Effect of thyrotropin-releasing hormone (TRH) on the synthesis and secretion of polysaccharides by the integument of gastropods

Internal chemical communication within flatworms

An understanding of reproductive function is important for control of parasitic helminths. In cestodes and trematodes virtually nothing is known about regulatory and coordinating mechanisms that control maturation, gamete formation, egg production, and related processes. Neurosecretory neurons have been reported in various species but specific modes of action of neurohormones have yet to be demonstrated. The role of ecdysone is being investigated.

Somatostatin and calcitonin stimulate neurite regeneration of molluscan neurons in vitro

Isolated neurons from the gastropod Physella heterostropha fail to regenerate their neurites if cultured in defined medium in the absence of growth factors. A significant number of cultured neurons extend neurites if they are cultured in brain-conditioned or hemocyte-conditioned medium. Synthetic somatostatin and salmon calcitonin also stimulate neurite regeneration in a dose-dependent manner. Thyrotropin-releasing hormone, arginine vasotocin, and eledoisin fail to promote neurite outgrowth. It is concluded that, like other molluscan neurons, isolated neurons from Physella require the presence of factors that are released by brain tissue or are present in the hemolymph, and that somatostatin and calcitonin can, in part, substitute for the endogenous neurite-regenerating activities.

Effect of thyrotropin-releasing hormone and its metabolites on the secretion of sulfated polysaccharides by foot integument of a pond snail

The effect of thyrotropin-releasing hormone (TRH), TRH metabolites, and a TRH analog on the secretion of 35S-labeled sulfated polysaccharides from in vitro incubated foot integument of the pond snail Lymnaea stagnalis palustris was assessed. Whereas TRH significantly inhibited the secretion of 35S-labeled polysaccharides, its metabolite deamido TRH significantly stimulated polysaccharide secretion. Histidyl-proline-diketopiperazine did not alter the secretion of 35S-labeled sulfated polysaccharides. Foot integument exhibited considerable TRH-peptidase activity in vitro. The principal proline-containing TRH metabolites were deamido-TRH and proline. The deamido-TRH content of the foot, mantle, and hemolymph was determined by radioimmunoassay. All tissues contained deamido-TRH. These findings suggest that the secretory activity of skin mucus glands of L. stagnalis palustris is the result of the stimulatory action of deamido-TRH and the inhibitory action of TRH. 3Methyl-2histidyl-TRH, TRH, vasotocin, and bombesin did not alter the polysaccharide secretion by in vitro incubated foot integument, indicating that the changes in mucus secretion after TRH and deamido-TRH administration are specific and that the gastropod "TRH receptors" may differ from the mammalian brain and anterior pituitary gland TRH receptors.