Pregnancy alters cerebrovascular adaptation to high-altitude hypoxia

We have previously shown alterations in cerebrovascular composition, contractility, and endothelial function in normoxic pregnant (P) and chronically hypoxic nonpregnant (HNP) adult sheep compared with nonpregnant normoxic controls (NP). This study focuses on a fourth group, pregnant sheep exposed to chronic high-altitude hypoxia (HP) (110 days at 3,820 m). The combined challenges of pregnancy and high-altitude hypoxia resulted in significant alterations in cerebrovascular function that were not simply the summation of the responses seen in the P and HNP animals. Compared with NP, HP arteries had increased protein content and increased intracranial arterial wall thickness. Both P and HP arteries showed increased contractility, while HNP artery maximum tensions were depressed. Endothelial function was depressed in the P common carotid and was enhanced in all HNP arteries. In contrast, an increased endothelial response was shown only in the HP common carotid. Thus, for contractility, the effects of pregnancy predominated in the HP arteries. For endothelial function, hypoxia effects were dominant in the common carotid but not in the intracranial arteries. Clearly, cerebrovascular characteristics are dynamic in nature, with artery-specific responses to both pregnancy and hypoxia.