The effect of parathyroid hormone (PTH) on transepithelial Na+, Cl-, K+, Ca2+ and Mg2+ transport was investigated in isolated perfused cortical thick ascending limbs (cTAL) and that of human calcitonin (hCT) was tested in both cortical and medullary thick ascending limbs (mTAL) of the mouse nephron. The transepithelial ion net fluxes (Jx) were determined by electron probe analysis of the perfused and collected fluids. Simultaneously, the transepithelial voltage (PDte) and resistance (Rte) were recorded. In cTAL segments, PTH and hCT significantly stimulated the reabsorption of Na+, Cl-, Ca2+ and Mg2+, hCT generated a net K+ secretion towards the lumen and PTH tended to exert the same effect. Neither PDte nor Rte were significantly altered by either PTH or hCT. However, in the post-experimental period a significant decrease in PDte was noted. Time control experiments carried out under similar conditions revealed a significant decrease in PDte with time, which could have masked the hormonal response. In mTAL segments, Mg2+ and Ca2+ transport was close to zero, hCT did not exert any detectable effect on either PDte or Jcl-, JNa+, JK+, JMg2+ and JCa2+ in these segments. In conclusion, our data demonstrate that PTH and hCT stimulate NaCl reabsorption as well as Mg2+ and Ca2+ reabsorption in the cTAL segment of the mouse. These data are in agreement with and extend data obtained in vivo in the rat.

The effect of antidiuretic hormone (arginine vasopressin, AVP) on transepithelial Na+, Cl-, K+, Ca2+ and Mg2+ net transports was investigated in medullary (mTAL) and cortical (cTAL) segments of the thick ascending limb (TAL) of mouse nephron, perfused in vitro. Transepithelial net fluxes (JNa+, JCl-, JK+, JCa2+, JMg2+) were determined by electron probe analysis of the collected tubular fluid. Transepithelial potential difference (PDte) and transepithelial resistance (Rte) were measured simultaneously. cTAL segments were bathed and perfused with isoosmolal, HCO3- containing Ringer solutions, mTAL segments were bathed and perfused with isoosmolal HCO3- free Ringer solutions. In cTAL segments, AVP (10(-10) mol.l-1) significantly increased JMg2+ and JCa2+ from 0.39 +/- 0.08 to 0.58 +/- 0.10 and from 0.86 +/- 0.13 to 1.19 +/- 0.15 pmol.min-1 mm-1 respectively. Neither JNa+ nor JCl-, (JNa+: 213 +/- 30 versus 221 +/- 28 pmol.min-1 mm-1, JCl-: 206 +/- 30 versus 220 +/- 23 pmol.min-1 mm-1) nor PDte (13.4 +/- 1.3 mV versus 14.1 +/- 1.9 mV) or Rte (24.6 +/- 6.5 omega cm2 versus 22.6 +/- 6.4 omega cm2) were significantly changed by AVP. No significant effect of AVP on net K+ transport was observed. In mTAL segments, Mg2+ and Ca2+ net transports were close to zero and AVP (10(-10) mol.l-1) elicited no effect. However NaCl net reabsorption was significantly stimulated by the hormone, JNa+ increased from 107 +/- 33 to 148 +/- 30 and JCl- from 121 +/- 33 to 165 +/- 32 pmol.min-1 mm-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucagon-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity was measured in nine different portions of the rat nephron. Each sample contained a single piece of tubule isolatedby microdissection from collagenase-treated kidney tissue. As compared to basal activity, 1 &M porcine glucagon stimulated adenylate cyclase 60-fold in the medullary prtion and 40-fold in the cortical portion of the thick ascending limb, 23-fold in the early distal convoluted tubule, I1-fold in the cortical collecting tubule, and 8-fold in the medullary collecting tubule. No stimulation was observed in proximal tubules and thin segments of the loop of Henle. Half-maximal stimulations were obtained with about 10 nM glucagon in the responsive nephron portions.Available evidence indicating that glucagon might exert direct regulatory actions on kidney functions in mammals is still equivocal. When administered intravenously in vivo, glucagon has often been found to increase electrolyte (mainly sodium) and water output in urine (1). However, pharmacological doses of glucagon were generally used in these studies, and the effects noted on urine excretion might have resulted from changes in renal blood flow and glomerular filtration rate. In vitro, glucagon has been found to stimulate adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity when added to membrane fractions prepared from kidney tissue homogenates (2-5). However, this stimulatory action was always of limited magnitude and, when tested, the sensitivity of the enzyme to low glucagon concentrations was rather poor compared to the values obtained in cell membrane fractions from the liver. The kidney, therefore, is generally not considered to be a target organ for glucagon. We reinvestigated this problem in the rat by using a micromethod developed in our laboratory (6-8) that allows hormone-dependent adenylate cyclase activity to be measured in samples containing single well-localized pieces of tubule isolated by microdissection from collagenase-treated kidneys. We found that the adenylate cyclase present in the distal nephron portions-i.e., the distal and collecting tubules-is highly responsive to glucagon, with a sensitivity similar to that of hepatocytes.MATERIALS AND METHODS Fed, adult Wistar rats (216 4 9 g body weight) were anesthetized (Nembutal,5

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.

The effects of glucagon and PTH on electrolyte reabsorption in the distal tubule were investigated in rats deprived of vasopressin, calcitonin, PTH, and glucagon. Micropunctures of distal tubule, at a late and an early site of a same nephron, have been performed in 23 rats, nine control, seven infused with glucagon (5 ng X min-1 X 100 g-1 b.w.) and seven with PTH (5 mU X min-1 X 100 g-1 b.w.). The Ca and Mg reabsorptive capacity of the distal segment was increased by glucagon and by PTH. Moreover, fractional Na and Cl reabsorption was significantly higher than in control during PTH administration. A K secretion appeared during the administration of both hormones. No phosphate net transport was observed in any group. Finally, the data presented here, together with those previously reported, indicate that the increase of Ca and Mg renal reabsorption observed with glucagon and PTH results from an effect located in both Henle's loop, where the bulk of Ca and Mg is reabsorbed, and the distal tubule.