BIOLOGICALLY-ACTIVE PEPTIDES IN THE SUBMANDIBULAR-GLAND - ROLE OF THE GRANULAR CONVOLUTED TUBULE

The granular convoluted tubule segment (GCT) of the rodent submandibular gland is a unique structure and consists of granular cell, dark granular cell, pillar cell, and transitional cell. The granular cells contain secretory granules and synthesize biologically active peptides and related processing enzymes; EGF, NGF, kallikrein and renin, erythropoietin, atrial natriuretic peptides, large mobile protein as cystain and serin proteinase inhibitors, S-100 protein, glucagon and somatostatin. Granular cells may have a multiproduction system for growth factors or biologically active peptides for related processing proteinases as well as proteinase inhibitors which are secreted by alpha-adrenergic stimulants. Pillar cells contain S-100 protein, neuron specific enolase and other nerve related materials, and involve regulation of the nerve-related system as neurotransmitter-like or paraneuron-like properties. Transitional cells show combined properties of granular convoluted tubule and striated duct, and may participate in secretion and reabsorption. Granular intercalated duct cells show similar category of granular cells in GCT segment.