This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following is not the action of calcitriol? 
Select and explain. 
A. Calcitriol increases the intestinal absorption of calcium, B. Calcitriol stimulates  calcium uptake  for deposition  as calcium phosphate in the osteoblasts  of bone, C. Calcitriol increases the excretion of calcium and phosphate  through the kidney, D. Calcitriol  action  is  similar  to  steroid hormones
C: Calcitriol increases the excretion of calcium and phosphate  through the kidney
Answer: C: Calcitriol increases the excretion of calcium and phosphate  through the kidney 
Explanation: Calcitriol increases the intestinal absorption of calcium and phosphate. 
In the osteoblasts of bone,  calcitriol stimulates calcium uptake for deposition as calcium phosphate, Thus calcitriol is essential  for bone formation. 
Calcitriol is also involved in minimizing the excretion of calcium and phosphate through the kidney, by decreasing their excretion' and enhancing reabsorption.  
Calcitriol action is similar to steroid hormones. lt binds to a receptor in the cytosol and the complex  acts on DNA to stimulate the synthesis of calcium binding protein.

Reference: Satyanarayana- Biochemistry, 3rd edition, pg-125