Increase in Leydig cell number in testes of adult rats treated chronically with an excess of human chorionic gonadotropin

Abstract

Leydig cell clusters in adult testes enlarge considerably under treatment with excess LH or hCG. However, it has been uncertain in the past whether this expansion involves an increase in the number of Leydig cells or merely an enlargement of the individual cells. We have used morphometric methods to investigate this question in the testes of rats treated chronically with hCG. Adult male Sprague-Dawley rats were injected s.c. daily with 100 IU hCG for up to 5 weeks. Testes were fixed by perfusion with Bouin's fixative, embedded in paraffin, sectioned longitudinally and stained for light microscopy with Mallory azan. To avoid counting macrophages, which are also numerous in the interstitial tissue, the animals were injected with trypan blue before sacrifice. The number of Leydig cells and their volume was determined by morphometric methods (Weibel and Bolender, 1973). Appropriate normal controls were included. The volume of Leydig cells clusters increased by a factor of 4.7 during the 5 weeks of hCG treatment. The number of Leydig cells (initially averaging 18.6x106/cm3 testis) increased to 3 times the control value by 5 weeks of treatment (P<0.001), while the average volume of individual Leydig cells (initially ~2200 μm3) enlarged only 1.6 times. We conclude that chronic treatment with an excess of hCG increases the number of Leydig cells in the testes of adult rats and that this hyperplasia is more important than cell hypertrophy in expansion of Leydig cell clusters.