The fate of newly synthesized hormone from neuroendocrine cells of Aplysia.
The neuroendocrine bag cells from Aplysia control reproductive functions through the regulated release of egg-laying hormone (ELH). The purposes of this study were to investigate (1) if synthesis of ELH in bag cells compensates for the release and degradation of the hormone, (2) the ratio of released to stored ELH, (3) the fate of newly synthesized ELH and its relative contribution to the overall pattern of ELH secretion, and (4) the consequences of blocking protein synthesis in bag cells on the pattern of ELH secretion and subsequent reproductive function. Excised bag cells were incubated with [3H]leucine to radiolabel newly synthesized ELH and were then electrically stimulated to trigger secretion of the hormone on 4 successive days, mimicking bag cell activities during the breeding season. Samples of bag cell secretion were collected; total (new and old) and radiolabeled (new) ELH levels were determined. The results showed that ELH synthesis could not keep up with the daily loss of ELH through release and degradation, but the ratio of released to stored ELH remained constant over the 4-day study. In addition, releasable ELH was secreted preferentially within 24 hr after it was synthesized. Blocking protein synthesis resulted in a 50% decrease in total ELH released, suggesting that newly synthesized ELH contributes to half of the total ELH secreted. Furthermore, this lowered level of total ELH, i.e., older ELH alone, was not sufficient to stimulate egg laying in Aplysia, indicating that the contribution of newly synthesized ELH was physiologically relevant.
Lee
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Department of Physiology, UCLA School of Medicine, Los Angeles, California, 90095-1751, USA.
Wayne
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NL
D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D001048:Aplysia / Q000378:metabolism*; D001345:Autoradiography; D001681:Biological Assay; D004558:Electric Stimulation; D015151:Immunoblotting; D007447:Invertebrate Hormones / Q000096:biosynthesis / Q000378:metabolism*; D007700:Kinetics; D009490:Neurosecretory Systems / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012098:Reproduction; D014316:Tritium
D007447:Invertebrate Hormones; D011500:Protein Synthesis Inhibitors; C026880:egg-laying hormone, Mollusca; D014316:Tritium; D000841:Anisomycin