Barb C R, Yan X, Azain M J, Kraeling R R, Rampacek G B, Ramsay T G
USDA-ARS, Russell Agriculture Research Center, Athens, GA 30604, USA.
Domest Anim Endocrinol. 1998 Jan;15(1):77-86. doi: 10.1016/s0739-7240(97)00064-7.
Two experiments (EXP) were conducted to test the hypothesis that porcine leptin affects GH, insulin-like growth factor-I (IGF-I), insulin, thyroxine (T4) secretion, and feed intake. In EXP I, prepuberal gilts received intracerebroventricular (i.c.v.) leptin injections. Blood was collected every 15 min for 4 hr before and 3 hr after i.c.v. injections of 0.9% saline (S; n = 3), 10 micrograms (n = 4), 50 micrograms (n = 4), or 100 micrograms (n = 4) of leptin in S. Pigs were fed each day at 0800 and 1700 hr over a 2-wk period before the EXP. On the day of the EXP, pigs were fed at 0800 hr and blood sampling started at 0900 h. After the last sample was collected, feeders were placed in all pens. Feed intake was monitored at 4, 20, and 44 hr after feed presentation. In EXP II, pituitary cells from prepuberal gilts were studied in primary culture to determine if leptin affects GH secretion at the level of the pituitary. On Day 4 of culture, 10(5) cells/well were challenged with 10(-12), 10(-10), 10(-8), or 10(-6) M [Ala15]-h growth hormone-releasing factor-(1-29)NH2 (GRF), 10(-14), 10(-13), 10(-12), 10(-11), 10(-10), 10(-9), 10(-8), 10(-7), or 10(-6) M leptin individually or in combinations with 10(-8) and 10(-6) M GRF. Secreted GH was measured at 4 hr after treatment. In EXP I, before injection, serum GH concentrations were similar. Serum GH concentrations increased (P < 0.01) after injection of 10 micrograms (21 +/- 1 ng/ml), 50 micrograms (9 +/- 1 ng/ml), and 100 micrograms (13 +/- 1 ng/ml) of leptin compared with S (1 +/- 2 ng/ml) treated pigs. The GH response to leptin was greater (P < 0.001) in 10 micrograms than 50 or 100 micrograms leptin-treated pigs. By 20 hr the 10, 50, and 100 micrograms doses of leptin reduced feed intake by 53% (P < 0.08), 76%, and 90% (P < 0.05), respectively, compared with S pigs. Serum IGF-1, insulin, T4, glucose, and free fatty acids were unaffected by leptin treatment. In EXP II, relative to control (31 +/- 2 ng/well), 10(-10), 10(-8), and 10(-6) M GRF increased (P < 0.01) GH secretion by 131%, 156%, and 170%, respectively. Only 10(-6) M and 10(-7) M leptin increased (P < 0.01) GH secretion. Addition of 10(-11) and 10(-9) M leptin in combination with 10(-6) M GRF or 10(-11) M leptin in combination with 10(-8) M GRF-suppressed (P < 0.05) GH secretion. These results indicate that leptin modulates GH secretion and, as shown in other species, leptin suppressed feed intake in the pig.
进行了两项实验（EXP）来检验猪瘦素是否会影响生长激素（GH）、胰岛素样生长因子 - I（IGF - I）、胰岛素、甲状腺素（T4）的分泌以及采食量这一假设。在实验I中，对青春期前的小母猪进行脑室内（i.c.v.）注射瘦素。在注射含0.9%生理盐水（S；n = 3）、10微克（n = 4）、50微克（n = 4）或100微克（n = 4）瘦素的生理盐水之前4小时和之后3小时，每隔15分钟采集一次血液。在实验前的2周时间里，每天于0800和1700时给猪喂食。在实验当天，于0800时给猪喂食，并于0900时开始采血。采集完最后一个样本后，在所有猪栏中放置喂食器。在提供饲料后4、20和44小时监测采食量。在实验II中，对青春期前小母猪的垂体细胞进行原代培养，以确定瘦素是否在垂体水平影响GH分泌。在培养的第4天，每孔10⁵个细胞分别用10⁻¹²、10⁻¹⁰、10⁻⁸或10⁻⁶ M [Ala¹⁵] - h生长激素释放因子 - (1 - 29)NH₂（GRF）、10⁻¹⁴、10⁻¹³、10⁻¹²、10⁻¹¹、10⁻¹⁰、10⁻⁹、10⁻⁸、10⁻⁷或10⁻⁶ M瘦素单独处理，或与10⁻⁸和10⁻⁶ M GRF联合处理。处理后4小时测量分泌的GH。在实验I中，注射前血清GH浓度相似。与注射生理盐水（1±2 ng/ml）的猪相比，注射10微克（21±1 ng/ml）、50微克（9±1 ng/ml）和100微克（13±1 ng/ml）瘦素后血清GH浓度升高（P < 0.01）。与50或100微克瘦素处理的猪相比，10微克瘦素处理的猪对瘦素的GH反应更大（P < 0.001）。到20小时时，与注射生理盐水的猪相比，10、50和100微克剂量的瘦素分别使采食量降低了53%（P < 0.08）、76%和90%（P < 0.05）。瘦素处理对血清IGF - 1、胰岛素、T4、葡萄糖和游离脂肪酸没有影响。在实验II中，相对于对照组（31±2 ng/孔），10⁻¹⁰、10⁻⁸和10⁻⁶ M GRF分别使GH分泌增加（P < 0.01）131%、156%和170%。仅10⁻⁶ M和10⁻⁷ M瘦素使GH分泌增加（P < 0.01）。10⁻¹¹和10⁻⁹ M瘦素与10⁻⁶ M GRF联合使用或10⁻¹¹ M瘦素与10⁻⁸ M GRF联合使用时抑制（P < 0.05）GH分泌。这些结果表明，瘦素调节GH分泌，并且如在其他物种中所示，瘦素抑制猪的采食量。
