Abstract
Thyrotropin (TSH) regulation of atrial natriuretic factor (ANF) receptors was studied in the rat thyroid follicular cell line, FRTL-5. Exposure of FRTL-5 cells to 1 mU/ml TSH for 7 days resulted in a tenfold increase in ANF receptors ( B max = 188 fmol/mg protein) compared with control ( B max = 18 fmol/mg protein), without affecting binding affinity. An identical treatment of porcine thyrocytes with TSH resulted in a 50% decrease in ANF binding sites. Displacement binding studies indicated that > 80% of the ANF receptors in FRTL-5 cells belong to the ANF-R 1 (guanylate cyclase-coupled) receptor subtype. By contrast, > 98% of the ANF receptors in porcine thyrocytes were of the ANF-R 2, or clearance, receptor subtype. Intracellular cGMP content was increased thirty-sixfold in FRTL-5 cells by 1 μ M ANF, but only 2.5-fold in procine thyrocytes. cAMP levels were unaffected by ANF in either cell type. Northern blot analysis of poly A mRNA extracted from FRTL-5 cells incubated 2 days in the presence of 100 n M ANF indicated a twofold increase in thyroglobulin mRNA content compared with control. These findings suggest that the ANF-R 1 receptor, preferentially expressed in FRTL-5 cells and regulated by TSH, might play a role in regulating thyroid hormone production.
Published Version
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