Summary
The aim of the study was to assess the involvement of the adenylate cyclase system in calcitonin (CT) secretion from thyroidal C-cells. The cAMP analogues Br-cAMP (10-6 and 10-4 mol/l) and DB-cAMP (10-4 mol/l) and the activators of adenylate cyclase cholera toxin (0.1 μg/ml and 5μg/ml) and forskolin (10-7 mol/l and 10-5 mol/l) were infused for 6 min periods in perfused dog thyroid lobes. CT was measured in thyroid effluent by radioimmunoassay. Br-cAMP and cholera toxin did not alter basal CT secretion. DB-cAMP had a minimal stimulatory effect and forskolin 10-5 mol/l a moderate stimulatory effect. This was much less than the effect of increasing perfusate Ca++ from 1.5 to 2.0 mmol/l. 10-4 mol/l Br-cAMP increased the response to Ca++ with approximately 50 per cent.
These results suggest that the activity of the adenylate cyclase system of the C-cells by itself is of little importance for CT secretion, but that it may have a role as modulator of the response to Ca++.
Key-Words
Cyclic AMP
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Forskolin
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Cholera Toxin
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Calcium
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C-Cells
