Endocrine Abstracts

The goal of this study was to determine whether orexin affects GnRH and LH secretions in the prepubertal rats fed normal or restricted diets. Forty prepubertal rats were randomly divided into 4 groups. Animals in groups 1 and 2 were fed normal and animals in groups 3 and 4 were fed restricted diet for 10 days. After 10 days, animals in groups 1 and 3 received infusions of 1 ug orexin and groups 2 and 4 received infusions of 2 ug orexin into their third ventricle. Blood samples were collected from jugular veins, every 30 min from 4 h before the first infusion of orexin until 4 h after the last orexin infusion. Restricted diet and infusions of 1 and 2 ug orexin significantly (P<0.01) decreased the mean plasma concentrations and pulse amplitudes of GnRH and LH. Infusion of 1 and 2 ug orexin did not change the secretions of GnRH and LH of the animals fed normal diet. Infusions of 1 and 2 μg, orexin significantly (P<0.01) decreased the glucose levels of the animals fed restricted but not in normal diet fed animals. Additionally, plasma glucose levels of the restricted fed animals in groups 3 and 4 were significantly (P<0.01) lower than those of the animals fed normal diet. The results of this experiment indicated that orexin may negatively affect the GnRH and LH in the prepubertal rats with negative energy balance, but not in those with the positive energy balance.