. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 268 M. P. MATTSON AND E. SPAZIANI ; .„ U « Sham. YOE Time (days) FIGURE 2. Effects of Y-organ removal on hemolymph ecdysteroid levels. Y-organectomy or sham operations were performed after serum sampling at time 0; hemolymph ecdysteroid levels were monitored at the given times thereafter. Points and lines are the mean and SEM from 4 to 5 crabs. Values for Y- organectomized crabs < corresponding sham values at days 4-6 (P < ); combined values for sham days 4 and 6 < sham day 2 value (P < ). roidogenesis fo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 268 M. P. MATTSON AND E. SPAZIANI ; .„ U « Sham. YOE Time (days) FIGURE 2. Effects of Y-organ removal on hemolymph ecdysteroid levels. Y-organectomy or sham operations were performed after serum sampling at time 0; hemolymph ecdysteroid levels were monitored at the given times thereafter. Points and lines are the mean and SEM from 4 to 5 crabs. Values for Y- organectomized crabs < corresponding sham values at days 4-6 (P < ); combined values for sham days 4 and 6 < sham day 2 value (P < ). roidogenesis for ganglia extracts from Y-organectomized and sham groups; 65% suppression for ganglia extracts from unoperated controls). DISCUSSION We found that injection of 20-hydroxyecdysone increased circulating ecdysteroid liters. The same was found by Adelung (1967) after injecting intermolt crabs with a single dose of ecdysone, followed by extraction of whole animals at intervals and measuring ecdysteroid by the Calliphora assay. He also observed that the ecdysteroid level fell rapidly within the first 4 hours after injection, to 10% of the administered dose, and then, surprisingly, rose again over the subsequent 18 hours to the 50% level before finally declining. These events were interpreted to result first from a rapid clearing of injected ecdysone and then endogenous secretion of ecdysone by the Y- organs, directly stimulated by the injected hormone through a positive feedback mech- anism. That the source of the secondary rise in ecdysteroid was endogenous was un- equivocally demonstrated: an injection of 3H-ecdysone was cleared rapidly over 4 hours as before but levels of the tracer continued downward over the subsequent time period (Adelung, 1967). In the present study, we show that elevated ecdysteroid levels in crab hemolymph inhibit release of MIH activity from subsequently isolated eyestalk ganglia (Fig. 3). It appears that the better interpretation of Adelung's results, b
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