Presence of insulin-like immunoreactivity and its biosynthesis in rat and human parotid gland.

Extracts from homogenates of rat and human parotid glands contained insulin-like immunoreactivity. The values were 5.6 +/- 2.8 ng/g wet tissue in six groups of rat parotid glands and 23.8 and 39.7 ng/g wet tissue in two human extracts. Upon gel filtration immunoreactive insulin of rat origin was eluted in a peak corresponding to the elution volume of isotopically labelled insulin. The material obtained from the two peak fractions showed an immunoassay dilution curve identical with that of rat insulin. Furthermore, biosynthesis of insulin-like immunoreactivity in rat and human parotid glands was confirmed in vitro by a specific separation method using anti-insulin antibody. These findings suggest that the parotid gland may be a further extrapancreatic source of insulin, and that insulin biosynthesis does occur in extrapancreatic tissues.