Changes in plasma amino acid and subjective sleepiness ratings in humans after consumingL-tryptophan/maltodextrin mixes.

In animals, there is some evidence that increasing brain tryptophan (TRP) levels can increase brain serotonin (5-HT) synthesis and facilitate sleep onset. The plasma ratio of TRP to the other large neutral amino acids (TRP/LNAA ratio) must at least triple before detectable increases in brain 5-HT occur. In young men, consumption of 500 mg TRP combined with a carbohydrate (CHO) load will triple this ratio. In a study on 72 volunteers with mild insomnia, using subjective ratings of sleep onset and quality, this combination significantly decreased sleep latency. We noticed, however, that young women seemed to be particularly responsive to the sleepiness-inducing effects of TRP/CHO mixes. The present study was designed to examine more closely the effects of TRP/CHO mixes on subjectively rated sedation in young women and to check if their plasma amino acid response differs from that of men. On three evenings, nine healthy young women consumed 0, 500, or 1000 mg TRP combined with 30 g of maltodextrin. Blood samples were collected at 0, 30, 60, 90 and 120 minutes. Sleepiness was rated during the evening. The study was carried out double-blind, and each woman received all 3 treatments balanced across days. Plasma TRP/LNAA ratios tripled after 500 mg and quadrupled after 1000 mg of TRP. All women reported a marked increase in sleepiness with TRP. We conclude that young women do seem to be more sensitive than men to the sedating effect of TRP/CHO mixes but their plasma amino acid responses are similar.

The effect of feeding soybean trypsin inhibitor and repeated injections of cholecystokinin on rat pancreas.

The effects of dietary soybean trypsin inhibitor (SBTI, Kunitz type) or repeated i.p. injections of 95% pure cholecystokinin (CCK-39) on rat pancreas were investigated in a 10-day experiment. SBTI and CKK -39 induced similar increases in pancreatic weight, which led to both cellular hypertrophy and hyperplasia. Trypsin and chymotrypsin activity increased with an increase in pancreatic weight. Amylase activity increased only after CCK-39 injection, whereas lipase activity was not affected by either SBTI or CCK-39 treatment. After both treatments, insulin content showed only a slight tendency to increase, whereas glucagon content was not different from controls. The results indicate that SBTI and CCK-39 mainly exert their effects on the exocrine pancreas in a similar but not identical manner. It is therefore suggested that SBTI is not only a potent stimulator of the secretion of CCK activity but also of other unidentified gastrointestinal factor(s).

Response of rat pancreatic proteases to dietary proteins, their hydrolysates and soybean trypsin inhibitor.

The present study was designed to determine whether the adaptation of pancreatic trypsin and chymotrypsin activities to dietary protein level can be attributed to the presence in the diet of the specific peptide bonds that are substrates for these enzymes. In addition, the effect of feeding soybean trypsin inhibitor (SBTI) was tested since this compound is known to stimulate synthesis of pancreatic proteases. For 3 weeks, rats were fed a diet containing 10, 20 or 30% protein as lactalbumin (control); lactalbumin predigested by trypsin, chymotrypsin or pancreatin; a mixture of amino acids; or lactalbumin supplemented with SBTI. At the end of the experiment, the activities of trypsin, chymotrypsin and amylase were determined in the rats' pancreatic homogenates. Trypsin and chymotrypsin activities at each protein level were exactly the same whether predigested lactalbumin or lactalbumin was fed. The 20 and 30% amino acid mixtures, however, produced a decrease in activities of both proteases. SBTI doubled the activities of both proteases at all three levels of protein. Amylase activity was maximal at 20% level of protein. It is concluded that adaptation of pancreatic proteases to dietary protein level is induced by small peptides that are digestion products of dietary protein. Induction of pancreatic trypsin or chymotrypsin therefore does not require the presence of substrate for these enzymes in the intestine. Dietary SBTI produced a considerable increase in pancreatic proteases compared to that produced by proteins or peptides. It is suggested that the increases in pancreatic proteases caused either by protein-rich diets or SBTI are mediated by two distinct mechanisms.

Amino acid-enriched plasteins: a source of limiting amino acids for the weanling rat.

The biological availability to the weanling rat of two amino acid-enriched plasteins, tryptophan and methionine plastein, was tested. In both experiments rats were fed diets containing graded levels of the amino acid either in the free form or as the amino acid-enriched plastein. The first experiment tested the utilization of tryptophan plastein. The results as indicated by weight gain, food intake and plasma levels of tryptophan showed that the tryptophan in the plastein was utilized to the same extent as the free amino acid. Brain tryptophan levels correlated better with plasma Trp:neutral amino acid ratios (r = 0.83) than with plasma tryptophan itself (r = 0.63) suggesting that the small changes observed in plasma amino acid profiles were responsible for differences in the brain tryptophan concentrations among the L-tryptophan and tryptophan plastein groups. In the second experiment, utilization of methionine plastein was tested. Based on weight gain and food intake data, it was concluded that methionine plastein was also utilized to the same extent as free L-methionine.