Hemolymph Insulin-Like Peptides (ILP) Titers and the Influence of ILP and Mammalian Insulin on the Amino Acid Incorporation in the Mantle Collar In Vitro in Helisoma (Mollusca).

In Helisoma duryi, the periostracum is the outermost organic layer of the shell and it is secreted by the mantle collar. Addition of porcine insulin (0.1 μg/ml) to the incubation medium increases the incorporation of labeled amino acids in the mantle collar in vitro. The immunoblotting technique revealed two immunoreactive insulin bands with a molecular weight of 16 and 7 kDa in the hemolymph. Partial purification of insulin-like peptides from the hemolymph by gel filtration chromatography showed that only one fraction containing approximately 7 kDa polypeptide stimulated the incorporation of amino acids into the mantle collar as well as into the periostracum in a dose-dependent manner. In laboratory populations of Helisoma, snails with two different shell growth rates can be recognized: fast and slow. Hemolymph titers of insulin-like peptide are low in fast-growing snails (2.3 +/- 0.25 mIU/ml) and higher in slow-growing snails (7.8 +/- 0.46 mIU/ml). When a piece of shell at the edge is removed, a structurally identical new piece is formed within either two days (fast regeneration) or a longer period of seven days (slow regeneration). Hemolymph titers of insulin-like peptide undergo fluctuations during the period of shell regeneration, but a general pattern can be recognized. The titers are low when the shell deposition rate is high and vice versa. We suggest that the insulin-like peptide in the hemolymph is involved in shell growth or shell regeneration.