Studies on the promoting effects of medium chain fatty acid salts on the nasal absorption of insulin in rats.

We investigated the promoting effect of medium chain fatty acid salts such as sodium caprylate, sodium caprate (Na C10) and sodium laurate on rat nasal absorption of insulin. Further, we studied the possible mechanism of the absorption promoting effect by fatty acid salts in terms of hemolytic activity, osmotic pressure, chelating effect and inhibition of leucine aminopeptidase activity. Na C10 exhibited the strongest absorption promoting effect on insulin among these fatty acid salts. The promoting effect of Na C10 was very rapid reaching the maximum immunoreactive insulin level within 5 min and its optimum concentration was about 1%. The amount of insulin absorbed after a nasal administration with Na C10 was about 98% of one half subcutaneous dose. The absorption promoting effect of fatty acid salts on insulin was at least in part associated with the chelating ability for calcium ions and the inhibitory action on leucine aminopeptidase activity.