PREGNANCY ALTERS CEREBROVASCULAR ADAPTATION TO HIGH-ALTITUDE HYPOXIA

We have previously shown alterations in cerebrovascular composition, c ontractility, and endothelial function in normoxic pregnant (P) and ch ronically hypoxic nonpregnant (HNP) adult sheep compared with nonpregn ant normoxic controls (NP). This study focuses on a fourth group, preg nant sheep exposed to chronic high-altitude hypoxia (HP) (110 days at 3,820 m). The combined challenges of pregnancy and high-altitude hypox ia resulted in significant alterations in cerebrovascular function tha t 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 arte ries showed increased contractility, while HNP artery maximum tensions were depressed. Endothelial function was depressed in the P common ca rotid and was enhanced in all HNP arteries. In contrast, an increased endothelial response was shown only in the HP common carotid. Thus, fo r contractility, the effects of pregnancy predominated in the HP arter ies. For endothelial function, hypoxia effects were dominant in the co mmon carotid but not in the intracranial arteries. Clearly, cerebrovas cular characteristics are dynamic in nature, with artery-specific resp onses to both pregnancy and hypoxia.