Uble-anabolic drive. In addition to BIBS39 web modulation of food intake, NPY may also be involved in the regulation of lipid metabolism. A recent study in rats showed that acute modulation of central NPY signaling, either by NPY or by an Y5 receptor agonist, increased hepatic VLDLTG production. Accordingly, central administration of a Y1 receptor antagonist decreased hepatic VLDL-TG 68181-17-9 production [12]. In mice, central NPY administration prevented the peripheral insulin-induced inhibition of glucose production by the liver, and reversed the insulin-induced inhibition of hepatic VLDL-TG production under hyperinsulinemic 1531364 conditions [13]. Hypertriglyceridemia, associated with increased hepatic VLDL-TG production and/or decreased VLDL-TG clearance, is an important risk factor for cardiovascular diseases such as arterial atherosclerosis (for review [14]). Since atherosclerosis is generally studied in hyperlipidemic mice rather than in rats, we set out to validate the effect of NPY on hepatic VLDL-TG production in mice, with the ultimate goal to investigate whether NPY, by increasing VLDLTG production, contributes to the development of atherosclerosis.Lateral Ventricle NPY Administration does not Affect Hepatic VLDL ProductionNext, we assessed the effects of a single injection of NPY (0.2 mg/kg BW) into the left lateral ventricle on VLDL production in 4 h-fasted anaesthetized mice. Acute central administration of NPY did not affect VLDL-TG production rate in mice (7.760.6 vs 7.361.1 mmol/h, n.s., Fig. 2A, B). Accordingly, hepatic VLDL-35S-apoB production was also unchanged upon NPY administration (84611 vs 796216103 dpm/h, n.s., Fig. 2C). Thus, although this dose of NPY increased food intake, it did not affect hepatic VLDL production. Subsequently, we performed a dose-finding study to assess whether either higher or lower dosages of NPY (0.0002, 0.002, 0.02, 0.2 or 2.0 mg/kg BW) were capable of increasing hepatic VLDL-TG production. Again, we did not observe any differenceResults Lateral Ventricle NPY Administration Stimulates Food Intake in MiceTo verify that central administration of NPY stimulates food intake, both basal and NPY-induced food intake were assessed during two hours, starting at 09:00 a.m. with all mice serving as their own control. Administration of NPY (0.2 mg/kg BW) in the left lateral ventricle (LV) increased food intake during the first hour after injection by +164 (0.3460.19 vs 0.9060.40 g, p,0.001, Fig. 1). Food intake during the second hour after injection 1662274 was similar to the basal food intake in this specific time frame (0.4060.17 vs 0.4960.20 g, n.s., Fig. 1).Figure 1. NPY administration into the lateral ventricle acutely increases food intake. NPY (0.2 mg/kg) was administered in the left lateral ventricle under light isoflurane anaesthesia, and food intake was measured for two hours, starting at 09:00 a.m. All animals served as their own controls (basal food intake). Values are means 6 SD (n = 9), ***p,0.001 compared to basal. doi:10.1371/journal.pone.0055217.gFigure 2. NPY administration into the lateral ventricle does not affect hepatic VLDL production in anesthetized mice. After a 4 hour fast, mice were fully anesthetized and hepatic VLDL production was assessed. Mice received an i.v. injection of Tran35S label (t = 230 min), followed by an injection of tyloxapol (t = 0 min), directly followed by an LV injection of NPY (0.2 mg/kg BW) or artificial cerebrospinal fluid (control). Plasma triglyceride (TG) levels were determined.Uble-anabolic drive. In addition to modulation of food intake, NPY may also be involved in the regulation of lipid metabolism. A recent study in rats showed that acute modulation of central NPY signaling, either by NPY or by an Y5 receptor agonist, increased hepatic VLDLTG production. Accordingly, central administration of a Y1 receptor antagonist decreased hepatic VLDL-TG production [12]. In mice, central NPY administration prevented the peripheral insulin-induced inhibition of glucose production by the liver, and reversed the insulin-induced inhibition of hepatic VLDL-TG production under hyperinsulinemic 1531364 conditions [13]. Hypertriglyceridemia, associated with increased hepatic VLDL-TG production and/or decreased VLDL-TG clearance, is an important risk factor for cardiovascular diseases such as arterial atherosclerosis (for review [14]). Since atherosclerosis is generally studied in hyperlipidemic mice rather than in rats, we set out to validate the effect of NPY on hepatic VLDL-TG production in mice, with the ultimate goal to investigate whether NPY, by increasing VLDLTG production, contributes to the development of atherosclerosis.Lateral Ventricle NPY Administration does not Affect Hepatic VLDL ProductionNext, we assessed the effects of a single injection of NPY (0.2 mg/kg BW) into the left lateral ventricle on VLDL production in 4 h-fasted anaesthetized mice. Acute central administration of NPY did not affect VLDL-TG production rate in mice (7.760.6 vs 7.361.1 mmol/h, n.s., Fig. 2A, B). Accordingly, hepatic VLDL-35S-apoB production was also unchanged upon NPY administration (84611 vs 796216103 dpm/h, n.s., Fig. 2C). Thus, although this dose of NPY increased food intake, it did not affect hepatic VLDL production. Subsequently, we performed a dose-finding study to assess whether either higher or lower dosages of NPY (0.0002, 0.002, 0.02, 0.2 or 2.0 mg/kg BW) were capable of increasing hepatic VLDL-TG production. Again, we did not observe any differenceResults Lateral Ventricle NPY Administration Stimulates Food Intake in MiceTo verify that central administration of NPY stimulates food intake, both basal and NPY-induced food intake were assessed during two hours, starting at 09:00 a.m. with all mice serving as their own control. Administration of NPY (0.2 mg/kg BW) in the left lateral ventricle (LV) increased food intake during the first hour after injection by +164 (0.3460.19 vs 0.9060.40 g, p,0.001, Fig. 1). Food intake during the second hour after injection 1662274 was similar to the basal food intake in this specific time frame (0.4060.17 vs 0.4960.20 g, n.s., Fig. 1).Figure 1. NPY administration into the lateral ventricle acutely increases food intake. NPY (0.2 mg/kg) was administered in the left lateral ventricle under light isoflurane anaesthesia, and food intake was measured for two hours, starting at 09:00 a.m. All animals served as their own controls (basal food intake). Values are means 6 SD (n = 9), ***p,0.001 compared to basal. doi:10.1371/journal.pone.0055217.gFigure 2. NPY administration into the lateral ventricle does not affect hepatic VLDL production in anesthetized mice. After a 4 hour fast, mice were fully anesthetized and hepatic VLDL production was assessed. Mice received an i.v. injection of Tran35S label (t = 230 min), followed by an injection of tyloxapol (t = 0 min), directly followed by an LV injection of NPY (0.2 mg/kg BW) or artificial cerebrospinal fluid (control). Plasma triglyceride (TG) levels were determined.
