Biology Reference
In-Depth Information
(
Luhovyy, Akhavan, & Anderson, 2007
). There is very little data on the
effect of individual amino acids on incretins and this is an area that requires
focus in future research.
Salehi et al. (2012)
found that insulin secretion in
response to amino acids was augmented when GIP was present. Another
study showed that GIP and also GLP-1 increased insulin secretion in the
presence of amino acids (
Fieseler et al., 1995
)
.
4.3. Impact of proteins and amino acids
on glucagon secretion
It is evident from the studies discussed above that proteins and amino acids
induce glucagon secretion. Postprandial plasma amino acid excursions have
been shown to stimulate glucagon secretion independent of glycemic status
(
Krebs et al., 2003
)
.
Kuhara et al. (1991)
assessed the metabolic response to
17 individual amino acids and found that all the amino acids stimulating glu-
cagon also stimulated insulin, suggesting that all amino acids potentiating
glucagon release also induce insulin. However, other studies disprove this.
Rocha et al. (1972)
evaluated the effects of 20 individual amino acids at a
dosage of 1 mM/kg body weight in dogs. Of the 20 amino acids, 17 caused
a notable increase in plasma glucagon. Asparagine, glycine, and phenylala-
nine were the most glucagonogenic while valine, leucine, and isoleucine
failed to stimulate the hormone. Unlike
Kuhara et al. (1991)
, this study
did not observe a relationship between glucagon and insulin stimulations.
The study suggested that amino acids entering the gluconeogenic pathway
as pyruvate seemed to be more glucagonogenic than those entering as
a
-ketoglutarates and succinyl CoA. Human studies also show that glycine,
lysine, and phenylalanine are glucagonogenic (
Gannon & Nuttall, 2010
).
However, they showed asparagine to only moderately stimulate glucagon.
Similar to animal work, human studies also showed that leucine and isoleu-
cine did not induce glucagon although valine stimulated a modest release.
Histidine, proline, glutamine, and tyrosine did not stimulate glucagon in
humans either (
Gannon & Nuttall, 2010
)
. Ingestion of whole proteins
has also been shown to induce glucagon release (
Gannon et al., 1992,
(1992)
observed that the glucagon response area under the curve (AUC)
closely correlated with the amount of protein metabolized (egg white and
cottage cheese). This may suggest that glucagon plays a key role in protein
metabolism and uptake. Indeed, one study showed that elevated plasma
glucagon levels stimulate gluconeogenesis from amino acids in the liver
