The ability of
ANP to inhibit the hydrolysis of
phosphoinositides was examined in [3H]
myoinositol-labeled intact murine Leydig
tumor (MA-10) cells.
Arginine vasopressin (AVP) stimulated the formation of
inositol monophosphate (IP1),
inositol bisphosphate (IP2), and
inositol trisphosphate (IP3) both in a time-and dose-dependent manner in MA-10 cells.
ANP inhibited the AVP-induced formation of IP1, IP2, and IP3 in these cells. The inhibitory effect of
ANP on the AVP-stimulated formation of IP1, IP2, and IP3 accounted for 30%, 38% and 42%, respectively, which was observed at the varying concentrations of AVP.
ANP caused a dose-dependent attenuation in AVP-stimulated production of IP1, IP2 and IP3 with maximum inhibition at 100 nM concentration of
ANP. The production of
inositol phosphates was inhibited in the presence of
8-bromo cGMP in a dose-dependent manner, whereas dibutyryl-cAMP had no effect on the generation of these metabolites. The
LY 83583, an inhibitor of
guanylyl cyclase and cGMP production, abolished the inhibitory effect of
ANP on the AVP-stimulated production of
inositol phosphates. Furthermore, 10 microM
LY 83583 also inhibited the
ANP-stimulated
guanylyl cyclase activity and the intracellular accumulation of cGMP by more than 65-70%. The inhibition of
cGMP-dependent protein kinase by H-8, significantly restored the levels of AVP-stimulated
inositol phosphates in the presence of either
ANP or exogenous
8-bromo cGMP. The results of this study suggest that
ANP exerts an inhibitory effect on the production of
inositol phosphates in murine Leydig
tumor (MA-10) cells by mechanisms involving cGMP and
cGMP-dependent protein kinase.