Natriuresis of Fasting in Intact and Adrenalectomized Rats

Abstract

Abstract-Experimentswere carried out in an attempt to elucidate the mechanism of fasting-induced natriuresis in conscious rats. Female animals were given a low sodium diet and saline in a fixed concentration for at least three days, and deprived of food thereafter. The sodium balance significantly shifted to negative independently of potassium supply in intact rats. Such was also observed in the dexamethasone replaced, adrenalectomized rats and was not affected by further administration of aldosterone.In addition, the diuretic effect of insulin in fasted intact rats was not evident in the fed diabetic rats in which diabetes had been induced by streptozotocin. Such findings suggested participation of factors other than insulin. The natriuresis of fasting in intact rats appears to involve two factors, one of which is independent of the sodium intake level. Dependence on the sodium intake level may be derived from alteration of the solute diuresis-like effect of drinking saline when animals are fasted. These results suggest that neither aldosterone nor insulin is a major causal factor involved in fasting-induced natriuresis.In man and rabbit, many workers have shown that fasting produced natriuresis, and such was arrested by carbohydrate feeding (1-8). Previous reports indicated that in rats also, food deprivation resulted in an increase in sodium excretion or a negative shift of sodium balance. Several hormones regulating the glucose metabolism may be involved in the occurrence of sodium imbalance during the early stage of fasting, however the mecha nism remains obscure.The antidiuretic effect of insulin (9, 10) has been attributed to fasting-induced natriuresis and anti -natriuresis by subsequent glucose feeding. In a preliminary report from this laboratory it was confirmed that the negative balance of sodium in fasted rats was not improved but rather enhanced by the administration of insulin (11). Since glucagon has a natriuretic effect in man and the dog (12)(13)(14), it is suggested that glucagon may contribute either directly or indirectly to the natriuretic effect of fasting. Moreover, well-known factors, such as aldosterone and antidiuretic hormone, may be implicated in the sodium imbalance.The present series of studies on the fasting-produced natruiresis was undertaken to determine: (a) The role of sodium and potassium loading in intact fasting rats; (b) the effect of aldosterone in glucocorticoid-replaced adrenalectomized rats; and (c) the effect of insulin in intact or diabetic rats. MATERIALS AND METHODSFemale Wistar rats weighing between 190 and 310 g were maintained on a regular diet

Effects of food restriction for 3 or 7 days on toxicity-related parameters in rats

“…The concentrations of Na and Cl in the male and female 40% groups were higher than those in the control group, when the urine volume was considered (Supplemental Table 2). Natriuresis has been shown to occur in humans during fasting (Schloeder and Stinebaugh, 1970;Sigler, 1975), and this has also been identified in fasted rats (Fitzgerald et al, 2001;Nohno et al, 1977). Although the mechanism underpinning natriuresis is not fully understood, it has recently been suggested to involve the sodium-glucose transporter 2 (SGLT-2) in the proximal tubules of the kidney.…”

Fluid and Electrolyte Excretion in Sheep: Comparison of the Effect of Reduced Food and Water Intake With Oestrus

“…It is said not to occur in rats (Van Liew, Eisenbach, Dlouha & Boylan, 1978) but this may reflect the very high levels of sodium frequently contained in rat diets (Michell, 1978); Nohno, Hayashi & Murayama (1977) have reported fasting natriuresis in rats on low sodium diets. Both human and animal studies generally involve complete food deprivation for periods ranging from 3-23 d whereas the present paper reports a very similar pattern of sodium excretion induced by a mild reduction of food intake for merely 48 h, with or without parallel restriction of drinking.…”

Role of antidiuretic hormone in fasting-induced natriuresis in conscious rats.

“…We have recently observed that fasting for one to four days resulted in the negative sodium balance in rats provided a low salt diet and saline (2). The fasting-induced natriuresis in the rat revealed two aspects, one dependent on the level of sodium intake, and the other not (3). The latter seems to be largely concerned with the negative value of sodium balance in the lower level of sodium intake maintained relatively constant.…”