3.3. Effects of pretreatment with TPA
Overnight incubation of MA-10 cells with TPA led to a reduction
of over 40% in the binding of [125I]hCG (Table 2). This result is
in reasonable agreement with the report by Wang et al. [7] in
which hCG binding was determined over a 48 h time course in the
presence of PMA; after 16 h the reduction in binding was about
20–30%. Whereas hCG binding was reduced 40–45% by TPA, hCGmediated
steroidogenesis was diminished by more than 80%
(Table 1C). In addition to heterologous LHR down-regulation, these
results are strongly indicative of cellular desensitization. Of comparative
interest with hCG, there was also a significant reduction