Orexin deficiency modulates the dipsogenic effects of angiotensin II in a sex-dependent manner.

The orexin (hypocretin) neuropeptide system is an important regulator of ingestive behaviors, i.e., it promotes food and water intake. Here, we investigated the role of orexin in drinking induced by the potent dipsogen angiotensin II (ANG II). Specifically, male and female orexin-deficient mice received intracerebroventricular (ICV) injections of ANG II, followed by measuring their water intake within 15min. We found that lower doses of ANG II (100ng) significantly stimulated drinking in males but not in females, indicating a general sex-dependent effect that was not affected by orexin deficiency. However, higher doses of ANG II (500ng) were sufficient to induce drinking in female wild-type mice, while female orexin-deficient mice still did not respond to the dipsogenic properties of ANG II. In conclusion, these results suggest sex-dependent effects in ANG II-induced drinking and further support the sexual dimorphism of orexin system functions.