By Megan Rauscher

NEW YORK (Reuters Health) Mar 07 - Insulin administered intranasally acutely decreases food intake in men but not in women; on the other hand, it acutely improves memory function in women but not in men, investigators observed in a small study.

"Our findings indicate that gender is a critical factor in brain insulin signaling that affects both food intake and cognitive functions," study investigator Dr. Christian Benedict of the University of Lubeck, Germany told Reuters Health.

The findings further suggest that intranasal insulin "may be helpful in the treatment of cognitive and metabolic disorders like Alzheimer's disease and obesity that are assumed to derive at least in part from malfunctions of central nervous insulin signaling," Dr. Benedict said.

Central nervous insulin is critically involved in the regulation of body weight and memory formation, the investigators point out in the February issue of the Journal of Clinical Endocrinology and Metabolism.

Dr. Benedict's team assessed the effects of a single intranasal dose (160 IU) of regular human insulin or vehicle on food intake and memory processing in 32 healthy, normal-weight men and women. "Because intranasal insulin reaches the brain but bypasses the circulation, it's possible to assess insulin effects on the central nervous system without affecting blood glucose levels," Dr. Benedict explained.

Insulin, given just before a buffet breakfast, decreased food intake in men but not in women, the investigators observed. The difference in intake relative to placebo was -192.57 kcal (p < 0.03) in men and 18.54 kcal in women (p > 0.67).

In contrast, memory and working memory improved in women (p < 0.03 and 0.05, respectively) whereas men did not benefit from intranasal insulin.

Mirroring animal data, the current results suggest that men are more sensitive than women to the acute anorexigenic effect of central nervous insulin signaling whereas women are more sensitive to insulin's memory improving effects, the investigators say.

"Importantly," Dr. Benedict noted, "gender differences will have to be considered in the possible future development of intranasal insulin therapeutics."

J Clin Endocrin Metab 2008.