Isoproterenol Increases Ca, Mg, and NaCl Reabsorption in Mouse Thick Ascending Limb

The effect of isoproterenol (Iso) on tubular transport in the thick ascending limb of Henle's loop (TAL) was investigated by in vitro microperfusion of MTAL (medullary) and CTAL (cortical) from White Swiss mouse kidney. The pattern of activation of adenylate cyclase along the distal tubule was investigated in this strain: results indicated that Iso stimulated adenylate cyclase fivefold in MTAL and ninefold in CTAL. Data from microperfusion experiments showed that Iso (10(-7) M in the bath) significantly and reversibly increased Ca and Mg reabsorption in CTAL. No net transport of Ca and Mg was observed in MTAL whether Iso was present or not. With regard to Na and Cl, Iso significantly stimulated their reabsorption in both segments and increased the transepithelial voltage in MTAL. Iso abolished K reabsorption in MTAL and induced a net K secretion in CTAL, the latter effect being also observed with 10(-9) M of Iso. When applied on CTAL, propranolol (10(-6) M in the bath) inhibited all these effects. These data indicate that beta-adrenergic agonists are involved in the multihormonal modulation of the TAL function.