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KMID : 0377619640060030285
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Korean Jungang Medical Journal
1964 Volume.6 No. 3 p.285 ~ p.304
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Experimental Studies on Homeostatic Regulation of Body Fluid Volume.
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Abstract
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In the past three decades the development of methods for quantitatively evaluating cardiovascular. renal and endocrine function has led to a significant advance in the understanding of the mechanisms which regulate fluid and electrolyte metabolism in health and disease. However, many important questions remain unanswered.
In .1916, Henderson emphasized that fluid volume must be regulated independently of osmotic pressure. As early as 1909, Starling had postulated that there must be a homeostatic relationship between the extracellular fluid and plasma volumes, renal hemodynamics and the general circulation. However, the renal mechanisms compensating for volume changes not associated with changes in tonicity were long neglected by renal physiologists.
In 1936, McCance reported that in normal men on low salt intakes several mechanisms for expanding the contracted extracellular fluid are activated following a severe depletion of s(xlium by acute forced sweating. Subsequently, Leaf and Mamby demonstrated that in sodium depleted, hyponatremic dogs, an antidiuretic mechanism. independent of osmoreceptor control, is invoked, and water is retained to maintain the lxxiy fluid volume.
Recent reviews have provided some evidence that in normal subjects acute and chronic hod fluid v UUlume changes may affect the excretion of water and sodium independently. However, the precise natures of these compensatory mechanisms are still not delineated.
The study presented herein was designed to provide evidence suggesting that homeostatic mechanisms maintain the constancy of volume of the body fluid in normal rabbits. Furthermore, an attempt teas"made to clarify the nature of these mechanisms.
In this experiment, male rabbits weighing around 2 Kg were used. The rabbits were divided into 3 groups, the first group was treated by a slow continuous infusion (O.5ml; rein.), the second anal the third by a rapid continuous infusion(1.5m1 !mir.) of 3% dextrose solution. Moreover, the third group was administered 2 units of pitressin on 2 hours of the infusion. Each group was subdivided further into the normal and the renal denervated. In the latter subdivided groups, body weight, blood pressure, serum Na and K concentrations, urinary volume, urinary Na and K excretions, and creatinin clearance were determined before and during the infusion for 5 hours. During the infusion, blood sugar levels in the all sub-divided groups were controlled within the normal limits by the administration of insulin. After the infusion, the kidney tissues were obtained from each rabbit for specific staining and quantitation of the juxtaglomerular granules by the Hartroft´s juxtaglomerular index method.
The results were summarized as follows.
1) No significant differences were noted between the normal and the renal denervated in all groups.
2) In the first group, during the slow continuous infusion, the urine flow in-creased gradually but no significant changes were noted on the body weight, blood pressure, serum Na and K concentrations, urinary Na and K excretions, and creatinine clearance. And the juxtaglomerular index of this group averaged within the normal linits.
These data support the fact that body fluid is regulated by the osmolarity which is independent of the renal nervous influence.
3) On the other hand, significantly different responses were noted in the second and the third groups as compared with the results of the first group. In the second group, during the rapid continuous infusion, the urine flow increased gradually, however, in the third group, the urine flow decreased markedly after the administration of pitressin, and, moreover, in these both groups significant increase in the body weight (body fluid volume), fall in serum Na and K levels, and marked increase in urinary Na and K excretions were noted, despite the fall in serum electrolyte concentration and the reduced urinary volume due to the administration of pitressin. No significant changes of the blood pressure and creatinine clearance were observed during the infusion in these both groups. At this time,the average juxtaglomerular indices of these both groups were significantly lower than that of the first group.
4) These data on the second and the third groups support the growing evidence that there is a homeostatic mechanism which maintains the constancy of the body fluid volume at the expense of tonicity independently of the renal nervous influence.
The results of these data also suggest that altered sodium reabsorption activity in the renal tubular epithelium plays a major role in this responses, and, furthermore, strongly suggest that the juxtaglomerular cell - renin system have important regulatory functions in this mechanism.
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