Table 4.

Serum amino acid concentrations after 1- or 2-day fasting in mice.

Amino acid (μM)	Ad libitum-fed	1-day fasting	2-day fasting
Gly	315.0 ± 44.3	210.6 ± 59.2∗	192.2 ± 21.7∗∗∗
Ala	397.1 ± 78.9	271.0 ± 79.0∗	227.8 ± 23.2∗∗∗
Val	261.6 ± 52.2	276.9 ± 53.2	223.7 ± 63.3
Leu	198.7 ± 50.0	230.0 ± 48.3	183.3 ± 57.4
Ile	115.4 ± 25.8	132.2 ± 24.4	104.9 ± 22.6
Met	71.2 ± 10.6	62.0 ± 9.4	53.2 ± 9.2∗∗
Pro	129.6 ± 37.5	85.5 ± 20.0∗	74.4 ± 12.3∗∗
Phe	94.6 ± 15.7	104.5 ± 14.5	84.9 ± 5.2##
Trp	82.0 ± 18.0	56.9 ± 7.9∗	50.0 ± 5.5∗
Ser	134.1 ± 27.4	109.9 ± 30.6	83.6 ± 13.2∗∗,#
Thr	159.7 ± 26.8	132.3 ± 16.9	126.5 ± 32.1∗
Asn/Asp	9.13 ± 3.11	5.83 ± 2.30	4.50 ± 1.54∗∗
Gln	1,695 ± 296	1,737 ± 401	1,569 ± 311
Tyr	134.8 ± 35.7	105.9 ± 40.8	82.2 ± 6.2∗∗
(Total) Cys	301.6 ± 28.9	342.0 ± 39.8	366.9 ± 54.8∗
Lys	382.0 ± 58.1	280.1 ± 68.3∗	229.0 ± 23.0∗∗∗
Arg	138.9 ± 20.0	103.2 ± 15.6∗∗	75.6 ± 7.2∗∗∗,##
His	64.3 ± 13.7	76.2 ± 18.0	54.6 ± 8.8
Glu	17.5 ± 8.1	15.5 ± 6.3	9.36 ± 3.91∗,#
(Total) Homocysteine	8.90 ± 0.76	8.76 ± 1.51	12.12 ± 1.98∗∗∗,##
(Total) Glutathione	190.6 ± 25.1	73.7 ± 11.9∗∗∗	56.8 ± 5.9∗∗∗,#
Taurine	392.2 ± 97.4	588.8 ± 153.3∗	530.5 ± 94.2∗
Ornithine	149.1 ± 52.0	84.1 ± 23.0∗∗	59.7 ± 12.7∗∗∗,#
Citrulline	67.4 ± 12.4	51.2 ± 7.7∗	43.5 ± 4.7∗∗∗

C57BL/6J male mice were fed ad libitum (day 0), or fasted for 1 or 2 day(s) between 2 pm and 2 pm with free access to water, and blood samples were collected after anesthetization. Serum amino acid levels were measured using a HPLC system. The (total) levels of cysteine, homocysteine, and glutathione were measured after reductive cleavage of its disulfide bonds. Data are means ± S.D. (n = 7); significant changes in ^∗p < 0.05, ^∗∗p < 0.01, and ^∗∗∗p < 0.001 versus ad libitum; ^#p < 0.05 and ^##p < 0.01 versus day 1 by Mann–Whitney U-test.