A factor from bursa of Fabricius inhibits in vitro the chorionic gonadotropin response of the chick testis.

The effect of bursa of Fabricius on the endocrine function of the chick testis was studied using an isolated testis cell preparation. Testosterone secretion, both basal and under hCG stimulation, was measured in the incubation medium. The bursal extract inhibited the response of the testis cells to hCG detected as a reduced testosterone secretion. The normal basal secretion of the testis cells was not modified by the bursal extract. To analyze some characteristics of the bursal factor, fractions of approximately known molecular weight were obtained by filtering through Amicon membranes. The active factor was found in the fraction corresponding to 1000-10000 Da. Its activity disappeared after heating of trypsin incubation, suggesting the peptidic nature of the bursal factor. Tissue extracts from gut and spleen did not modify the hCG response of the testis cells. There was inhibition of the hCG response by thymus extracts of the newly hatched chicken. These results add new evidence of a modulatory effect of the immunogenic organs on the endocrine function of the testis in the newly hatched chicken.