We investigated the immunohistochemical expression of progesterone receptors (PRs) in the prostate and bulbourethral glands of thirty-two 10-14-mo-old Charolais bulls following treatment with a low dosage of estrogens. Animals were divided into 2 groups: 16 animals (group T) were treated for 71 d with a therapeutic dose of trenbolone acetate and estradiol by subcutaneous implant, 16 animals (group C) received no treatment. Urine samples were collected both at the beginning of the trial and 9 times during the study. A semiquantitative analysis of immunohistochemistry (IHC) was performed by counting the number of positive cells in 10 randomly selected high-power fields (hpf). Both groups showed no significant histologic lesions. IHC examination showed positive cells in the epithelium of both glands, with different patterns of distribution between groups. In group C, IHC-positive cells per hpf varied from 0 to 40 in the prostate and from 0 to 32 in the bulbourethral gland. In group T, positive cells varied from 0 to 85 per hpf in the prostate and from 0 to 75 in the bulbourethral gland. The treated group showed significantly higher median numbers of positively stained cells in both organs than the controls ( p < 0.001). Chemical analysis of the urine samples confirmed that the experimental treatment mimics continuous, low-dose administration of anabolic steroids. IHC quantification showed good sensitivity with a high predictive power to correctly classify treated animals and could be used as a preliminary screening test in bulls.
Keywords: Bulls; estrogens; immunohistochemistry; progesterone receptors.