An ultrastructural and ultrahistochemical study of the human placenta in maternal essential hypertension.

An electron-optical study of the placenta in essential hypertension indicates that the morphological changes seen in this disease are qualitatively very similar to those found in placentae from pre-eclamptic women: these changes are accentuated if pre-eclampsia is superimposed on essential hypertension. It is therefore suggested that the abnormalities seen in placentae from hypertensive women are due solely to ischaemia. The extent and degree of ischaemic damage suffered by the placenta is essential hypertension were, however, much less marked and extensive than in placentae from pre-eclamptic patients whilst in placentae from cases of essential hypertension complicated by pre-eclampsia there was less evidence of ischaemic damage than in placentae from cases of pre-eclampsia or comparable severity developing in previously normotensive women. It is suggested that the placenta is able to adapt to a state of chronic ischaemia in a manner that it is not able to do in late onset ischaemia and that the adaptive mechanisms adopted not only limit ischaemic damage but also afford protection to the placenta against the effects of superimposed pre-eclampsia.