Aromatase activity in purified Leydig cells from adult rat. Comparative effects of insulin, IGF-I, and hCG.
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 [1 beta-3H] and androstenedione as substrate. In the presence of varying concentrations of substrate, the apparent Km for androstenedione was 0.945 mol/l; 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.
Rigaudière
N
N
URA CNRS 164, Laboratoire de Physiologie, Faculté de Médecine, Université de Clermont-Ferrand I, France.
Grizard
G
G
Boucher
D
D
D000818:Animals; D001141:Aromatase / Q000378:metabolism* / Q000493:pharmacokinetics; D002469:Cell Separation; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007985:Leydig Cells / Q000201:enzymology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000494:pharmacology*
D006063:Chorionic Gonadotropin; D007328:Insulin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D001141:Aromatase