Age, weight and circulating concentrations of total testosterone are associated with the relative prostatic size in adult intact male dogs

Prostatic hyperplasia (PH) is an androgen-dependent condition associated with increased prostatic size that is common in intact dogs, and similar to the condition in men. In dogs, the increase in prostatic size is most prominent the first years, and after approximately four years (in beagles), a plateau is reached, and further growth is slower. Why the prostate continues to grow more in some individuals is not clear. Most testosterone in the circulation is bound to albumin or sex hormone binding globulin (SHBG) and only a minor part is unbound and biologically active. The binding to SHBG has higher affinity than that to albumin. In addition, SHBG has own biological functions, modifying testosterone action. The aim of the present study was to investigate if there is an association between relative prostatic size and the vari-ables total testosterone concentration, SHBG concentration, an estimation of bioavailable testosterone: the ratio between testosterone and SHBG (free androgen index, FAI), estradiol concentration, the estradiol/testosterone ratio, dog age and dog weight. Hormone concentrations were measured in serum from 79 intact male dogs aged >= four years, weighing >= five kg. The size of the prostate was estimated using ultrasonography, and relative prostate size, Srel, was calculated as the estimated size related to the normal size for a 4-year-old dog of the same weight. There as a negative correlation between testos-terone concentration and age (p =-0.27, P = 0.018) and a positive correlation between age and Srel (p = 0.27, P = 0.016) and between SHBG and weight (p = 0.38, P = 0.001). The FAI was negatively correlated with dog weight (p =-0.32, P = 0.004). There were no significant correlations between Srel and SHBG or FAI or between estradiol or estradiol/testosterone and Srel, age or weight. A multiple regression analysis showed significant associations between log Srel and log testosterone concentration, log age and log weight of the dog, with an adjusted R2 of 9.5%. Although the variables total testosterone concentration, age and weight of the dog were all significantly associated with Srel, the coefficient of determination was low, indicating that they only explained a minor part of the prostatic size. The results support the analysis of total testosterone in studies of prostatic growth in the dog.(c) 2023 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)