AMP-activated protein kinase (AMPK) is the downstream component of a protein kinase cascade that actsas an intracellular energy sensor maintaining the energy balance within the cell. The finding that leptin and adiponectin activate AMPK to alter metabolic pathways in muscle and liver provides direct evidence for this role in peripheral tissues. The hypothalamus is a key regulator of food intake and energy balance, coordinating body adiposity and nutritional state in response to peripheral hormones, such as leptin, peptide YY-(3-36), and ghrelin. To date the hormonal regulation of AMPK in the hypothalamus, or its potential role in the control of food intake, have not been reported. Here we demonstrate that counter-regulatory hormones involved in appetite control regulate AMPK activity and that pharmacological activation of AMPK in the hypothalamus increases food intake. In vivo administration of leptin, which leads to a reduction in food intake, decreases hypothalamic AMPK activity. By contrast, injection of ghrelin in vivo, which increases food intake, stimulates AMPK activity in the hypothalamus. Consistent with the effect of ghrelin, injection of 5-amino-4-imidazole carboxamide riboside, a pharmacological activator of AMPK, into either the third cerebral ventricle or directly into the paraventricular nucleus of the hypothalamus significantly increased food intake. These results suggest that AMPK is regulated in the hypothalamus by hormones which regulate food intake. Furthermore, direct pharmacological activation of AMPK in the hypothalamus is sufficient to increase food intake. These findings demonstrate that AMPK plays a role in the regulation of feeding and identify AMPK as a novel target for anti-obesity drugs. AMP-activated protein kinase (AMPK)1 plays a pivotal role in the regulation of energy metabolism and has been dubbed a cellular fuel gauge (1). AMPK is activated following an increase in the AMP:ATP ratio within the cell that occurs following a decrease in ATP levels (2, 3). Once activated, AMPK switches on ATP-generating (catabolic) pathways, e.g. fatty acid oxidation, and switches off ATP-using pathways (anabolic) pathways, e.g. fatty acid synthesis, allowing the cell to restore its energy balance (2, 3). In addition to acute effects on metabolism, AMPK has more long term effects, altering both gene (4) and protein expression (5, 6). Recent results have demonstrated activation of AMPK in the absence of changes in adenine nucleotide levels, indicating that there may be multiple pathways upstream of AMPK (7,8). The molecular mechanisms leading to activation of AMPK have not been fully elucidated, but it is clear that activation of AMPK requires phosphorylation of threonine 172 (Thr 172 ) within the activation loop segment of the catalytic (␣) subunit (9, 10). Very recently, LKB1, a protein kinase that is inactivated in a hereditary form of cancer termed Peutz-Jeghers syndrome, was shown to account for most of the AMPK kinase activity in cell extracts (11,12) raising the possibility that AMPK could l...

Peptide YY (PYY) and glucagon like peptide (GLP)-1 are cosecreted from intestinal L cells, and plasma levels of both hormones rise after a meal. Peripheral administration of PYY(3-36) and GLP-1(7-36) inhibit food intake when administered alone. However, their combined effects on appetite are unknown. We studied the effects of peripheral coadministration of PYY(3-36) with GLP-1(7-36) in rodents and man. Whereas high-dose PYY(3-36) (100 nmol/kg) and high-dose GLP-1(7-36) (100 nmol/kg) inhibited feeding individually, their combination led to significantly greater feeding inhibition. Additive inhibition of feeding was also observed in the genetic obese models, ob/ob and db/db mice. At low doses of PYY(3-36) (1 nmol/kg) and GLP-1(7-36) (10 nmol/kg), which alone had no effect on food intake, coadministration led to significant reduction in food intake. To investigate potential mechanisms, c-fos immunoreactivity was quantified in the hypothalamus and brain stem. In the hypothalamic arcuate nucleus, no changes were observed after low-dose PYY(3-36) or GLP-1(7-36) individually, but there were significantly more fos-positive neurons after coadministration. In contrast, there was no evidence of additive fos-stimulation in the brain stem. Finally, we coadministered PYY(3-36) and GLP-1(7-36) in man. Ten lean fasted volunteers received 120-min infusions of saline, GLP-1(7-36) (0.4 pmol/kg.min), PYY(3-36) (0.4 pmol/kg.min), and PYY(3-36) (0.4 pmol/kg.min) + GLP-1(7-36) (0.4 pmol/kg.min) on four separate days. Energy intake from a buffet meal after combined PYY(3-36) + GLP-1(7-36) treatment was reduced by 27% and was significantly lower than that after either treatment alone. Thus, PYY(3-36) and GLP-1(7-36), cosecreted after a meal, may inhibit food intake additively.

Study queStion

Although pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates insulin secretion, its net influence on glucose homeostasis in vivo has not been established. We therefore examined the action of PACAP-27 and PACAP-38 on insulin secretion, insulin sensitivity, and glucose disposal as derived from the minimal model of glucose disappearance during an intravenous glucose tolerance test in anesthetized mice. PACAP-27 and PACAP-38 markedly and equipotently potentiated glucose-stimulated insulin secretion, with a half-maximal effect at 33 pmol/kg. After PACAP-27 or PACAP-38 (1.3 nmol/kg), the acute (1–5 min) insulin response was 3.8 ± 0.4 nmol/l (PACAP-27) and 3.3 ± 0.3 nmol/l (PACAP-38), respectively, vs. 1.4 ± 0.1 nmol/l after glucose alone ( P < 0.001), and the total area under the curve for insulin (AUCinsulin) was potentiated by 60% ( P < 0.001). In contrast, PACAP-27 and PACAP-38 reduced the insulin sensitivity index (SI) [0.23 ± 0.04 10−4min−1/(pmol/l) for PACAP-27 and 0.29 ± 0.06 10−4min−1/(pmol/l) for PACAP-38 vs. 0.46 ± 0.02 10−4min−1/(pmol/l) for controls ( P < 0.01)]. Furthermore, PACAP-27 or PACAP-38 did not affect glucose elimination determined as glucose half-time or the glucose elimination rate after glucose injection or the area under the curve for glucose. Moreover, glucose effectiveness and the global disposition index (AUCinsulin times SI) were not affected by PACAP-27 or PACAP-38. Finally, when given together with glucose, PACAP-27 did not alter plasma glucagon or norepinephrine levels but significantly increased plasma epinephrine levels. We conclude that PACAP, besides its marked stimulation of insulin secretion, also inhibits insulin sensitivity in mice, the latter possibly explained by increased epinephrine. This complex action explains why the peptide does not enhance glucose disposal.

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Pituitary adenylate cyclase-activating polypeptide (PACAP) has been localized to pancreatic nerves and demonstrated to stimulate insulin and glucagon secretion in experimental animals. This study examined the occurrence and possible function of PACAP in the human pancreas. The content of PACAP27 was 0.44 +/- 0.04 pmol/g tissue, and that of PACAP38 was 29.6 +/- 6.4 pmol/g tissue in extracted human pancreas (n = 4). Furthermore, in a homogeneous group of seven healthy postmenopausal women, all aged 57 yr, iv infusion of synthetic human PACAP27 (3 pmol/kg.min for 75 min) increased basal levels of insulin, C peptide, and glucagon without significantly influencing basal glucose after 14 min. At 15 min, glucose was administered rapidly (0.3 g/kg, iv). The peak insulin after bolus glucose was 797 +/- 232 pmol/L during PACAP27 infusion vs. 559 +/- 164 pmol/L during saline infusion (P = 0.018). Also, the peak in C peptide after glucose was potentiated by PACAP27 (P = 0.018). In contrast, hepatic extraction, calculated as the C peptide/insulin molar ratio, was not significantly affected by PACAP27, and neither the glucose elimination rate nor reduction of serum insulin after the glucose-induced peak was changed by PACAP27. We conclude that PACAP occurs in human pancreas and stimulates insulin and glucagon secretion in humans. This suggests that PACAP is involved in the regulation of islet function in humans.

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is ubiquitously distributed in both the central and peripheral nervous systems and exerts a variety of effects. PACAP is a neuropeptide in pancreatic islets, where it has been suggested as a parasympathetic and sensory neurotransmitter. PACAP stimulates insulin secretion in a glucose-dependent manner, by an effect executed mainly through augmenting the formation of cAMP and stimulating the uptake of calcium. Accumulating evidence in animal studies points to a physiological importance of PACAP in the regulation of the insulin response to feeding. This review summarizes the current knowledge of islet actions and mechanisms and the function of PACAP. Diabetes 50: 1959

Gas chromatography/mass spectrometry-based metabolomics was applied to investigate dynamic changes in the plasma metabolome upon an oral glucose tolerance test (OGTT). The OGTT is a frequently used diagnostic test of glucose homeostasis and diabetes. Diabetes is diagnosed either when glucose levels C7.0 mM in the fasting state or C11.0 mM at 2 h after oral glucose intake. The accuracy of the OGTT would, however, most likely improve if additional variables could be identified. In the present study, plasma samples were drawn every 15 min for 2 h after an oral glucose load of 75 g preceded by an overnight fast in healthy individuals. Blood plasma levels of more than 200 putative metabolites were measured. Multivariate modelling was used to distinguish metabolic regulation due to the glucose challenge from that of other variability. Two data scaling methods were applied, yielding similar results when evaluated by appropriate diagnostic tools. Fatty acid levels were found to be strongly decreased during the OGTT. Also, the levels of amino acids were shown to decrease. However, technical and uninduced biological variations were found to affect the amino acid levels to a greater extent than the fatty acid levels, making the fatty acids more reliable as indicators of metabolic regulation. Levels of several metabolites correlated with the quadratic glucose profile and two were found having an inverse correlation. Raw data plots of all identified significantly altered metabolites confirmed the excellent performance of the multivariate models. Using this approach, a better understanding of the metabolic response to an OGTT can be achieved, paving the way for inclusion of other variables describing appropriate metabolic control.