The effect of insulin upon the influx of tryptophan into the brain of the rabbit.

Abstract

SUMMARY1. The effect of hyperinsulinaemia upon the influx of tryptophan into the brain was determined. A raised level of insulin was maintained in the circulation of rabbits for periods of up to 120 min by means of a continuous, programmed intravenous injection of the hormone, given by an electronically controlled variable-drive syringe. A similar, appropriately programmed, intravenous injection of glucose, given simultaneously with the insulin, maintained the concentration of the blood glucose within normal limits throughout each experiment, so that the results were not vitiated by the development of hypoglyeaemia.2. Raised levels of insulin in the blood affect the supply of tryptophan to the brain in two opposing ways: (a) by increasing the binding of tryptophan to the albumin in the blood, thereby reducing the level of the free tryptophan in the circulation by about a half, which would decrease the influx of tryptophan into the brain; (b) by simultaneously reducing the levels in the blood of six or more ofthe amino acids which compete with tryptophan for transport carriers into the brain, which would increase the influx of tryptophan. The net result of these two opposing effects is that insulin causes only a slight increase in the influx of tryptophan into the brain.3. To account in quantitative terms for the effect of insulin upon the influx of tryptophan into the brain it proved necessary to make one assumption. This assumption was that a predictable proportion of the tryptophan which is loosely bound to blood albumin is being stripped off this protein by the transport carrier located on the luminal surface membranes of the endothelial cells during the passage of the blood through the cerebral capillaries. If this assumption is accepted the work reported here explains adequately the effect of insulin on the influx of tryptophan into the brain.

Insulin in the brain: There and back again

“…Insulin enhances transport of the amino acids tyrosine and tryptophan (Cangiano, et al, 1983; Daniel, Love, Moorhouse, & Pratt, 1981; Tagliamonte, DeMontis, Olianas, Onali, & Gessa, 1976), increases the blood-to-brain transport of leptin (Kastin & Akerstrom, 2001), increases expression and function of the efflux transporter P-glycoprotein, but decreases expression and function of another efflux transporter, breast cancer resistance protein (H. Liu, Yang, Wang, Liu, Li, et al, 2009; X.…”

The Effect of Glucose Consumption on Customers’ Price Fairness Perception

“…Raised tryptophan levels are strongly connected to increased levels of serotonin in the brains of humans (Crockett et al (2008)). In addition, animal studies suggest that tryptophan is affected by insulin (Daniel et al (1981)), thus leading researchers to hypothesize that this effect is similar in humans (Benton (2002)). With the additional evidence that glucose consumption influences insulin levels, we theorize that the glucose-insulin-tryptophanserotonin-chain can be used to assess the relationship between the glucose intake and price fairness perception, because the application of sugar activates the glucose-insulintryptophan-serotonin-chain and leads to an increased serotonin level in the brain.…”

Changes in Regional Blood–Brain Transfer of l‐Leucine Elicited by Arginine‐Vasopressin

“…Correspondingly, there are conflicting or unconfirmed reports about modulations of BBB amino acid transport by hormones (Pardridge, 1983). Daniel and co-workers (1975) found a reduced influx of L-leucine, L-valine, and L-lysine into the brains of hypothyroid rats, and a slight increase of L-tryptophan influx into rabbit brain as a result of two opposite effects of insulin was described (Daniel et al, 1981). It was suggested from investigations using isolated brain capillaries that insulin affects the A-system on the abluminal membrane of endothelial cells (Cangiano et al, 1983).…”