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Effects of adenosine and related compounds on the regulation of steroid production by isolated Leydig cells have been investigated. Steroid production by freshly isolated Leydig cells from testes of immature or mature rats and mice, or from Leydig tumor tissue could not be stimulated with adenosine, nicotinamide-adenine dinucleotide (phosphate) [NADPH, NAD(P)] or N6-(1-2-phenylisopropyl)-adenosine (PIA) (50 microM), whereas luteinizing hormone (LH) stimulated steroid production more than 10-fold. After 24 h incubation all adenosine-related compounds, but not inosine, stimulated steroid production to 20-100% of the maximal LH-stimulated activity. LH- or 22R -hydroxycholesterol-stimulated steroidogenesis in Leydig cells from immature rats did not decrease during the 24-h culture period, whereas ATP levels increased. The first significant effect of adenosine on steroid production in these cells was found after an incubation period of 3 h. In cells incubated for 1 h and 24 h, LH stimulated cyclic adenosine 3':5'-monophosphoric acid (cAMP) production 10-fold. Significant effects of adenosine and PIA on cAMP production or protein phosphorylation could only be shown in cells incubated for 24 h. Effects of adenosine on Leydig cells in intact testis tissue of immature rats could not be determined. The results suggest that after isolation of Leydig cells, specific alterations in the cell membrane occur, causing increased sensitivity to adenosine and related compounds. Adenosine apparently does not play a role in the role of steroid production in Leydig cells in vivo.

Development of Adenosine Responsiveness After Isolation of Leydig Cells