An elderly person becomes confused and takes an overdose of a medication designed to block both cholesterol uptake from the GI tract and cholesterol synthesis by all cells.After 24 hours,the individual is severely hypocholesterolemic (i.e.,has very low levels of circulating cholesterol).This effect is transient: as the effects of the drug wear off,hormone levels rebound.Which of the following is most responsible for stability of hormone levels in this situation?