although the overall hypercortisolemia of pregnancy may be driven by placental CRH, there must be another major ACTH secretagogue, and that the most likely candidate
is arginine vasopressin (AVP). This is secreted into the portal system by parvocellular neurons of the paraventricular nucleus of the hypothalamus, in a pulsatile fashion with a circadian increase in amplitude. It has been suggested that this AVP stimulated system enables the pregnant woman to continue to respond to stress even if the response to CRH is desensitised. However the results presented here suggest that the whole physiological system becomes desensitised.