Dose-response effects of adrenergic and cholinergic stimulation on atrial natriuretic peptide secretion from beating isolated guinea-pig atria.

1. The possible role of autonomic neurotransmitters in atrial natriuretic peptide secretion was investigated using spontaneously beating guinea-pig atria in vitro. Dose responses were determined for adrenaline, noradrenaline and acetylcholine and the selective alpha- and beta-adrenoceptor agonists phenylephrine and isoprenaline, respectively. Adrenoceptor effects were further studied using the selective alpha- and beta-adrenoceptor antagonists prazosin and propranolol, respectively, in conjunction with maximal adrenaline challenge. Results for rate and force of contraction and atrial natriuretic peptide secretion are expressed as a ratio (mean +/- SEM) of a 15 min treatment period (stage 2) to a corresponding pretreatment period (stage 1). 2. Adrenaline and noradrenaline caused dose-dependent increases in the rate and force of contraction and in atrial natriuretic peptide secretion with a peak secretory response at 2 x 10(-6) mol/l of 1.54 +/- 0.08 (P < 0.01) and 1.34 +/- 0.08 (P < 0.01) for adrenaline and noradrenaline, respectively. Acetylcholine decreased the rate and force of contraction, and ANP secretion was reduced to 0.47 +/- 0.06 at 3 x 10(-5) mol/l (P < 0.01). Isoprenaline increased the rate and force of contraction and atrial natriuretic peptide secretion with a peak secretory response of 1.52 +/- 0.22 at 2 x 10(-6) mol/l (P < 0.01). Phenylephrine increased the force but had no effect on the rate of contraction, and stimulated atrial natriuretic peptide secretion to 1.13 +/- 0.09 at 2 x 10(-5) mol/l (P < 0.05). After both alpha- and beta-adrenoceptor blockade, adrenaline was still able to significantly stimulate atrial natriuretic peptide secretion and positive inotropy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of phosphate-buffered sucrose flush solution upon the initial phase of ischaemic acute renal failure in the rat.

1. Experiments were performed upon anaesthetized rats to investigate the effect upon the initial 4 h of ischaemic acute renal failure of intrarenal flush with phosphate buffer (PB), sucrose alone and phosphate-buffered sucrose (PBS) solutions of differing compositions. 2. Kidneys flushed with PB immediately before 45 min pedicle clamp ischaemia exhibited a post-ischaemic function similar to that of control, non-flushed kidneys: they were isosthenuric and non-oliguric with a clearance of inulin (Cin) depressed to 10% of the pre-ischaemic value. 3. Kidneys flushed with 50 mmol/l sucrose in saline before ischaemia became isosthenuric, oliguric and had a more severely depressed post-ischaemic Cin compared with non-flushed kidneys. 4. Kidneys flushed with PBS containing either 50 (PBS50) or 140 (PBS140) mmol/l sucrose at pH 7 became polyuric after ischaemia, produced concentrated urine and had Cin values significantly higher than control kidneys. 5. Raising the pH of the PBS50 to 7.4 resulted in isosthenuric, polyuric kidneys that had a post-ischaemic Cin not significantly different from that of the control group. 6. It is concluded that the severity of the initial phase of ischaemic acute renal failure was significantly reduced by intrarenal flush with a PBS solution of pH 7; flush with PB or sucrose alone had no protective action.

Unilateral renal ischaemia in the rat: effect of contralateral nephrectomy and intrarenal flush with phosphate-buffered sucrose.

1. This study examined whether the severity of acute renal failure seen within 4 h of a 45 min period of unilateral occlusion of the renal pedicle could be reduced by removal of the contralateral healthy kidney and/or intrarenal flush with a phosphate-buffered sucrose (PBS50) solution. 2. After ischaemia, unflushed kidneys became oliguric and isosthenuric, with a fall in inulin clearance (Cin) to 0.1% of the pre-ischaemic value. Removal of the healthy contralateral kidney upon release of the occlusion caused no improvement in immediate post-ischaemic function. 3. Intrarenal flush with 1.5 ml of PBS50 resulted in a significantly improved post-ischaemic Cin, with increased urine flow rate and solute excretion; urine was also concentrated. 4. Protection of renal function against ischaemic damage was seen only when kidney tissue remained blood-free and exposed to PBS50 throughout the period of ischaemia, and when the speed of flush was similar to the expected renal blood flow (6 ml/min). Protection did not depend upon the presence or absence of the contralateral kidney. 5. The study also showed that functional removal of one kidney, either by pedicle occlusion or nephrectomy, caused an immediate rise in solution excretion from the contralateral kidney, but Cin remained unchanged. Unflushed severely damaged kidneys showed no compensatory response to unilateral nephrectomy, whereas kidneys flushed with PBS50 exhibited increases in solute excretion similar to those seen in healthy non-ischaemic kidneys.

Unilateral renal ischaemia in the rat: effect of method of occlusion of the blood supply on function of ipsilateral and contralateral kidneys.

The functions of right and left kidneys were measured immediately preceding, during and for 4 h after 45 min occlusion of the blood supply to the left kidney. The blood supply was occluded by placing a clamp around the renal artery near to the aorta (group 1), near to the renal hilus (group 2) or by clamping the renal pedicle after prior separation of the kidney from perirenal tissue (group 3). During ischaemia right kidneys had increased urine flow rates and excretion of sodium and water, but inulin clearances (CIn) remained unchanged. After ischaemia left kidneys were isosthenuric with depressed CIn. Occlusion of the renal artery alone resulted in nonoliguric kidneys in which CIn was reduced to 10% and 1% respectively for groups 1 and 2. The most severe damage to function was seen in the kidneys of group 3 which were oliguric and in which CIn was depressed to 0.1% of the pre-ischaemic value. It is concluded that the pedicle clamp method produced complete renal ischaemia and the most severe damage to function. Occlusion of the renal artery produced incomplete ischaemia and a less severe fall in function which depended upon the site of occlusion.

A comparison of the relative effectiveness of three transplant preservation fluids upon the integrity and function of rabbit proximal convoluted tubules perfused in vitro.

Rabbits were anaesthetized and kidneys removed directly with no flush (group NF), or alternatively kidneys were flushed (group F) with sodium phosphate buffered 140 mmol/l sucrose (PBsuc 140), Collins C2 (C2) or Euro-Collins (EC) transplant preservation solutions and stored at 4 degrees C for 0-4, 24 or 48 h. Mid-cortical proximal convoluted tubule (PCT) segments were dissected from all groups and set up for microperfusion in vitro. Observations were made of tubule morphology, fluid reabsorption rate (Jv), bath leak of the glomerular marker iothalamate and transmural potential difference (p.d.), both at 37 degrees C and at 15-20 degrees C, in order to compare the relative effectiveness of the solutions in the preservation of tubule integrity and immediate function. Tubules from kidneys flushed with EC and C2 contained luminal debris and frequently had high bath leaks of iothalamate, both indicative of poor preservation of tubule integrity. In contrast, tubules from NF kidneys and PBsuc 140-flushed kidneys were free of luminal debris with a lower incidence of high iothalamate leaks. Tubules from PBsuc 140-flushed and EC-flushed kidneys after 0-4 and 24 h storage had Jv that were similar to those of NF kidneys. Tubules from all groups of flushed kidneys after 48 h cold storage and all tubules from C2-flushed kidneys showed reduced Jv values. In all cases Jv was reduced to approximately zero when the temperature was lowered to 15-20 degrees C. Transmural p.d. was similar in all groups except for particularly low p.d. values observed in tubules from C2-flushed kidneys after 48 h storage. These observations suggest that PBsuc 140 is more effective in the preservation of tubule function during prolonged cold storage than the glucose-based Collins solutions. The marked difference in the effectiveness of C2 and EC contraindicates the inclusion of magnesium (present in C2) for preservation of kidneys, as judged by experiments on the rabbit.

The effect of peritubular protein upon fluid reabsorption in rabbit proximal convoluted tubules perfused in vitro.

This paper describes an investigation of the effects of varying the peritubular protein concentration upon the rate of fluid reabsorption of proximal convoluted tubule segments of the rabbit kidney, isolated and perfused in vitro. Eleven moderately distended tubules, bathed with rabbit serum (60 g l.-1 protein) and perfused with an ultrafiltrate of serum (ca. 0 g l.-1) protein, reabsorbed fluid at a rate of 1.0 +/- 0.07 nl. mm-1 min-1. When the protein of the bathing solution was reduced by replacing the serum with ultrafiltrate there was little change in fluid reabsorption rate. A further eleven moderately distended tubules, bathed with physiological saline containing bovine serum albumin (60 g l.-1) and perfused with saline, reabsorbed fluid at 1.0 +/- 0.06 nl. mm-1 min-1. There was little change in fluid reabsorption when the protein concentration was reduced to either 20 or 0 g l.-1; these tubules responded to 10(-5) M-ouabain in the bath, or a temperature of 25 degrees C, by reducing their absorption rate to 0.13 +/- 0.05 nl. mm-1 min-1. Nine minimally distended tubules reabsorbed fluid at 0.8 nl. mm-1 min-1 when bathed with physiological saline containing bovine serum albumin (60 g l.-1) and perfused with saline. Under these circumstances reabsorption rate fell by 26% when protein was removed from the bath. A study of the pressure-diameter relationship was made for eight tubules typical of those used in this laboratory. The probable range of lumen hydrostatic pressures was discussed for the distended and undistended states. We conclude that the effect of peritubular protein concentration upon fluid reabsorption in proximal convoluted tubule segments perfused in vitro is dependent upon some property of the tubule wall that is changed when distension occurs.

The effect of pseudopregnancy on glomerular filtration rate and salt and water reabsorption in the rat.

1. Glomerular filtration rate (G.F.R.) and salt and water reabsorption were measured in age-matched virgin rats and rats at different stages of pseudopregnancy and post-pseudopregnancy. 2. Tubular reabsorption and G.F.R. were significantly higher in later pseudopregnancy. Values at mid-pseudopregnancy were intermediate between virgin controls and late-pseudopregnancy. In post-pseudopregnancy G.F.R. and reabsorption had returned to values not different from the virgins. 3. Expansion of extracellular fluid volume (e.c.f.v.) and elongation of proximal tubules were observed during pseudopregnancy. In post-pseudopregnancy increased tubular length was still apparent but e.c.f.v. was not. 4. The remarkable similarity in the changes in e.c.f.v. and renal functions and structure during pseudopregnancy to those in early pregnancy suggests that the feto-placental unit is not necessary for the pregnancy changes. 5. The differences between the time course of change in plasma progesterone and the time courses of changes in e.c.f.v., renal functions and tubular morphology in late pseudopregnancy suggest that progesterone is not directly involved.

The effect of pregnancy on glomerular filtration rate and salt and water reabsorption in the rat.

1. Glomerular filtration rate (G.F.R.) and salt and water reabsorption were measured in age-matched (12- to 13-week-old) virgin rats and rats at different stages of pregnancy and infused with saline at 37.5 and 200 microliters/min. 2. G.F.R. and salt and water reabsorption were significantly higher in early pregnancy and remained at steady, high values until at least mid-pregnancy. G.F.R. was slightly lower close to term, but sodium and water reabsorption remained significantly enhanced. 3. Significant expansion of extracellular fluid volume (e.c.f.v) was first apparent during mid-pregnancy, indicating that e.c.f.v. expansion could not be directly responsible for the early increase in G.F.R. 4. Proximal tubules were significantly elongated 5- days after mating until term, indicating that an increased reabsorptive area in the proximal tubule may be at least partly responsible for the increased reabsorption in pregnancy.