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: Gynaecology & Obstetrics
Lactational amenorrhea is due to : 
Select and explain. 
A. Prolactin induced inhibition of GnRH, B. Prolactin induced inhibition of FSH, C. Oxytocin induced inhibition of GnRH, D. All
A: Prolactin induced inhibition of GnRH
Answer: A: Prolactin induced inhibition of GnRH 
Explanation: Ans. is a i.e. Prolactin induced inhibition of GnRH In breast feeding females, prolactin levels are increased in response to suckling stimulus of breast feeding. Besides iProlactin, FSH concentrations are normal and LH concentrations are low. Despite the presence of gonadotropin the ovary during lactational hyperprolactinemia does not display follicular development and does not secrete estrogen. These observations suggest that high concentrations of prolactin can work at both central level (by inhibiting pulsatile secretion of GnRH) and peripheral level i.e. ovarian sites (by inhibiting synthesis of progesterone and by changing testosterone/dihydrotestosterone ratio i.e. increasing local anti estrogen concentrations) to produce lactational amenorrhea and anovulation. The principle of GnRH suppression by prolactin is reinforced by the demonstration that, treatment of amenorrheic, lactating women with pulsatile GnRH, fully restores pituitary secretion and normal ovarian cyclic activity.