<prompt> Impoant difference between leuprolide and ganirelix is that ganirelixCan be given orallyImmediately reduces gonadotropin secretionMust be given in a pulsatile fashionInitially stimulates release of LH and FSH  <response>: Superactive long-acting GnRH agonists Many analogues of GnRH, e.g. Goserelin, Leuprolide,Nafarelin, Triptorelin, have longer action t 12 2-6 hours because of high affinity for GnRH receptor and resistance to enzymatic hydrolysis. Because physiological release of GnRH is in pulses, whereas these agonists act continuously; they only initially increase Gn secretion. After 1-2 weeks they cause desensitization and down regulation of GnRH receptors -inhibition of FSH and LH secretion - suppression of gonadal function. GnRH antagonists:- Some more extensively substituted GnRH analogues act as GnRH receptor antagonists. They inhibit Gn secretion without causing initial stimulation. The early GnRH antagonistsLeuprolide, gosereline etc.had the limitation of producing reactions due to histamine release. Later agents like ganirelix and cetrorelix have low histamine releasing potential and are being clinically used. Ref :- kd tripathi; pg num:-242,243 