Tumor Growth and Calcitonin during Serial Transplantation of Rat Medullary Thyroid Carcinoma*

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Abstract
We have recently reported immunochemical methods for the measurement and purification of rat calcitonin (CT). To identify a convenient source of CT-producing cells for studies of rat CT biosynthesis, we have propagated 16 transplantable series of medullary thyroid carcinoma (MTC) from 2 types of WAG/Rij rat MTC from The Netherlands. Tumor CT concentrations and growth and plasma CT accumulation were studied in successive transplant generations of each MTC series. Although most MTC series maintained characteristic predictable tumor CT levels, some MTC series acquired nearly 90% lower CT levels. While related MTC series tended to maintain similar predictable growth rates, several spontaneous and propagatable increases (up to 5-fold) in tumor growth rates were noted. These increases occurred with and without concomitant decreases in tumor CT. Tumor CT production ranged over 20- fold among these 16 MTC series. Serial plasma CT analyses can be used to estimate tumor growth and CT production in live MTC rats. Using serial plasma CT analyses, we can select for serial transplantation tumors with specific growth and CT characteristics. This should facilitate propagation of MTC series needed for particular studies of CT production and cancer.