Pubertal development of the boar: age-related changes in testicular morphology and in vitro production of testosterone and estradiol-17 beta.

The responsiveness of testicular tissue, in terms of testosterone (T) and estradiol-17 beta (E2) production, to human chorionic gonadotropin (hCG) stimulation in vitro was assessed during pubertal development of the boar. A morphometric investigation was conducted concurrently to quantitate Leydig cell and seminiferous tubule changes in the testes of developing boars. Testicular volume percentage of seminiferous tubules increased from 36% at 40 days of age to a maximum of 72% at 190 days of age. Increases in tubular diameter were from 65 micrometers at 40 days of age to 236 micrometers at 250 days of age. Testicular volume percentage of Leydig cells decreased from 40% at 40 days of age to 10% at 250 days of age. Leydig cell number increased rapidly to 130 days of age, remained constant through 160 days, and then increased steadily to 220 days of age. Volume per Leydig cell changed little from 40 to 130 days of age, increased by 75% at 160 days, and declined thereafter. Total Leydig cell weight increased steadily from 40 to 160 days of age and then declined slightly. The capacity of Leydig cells for T production and testicular tissue for E2 production was greatest (P less than 0.05) after hCG stimulation in boars that were 130 and 160 days of age. In addition, sensitivity, as judged by the regression coefficient of T or E2 production per Leydig cell on log dosage of hCG was greater (p less than 0.05) for T at 130 days of age and for E2 at 160 days of age. The data presented support the hypothesis that one factor in pubertal development of boars is an increased capacity and sensitivity of the testes to gonadotropin stimulation.