Histomorphometric aspects of testicular morphogenesis in the pig

Abstract

The morphogenesis of the pig's testis has been investigated histomorphometrically from the early fetal period to sexual maturity. Data are presented on the development of the proportional composition of the testis (Leydig cells, seminiferous tubules and interstitium; weights of testis and the intratesticular components; growth in length and diameter of the seminiferous tubules; and number of germ cells. Functional interrelations between the several parameters as well as with LH during the morphogenetic process are discussed. From 7-14 weeks postcoitum testis growth lags behind body growth. The intratesticular composition does not change. From 14 weeks postcoitum to 3 weeks postpartum testis growth exceeds body growth markedly, mainly caused by Leydig cell development, though the other structures also show an increased growth. The volume percentage of the Leydig cells reaches 64% at 3 weeks. The increased growth of the seminiferous tubules is due to an increasing growth in length. The number of germ cells per testis shows a constant doubling rate, but their number per tubular transverse section decreases due to the increased tubular length growth. Between 3 and 7 weeks postpartum Leydig cells regress, and as a consequence the testis weight decreases. A delay in increase of the number of germ cells and of tubular length occurs during this period. After 7 weeks postpartum testis growth again exceeds body growth. This growth is mainly determined by increases in length and diameter of the seminiferous tubules. Though Leydig cell weight also increases, its volume percentage decreases to minimal values. At 25 weeks most parameters approximate values of the testis of the adult.