Herm G, Muscher-Banse A S, Breves G, Schröder B, Wilkens M R
J Anim Sci. 2015 Apr;93(4):1608-21. doi: 10.2527/jas.2014-8450.
In small ruminants, the renal excretion of calcium (Ca) and phosphate (Pi) is not modulated in response to dietary Ca restriction. Although this lack of adaptation was observed in both sheep and goats, differences in renal function between these species cannot be excluded. Recent studies demonstrated that compared with sheep, goats have a greater ability to compensate for challenges to Ca homeostasis, probably due to a more pronounced increase in calcitriol production. Therefore, the aim of the present study was to examine the effect of 1) dietary Ca restriction, 2) administration of calcitriol, and 3) lactation on Ca and Pi transport mechanisms and receptors as well as enzymes involved in vitamin D metabolism in renal tissues of sheep and goats. Whereas RNA expression of renal transient receptor potential vanilloid channel type 5 was unaffected by changes in dietary Ca content, a significant stimulation was observed with administration of calcitriol in both sheep (P < 0.001) and goats (P < 0.01). Calbindin-D28K was downregulated during dietary Ca restriction in goats (P < 0.05). Expression of the sodium/Ca exchanger type 1 was decreased by low Ca intake in sheep (P < 0.05) and upregulated by calcitriol treatment in goats (P < 0.05). A significant reduction in RNA expression of the cytosolic and the basolateral Ca transporting proteins was also demonstrated for lactating goats in comparison to dried-off animals. Species differences were found for vitamin D receptor expression, which was stimulated by calcitriol treatment in sheep (P < 0.01) but not in goats. As expected, expression of 1α-hydroxylase was upregulated by dietary Ca restriction (P < 0.001; P < 0.05) and inhibited by exogenous calcitriol (P < 001; P < 0.05) in both sheep and goats. However, whereas 24-hydroxylase expression was stimulated to the same extent by calcitriol treatment in sheep, irrespective of the diet (P < 0.001), a modulatory effect of dietary Ca supply on 24-hydroxylase induction was observed in goats (P < 0.05). Taken together, our results confirm observations that modulation of renal Ca excretion does not contribute to maintenance of Ca homeostasis in these ruminants during restricted dietary supply, unlike responses in monogastric animals. The interesting species differences related to vitamin D metabolism might explain the greater capacity of goats to compensate for challenges of Ca homeostasis and should be further investigated.
在小型反刍动物中，钙（Ca）和磷（Pi）的肾脏排泄不会因饮食中钙的限制而受到调节。尽管在绵羊和山羊中均观察到这种缺乏适应性的情况，但不能排除这两个物种在肾功能上存在差异。最近的研究表明，与绵羊相比，山羊具有更强的能力来应对钙稳态的挑战，这可能是由于其骨化三醇产量的增加更为显著。因此，本研究的目的是考察以下因素对绵羊和山羊肾组织中钙和磷转运机制、受体以及参与维生素D代谢的酶的影响：1）饮食中钙的限制；2）骨化三醇的给药；3）泌乳。肾脏瞬时受体电位香草酸亚型5的RNA表达不受饮食中钙含量变化的影响，但在绵羊（P < 0.001）和山羊（P < 0.01）中，骨化三醇给药后均观察到显著刺激。在山羊中，饮食中钙限制期间钙结合蛋白-D28K表达下调（P < 0.05）。绵羊低钙摄入时钠/钙交换蛋白1的表达降低（P < 0.05），而山羊经骨化三醇处理后其表达上调（P < 0.05）。与干奶期动物相比，泌乳山羊胞质和基底外侧钙转运蛋白的RNA表达也显著降低。维生素D受体表达存在物种差异：骨化三醇处理可刺激绵羊的该受体表达（P < 0.01），但对山羊无此作用。正如预期的那样，饮食中钙限制可上调绵羊和山羊中1α-羟化酶的表达（P < 0.001；P < 0.05），而外源性骨化三醇则抑制其表达（P < 0.001；P < 0.05）。然而，在绵羊中，无论饮食如何，骨化三醇处理均能同等程度地刺激24-羟化酶表达（P < 0.001），而在山羊中，饮食中钙供应对24-羟化酶的诱导具有调节作用（P < 0.05）。综上所述，我们的结果证实了以下观察结果：与单胃动物的反应不同，在饮食供应受限期间，调节肾脏钙排泄无助于维持这些反刍动物的钙稳态。与维生素D代谢相关的有趣物种差异可能解释了山羊应对钙稳态挑战的能力更强，对此应进一步研究。
