Degradation of juvenile hormone and methylation of juvenile hormone acid by corpora cardiaca–corpora allata of the cockroach, Nauphoeta cinerea: II. Physiological aspects

Abstract

AbstractIn vitellogenic females of Nauphoeta cinerea, injected (10R)‐juvenile hormone (JH) III was degraded more rapidly than racemic JH III: we measured a half‐life of 21 min (with or without coinjection of lipophorin) for the former and 24 min (with coinjection of lipophorin) and 43 min (without coinjection of lipophorin) for the latter. One to two hours after injection, JH III acid was the major metabolite observed; in addition, several highly polar products were found. The half‐life of injected racemic JH III acid was 19 min with coinjection of lipophorin and 4 min without. The JH III acid titer in hemolymph was low (around 5–10 pmol/ml) in last instar larvae and previtellogenic and pregnant females and reached higher values (40–100 pmol/ml) in vitellogenic and ovulating females. Racemic JH III acid could be methylated in vitro to JH III by corpora cardiaca–corpora allata (CC‐CA) from penultimate instar larvae and females at stages between adult ecdysis and ovulation and at the very end of pregnancy, but not by CC‐CA from last instar larvae and adult females at earlier stages of pregnancy. This indicates that CC‐CA are capable of methylating JH III acid only at stages when JH III is detectable in the hemolymph. In double‐labelling experiments with CC‐CA from vitellogenic females and L‐[14C]methionine and [3H]JH III acid as precursors, we observed that only a small proportion (1–8%) of total biosynthesized JH III was derived from JH III acid when the latter was present at physiological concentration. This suggests that in vivo recycling of JH III acid by CC‐CA plays only a minor role in the regulation of the titer of JH III and JH III acid.