EVALUATION OF THE MOLECULAR AND CELLULAR BASIS FOR THE MODULATION OF THYROID C-CELL HORMONES BY AGING AND FOOD RESTRICTION

Male F344 rats fed ad libitum or maintained on 60% of the ad libitum f ood intake were sacrificed at 6, 12, 18 and 24 months of age. The thyr oids were removed for the analysis of the C-cell hormones, calcitonin, calcitonin gene-related peptide (CGRP) and somatostatin. In the anima ls fed ad libitum, the peptide content of all three hormones and their mRNA pools increased significantly with age. The increases were marke dly suppressed by food restriction. Similarly, the rate of mRNA synthe sis of the hormones increased with age and was attenuated by food rest riction. Calcitonin and CGRP containing cells increased in number with age in the ad libitum fed animals. In the food restricted animals the numbers of calcitonin positive cells were consistently but not signif icantly lower than those of ad libitum fed animals at similar ages. In the case of CGRP containing cells, their numbers were significantly l ower in the food restricted than in the ad libitum fed animals from 18 months of age. Our findings indicate that aging and food restriction modulate the levels of the thyroidal C-cell hormones at the levels of cell proliferation and possibly gene transcription.