Daily Rhythms in the Concentrations of Various Amino Acids in Human Plasma

Publisher Website
Google Scholar
Abstract
Blood was collected at intervals during a 24-hour period from 23 healthy male volunteers on diets containing various amounts of protein; the plasma was assayed for 16 amino acids. Among subjects receiving 0.71 or 1.5 gm of protein per kilogram of body weight, the concentrations of tyrosine, phenylalanine and tryptophan tended to be lowest at 2:00 and highest at or after 10:30 a.m. Volunteers given a diet containing less than 0.04 gm of protein per kilogram showed similar fluctuations in the concentrations of the above amino acids and methionine, but peak plasma levels were observed somewhat earlier in the morning. All the amino acids studied showed some tendency to vary with time of day. Tyrosine, tryptophan, phenylalanine, methionine, cysteine and isoleucine underwent the greatest per cent changes; the amino acids whose plasma concentrations were highest (that is, alanine, glycine and glutamic acid) showed the least tendency to vary.