We examined whether the effects (efficacy on the urethra and
hypotension) of
silodosin (alpha(1A)-adrenoceptor antagonist) and
tamsulosin (alpha(1A+1D)-
adrenoceptor antagonist) in dogs with
benign prostatic hyperplasia altered with age. We used young and old dogs, diagnosed as having
benign prostatic hyperplasia by veterinarian's palpation. Under
anesthesia, the increase in intraurethral pressure evoked by hypogastric nerve stimulation was measured, together with the level of systemic mean blood pressure. Each
drug was administered intravenously in progressively increasing doses. At the end of the experiment, the prostate was isolated from each dog, then weighed and investigated pathologically to confirm
benign prostatic hyperplasia. The wet weight of the prostate was greater in old dogs with
benign prostatic hyperplasia than in young dogs with
benign prostatic hyperplasia. By light microscopy,
hyperplasia in the prostatic epithelium was confirmed in both groups.
Silodosin (0.3-300 microg/kg) dose-dependently inhibited the hypogastric nerve stimulation-induced increase in intraurethral pressure (without significant hypotensive effects) in both young and old dogs with
benign prostatic hyperplasia.
Tamsulosin (0.3-300 microg/kg) also dose-dependently inhibited the intraurethral pressure increase in both groups, but it had a hypotensive effect that was significantly greater in old than in young dogs with
benign prostatic hyperplasia. In conclusion, as regards the effect of
silodosin on intraurethral pressure, potency was similar between young and old dogs with
benign prostatic hyperplasia, and it was without significant hypotensive effects. We therefore suggest that
silodosin might be a good medication for
lower urinary tract symptoms in patients with
benign prostatic hyperplasia in all age groups.