 mmHg in all groups), the increase in plasma vasopressin was greater in SpAC (281 ± 74 pg/ml) and SpHG (209 ± 74), but not SpHPX (116 ± 36) fetuses, relative to controls (139 ± 47).

The fetal plasma vasopressin response to acute hypoxaemia is altered by prevailing adverse intrauterine conditions, but the partial contribution of prevailing hypoxaemia, acidaemia or hypoglycaemia on this response can vary. These data have important clinical implications for pregnancies with abnormal fetal oxygen, acid/base or metabolic status.