In this task, you are given a sentence. You are expected to recognize the name of any form of chemical substances. Although there might be several correct answers, you need to write one of them.
Example: Inhibition of the human ether-a-go-go-related gene (HERG) potassium channel by cisapride: affinity for open and inactivated states. 
Example solution: potassium
Example explanation:  Potassium is a type of electrolyte mineral that helps our nerves to function and muscles to contract. Hence, it should be tagged as chemical.

Problem: Role of oestrogen receptors on the modulation of NADPH-diaphorase-positive cell number in supraoptic and paraventricular nuclei of ovariectomised female rats.

Solution: oestrogen