Modulation of renal calcium and phosphate transporting proteins by dietary nitrogen and/or calcium in young goats

J Anim Sci. 2018 Jul 28;96(8):3208-3220. doi: 10.1093/jas/sky185.

Abstract

In young goats, a reduction in dietary nitrogen (N) had an impact on mineral homeostasis although ruminants are able to recycle N effectively due to rumino-hepatic circulation. A solitary calcium (Ca) reduction stimulated calcitriol synthesis and Ca concentrations remained unchanged, whereas a dietary N reduction led to a decrease in calcitriol, which could not be prevented by a simultaneous reduction of N and Ca. In a previous study, it was shown that a reduced dietary N intake caused a decrease in intestinal Ca absorption due to a reduction of intestinal Ca transporting proteins. As no data on the potential role of the kidneys are available, it was the aim of the present study to evaluate whether an N- and/or Ca-reduced diet had an impact on renal Ca and phosphate (Pi) transporting protein expression in young goats. The animals were divided into 4 feeding groups, each receiving an adequate N and Ca supply, a reduced N supply, a reduced Ca supply, or a combined N and Ca reduction for 6 to 9 wk. The protein expression of the renal Ca channel transient receptor potential cation channel subfamily V member 5 (TRPV5) was diminished in N-reduced fed goats (P = 0.03), whereas in Ca restricted animals, the expression remained unaltered. The mRNA and protein expression of the Ca-binding protein calbindin-D28K (CaBPD28K) and the sodium-Ca exchanger 1 (NCX1) were significantly decreased due to the N-reduced feeding (mRNA, P = 0.003; P < 0.0001; protein, P = 0.002; P = 0.02), whereas dietary Ca reduction increased the CaBPD28K and NCX1 mRNA expression (P = 0.05; P = 0.01). The mRNA and protein expression of the parathyroid hormone receptor (PTHR) decreased due to the N-reduced feeding (P = 0.02; P = 0.03). These results confirm that a reduced dietary N intake led to decreased TRPV5, CaBPD28K, PTHR, and NCX1 expression levels, contributing to low levels of calcitriol and plasma Ca. In contrast to this, sodium-phosphate cotransporter type IIa expression and plasma Pi concentration were increased during dietary N reduction, thus indicating that Pi homeostasis is modulated in a calcitriol-independent manner. In conclusion, the modulation of Ca transporting proteins expression in the kidney is not able to prevent changes in mineral homeostasis in young goats receiving an N-reduced diet.

MeSH terms

  • Animals
  • Biological Transport
  • Calcitriol / metabolism*
  • Calcium, Dietary / metabolism*
  • Goats / metabolism*
  • Homeostasis
  • Intestinal Absorption
  • Intestinal Mucosa / metabolism
  • Kidney / metabolism
  • Male
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Nitrogen / metabolism*
  • Phosphate Transport Proteins / genetics
  • Phosphate Transport Proteins / metabolism
  • Phosphates / metabolism
  • Receptor, Parathyroid Hormone, Type 1 / genetics
  • Receptor, Parathyroid Hormone, Type 1 / metabolism
  • Receptors, Calcium-Sensing / genetics
  • Receptors, Calcium-Sensing / metabolism
  • Sodium-Calcium Exchanger / genetics
  • Sodium-Calcium Exchanger / metabolism

Substances

  • Calcium, Dietary
  • Membrane Transport Proteins
  • Phosphate Transport Proteins
  • Phosphates
  • Receptor, Parathyroid Hormone, Type 1
  • Receptors, Calcium-Sensing
  • Sodium-Calcium Exchanger
  • sodium-calcium exchanger 1
  • Calcitriol
  • Nitrogen