Changes in Leydig Cell Ultrastructure and Function during Pubertal Development in the Boar1

Changes in the ultrastructure of Leydig cells during pubertal development in the boar (40 to 250 days of age) were assessed using quantitative morphometric procedures, and the results were compared to the in vitro steroid-producing capacity and gonadotropin sensitivity of testicular tissue obtained from the same boars. Volume of individual Leydig cells declined through 100 days of age, increased rapidly to a peak at 130-160 days (i.e., puberty), and then declined to intermediate levels by 220-250 days of age. The pattern of change in the number of intracellular organelles per Leydig cell was very similar to the change that occurred in Leydig cell volume. Changes in the total intracellular volume occupied by each type of organelle were highly correlated with changes in Leydig cell volume (r = 0.40-0.99, p less than 0.01), and this was particularly true for the nucleus (r = 0.63), mitochondria (r = 0.88), smooth endoplasmic reticulum (SER; r = 0.97), and total cytoplasm (r = 0.99) of the boar Leydig cell. In vitro production of testosterone and estradiol, expressed per Leydig cell, also peaked at 130-160 days, and was highly correlated to average Leydig cell volume, volume of SER, and number and total volume of mitochondria (r = 0.63-0.84; p less than 0.01). Observations in the present study indicated that onset of puberty in boars coincides with a dramatic increase in average Leydig cell size and SER volume per Leydig cell, accompanied by an increase in number of other intracellular organelles, including mitochondria, lysosomes, and lipid droplets, and a peak in the steroid-producing capacity per Leydig cell. A decline in Leydig cell size, intracellular organelles, and sensitivity to gonadotropin stimulation occurred postpubertally.