Effect of Stress Induced by Epinephrine and Cortisol Injection on Orexin Secretion in Male Rats Fed with Different Levels of Their Energy Requirement

Orexin is a potent orexigenic agent in rodents and humans. Some research shows that orexin participates in the adaptive response to weight loss and its levels rise with dieting. On the other hand, weight loss and fasting is accompanied by increased levels of epinephrine and cortisol. In this study we investigated the effects of epinephrine (EN) and cortisol on fasting-induced orexin secretion in rats fed different levels of their energy requirements.

Forty-five male wistar rats (300-350 g, 15 per group) were fed a diet containing 100%, 50% and 25% of their energy requirement for 10 days, rats were anesthetized following 48 hour prolonged fasting and then cannulated in the carotid artery for drug injection and blood sampling. Animals were divided into 3 treatment groups that received either (3 µg/Kg BW) EN, cortisol or a combination of those two (0.1 mg in 1 ml of PBS). Orexin and glucose levels were analyzed before (time 0), and 30, 60 and 120 min after injection.

In the 50% and 100% food restricted groups, fasting orexin levels fell after EN and the combination of EN and cortisol injection respectively (p≤0.05). In contrast, the group that had 25% food restriction showed no response to cortisol, EN or the combination of both (p>o.o5).

These results indicate that injection of EN suppresses starvation-induced secretion of orexin in normal (100%) and starved (50%) rats, and that orexin secretion response to EN might be affected by weight loss.