Aromatase activity in purified Leydig cells from adult rat. Comparative effects of insulin, IGF-I, and hCG

Abstract

Abstract. The comparative effects of insulin and IGF-I on aromatization in adult rat purified Leydig cells were examined to elucidate the mechanism of action of the peptides in testicular steroidogenesis. Aromatase activity was measured in short-time incubations, using the tritiated water release method with [1β-3H] androstenedione as substrate. In the presence of varying concentrations of substrate, the apparent Km for androstenedione was 0.945 mol/1; treatment of cells with insulin, IGF-I and hCG markedly increased the apparent maximal velocity, without modifying Km; peptides were more potent in aromatase stimulation than hCG alone or in combination with either peptides. When related to time (0–4 h) and expressed as percent of control values, aromatase activity in the presence of insulin, IGF-I and/or hCG exhibited a significant and transient increase at 15–30 min. In order to clarify the nature of this early stimulation, the effects of dibutyryl cAMP, various antibiotics, and cytochalasin B on treated Leydig cells were analysed. Results indicated that insulin and IGF-I action on aromatization was not cAMP-dependent; peptides could intervene by increasing RNA and protein, but not DNA, synthesis; they were also effective in glucose transport. These data suggest that insulin and IGF-I are able to modulate aromatization in Leydig cells.