THE DEVELOPMENT OF THE BABOON PROSTATE - ULTRASOUND METHODOLOGY, MODELING, AND NATURAL-HISTORY

In order to evaluate the potential of ultrasound for serial, nontrauma tic estimation of prostate size in the hamadryas baboon (Papio hamadry as), we adapted the technique of planimetric ultrasound to study a cap tive-bred colony of 30 male baboons (median age 8.4 years, range 3.3-1 7 years) including 4 long-term castrates. Most (19) were studied on an other two occasions (at 33- and 43-day intervals) to estimate reproduc ibility of the prostate size (dimensions, volume) measurement. Prostat ic dimensions were measured with a B-mode sector ultrasound using a 7. 5-MHz transrectal transducer by planimetry at 2.5-mm steps from base t o apex as well as the maximum three dimensions of the prostate. The pl animetric volume estimate was reproducible (intraclass coefficient 0.8 1) with coefficient of variation (CV) of 24.3% for all, acid 16.0% for mature, baboons. The prostate dimensions were also reproducible (CVs 7.9-13.4%). Prostate volume estimates based on the general ellipsoidal model were reasonably reproducible (19.9% for all, 12.9% for mature) but were biased in relationship to the planimetric volume (0.57+/-0.19 , P=0.004). Using the independent estimates of prostate volume and dim ensions, we developed an empirical power-function model of prostate sh ape based on the generalized ellipsoidal model that was robust and unb iased (-0.07+/-0.15, P=0.64) with respect to the planimetric volume. T his model provides a simpler and accurate formula for prostate volume based on its three maximal dimensional measurements. The natural histo ry of prostate growth in the hamadryas baboon was illustrated by sigmo idal correlations with age (ED(50)=6.0 years, plateau ED(95)=8.3 years ), body weight (ED(50) =14.6 kg, ED(95)=16.1 kg), and testis volume (E D(50)=7.8 ml, ED(95) =18.4 ml). Between-animal variability among matur e baboons was greater for prostate weight (27%) than body weight (10%) , raising the possibility that a subgroup of these baboons may develop spontaneous age-related prostatic hyperplasia. These findings suggest that ultrasonic evaluation of prostate size in the hamadryas baboon m ay constitute a suitable model for spontaneous benign prostatic hyperp lasia and for experimental studies of prostate growth, development, an d hormonal regulation.