Changes in the sensitivity of adult cockroach corpora allata to a brain allatostatin

There are major changes in the sensitivity of corpora allata from the cockroach Diploptera punctata toward the allatostatic tridecapeptide APSGAQRLYGFGL-amide (ASAL) during the female reproductive cycle, as revealed by measurement of juvenile hormone (JH) biosynthesis in vitro. Glands from recently molted adult females show only 30-40% inhibition at 10 nM ASAL, falling to a minimum of less than 10% on day 5 at the peak of spontaneous JH synthesis in vitro. The decline in JH synthesis observed in post-vitellogenic females is accompanied by a dramatic increase to ca. 90% ASAL sensitivity at 10 nM by day 6. Then sensitivity slowly wanes during subsequent ovulation and pregnancy to the levels typical of previtellogenic and virgin females. Full dose/response studies reveal a second level of response at ca. 1 microM, which resembles the pattern obtained from whole brain extracts. We conclude that physiological sensitivity to ASAL (IC50 ca. 0.1 nM) is correlated with the preparation for choriogenesis, and we suggest that 1000 times higher doses give a cross-reaction with related allatostatic receptor(s) that confer important sensitivity at other development stages.