VPAC2-R Mediates the Lipolytic Effects of Pituitary Adenylate Cyclase-Activating Polypeptide/Vasoactive Intestinal Polypeptide in Primary Rat Adipocytes

Oct 30, 2004Endocrinology

VPAC2-R helps pituitary peptides trigger fat breakdown in rat fat cells

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Abstract

VIP stimulates lipolysis in isolated adipocytes similarly to PACAP38, with effects mediated by the VPAC2-R receptor subtype.

All three receptor subtypes (PAC1-R, VPAC1-R, and VPAC2-R) are present in rat adipocytes.
VIP (1-100 nm) induces lipolysis as measured by glycerol release, comparable to the effects of PACAP38.
Antagonists of PAC1-R and VPAC1-R do not inhibit lipolysis induced by PACAP38 or VIP.
VPAC2-R agonists mimic the lipolytic effects of PACAP38 and VIP.
The VPAC2-R antagonist PG99-465 shifts the dose-response curves for lipolysis induced by PACAP38 and VIP.

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The neuropeptides pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are structurally and functionally related. Their actions have been shown to be mediated by three different receptor subtypes: PAC1-R, which has exclusive affinity for PACAP, and VPAC1-R and VPAC2-R, which have equal affinity for PACAP and VIP. We recently showed that PACAP38 induces lipolysis in rat adipocytes, and in the present study we examined whether VIP has similar effects and which of the three receptors mediates this PACAP/VIP action. We showed by RT-PCR that all three receptor subtypes are present in rat adipocytes. We demonstrated that VIP (1-100 nm), like PACAP38, stimulates lipolysis in isolated adipocytes, as determined by glycerol release. By a pharmacological approach, using antagonists and agonists specific for the receptor subtypes, we elucidated the mechanisms by which PACAP38 and VIP mediate their lipolytic effects. We found that antagonists of PAC1-R [PACAP(6-38)] and VPAC1-R (PG97-269) did not affect lipolysis induced by 0.1-100 nm PACAP38 or VIP, and that a VPAC1-R agonist [K15, R16, L27VIP(1-7)GRF(8-27)] did not affect lipolysis at 1-1000 nm. However, two different VPAC2-R agonists [Hexa-VIP(1-28) and Ro25-1553] clearly mimicked the lipolytic effect of PACAP38 and VIP. In addition, the VPAC2-R antagonist PG99-465 (100 nm) caused right-shifted dose-response curves of PACAP38- and VIP-induced lipolysis. These results therefore provide evidence that all three PACAP/VIP receptor subtypes are expressed in primary rat adipocytes, but that the VPAC2-R subtype is responsible for mediating the lipolytic effects induced by PACAP38 and VIP.

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VPAC2-R Mediates the Lipolytic Effects of Pituitary Adenylate Cyclase-Activating Polypeptide/Vasoactive Intestinal Polypeptide in Primary Rat Adipocytes

Abstract

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