The interstitial cells of the albino rat testis were studied in animals ranging from the 15th day of fetal life until adulthood. The interstitial cells developed in two phases, a fetal phase from the 17th fetal day to the 2nd postnatal week and an adult phase from the 3rd week onwards. Lipid histochemical and ultrastructural techniques demonstrated the abundance of lipid droplets in the fetal interstitial cells and the paucity of lipid in the adult interstitial cells. The enzyme Δ5-3β-hydroxysteroid dehydrogenase (HSD) was studied in the interstitial cells throughout development using dehydroepiandrosterone (DHEA), pregnenolone and 17α-hydroxy pregnenolone as substrates. The enzyme activity was found with all substrates in both types of interstitial cells, DHEA producing the greatest reaction. The activity of HSD using pregnenolone on substrates was greater in the fetal interstitial cells.
The ultrastructural studies demonstrated the presence of abundant agranular endoplasmic reticulum in both the fetal and adult interstitial cells. The prominent cup-shaped mitochondria and lipid droplets present in the fetal cells were not present in the adult interstitial cells. The differences in the histochemical and ultrastructural features of the cells of each phase suggests that they represent separate generations of interstitial cells.