Urine concentration in the rat during acute and prolonged dehydration

Natriuretic response of the rat to plasma concentrations of arginine vasopressin within the physiological range

The relationship of plasma vasopressin concentrations in the physiological range to renal electrolyte excretion was investigated. Unanaesthetized rats, when normally hydrated, were found to have a plasma vasopressin concentration of 1.13 +/- 0.15 mu u./ml. 16 h water deprivation raised this to 1.98 +/- 0.21 mu u./ml. Inactin-anaesthetized rats infused with 0.45% NaCl had a plasma vasopressin concentration of 1.19 +/- 0.18 mu u./ml. Administration of synthetic arginine vasopressin at 6 and 24 mu u./min raised plasma vasopressin levels to 1.88 +/- 0.17 and 4.26 +/- 0.43 microunits./ml respectively. In addition to the expected antidiuresis, vasopressin at a rate of 6 microunits./min also produced a highly significant increase in Na+ excretion from 8.9 +/- 0.6 to 10.5 +/- 0.6 mumol/min and Cl- excretion from 9.1 +/- 0.7 to 10.5 +/- 0.7 mumol/min. At 24 microunits./min it produced larger increases in Na+ and Cl- excretion. Inactin-anaesthetized hypophysectomized rats infused with 0.45% NaCl had a plasma vasopressin concentration of only 0.17 +/- 0.04 microunits./ml. Administration of vasopressin at 6 and 24 microunits./ml raised plasma vasopressin levels in these animals to 0.63 +/- 0.17 and 2.20 +/- 0.11 microunits./ml respectively. Hypophysectomized rats failed to exhibit a natriuresis in response to the lower dose of vasopressin, despite exhibiting an undiminished antidiuresis. The failure of the natriuresis may be related to the lower plasma vasopressin concentration achieved. It is concluded that in the rat plasma vasopressin concentrations within the physiological range do influence Na+ and Cl- excretion by the kidney as well as controlling urine flow rate.

Effects of lithium and neuroleptics and combinations of the two on renal function and structure in rats

The effects of 8 weeks of treatment with lithium and neuroleptics, alone and combined, on renal concentrating ability and morphology were studied in rats. LiCl was administered in the diet and neuroleptics were given as one daily dose: haloperidol 1 mg/kg, chlorpromazine 15 mg/kg, and perphenazine 4 mg/kg. Plasma lithium levels were about 1 mmol/l, and the area under the plasma concentration curve was not statistically different in the control and neuroleptic groups. Rats treated with lithium developed marked polyuria which was less in rats receiving neuroleptics concomitantly. After 8 weeks, rats treated with lithium alone showed marked impairment of renal concentrating ability and moderate degree of structural renal changes. Neuroleptics alone had no effect on concentrating ability or renal morphology, nor did they aggravate the changes caused by lithium. In fact, neuroleptics seemed to improve the concentrating ability in rats treated with lithium. It is concluded that in rats high doses of neuroleptics do not potentiate lithium-induced functional and structural renal changes.

The effect of vasopressin (Pitressin) administration and dehydration on the concentration of solutes in renal fluids of rats with and without hereditary hypothalamic diabetes insipidus

1. The method of sequential centrifugation has been used to obtain fluid samples from both the renal papilla and inner medulla of the rat.2. Experiments were carried out on Brattleboro rats with hereditary hypothalamic diabetes insipidus (DI; homozygous recessive), and on their (heterozygous) litter-mates with normal quantities of neurohypophysial vasopressin. Initial classification of the animals by measurement of urine volume and osmolality was confirmed by post-mortem bio-assay of the pituitary glands, in thirty-five out of forty-seven animals.3. In rats with DI, urine osmolalities comparable to those of heterozygous rats were obtained after four daily injections of 1 u. Pitressin Tannate in Oil (PTO). Under these conditions, when dehydration was superimposed for 72 hr, urine osmolality did not increase markedly. In heterozygous rats dehydrated for the same period of time, urine osmolality increased by some twofold.4. In rats with DI, the administration of PTO induced a rise of both sodium and urea concentrations in renal fluids and in urine. Dehydration during PTO administration caused a further rise of urea concentrations only. Dehydration per se significantly raised urinary and renal fluid urea concentrations, but sodium concentrations did not rise.5. In heterozygous rats dehydration per se increased both urea and sodium concentrations in renal fluids and urine.6. The evidence is discussed that the action of vasopressin involves factors apart from increasing the permeability of the distal nephron to water and urea.