1. Central Animal Laboratory, Catholic University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
2. Department of Animal Physiology, Agricultural University, Wageningen, The Netherlands
3. Department of Obstetrics and Gynaecology, Catholic University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands