In ovarian cycle increased levels of LH are due to :

Luteinising Hormone LH is a water-soluble glycoprotein of high molecular weight secreted by beta cells of the anterior pituitary gland LH surge initiated by estrogen lasts for 48 h. LH level doubles up in 2 hrs and peak plateaus for 14 hours before declining. Minimum of 75 ng/ml is required for ovulation Ref: Shaw's Textbook of Gynaecology, 16th edition, page no: 39