Cholinergic and α-Adrenergic Stimulation of Prostaglandin Release by Dog Thyroid in Vitro*

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Abstract
Dog thyroid slices released in their incubation medium prostaglandins E2 (PGE2), F2a, (PGF2a), 15-keto-13,14-dihydro-F2a, and thromboxane B2 (TxB2), as measured by direct RIA. This release could be inhibited by indomethacin and naproxen, indicating that it corresponded to a neosynthesis. Carbamylcholine (2-100μM) stimulated the release of PGE2, PGF2a, and TxB2, whereas epinephrine (20 μM to 1 mM) enhanced the release of PGE2 and PGF2a(, but had no effect on TxB2. These stimulations were inhibited by atropine and dihydroergocryptine, respectively, suggesting that a muscarinic and an α-adrenergic receptor were involved. The ionophore A23187 reproduced these stimulations, and the stimulatory effects of carbamylcholine and epinephrine were inhibited in the absence of exogenous Ca++ and after EGTA depletion. Ca++ thus appears as a major regulator of PG production in the thyroid. TSH (0.06-10 mU/ml) and dibutyryl cAMP had no effect on the release of PGE2, PGF2a, or TxB2 by dog thyroid in vitro.