Mezoff A G, Jensen N J, Cohen M B
Division of Gastroenterology and Nutrition, Children's Hospital Research Foundation, Cincinnati, Ohio 45229.
Pediatr Res. 1991 May;29(5):424-8. doi: 10.1203/00006450-199105010-00003.
Pigs demonstrate an increased sensitivity and susceptibility to Escherichia coli heat-stable enterotoxin (STa) in the 1st wk of life and immediately after weaning. To determine the possible mechanisms for this increased susceptibility, we compared STa binding, guanylate cyclase activation, and photoaffinity cross-linking to porcine jejunal brush border membranes prepared from immature (less than or equal to 1 wk of age) versus adult pigs as well as 3-wk-old weaned versus unweaned pigs. The STa binding capacity of immature pigs was nearly twice that of adult pigs (11.73 +/- 1.52 versus 6.00 +/- 0.96 x 10(-11) mol/L, p less than 0.001), and the STa binding capacity of weaned pigs was nearly three times greater than that of unweaned pigs (17.48 +/- 2.10 versus 4.86 +/- 1.02 x 10(-11) mol/L, p less than 0.001). Scatchard analysis suggested a single class of STa receptor, with an association of binding constant of approximately 10(9) L/mol at all ages. Maximum guanylate cyclase response (expressed as pmol cyclic GMP generated/mg brush border membrane protein/min) was greater in immature versus adult pigs (1312 +/- 831 versus 320 +/- 92, p less than 0.02). Weaned pigs had a greater maximum guanylate cyclase activation than unweaned pigs (1126 +/- 692 versus 624 +/- 298); however, this difference was not statistically significant. Autoradiograms demonstrated specific cross-linking of 125I-STa to a number of distinct radiolabeled bands (62, 66, 84, 92, 160, and 165 kD). There was a difference in the size and trypsin sensitivity of these radiolabeled bands as a function of age and weaning. Treatment with trypsin decreased the intensity of the 160 to 165-kD bands while increasing the intensity of the 62- to 66- and 84- to 92-kD bands. These differences in STa binding, guanylate cyclase activation, and STa receptor size may increase the susceptibility of pigs during the 1st wk of life and at weaning to STa-mediated diarrheal disease.
仔猪在出生后第1周和刚断奶后对大肠杆菌热稳定肠毒素（STa）表现出更高的敏感性和易感性。为了确定这种易感性增加的可能机制，我们比较了从幼龄（小于或等于1周龄）与成年猪以及3周龄断奶与未断奶猪制备的猪空肠刷状缘膜上STa的结合、鸟苷酸环化酶激活和光亲和交联情况。幼龄猪的STa结合能力几乎是成年猪的两倍（11.73±1.52对6.00±0.96×10⁻¹¹mol/L，p＜0.001），断奶猪的STa结合能力比未断奶猪大近三倍（17.48±2.10对4.86±1.02×10⁻¹¹mol/L，p＜0.001）。Scatchard分析表明存在单一类别的STa受体，在所有年龄段结合常数的缔合约为10⁹L/mol。幼龄猪的最大鸟苷酸环化酶反应（以每分钟每毫克刷状缘膜蛋白产生的pmol环磷酸鸟苷表示）高于成年猪（1312±831对320±92，p＜0.02）。断奶猪的最大鸟苷酸环化酶激活高于未断奶猪（1126±692对624±298）；然而，这种差异无统计学意义。放射自显影片显示¹²⁵I-STa与多个不同的放射性标记条带（62、66、84、92、160和165kD）发生特异性交联。这些放射性标记条带的大小和对胰蛋白酶的敏感性随年龄和断奶情况而有所不同。用胰蛋白酶处理会降低160至165kD条带的强度，同时增加62至66kD和84至92kD条带的强度。STa结合、鸟苷酸环化酶激活和STa受体大小的这些差异可能会增加仔猪在出生后第1周和断奶时对STa介导的腹泻病的易感性。
