Changes in pancreatic tryptophan in the rat in response to fasting. The effect of B-cytotoxic agents and variation through the oestrous cycle.

The concentration of tryptophan not incorporated into protein or polypeptides in the pancreas of male rats rose two- to three-fold in response to a 24 hrs period of food deprivation. On refeeding or intra-peritoneal administration of glucose the level of tryptophan in the pancreas fell, while that in the serum rose. The pancrease B-cytotoxic agents alloxan and streptozotocin both abolished this response to fasting, while neutral red (an A-cytotoxic agent) had no effect. It therefore appears that the tryptophan which accumulates in the pancreas during fasting is located mainly in the B-cells of the Islets of Langerhans. In female rats, the concentration of tryptophan in the pancreas was greater at dioestrus than at any other stage of the oestrous cycle. The increase in pancreatic tryptophan was maximal at metoestrus and minimal at oestrus.