Mechanisms of norepinephrine induced calcium responses in perivascular adipocytes

Perivascular adipose tissue (PVAT) surrounds the majority of blood vessels and regulates vascular tone by releasing anticontractile factors such as nitric oxide, hydrogen sulfide, adiponectin, and leptin. Norepinephrine (NE) regulates the production of these anticontractile factors but mechanisms whereby NE stimulates PVAT adipocytes are not understood. We hypothesized that NE primarily acts on beta II and III adrenergic receptors based on the role of beta-adrenergic receptors in other fat depots. We tested this hypothesis using calcium imaging in adiponectin Cre;GCaMP5g mice which express a genetically encoded calcium indicator in adipocytes. Cells were challenged with NE and calcium responses were measured using GCaMP fluorescence. Selective B2/3 (SR 59230A, 6.5µM) and a1a (RS 100329, 1µM) antagonists were used to study the relative contributions of these receptors in the calcium responses of white adipose tissue (WAT), aortic PVAT (aPVAT), and mesenteric PVAT (mPVAT). SR 59230A decreased responses to NE in WAT by 88% (p<0.0001), mPVAT by 75% (p<0.0001), and aPVAT by 57% (p<0.0001). RS 100329 decreased responses to NE by 88% in WAT (p<0.0001), 75% in mPVAT (p<0.0001), and 68% in aPVAT (p<0.0001). Co-incubation with both antagonists decreased responses by 73% in WAT (p<0.0001), 52% in mPVAT (0.0001), and 24% in aPVAT (p=0.1553). These data, and subsequent immunolabeling with receptor antibodies, suggest that mechanisms responsible for NE induced calcium responses are tissue dependent. Ongoing experiments use H89, U71332, and Gallein to understand the intracellular signal transduction pathways that underly these responses. To understand the signal transduction mechanisms underlying adipocyte calcium responses, external and internal calcium were manipulated using 0 calcium buffer and thapsigargin, respectively. Eliminating external calcium had no effect on adipocyte responses to NE. However, when intracellular calcium stores were depleted with thapsigargin in the presence of 0 external calcium, this decreased responses in WAT by 67% (p<0.0001), in mPVAT by 60% (p<0.0001), and in aPVAT by 40% (p=0.0034). These results indicate that B2, B3, and a1a receptors contribute to adipocyte calcium responses to NE in PVAT by initiating calcium release from intracellular stores. Calcium influx through membrane channels does not appear to play a major role in these responses. A more thorough understanding of these mechanisms is important to understand how PVAT exerts anticontractile effects on blood vessels and how this function changes in cardiovascular disease. 1P01HL152951-01A1 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.