| Abstract: | As doses of zeranol implants (0 (control), 12, 24, 48, and 96 mg) were increased, there were increased reaction and activity in target organs (such as urogenital tract and mammary, adrenal, hypophyseal, and thyroid glands) of castrated male sheep (wethers). Hyperplasia and transitional and squamous transformation in the prostate were mild (1+) in the wethers given 12- and 24-mg doses, moderate to marked (2.5+) in the wethers given 48-mg doses, and severe (4+) in the wethers given 96-mg doses. Papillary proliferation and fibrosis increased correspondingly in the seminal vesicle. Changes in the distal penile urethra increased from papillary hyperplasia in the wethers given a 24-mg dose to 100% squamous transformation in the wethers given a 96-mg dose. Mammary gland development was noticeable in the wethers given a 24-mg dose and increased thereafter to progressive alveolar growth and secretory activity in the wethers given 48- and 96-mg doses. Along with a progressive increase of adrenal gland weight and adrenal gland/thyroid gland ratios over the controls, the principals had hypertrophy and hyperplasia of the adrenal cortex. Mean adrenal cortex widths for control wethers and wethers given 24-, 48-, and 96-mg doses were 2,089, 2,140 (adjusted value, 2,194), 2,416, and 2,425 mum, respectively. Mean adrenal gland weights for control wethers and wethers given 12-, 24-, 48-, and 96-mg doses were 2.50, 2.61, 2.53, 2.70, and 2.78 g. respectively. Hyperplasia (nodule formation) plus exhaustive and pyknotic changes of the adrenal cortex increased similarly with increasing zeranol dose. After the thyroid gland weights decreased (2.19, 2.04, 2.00, and 1.72 g, respectively, for control wethers and wethers given 12-, 48-, and 96-mg doses), secretory activity of thyroid epithelial cells decreased. In the glandular portion of the hypophysis, secretory activity and proliferation of eosinophilic cells increased with the larger zeranol doses (48 and 96 mg). There was a corresponding decrease in the number of basophils. These changes are consistent with increased somatotropin and adrenocorticotropin secretion and decreased thyrotropin secretion. Muscle and ligament structures appeared looser and widened in the wethers given the 96-mg dose, and fat cell formation was increased in the muscles along ligament muscle junctions. |
