Immunoreactive somatostatin in two pulmonate gastropods

The distribution of immunoreactive somatostatin (IRSRIF) was studied in the pond snails Lymnaea stagnalis and Physa spp. In both species, IRSRIF could be detected in extracts from pooled circumesophageal ganglia and hemolymph. In Lymnaea, the distribution of IRSRIF roughly paralleled that of the distribution of the perikarya and neurohemal regions of the neurosecretory neurons which are involved in the stimulation of growth. The IRSRIF concentration in the hemolymph of young Physa was significantly higher than that in the hemolymph of old animals. When the shell edge was removed in old Physa, a procedure which leads to stimulation of shell growth, the IRSRIF concentration in the hemolymph increased. We interpret these findings to mean that IRSRIF might act as a growth factor in gastropods. Immunoreactive somatostatin was present in acid extracts of various parts of the gastrointestinal tract of Physa. The possible physiological role of this immunoreactive material was not studied. Neither the IRSRIF from the nervous system nor that from the hemolymph of Physa behaved like synthetic somatostatin during reverse-phase thin-layer chromatography, indicating that the immunoreactive material from Physa, although it might be a growth hormone, is not somatostatin.