Sugiura Shozo H, Roy Prabir K, Ferraris Ronaldo P
Department of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA.
J Exp Biol. 2006 Oct;209(Pt 19):3719-28. doi: 10.1242/jeb.02436.
Oxynticopeptic cells of fish stomach are thought to secrete less acid than the specialized parietal cells of mammalian stomach. Gastric acidity, however, has not been directly compared between fish and mammals. We therefore fed rainbow trout and rats the same meal, and found that the lowest postprandial pH of trout stomach was 2.7, which was only transiently sustained for 1 h, whereas that of rat stomach was 1.3, which was sustained for 3 h. Postprandial pH of the small intestine was slightly higher in trout (approximately 8.0) than in rats (approximately 7.6), but pH of the large intestine was similar (approximately 8.0). Addition of acids to fish feeds, in an attempt to aid the weak acidity of fish stomach, has been known to improve phosphorus digestibility, but its physiological effect on fish stomach is not known. Exogenous acids did improve phosphorus digestibility but also decreased steady-state mRNA expression of trout H(+)/K(+)-ATPase (ATP4A, the proton pump) as well as Na(+)/bicarbonate cotransporter (NBC), and had no effect on gastrin-like mRNA and somastostatin (SST) mRNA abundance. Gastrin-like mRNA and SST-2 mRNA were equally distributed between corpus and antrum. ATP4A mRNA and NBC mRNA were in the corpus, whereas SST-1 mRNA was in the antrum. Trout gastrin-like EST had modest homology to halibut and pufferfish gastrin, whereas trout ATP4A mRNA had > or = 95% amino acid homology with mammalian, Xenopus and flounder ATP4A. Although ATP4A seems highly conserved among vertebrates, gastric acidity is much less in trout than in rats, explaining the low digestibility of bone phosphorus, abundant in fish diets. Dietary acidification does not reduce acidity enough to markedly improve phosphorus digestibility, perhaps because exogenous acids may inhibit endogenous acid production.
鱼类胃中的泌酸胃蛋白酶细胞被认为比哺乳动物胃中的特化壁细胞分泌的酸更少。然而，鱼类和哺乳动物之间的胃酸度尚未直接比较过。因此，我们给虹鳟鱼和大鼠喂食相同的食物，发现虹鳟鱼胃餐后最低pH值为2.7，仅短暂维持1小时，而大鼠胃的餐后最低pH值为1.3，持续3小时。虹鳟鱼小肠餐后pH值略高于大鼠（约8.0），但大肠pH值相似（约8.0）。已知在鱼饲料中添加酸以辅助鱼类胃的弱酸性可提高磷的消化率，但其对鱼胃的生理作用尚不清楚。外源酸确实提高了磷的消化率，但也降低了虹鳟鱼H(+)/K(+)-ATP酶（ATP4A，质子泵）以及钠/碳酸氢根共转运体（NBC）的稳态mRNA表达，并且对胃泌素样mRNA和生长抑素（SST）mRNA丰度没有影响。胃泌素样mRNA和SST-2 mRNA在胃体和胃窦中分布均匀。ATP4A mRNA和NBC mRNA在胃体中，而SST-1 mRNA在胃窦中。虹鳟鱼胃泌素样EST与大比目鱼和河豚胃泌素具有适度的同源性，而虹鳟鱼ATP4A mRNA与哺乳动物、非洲爪蟾和比目鱼的ATP4A具有≥95%的氨基酸同源性。尽管ATP4A在脊椎动物中似乎高度保守，但虹鳟鱼的胃酸度比大鼠低得多，这解释了鱼类饲料中丰富的骨磷消化率较低的原因。日粮酸化不足以显著提高磷的消化率，可能是因为外源酸可能会抑制内源性酸的产生。
