NEUROPEPTIDE-Y RECEPTOR NUMBERS ARE REDUCED IN THE HYPOTHALAMUS OF STREPTOZOTOCIN-DIABETIC AND FOOD-DEPRIVED RATS - FURTHER EVIDENCE OF INCREASED ACTIVITY OF HYPOTHALAMIC NPY-CONTAINING PATHWAYS

Neuropeptide Y (NPY) injected into the hypothalamus stimulates feeding and affects pituitary secretion. Insulin-deficient diabetes and food deprivation markedly increase hypothalamic NPY and NPY mRNA levels, su ggesting increased activity of NPYergic pathways in the hypothalamus, which could account for hyperphagia and neuroendocrine changes in thes e conditions. To clarify these changes, NPY receptor characteristics w ere compared amongst rats with 3-weeks' untreated streptozotocin diabe tes, insulin-treated normoglycemic diabetics, and non-diabetics, and a lso in food-deprived (72 h), food-deprived then refed, and in freely f ed rats- Hypothalamic tissue homogenates (pooled from 3 rats; n = 9 pe r group) in Tris/HCl buffer were incubated with 30 pM [I-125]porcine N PY and unlabeled NPY (range, 1 pM to 1 muM) for 1 h. Bound and free fr actions were separated by vacuum filtration. Scatchard analysis reveal ed both high-affinity (K(d) 0.3-0.8 nM) and low-affinity (K(d) 14-40 n M) NPY receptor populations. Compared with nondiabetics. diabetic rats showed significantly reduced numbers (B(max)) of both high-affinity r eceptors (10 +/- 2 vs. 57 +/- 2 pmol/mg protein; p < 0.001) and low-af finity receptors (113 +/- 25 vs. 544 +/- 48 pmol/mg protein; p < 0.00 1). Insulin treatment partially restored B(max) of both high- and low- affinity receptors (24 +/- 1 and 334 +/- 60 pmol/mg protein, respectiv ely; p < 0.01 vs. both other groups). Food deprivation also reduced B( max) of high-affinity (36 +/- 2 vs. 56 +/- 7 pmol/mg protein in freely fed; p < 0.05) and low-affinity receptors (288 +/- 6 vs. 457 +/- 17 p mol/mg protein; p < 0.05). Refeeding for 48 h after 72-h fasting did n ot significantly alter B(max) of either high- or low-affinity receptor s (35 +/- 3 and 318 +/- 53 pmol/mg protein, respectively; p > 0.05 vs. food-deprived rats; p < 0.05 vs. freely fed rats). Neither diabetes n or food deprivation significantly affected the NPY receptors' affiniti es. Reduced hypothalamic NPY receptor numbers in diabetes and food dep rivation suggest downregylation due to increased NPY release in the hy pothalamus. This may mediate food-seeking behavior, hyperphagia, and p ituitary dysfunction in diabetes and food deprivation.