EFFECTS OF AN INTRAVENOUS-INJECTION OF NPY ON LEPTIN AND NPY-Y1 RECEPTOR MESSENGER-RNA EXPRESSION IN-OVINE ADIPOSE-TISSUE

Neuropeptide Y (NPY) is highly expressed in hypothalami of undernouris hed and genetically obese animals, and is a potent regulator of food i ntake and reproduction. Leptin, a protein expressed by adipocytes, has been reported to reduce hypothalamic NPY expression. We recently dete cted (by ribonuclease protection assay [RPA]) expression of the NPY re ceptor subtype Y1 (but not Y2) mRNA in adipose tissue. Based on these observations we hypothesized that NPY-YI receptors in adipose may repr esent a peripheral mechanism by which NPY can regulate leptin expressi on in a direct and rapid manner. To test this hypothesis, adipose samp les were biopsied from the tailhead region of 48 +/- 3 kg wether lambs immediately before and 30 min after a single intravenous injection of 50 mu g porcine NPY (''treated'' animals, n = 5), or vehicle (''contr ol'' animals, n = 4). Injection of NPY resulted in an increase in expr ession (P = 0.013; as measured by RPA) of both leptin and NPY-Y1 mRNA. In treated animals, negative correlations were found between response in leptin expression and body weight (r = -0.82, P = 0.092), and betw een leptin response and initial leptin mRNA levels (r = -0.81, P = 0.0 97). These data provide evidence of a peripheral mechanism by which NP Y may regulate adipocyte expression of both leptin and NPY-Y1 receptor mRNA. (C) Elsevier Science Inc. 1997.