Multiple Choice
Passage
Leptin signaling is vital for maintaining adequate body mass and preventing insulin resistance. When energy stores are abundant, adipocytes produce leptin to stimulate fatty acid oxidation and glucose utilization. One result of leptin signaling in skeletal muscle cells is the phosphorylation and activation of adenosine monophosphate-activated protein kinase (AMPK) . AMPK facilitates the breakdown of triglycerides by decreasing the activity of acetyl-coenzyme A carboxylase (ACC) ; this leads to downregulation of fatty acid synthesis and upregulation of β-oxidation.Fatty acid oxidation has been studied by analyzing the effect of leptin on activation of AMPK and ACC in soleus muscles. To identify leptin's mode of action, injections were administered to transgenic mice via the intravenous (1 mg/kg i.v.) and intrahypothalamic (1 ng i.h.p [faster drug delivery]) routes. Phentolamine (PH) , an α-adrenergic receptor ligand that binds to the same receptor as leptin, was administered concurrently in some of the mice. Signaling to ACC from the citric acid cycle was also examined through the addition of citrate.
![Passage Leptin signaling is vital for maintaining adequate body mass and preventing insulin resistance. When energy stores are abundant, adipocytes produce leptin to stimulate fatty acid oxidation and glucose utilization. One result of leptin signaling in skeletal muscle cells is the phosphorylation and activation of adenosine monophosphate-activated protein kinase (AMPK) . AMPK facilitates the breakdown of triglycerides by decreasing the activity of acetyl-coenzyme A carboxylase (ACC) ; this leads to downregulation of fatty acid synthesis and upregulation of β-oxidation.Fatty acid oxidation has been studied by analyzing the effect of leptin on activation of AMPK and ACC in soleus muscles. To identify leptin's mode of action, injections were administered to transgenic mice via the intravenous (1 mg/kg i.v.) and intrahypothalamic (1 ng i.h.p [faster drug delivery]) routes. Phentolamine (PH) , an α-adrenergic receptor ligand that binds to the same receptor as leptin, was administered concurrently in some of the mice. Signaling to ACC from the citric acid cycle was also examined through the addition of citrate. <strong>Figure 1</strong> AMPK activity measured in soleus muscle injected with leptin and PH via i.v. and i.h.p.<strong>Table 1</strong> ACC Activity in Soleus Muscle Exposed to Leptin Delivered via i.v. and i.h.p Injections in vivo Adapted from Minokoshi Y, Kim YB, Peroni OD, et al. Leptin stimulates fatty-acid oxidation by activating AMP-activated protein kinase. Nature. 2002;415(6869) :339-43. -What best describes the action of PH on AMPK activity? A) Long-term agonist B) Immediate antagonist C) Time-dependent antagonist D) Rapid agonist](https://d2lvgg3v3hfg70.cloudfront.net/MD0008/11ecba2d_0dc2_af71_a3bf_719de41c80b7_MD0008_00.jpg)
Figure 1 AMPK activity measured in soleus muscle injected with leptin and PH via i.v. and i.h.p.Table 1 ACC Activity in Soleus Muscle Exposed to Leptin Delivered via i.v. and i.h.p Injections in vivo
![Passage Leptin signaling is vital for maintaining adequate body mass and preventing insulin resistance. When energy stores are abundant, adipocytes produce leptin to stimulate fatty acid oxidation and glucose utilization. One result of leptin signaling in skeletal muscle cells is the phosphorylation and activation of adenosine monophosphate-activated protein kinase (AMPK) . AMPK facilitates the breakdown of triglycerides by decreasing the activity of acetyl-coenzyme A carboxylase (ACC) ; this leads to downregulation of fatty acid synthesis and upregulation of β-oxidation.Fatty acid oxidation has been studied by analyzing the effect of leptin on activation of AMPK and ACC in soleus muscles. To identify leptin's mode of action, injections were administered to transgenic mice via the intravenous (1 mg/kg i.v.) and intrahypothalamic (1 ng i.h.p [faster drug delivery]) routes. Phentolamine (PH) , an α-adrenergic receptor ligand that binds to the same receptor as leptin, was administered concurrently in some of the mice. Signaling to ACC from the citric acid cycle was also examined through the addition of citrate. <strong>Figure 1</strong> AMPK activity measured in soleus muscle injected with leptin and PH via i.v. and i.h.p.<strong>Table 1</strong> ACC Activity in Soleus Muscle Exposed to Leptin Delivered via i.v. and i.h.p Injections in vivo Adapted from Minokoshi Y, Kim YB, Peroni OD, et al. Leptin stimulates fatty-acid oxidation by activating AMP-activated protein kinase. Nature. 2002;415(6869) :339-43. -What best describes the action of PH on AMPK activity? A) Long-term agonist B) Immediate antagonist C) Time-dependent antagonist D) Rapid agonist](https://d2lvgg3v3hfg70.cloudfront.net/MD0008/11ecba2d_0dc2_af72_a3bf_e9a0f8dccdf8_MD0008_00.jpg)
Adapted from Minokoshi Y, Kim YB, Peroni OD, et al. Leptin stimulates fatty-acid oxidation by activating AMP-activated protein kinase. Nature. 2002;415(6869) :339-43.
-What best describes the action of PH on AMPK activity?
A) Long-term agonist
B) Immediate antagonist
C) Time-dependent antagonist
D) Rapid agonist
Correct Answer:
Verified
Correct Answer:
Verified
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