Which of the following best describes the relation between leptin and NPY in regulating food intake?

Question

BlackTom AI · Accepted Answer

Leptin is an adipocyte-derived hormone that normally inhibits NPY/AgRP neurons in the arcuate nucleus and stimulates POMC neurons, producing decreased appetite and reduced NPY-mediated orexigenic signaling.

1) Relevant knowledge points and concepts
- Leptin: secreted in proportion to fat mass, signals energy sufficiency to hypothalamus via Ob-Rb receptors.
- NPY (neuropeptide Y): produced in arcuate nucleus; a potent orexigenic (appetite-stimulating) peptide.
- Normal physiology: increased leptin → activation of anorexigenic pathways (POMC) and inhibition of orexigenic neurons (NPY/AgRP) → appetite suppression.
- Pathophysiology: leptin resistance (common in obesity) means high circulating leptin fails to activate hypothalamic signaling; NPY remains active despite elevated leptin.

2) Step-by-step reasoning
Step 1: Under normal conditions, rising leptin levels bind hypothalamic receptors and inhibit NPY neurons; consequence = decreased food intake.
Step 2: In many individuals with chronic high adiposity, leptin levels are elevated yet hypothalamic responsiveness declines (leptin resistance). Thus, experimentally or clinically increasing leptin does not reliably reduce appetite or sufficiently inhibit NPY signaling.
Step 3: Therefore any statement that assumes a simple one-to-one relationship (higher leptin always → lower appetite/NPY) is incorrect. The correct statement must allow for contexts (e.g., leptin resistance) where increased leptin fails to suppress appetite or NPY.

3) Why the correct answer is correct
Option B states that increasing leptin levels does not always lead to a reduction in appetite and inhibition of NPY. This acknowledges both the normal inhibitory role of leptin and the clinically important exception of leptin resistance, so it accurately describes the real-world relationship.

4) Why the other options are incorrect
- A (High leptin levels increase appetite and inhibit NPY): Contradicts physiology—high leptin normally suppresses appetite rather than increasing it.
- C (Low leptin levels increase appetite and inhibit NPY): Low leptin increases appetite but does so by relieving inhibition of NPY (i.e., it would disinhibit/activate NPY, not inhibit it).
- D (Decreasing leptin levels always leads to a reduction in appetite and inhibition of NPY): Opposite of reality—decreasing leptin typically increases appetite and activates NPY; the word “always” is also incorrect because responses vary.

Conclusion: Considering normal leptin action and the common phenomenon of leptin resistance, the best description is option B: Increasing leptin levels does not always lead to a reduction in appetite and inhibition of NPY. This matches the provided correct answer.

Which of the following best describes the relation between leptin and NPY in regulating food intake?Single choice

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