The cellular localization of beta-
adrenergic and
prostaglandin (PG) receptors and their effects on
adenylate cyclase activity (AC) and
testosterone production in vitro were investigated in a transplantable rat
Leydig cell tumor (H-540). Separation of the
tumor cells in
Percoll gradients revealed that the specific binding of [3H]
PGE1 and [125I]
Cyanopindolol was found in the same fraction as that of [125I]LH. This fraction--judged by light microscopy of smears--consisted of
tumor Leydig cells. In addition, [125I]
cyanopindolol was found specifically bound in the red blood cell fraction. In the Leydig
tumor cells, approx 25% of the
beta-adrenergic receptors was identified as beta 1-receptors, whereas approx 75% of the receptors were of the beta 2-subtype. The AC in
Percoll purified Leydig
tumor cells was stimulated by hCG (6-fold),
PGE1 (2-fold),
PGE2 (1.5-fold), PGI1 (2-fold) and
isoproterenol (2-fold). The AC in the red blood cell fraction was stimulated by
isoproterenol whereas the PGs and hCG had little or no effect. hCG,
isoproterenol and
PGE1 were able to stimulate
testosterone production in vitro. At 44 h incubation,
PGE1 was the most potent stimulator of
testosterone production. In conclusion,
tumor Leydig cells possess hCG,
PGE1, PGI2 and
beta-adrenergic receptors coupled to the AC.
PGE1 and
beta-adrenergic agonists stimulate
testosterone production after prolonged incubation in vitro.