Alterations in Testicular Morphology and Function in Rabbits Following Active Immunization with Testosterone

Abstract

White male New Zealand rabbits immunized with testosterone protein conjugates developed antibodies with high binding affinities. The animals were semicastrated either 7 or 14 weeks following immunization. At the time of semicastration serum testosterone ranged from 8,480 to 32,000 ng per 100 ml, compared to normal values ranging from 214 to 674 ng per 100 ml. Almost 100% of the serum testosterone was found in the bound fraction of the immunized animals while the normal animals showed values of 90%. Seven weeks after immunization the testicular weight of the immunized animals exceeded normal values by a factor of 1.5 and had doubled within fourteen weeks. The immunized rabbits showed an increase in the number of Leydig cells in a ratio of 3:1. The greater activity of the Leydig cells was reflected by an increase of the cell nucleus volume from 132 μ³ to 172 μ³. No influence on spermatogenesis was observed. A decrease in the amount of testosterone available to the androgen—sensitive receptor cells in the hypothalamo—pituitary system accompanied by a consecutive increase in interstitial cell stimulating hormone is considered the cause of the Leydig cell hyperplasia and hypertrophy observed in the experiments. (Endocrinology92: 1142, 1973)