SIGNAL-TRANSDUCTION IN THE INHIBITION OF JUVENILE-HORMONE BIOSYNTHESIS BY ALLATOSTATINS - ROLES OF DIACYLGLYCEROL AND CALCIUM

The effects of pharmacological agents that interfere with the 1,4,5-in ositol trisphosphate (IP3)/diacylglycerol (DAG) pathway on juvenile ho rmone (JH) biosynthesis by corpora allata (CA) of the cockroach Diplop tera punctata have been investigated. These effects were assessed in t he presence of the inhibitory neuropeptides, allatostatins, with a vie w to elucidating the pathway for signal transduction in the inhibition of JH biosynthesis. Treatment of CA with inhibitors of DAG kinase to elevate the concentration of DAG within the CA cells, resulted in a si gnificant, dose-dependent decrease in JH biosynthesis. Simultaneous tr eatment of glands with both DAG kinase inhibitors and allatostatins fu rther enhanced this effect, suggesting that DAG is an intermediate in the allatostatin-induced inhibition of JH production. The inhibitory a ctions of the phorbol ester activator of PKC, PDBu, or of allatostatin on JH biosynthesis were partially blocked by pre-incubating the CA wi th PKC inhibitors. Treatment of CA with the calcium-mobilizing drug th apsigargin resulted in a significant stimulation in JH biosynthesis in glands from mated females producing JH at high rates. Thapsigargin wa s also able to reverse the effect of allatostatins in high-activity ma ted CA. This suggests an involvement of the other product of phosphoin ositide hydrolysis, IP3, in the modulation of JH biosynthesis at speci fic developmental times and in glands showing specific levels of activ ity.