Effects of Salmon Nasal Cartilage Proteoglycan on Plasma Glucose Concentration and Active Glucose Transport in the Small Intestine.

Recently, proteoglycan was purified from the nasal cartilage of salmon. Although several physiological effects have been reported, the effect of salmon nasal cartilage proteoglycan (salmon PG) on glucose metabolism remains unclear. We studied the effect of salmon PG on rat plasma glucose levels. Oral administration of 1% salmon PG significantly attenuated the increase in portal plasma glucose levels following an oral glucose tolerance test (OGTT). Additionally 1% salmon PG delayed the increase in peripheral glucose concentration induced by the OGTT. Mucosal administration of 1% salmon PG significantly decreased active glucose transport using the everted jejunal sac method. Furthermore, transmural potential difference (ΔPD) measurements using the everted jejunum revealed that 1% salmon PG significantly decreased glucose-dependent and phlorhizin (inhibitor of sodium-glucose co-transporter 1; SGLT1)-sensitive ΔPD. These results suggest that salmon PG decreases glucose absorption via SGLT1 in the jejunum, thereby attenuating the increase in portal and peripheral plasma glucose levels in rats.

Absorption of proteoglycan via clathrin-mediated endocytosis in the small intestine of rats.

The mechanism underlying proteoglycan (PG) absorption in the intestine is not clear. Hence we analyzed the transport of salmon PG in the rat jejunum, ileum, and colon by the everted-sac method. The jejunum showed the largest capacity for PG transport. Jejunal transport of PG was also greater than that of chondroitin A and C. An inhibitor of clathrin-mediated endocytosis reduced jejunal PG transport. We conclude that intestinal PG transport is highest in the jejunum, and is partially dependent on clathrin-mediated endocytosis.