THE ANTIDIURETIC ACTION OF HYDROCHLOROTHIAZIDE IN THE HYDRATED RAT

Selective pharmacological modulation of renal peripheral-type benzodiazepine binding by treatment with diuretic drugs

We have assessed the effects of in vivo administration of different classes of diuretic drugs on the expression of the peripheral-type benzodiazepine binding site (PBBS) in crude membranes derived from the cortex and outer medulla of rat kidney by saturation analysis with the PBBS-selective ligands [3H]RO5-4864 and [3H]PK 11195 in cortex and [3H]RO5-4864 in outer medulla. Administration for 14-15 days of furosemide, a drug that blocks NaCl-KCl coupled transport in the thick ascending limb of the loop of Henle, produced a significant doubling in the PBBS density (Bmax) in outer medulla, a region of the kidney rich in thick ascending limbs, and produced a lesser but significant increase in PBBS density in the cortex. Conversely, administration for 14-15 days of the carbonic anhydrase inhibitor acetazolamide, which acts predominantly in the proximal tubule, and hydrochlorothiazide, which acts predominantly in the early distal tubule, elicited statistically significant increases in PBBS density in renal cortex but not in renal outer medulla. Furthermore, all drug treatments were without effect on the equilibrium dissociation constants (Kds) of [3H]RO5-4864 and [3H]PK 11195 binding to cortical and outer medullary membrane preparations. These findings demonstrate that the PBBS can be selectively "up-regulated" in different regions of the kidney by diuretic drugs with different modes/sites of action.

Micropuncture study of diuretic effects on sodium and calcium reabsorption in the dog nephron

A close relationship has been observed between the clearance rates of sodium and calcium under a variety of diuretic conditions. The thiazide diuretics act differently in dissociating the renal tubular reabsorption of sodium and calcium. This phenomenon has been further investigated using recollection micropuncture and clearance techniques in a group of 14 dogs subjected to three consecutive experimental phases: expansion to 3% of body weight (BWt) with Ringer's solution, chlorothiazide infusion at 20 mg/kg/h, and furosemide in a prime of 10 mg/kg/ and a 10 mg/kg/h infusion. Diuretic losses were balanced with infusion of equal volumes of Ringer's solution throughout the experiment. Chlorothiazide increased the fractional excretion (FE) of sodium almost threefold while FE(Ca) was not significantly altered. Furosemide increased FE(Na) and FE(Ca) to an approximately equal, and more marked, degree. This dissociation of sodium and calcium reabsorption after chlorothiazide was also evident in the superficial distal tubule, where (tubule fluid/plasma sodium) (TF/P(Na)) increased from 0.32 to 0.49 (P < 0.01) and TF/(ultrafiltrate)UF(Ca) was unchanged (0.35-0.31). Furosemide markedly reduced the transtubular concentration gradient for both sodium (0.86) and calcium (0.94). TF/P(Inul in) decreased progressively from 3.79 to 2.78 to 2.33 in three phases. In the late proximal tubule, chlorothiazide induced a fall of TF/P(Inul in) from 1.57 to 1.44 (P < 0.01), but the ratio TF/UF(Ca): TF/P(Na) was unchanged. Furosemide had no significant proximal effect. It is concluded that acute administration of chlorothiazide reduces sodium reabsorption in the distal hephron, presumably the cortical diluting segment, without affecting calcium reabsorption.

The effects of urea and hydrochlorothiazide on the renal functions of rat and domestic fowl

1. Rats and domestic fowls were given by stomach tube water, urea and hydrochlorothiazide, alone or in combination, in the following amounts: water, 5 ml./100 g; urea, 4 ml. of 1.5% solution + 1 ml. water/100 g; hydrochlorothiazide, 4 ml. of 1.5% urea solution + 1 ml. containing 0.1 mg hydrochlorothiazide/100 g.2. The onset of water diuresis was faster in the fowl than in the rat. It was accompanied by a lower rate of excretion of osmotically active solutes in the former than in the latter. The rate of excretion of creatinine in rats was fourfold that in birds.3. After urea administration, the amount of urea excreted by the fowl was about one fifth that excreted by the rats. While urea produced in rats an osmotic diuresis, with enhanced excretion of osmotically active solutes, in birds it had little effect on either urine flow or solutes excretion.4. Administration of hydrochlorothiazide in rats produced a moderate antidiuresis accompanied by a marked increased excretion of Na and K; in birds, a small increase in the excretion of Na and K but no effect on the urine flow.5. The differences observed between rats and birds can be attributed to the poor development of filtration rate and the absence of a well developed counter-current system in the fowl.