Effects of 1 M NaCl cerebroventricular injection on renal and baroreceptor reflex functions.

Our purpose was to study the influence of the stimulation of the cerebroventricular system on some mechanisms related to hydrosaline equilibrium and blood pressure regulation. Renal function and blood pressure (group 1) as well as the baroreceptor reflex (group 2) were studied. In group 1, we measured diuresis, natriuresis, creatinine clearance, lithium clearance, and blood pressure in control rats and after stimulation of the cerebroventricular system with 1 M NaCl solution. In group 2, we evaluated the baroreceptor reflex, producing an increase of blood pressure with an injection of phenylephrine to obtain baroreceptor reflex curves--characterized by threshold, point of inflection, heart period range, gain, and systolic pressure corresponding to half the heart period range (SBP50)--in control and experimental rats injected with saline and 1 M NaCl solution, respectively. In group 1 experimental rats, we observed a significant increase in diuresis, natriuresis, blood pressure, and glomerular filtration rate. A substantial increase was also registered in sodium filtered load and reabsorbed sodium in the proximal convoluted tubule and distal nephron. No differences were observed either in fractional proximal tubule or in distal nephron sodium reabsorption. In group 2 experimental rats, mean arterial blood pressure, threshold, point of inflection, and SBP50 were significantly higher than in control rats. By contrast, a decrease in gain and heart period range was observed. No difference was obtained in heart rate. Our results demonstrate that the increase of the natriuresis is due, at least in part, to an increase in sodium filtered load.(ABSTRACT TRUNCATED AT 250 WORDS)

Body water distribution after intracerebroventricular injection of NaCl in rats.

The aim of the investigation was to evaluate the effects of the intracerebroventricular (ICV) injection of 0.1 ml of 1 M NaCl, on the body water distribution in nephrectomized male rats. In comparison with the control rats injected with an equal volume of isotonic saline, the ICV injection of 1 M NaCl elicited 90 min later a significant increase of plasma volume whereas the total water, the inulin space, the calculated interstitial space and the intracellular water were not altered. The increase of plasma volume could be explained by a decrease of capillary efflux to the interstitial space. These results suggest that the ICV injection of 1 M NaCl releases a substance which could regulate the plasma volume.

Atrial natriuretic factor and body water distribution.

In the rat, the effects of an atrial natriuretic factor (ANF) (Rat, 8-33 Peninsula Lab) on body water distribution have been evaluated. The ANF administration to nephrectomized animals produced a decrease in plasma volume and a slight increase in haematocrit and in plasma albumin concentration. No modifications were observed in total and intracellular water. The fluid efflux from the capillaries appeared to be located in the interstitial space. These results suggest that ANF could regulate plasma volume and systemic blood pressure, concurrently with its other known effects.