Acquired immunologic tolerance has been produced in several similar animal species by injection of hemopoietic cells during the embryonic or immediate neonatal period.1-3 Adult mice have been rendered tolerant by splenic cell injection.4 We have previously reported acquired tolerance in rats by repeated parabiosis.5 The present experiment was designed to determine if a similar tolerance could be induced in parabionts of dissimilar species.
Ten pairs of adult female Sprague-Dawley rats and guinea pigs were used in this experiment. Selection of paired animals was based on approximate weight and length. Anesthesia consisted of intra-peritoneal sodium pentobarbital. Parabiosis was then done along contiguous medial shaved skin painted with thimerosal (Merthiolate). The incision extended from the scapula to the iliac crest. The ventral pedicle skin flaps were sutured with a running 4-0 everting silk suture. Abdominal and thoracic musculature was sutured with interrupted silk suture. The dorsal pedicle skin