EFFECTS OF PROTEOLYTIC-ENZYME INHIBITORS ON NASAL ABSORPTION OF SALMON-CALCITONIN IN RATS

Proteolytic enzyme inhibitors were examined as absorption enhancers fo r the nasal absorption of salmon calcitonin (SCT) in rats. Bestatin, d iprotinin, leupeptin, aprotinin, soybean trypsin inhibitor and camosta t mesilate were used as enzyme inhibitors. The nasal absorption of SCT was evaluated by measuring its hypocalcemic effects. The peptidase ac tivities of rat nasal mucosal tissue were high and found to be in the following order: leucine aminopeptidase (2.72 nmol/min per mg protein) > dipeptidyl aminopeptidase (1.84 nmol/min per mg protein) > cathepsi n (650 pmol/min per mg protein)> trypsin.(4.61 pmol/min per mg protein ). Nasal administration of SCT (10 IU/kg, pH 7.0) showed low pharmacol ogical availability (3.2%). Coadministration with bestatin (aminopepti dase inhibitor, 0.01-1 mM) or diprotinin A (dipeptidyl peptidase inhib itor, 0.1-1 mM) did not change the hypocalcemic effects. Coadministrat ion with aprotinin (trypsin inhibitor, 10(3)-10(4) KIU/ml), camostat m esilate (aminopeptidase and trypsin inhibitor, 0.1-10 mM) or leupeptin (trypsin and cathepsin B inhibitor, 0.1-1 mM) enhanced the hypocalcem ic effects and, thus, the nasal absorption of SCT. The hypocalcemic ef fects of SCT at various pH values (pH 4.0, 7.0 and 8.0) with or withou t aprotinin were the highest at pH 4.0. The pharmacological availabili ties after nasal administration of SCT (10 IU/kg) at pH 4.0 and 7.0 we re increased from 5.4 to 7.5% and from 3.2 to 6.9% by aprotinin (10(4) KIU/ml), respectively. Therefore, inhibitors which have a trypsin inh ibitory activity are useful for enhancing nasal absorption of SCT.