Hocking Edwards J E, Khalaf S K, Sinclaire B R, Lee J, Prosser C G, Harris P M
New Zealand Pastoral Agriculture Research Institute, Dairy and Beef Division, Palmerston North.
Biochem J. 1995 Jun 1;308 ( Pt 2)(Pt 2):411-8. doi: 10.1042/bj3080411.
The effects of a chronic (21-day) skin infusion of a variant of insulin-like growth factor I (IGF-I) (long-Arg3-IGF-I; LR3IGF-I) on short-term (48 h) responses of skin metabolism and 21-day plasma hormone concentration, wool-follicle characteristics and wool production were investigated in well-fed castrated Romney sheep. A bilateral arteriovenous preparation was used to infuse LR3IGF-I continuously into the skin on one abdominal flank and saline into the other abdominal flank of six sheep; a further six sheep had one flank infused with saline (controls). LR3IGF-I caused an initial (4-24 h) reduction in the plasma concentrations of amino acids, especially tyrosine, valine and lysine, and, after 24 h, significant (P < 0.05) reductions in blood oxygen and plasma glucose concentrations. After 4 h of LR3IGF-I infusion, there was a significant increase in blood flow (P < 0.05) and oxygen uptake (P < 0.05), and net uptake of amino acids [which was significant (P < 0.05) for valine and phenylalanine] by the LR3IGF-I-infused skin was increased. Total uptake of phenylalanine for skin protein synthesis, measured using [3H]phenylalanine uptake, was also significantly increased after 4 and 24 h of infusion. After 48 h of infusion all LR3IGF-I-dependent measurements of metabolic parameters had fallen to preinfusion values. By day 7 of the 21-day infusion there was a significant (P < 0.05) decrease in circulating endogenous IGF-I in plasma of treated sheep compared with that of control sheep, followed by a significant (P < 0.05) increase between day 7 and 21. Plasma insulin levels followed a similar pattern. There was no change at any stage of infusion in IGF-binding proteins in the plasma of the two LR3IGF-I-infused sheep tested, and it is concluded that LR3IGF-I caused a down-regulation of the type-I IGF-I receptors followed by a rise in endogenous IGF-I concentration consequent on lack of feedback regulation. After 21 days of infusion there was no effect of LR3IGF-I on wool-follicle-bulb-cell mitotic rate, bulb diameter or wool production.(ABSTRACT TRUNCATED AT 400 WORDS)
在营养良好的去势罗姆尼绵羊中，研究了长期（21天）经皮肤输注胰岛素样生长因子I（IGF-I）变体（长精氨酸3-IGF-I；LR3IGF-I）对皮肤代谢的短期（48小时）反应、21天血浆激素浓度、毛囊特征和羊毛产量的影响。采用双侧动静脉制备法，对6只绵羊的一侧腹侧皮肤持续输注LR3IGF-I，另一侧腹侧皮肤输注生理盐水；另外6只绵羊一侧腹侧输注生理盐水作为对照。LR3IGF-I导致血浆氨基酸浓度最初（4 - 24小时）降低，尤其是酪氨酸、缬氨酸和赖氨酸，24小时后，血氧和血浆葡萄糖浓度显著（P < 0.05）降低。输注LR3IGF-I 4小时后，血流量（P < 0.05）和氧摄取量（P < 0.05）显著增加，输注LR3IGF-I的皮肤对氨基酸的净摄取量增加[缬氨酸和苯丙氨酸的摄取量显著（P < 0.05）]。使用[3H]苯丙氨酸摄取量测量的皮肤蛋白质合成中苯丙氨酸的总摄取量在输注4小时和24小时后也显著增加。输注48小时后，所有依赖LR3IGF-I的代谢参数测量值均降至输注前水平。在21天输注的第7天，与对照绵羊相比，治疗绵羊血浆中循环内源性IGF-I显著（P < 0.05）降低，随后在第7天至21天显著（P < 0.05）升高。血浆胰岛素水平遵循类似模式。在测试的两只输注LR3IGF-I的绵羊血浆中，IGF结合蛋白在输注的任何阶段均无变化，得出的结论是，LR3IGF-I导致I型IGF-I受体下调，随后由于缺乏反馈调节导致内源性IGF-I浓度升高。输注21天后，LR3IGF-I对毛囊球细胞有丝分裂率、球直径或羊毛产量没有影响。（摘要截短至400字）
