Solid-Phase Radioimmunoassay of Tonin in Extracts of Submandibular Glands of Rats Treated Chronically with Isoproterenol

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Abstract
Tonin, a proteolytic enzyme isolated from rat submandibular gland, can generate angiotensin II directly from angiotensin I, from angiotensin I-tetradecapeptide, and from angiotensinogen. A sensitive and specific solid-phase radioimmunoassay for measurement of tonin concentration and a method for measurement of tonin activity have been developed. Excellent correlation (coefficient r = 0.95) was found between the two methods. Tonin concentration and activity were studied in submandibular glands of rats chronically treated with isoproterenol. Almost complete depletion of tonin in rat submandibular gland was observed after 33 days of treatment. This observation was confirmed by polyacrylamide gel electrophoresis of homogenates of rat submandibular gland and immunocytochemistry. The immunocytochemical study revealed the presence of tonin in the cells of the granular convoluted tubules.