Neuropeptide B/W receptor 1 (NPBWR1) and neuropeptide B/W receptor 2 (NPBWR2) are two structurally related orphan receptors linked to protein G. In rodents NPBWR2 is absent, and its counterpart is described as being similar to neuropeptide B/W receptor 2. Endogenous ligands of these receptors have been identified. One of them is 29 amino acid residues long, uniquely modified with bromine and, thus, termed neuropeptide B (NPB). The other, neuropeptide W (NPW), has been identified in two molecular forms of 23 and 30 amino acids (NPW23 and NPW30), respectively. Both NPB and NPW affect food intake and energy expenditure. Since leptin, a potent anti-obesity hormone, and insulin are involved in the control of energy homeostasis, the present study aimed to investigate whether NPB and NPW affect leptin and insulin secretion in the rat. RT-PCR technique revealed the presence of ppNPB, ppNPW, NPBWR1 and NPBWR2-like mRNAs in isolated pancreatic islets of the rat. NPB and NPW immunoreactivities were observed in all of the cells of the pancreatic islets. Only when a higher dose was administered (3 nmol/100 g body weight) did NPW transiently lower blood insulin levels whereas NPB injection did not alter insulinaemia in the studied rats. At 30 min, but not 60, of the experiment, NPW notably lowered blood leptin concentrations at both tested doses. On the contrary, NPB injections had no effect on blood leptin and insulin concentrations. Thus, the results suggest that NPW but not NPB exerts a potent suppressive effect on blood leptin concentrations in the rat, and this mechanism may be involved in NPW regulation of energy homeostasis.

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