Effect of chronic administration of a highly potent LHRH agonist on prostate size and secretory function in geriatric dogs.

Four geriatric male dogs of mixed breed were selected for study on the basis of palpable prostatic hyperplasia. Testosterone levels were determined by radioimmunoassay on plasma samples collected three times weekly. Prostate size was determined from lateral pneumocystograms taken at weekly intervals. Prostatic secretion was followed by ejaculating the dogs at weekly intervals. Two dogs were implanted with 125 micrograms/kg of pelleted D-Trp6-LHRH ethylamide (LHRH analog) and two were sham implanted. The pellets were removed 71 days later. Three months after the removal, one previously treated dog was sham implanted and one previously sham implanted dog was implanted with 170 micrograms/kg of pelleted analog. In each case, following analog implantation, plasma testosterone levels were elevated for up to 7 days, then declined precipitously, and were then maintained at less than 0.02 ng/ml for a prolonged period. Plasma testosterone levels returned to the pretreatment range 44 and 58 days after implantation, respectively, in two dogs, but remained low through the 60 days studied in the third. The radiographs in one treated animal were of insufficient quality for analysis. In the remaining two treated animals, prostate size progressively declined following implantation, after about a 2 wk lag time. In one animal the prostate dimensions reached a nadir of 40% of pretreatment values at five wk after implantation. In the other treated animal the prostate regressed to a position within the pelvic brim, a state resembling that seen in young dogs, and so the dimensions could not be accurately determined. After plasma testosterone levels reverted to pretreatment values, prostate dimensions slowly but progressively increased. A decline in ejaculate volume paralleled the decline in plasma testosterone and prostate size until the fifth week after implantation from when no ejaculate could be obtained. The data suggests that LHRH agonists may have utility in the therapy of hormone-responsive prostatic pathologies.