Down-regulation is
Downregulation: An decrease in the number of receptors on the surface of target cells, making the cells less sensitive to a hormone or another agent Downregulation of receptors happens when receptors have been chronically exposed to an excessive amount of hormone Ref : Biochemistry by U. Satyanarayana 3rd edition Pgno : 428
Increased destruction of a hormone
Feed back inhibition of hormone secretion
Decreased concentration of a hormone in blood
Decrease in number of receptors for a hormone
vitamins