Involvement of agouti-related protein, an endogenous antagonist of hypothalamic melanocortin receptor, in leptin action

Ken Ebihara, Yoshihiro Ogawa, Goro Katsuura, Yoshito Numata, Hiroaki Masuzaki, Noriko Satoh, Mikio Tamaki, Takeshi Yoshioka, Minoru Hayase, Naoki Matsuoka, Megumi Aizawa-Abe, Yasunao Yoshimasa, Kazuwa Nakao

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Abstract

To understand the role of agouti-related protein (AGRP), an endogenous antagonist of hypothalamic melanocortin receptor, in leptin action, we produced a full-length recombinant AGRP and examined its effect on the satiety effect of leptin. We also studied leptin's regulation of hypothalamic AGRP mRNA expression. A single intracerebroventricular (ICV) injection of AGRP significantly increased cumulative food intake and body weight in a dose-dependent manner in rats. The leptin-induced inhibition of food intake and body weight was reversed by co-injection of AGRP in a dose-dependent manner. Hypothalamic AGRP mRNA expression was upregulated in leptin-deficient ob/ob mice and leptin receptor-deficient db/db mice and downregulated in lethal yellow agouti mice (KKA(y) mice) with hyperleptinemia. A single ICV injection of leptin reversed the increased AGRP mRNA levels in ob/ob mice but not in db/db mice. In control mice and KKA(y) mice, AGRP mRNA expression was upregulated during fasting, when plasma leptin concentrations were decreased. No significant increase in AGRP mRNA expression was noted during fasting in control mice and KKA(y) mice treated with leptin. This study provides the first direct evidence that AGRP is a negative regulator of leptin action, and leptin downregulates hypothalamic AGRP production. Because leptin is shown to increase hypothalamic α-melanocyte stimulating hormone (e-MSH) production, our data suggest that its action via the hypothalamic melanocortin system is determined by the balance between the levels of its agonist and antagonist, α-MSH and AGRP.

Original languageEnglish
Pages (from-to)2028-2033
Number of pages6
JournalDiabetes
Volume48
Issue number10
DOIs
Publication statusPublished - Oct 1 1999
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Internal Medicine
  • Endocrinology, Diabetes and Metabolism

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