Effects of IGFBPs and Anti-IGF-I Antibody on Inh-a Production
To determine whether endogenous IGF-I is necessary for activin-stimulated Inh-a expression, we tested the effects of IGFBP-4 and -5, and an anti-IGF-I antibody on the activin response. As shown in Figure ЗА, the activin stimulation of Inh-a production was suppressed in a dose-dependent manner by cotreatment with IGFBP-4 (/C50 = 3.5 ± 0.5 nM) or IGFBP-5 (ICS0 = 5.7 ± 1.9 nM). A nearly 100% inhibition of Inh-a production was achieved at the 30 nM concentrations of the IGFBPs. To rule out the possibility that the observed IGFBP-4 and -5 inhibition might be due to some interaction with activin, the ability of 125I-activin A to bind IGFBPs was tested. Western ligand blotting analу sis demonstrated that 125I-activin A was able to bind FS-315, but no detectable binding to IGFBP-4 or -5 was observed (data not shown). buy ortho tri-cyclen
The effect of treatment with an anti-IGF-I monoclonal antibody was also tested. As shown in Figure 3B, the presence of the anti-IGF-I antibody caused a decrease in the activin stimulation of Inh-a production, with 30 fil of antibody causing a near total inhibition. Addition of 30 jjlI of control mouse ascites fluid did not significantly alter (p > 0.05) the activin response.