N 6 -Isopentenyladenosine (i 6 A), an adenosine and mevalonate derivative, inhibits, like adenosine, TSH-induced cAMP increase and its related events (I − uptake and DNA synthesis) in FRTL-5 cells. This inhibition is dose-dependent and is measurable at 10 −8 M. However, unlike adenosine, i 6 A prevents TSH-promoted microfilament disassembly. The effect of i 6 A on cytoskeletal structure is antagonized by pertussis toxin and could be assigned to its N 6 substitution since it can be mimicked by other synthetic N 6 -adenosine derivatives. It is suggested that a step beyond cAMP is involved, since i 6 A prevents also microfilament disassembly induced by 8-bromo-cAMP. This is the first demonstration that an adenosine derivative, which is also an end-product of the isoprenoid pathway, affects cAMP-dependent microfilament organization.
