Stimulation of the Adenyl Cyclase-Cyclic AMP System in the Thyroid of the Rat1

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Abstract
Adenyl cyclase activity was measured in thyroid homogenates from rats fed Purina, Purina + 0.1% propylthiouracil, Purina + 0.066% thyroid USP or low—iodine diet; a month or more of goitrogenic diet led to an increase in enzyme activity and thyroid USP to a decrease. Propylthiouracil or low—iodine diet, after one month, resulted in increase in the thyroid concentration of cyclic AMP to a maximum of 2-fold. Both thyrotropin (5–2 SO mU per ml) and prostaglandin E1 (1–100 ¼M) in vitro increased adenyl cyclase activity in thyroid homogenates, but no more than 50% over control values. On the other hand, these agents increased the concentration of cyclic AMP in thyroid lobes incubated for 10 min in buffer with 10 mM theophylline. Similarly 50 mU thyrotropin iv led to an increased concentration of cyclic AMP within 5 min. Since we previously showed goitrogenic diet enhanced thyroid phosphodiesterase activity, the data presented here from dietary experiments suggest that chronic hypersecretion of thyrotropin results in an increased rate of turn—over of cyclic AMP as well as an enhanced concentration of the nucleotide. (Endocrinology92: 1349, 1973)

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