Intranasal insulin boosts gustatory sensitivity

Abstract

Intranasal insulin had been in the spotlight not only for enhancing memory processes but also for its anorexic effects, as well as its effects on olfactory sensitivity. Here, the influence of intranasal insulin on gustatory sensitivity was investigated using intranasal applications of insulin or placebo in a double-blind manner alongside a control condition without any application.

We hypothesized that intranasal insulin, as it mediates satiety, alters gustatory sensitivity whereas placebo application and control should not alter gustatory sensitivity. We did not expect the sensitivity to the different taste solutions to differ. Sweet, salty, bitter and sour liquids in four different concentrations were sprayed on the tongue of healthy male subjects. Additionally, non-tasting water was applied to be able to calculate taste sensitivity referring to the parameter d prime (d') of the signal detection theory (SDT). The task of the subject was to identify the quality of the respective tastant. Gustatory sensitivity as well as blood parameters were evaluated using repeated-measures ANOVAs.

Gustatory sensitivity, implying all tastants, improved significantly following intranasal insulin application compared to application of placebo, but did not reach significance compared to the control condition. Subjects performed best in detecting the sweet taste and worst in detecting the bitter taste. The blood parameters glucose, insulin, HOMA and leptin did not differ with respect to insulin or placebo condition, nor did they differ regarding measurements preceding or following intranasal application, proving peripheral euglycaemia during the experiment. Thus, it can be concluded that application of intranasal insulin in comparison to placebo led to an improved gustatory sensitivity.

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