INCREASED NEUROPEPTIDE-Y CONCENTRATIONS IN SPECIFIC HYPOTHALAMIC REGIONS OF LACTATING RATS - POSSIBLE RELATIONSHIP TO HYPERPHAGIA AND ADAPTIVE-CHANGES IN ENERGY-BALANCE

Lactation is accompanied by hyperphagia and a reduction in brown adipo se tissue (BAT) thermogenesis, which are unexplained. Neuropeptide Y ( NPY) powerfully stimulates feeding and inhibits BAT thermogenesis when injected into the paraventricular nucleus and other specific regions of the rat hypothalamus. We have tested the hypothesis that hypothalam ic NPY activity is increased in lactating rats. Lactating rats consume d over four times as much food as nonlactating controls (n = 10; p < 0 .001). Final plasma insulin concentrations in lactating rats were lowe r than in controls (6.8 +/- 0.8 vs. 11.7 +/- 2.1 pmol/l; p < 0.05) alt hough plasma glucose and corticosterone concentrations were comparable (p > 0.05). Lactating rats showed significantly higher NPY levels tha n controls in specific hypothalamic regions, namely the arcuate nucleu s-median eminence complex (a 41% rise; p < 0.001), paraventricular nuc leus (35%; p < 0.001), ventromedial nucleus (66%; p = 0.003), and dors omedial nucleus (78%; p < 0.001). Other hypothalamic regions showed no significant differences between groups. Increased NPY concentrations in specific hypothalamic regions, particularly the arcuate nucleus whe re NPY is synthesized, suggest increased activity of the hypothalamic NPYergic system in lactation. Neuropeptide Y may mediate hyperphagia a nd reduced BAT thermogenesis in lactation. Hypoinsulinemia may be a st imulus to hypothalamic NPY in lactation, as has been postulated in oth er conditions of negative energy balance.