DIFFERENTIAL-EFFECTS OF THYROID-HORMONE ON RENIN SECRETION, CONTENT, AND MESSENGER-RNA IN JUXTAGLOMERULAR CELLS

The effects of thyroid hormone on renin secretion, renin content, and renin mRNA levels in juxtaglomerular (JG) cells harvested from rat kid neys were determined by radioimmunoassays and reverse transcriptase-po lymerase chain reaction. Despite a lack of immediate effect, incubatio n with triiodothyronine dose dependently increased renin secretion dur ing the first 6 h and elevated renin content and renin mRNA levels dur ing the subsequent period. Simultaneous incubation with triiodothyroni ne and the calcium ionophore A-23187 abolished the increase in renin s ecretion and attenuated the increase in renin content but did not affe ct the increase in renin mRNA levels. During simultaneous incubation w ith triiodothyronine and the adenylate cyclase inhibitor SQ-22536 or m embrane-soluble guanosine 3',5'-cyclic monophosphate (cGMP), the incre ases in renin secretion, content, and mRNA were similar to those obser ved in the presence of triiodothyronine alone, except for a cGMP-induc ed attenuation of the increase in renin secretion. These findings sugg est that thyroid hormone stimulates renin secretion by JG cells throug h the calcium-dependent mechanism, whereas the stimulation of renin ge ne expression by thyroid hormone does not involve intracellular calciu m or cyclic nucleotides.