Delayed ovulation and pregnancy outcome: effect of environmental toxicantson the neuroendocrine control of the ovary

In the female rat, we have shown that a burst exposure to environmental tox icants known to alter noradrenergic function will block the ovulatory surge of LH when administered during a sensitive period on the day of vaginal pr oestrus. Such treatments will delay ovulation by 24 h and affect embryo sur vival. These results demonstrate clearly that brief, appropriately timed, t oxicant exposure can initiate a cascade of changes that can alter reproduct ive outcome. However, we also found that continued exposure to the same com pound is without an apparent influence on the reproductive capacity of the female, indicating that the female can become tolerant to such adverse repr oductive effects. These observations raise a number of questions concerning the approaches currently used to examine potential reproductive toxicants. In this review, we describe the consequences of appropriately timed exposu res to chlordimeform and dithiocarbamates on the timing of ovulation and su bsequent alterations in pregnancy outcome. We also review the available lit erature on phenobarbital delays in ovulation and oocyte function in the rod ent and the relevance to ovulatory delays in the human. (C) 2001 Elsevier S cience B.V. All rights reserved.