Depression of proximal tubular sodium reabsorption in the dog in response to renal beta adrenergic stimulation by isoproterenol

Glomerular effects of cholera toxin in isolated perfused rat kidney: a potential role for platelet activating factor

Cholera toxin (MW 84 kDa) is now considered a pharmacological tool to study the adenylyl cyclase system and a stimulus to generate platelet activating factor in the intestinal tract. We used this toxin to evaluate the renal haemodynamics, glomerular filtration function, tubular sodium transport and toxicity in isolated perfused rat kidney. Kidneys from adult male Wistar rats were isolated for perfusion. The perfusion fluid was modified Krebs-Henseleit solution and the samples were analyzed for sodium, potassium, inulin and osmolality. Clearance techniques were used to calculate physiological parameters. Cholera toxin (1.0 microg/ml) caused a significant time-dependent reduction of glomerular filtration rate and urinary flow. This toxin also caused a small, but consistent reduction in fractional proximal sodium reabsortion (toxin = 67.43+/-2.42% versus control = 79.26+/-5.80%; P<0.025). WEB 2086, a platelet activating factor receptor antagonist at 100 microg/ml completely blocked the effects induced by cholera toxin on glomerular filtration rate, fractional proximal sodium reabsortion and urinary flow. In contrast to cholera toxin, dibutyryl-cyclic AMP (10(-5) M) significantly increased glomerular filtration rate (Db-cyclic AMP = 0.651+/-0.035 versus control = 0.514+/-0.043 ml x g(-1) x min(-1); P<0.025) in isolated perfused kidneys. Db-cyclic AMP caused a similar, but more severe reduction in fractional proximal sodium reabsortion (Db-cyclic AMP = 54.21+/-2.35% versus control = 70.10+/-3.24%; P<0.025). In addition Db-cyclic AMP increased significantly the urinary flow (Db-Cyclic AMP = 0.290+/-0.018 versus control = 0.179+/-0.026 ml x g(-1) x min.(-1); P<0.025). WEB 2086+ Db-cyclic AMP also caused a significant increase in the urinary flow with maximal effect at 90 min. (WEB+Db-cyclic AMP = 0.26+/-0.01 versus control = 0.15+/-0.01 ml x g(-1) x min.(-1); n = 8, P<0.025). Cholera toxin caused a decrease of urinary flow (toxin = 0.034+/-0.004 versus control = 0.145+/-0.02 ml x g(-1) x min.(-1); P<0.025), this effect was also completely abolished by WEB 2086 when it was injected previously to toxin. When only WEB 2086 was injected, the functional parameters remained stable throughout the perfusion time. Cholera toxin had no effect on renal vascular resistance, renal perfusate flow or tissue potassium, suggesting renal integrity in kidneys treated with this toxin. The results suggest that cholera toxin effects in the perfused rat kidney are primarily mediated by platelet activating factor.

Proximal tubular function in essential hypertensives on beta-blocker therapy with atenolol

Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured during waterloading and constant infusion of [131I]hippuran and [125I]iothalamate in 24 mild to moderate essential hypertensive patients before and after 3.5 months treatment with atenolol. Clearances of sodium and potassium were measured 2-3 hours post-dosing and renal vascular resistance (RVR) and filtration fraction (FF) were calculated. Measurement of clearance of lithium (CLi) and uric acid (Curic acid) was employed to investigate specifically proximal tubular function. Beta-blockade with atenolol produced a borderline significant decrement in RPF but no change in GFR, RVR and FF. There was a significant reduction in CLi, fractional proximal escape of sodium and water, Curic acid and an increase in absolute proximal reabsorption of sodium, indicating an inhibition of proximal tubular function. The distal tubular parameters exhibited changes tending to normalize excretion of sodium, but not water. Changes in RVR were inversely related to changes in CLi and Curic acid, suggesting unopposed alfa-adrenergic stimulation to be implicated in the renal counterregulation at a proximal tubular site following long-term administration of atenolol in essential hypertension.

Distribution of beta 2-adrenergic receptor mRNA expression along the hamster nephron segments

Distribution of beta 2-adrenergic receptor mRNA expression along the microdissected hamster nephron segments was examined by the reverse transcription-polymerase chain reaction (RT-PCR) technique. Conventional RT-PCR using a set of primers on separate exons could not be applied for the detection of beta 2-adrenergic receptor mRNA because of its intronless nature. We used the 'rapid amplification of cDNA ends' protocol [(1985) Proc. Natl. Acad. Sci. USA 85, 8998-9002] as a maneuver for RT-PCR of an intronless gene. Using this method, we successfully located hamster beta 2-adrenergic receptor mRNA only in glomeruli and early proximal convoluted tubule along the nephron segments tested.

Inverse regulation of alpha-2 and beta-2 adrenoceptors in salt-sensitive hypertension: an hypothesis

A high salt diet leads to up-regulation of alpha-2 adrenoceptors and down-regulation of beta-2 adrenoceptors in normotensive subjects. Although the increase in blood pressure with a high salt diet is not related to the magnitude of the alpha-2 or beta-2 adrenoceptor changes alone, it is related to the increase in the ratio of the receptor changes (operative alpha/beta adrenoceptor ratio). An increase in the operative alpha/beta adrenoceptor ratio with a high salt intake results in vasoconstriction and reduced vasodilatation at resistance vessels, as well as increased renal proximal tubular sodium reabsorption. An influence of heredity on this relationship is supported by four lines of evidence: 1) salt-sensitivity of blood pressure occurs predominantly in subjects with a family history of hypertension; 2) studies in twin children document the influence of genetic variance on salt-sensitivity of blood pressure; 3) subjects with a family history of hypertension have a significantly lower salivary sodium concentration and an altered urinary sodium excretion after salt loading compared to subjects with no such history; 4) salt-sensitivity of blood pressure may be associated with specific genetic markers. On the basis of these observations, we propose the hypothesis that enhanced inverse alpha-beta-adrenoceptor regulation in response to a high salt intake may be responsible for salt sensitivity in the normal population, and may contribute to the development of essential hypertension in susceptible individuals. This alteration is likely to be genetically mediated.

The distribution of beta-adrenoceptors in dog kidney: an autoradiographic analysis

The distribution of beta-adrenoceptors in slide-mounted dog kidney sections was determined using the radioligand (-)-[125I]cyanopindolol ((-)-[125I]CYP) and autoradiography. Using conditions designed to prevent (-)-[125I]CYP binding to non-beta-adrenoceptor sites, biochemical studies revealed that (-)-[125I]CYP binding equilibrated within 150 min (K1 = 3.2 X 10(8) M-1 min-1), was saturable (KD = 30.72 +/- 2.96 pM; Bmax = 0.57 +/- 0.03 fmol/section, n = 4) and stereoselective with respect to the stereoisomers of propranolol and pindolol. Delineation of beta-adrenoceptor subtypes with the selective beta 1-adrenoceptor antagonist betaxolol and beta 2-adrenoceptor antagonist ICI 118,551 demonstrated that the proportions of beta 1-: beta 2-adrenoceptors was between 1:6 and 1:11. Autoradiographic studies showed that beta 1-adrenoceptors were localized on the juxtaglomerular apparatus and glomeruli, while beta 2-adrenoceptors were localized on medullary rays. The distribution of beta-adrenoceptors with respect to renal function in the dog kidney is discussed.

Adrenergic receptors and sodium reabsorption in normotensive subjects as related to salt sensitivity

We have studied proximal tubular sodium reabsorption as measured by lithium clearance, alpha-2 and beta-2 adrenergic receptors on circulating platelets and lymphocytes, respectively, and urinary aldosterone after variations of sodium intake in 24 normotensive volunteers. Fractional lithium clearance was 14.8% +/- 2.64 under a high salt diet of 200 mmol per day. After a low salt diet of 50 mmol/d for two weeks fractional lithium clearance did not change significantly (13.3% +/- 3.35). There were no correlations between alpha-2 adrenergic receptors, beta-2 adrenergic receptors or the alpha-2/beta-2 ratio and fractional lithium clearance, irrespective of the high or low salt diet. In contrast, a significant correlation was found between urinary aldosterone excretion and alpha-2 receptor densities under low salt diet (r = -0.55, n = 17, p less than 0.02). There were no correlations between beta-2 adrenoceptor density, alpha-2/beta-2 ratio and urinary aldosterone during high or low salt diet. Whereas our results are inconclusive about the value of lithium clearance determinations as a measure of proximal tubular sodium reabsorption during variations of sodium intake, we conclude, that alpha-adrenoceptor density, as measured on circulating blood cells, may possibly be representative for alpha-adrenergic equipment of the kidney. The inverse correlation between urinary aldosterone excretion in subjects equilibrated on a low salt diet of 50 mmol/d and alpha-2 adrenoceptor densities could be interpreted as an indirect evidence, that those subjects with a high alpha-2 adrenoceptor equipment show a high proximal tubular sodium reabsorption and thus can afford a low rate of aldosterone mediated distal tubular sodium reabsorption to maintain sodium balance. Our results are thus in accord with our previous hypothesis, that different receptor equipment of individual subjects may cause marked differences in sodium handling by the kidney. These differences may be responsible, at least in part, for the degree of salt sensitivity in individual subjects.

Mechanisms of release of atrial natriuretic factor. II. Effect of chronic administration of alpha- and beta-adrenergic and cholinergic agonists on plasma and atrial ANF in the rat

The effect that chronic subcutaneous infusion of alpha- and beta-adrenergic and cholinergic agonists on plasma and atrial ANF was investigated. Isoproterenol, a beta-adrenergic agonist, and carbachol, a cholinergic agonist produced a 3-fold increase in plasma ANF levels which were constant until the end of the infusion period. An increased natriuresis was observed in the same groups which was positively correlated with plasma ANF. No differences were observed in atrial content of ANF between the experimental groups. A sharp post-surgery decline in plasma ANF was observed in control, phenylephrine and epinephrine-treated groups which was maintained during the observation period of five days. This suggests that the rise in plasma ANF induced by isoproterenol and carbachol may be secondary to hemodynamic changes and not to direct receptor stimulation, and may play a role in the observed natriuresis. It is also suggested that the depression of plasma ANF may contribute to the well known post-surgery sodium retention.

Effect of norepinephrine and angiotensin II on intrarenal oxygen availability

Oxygen availability (O2a) in the cortex, outer medulla, inner medulla, and papilla of the left kidney was measured in 12 unanesthetized rabbits implanted with O2 sensitive electrodes. Each was injected with a single i.v. bolus of either norepinephrine (NE) or angiotensin II (AII) in equipressor doses, and intrarenal O2a was continuously recorded. The NE response consisted of parallel and proportional intrarenal O2a decreases and overshoots in all zones; AII response consisted of progressively smaller O2a decreases from outer to inner zones during maximum response and smaller increases during maximum overshoot. These response differences may be important under various physiologic or pathologic conditions.

The role of the adrenergic nervous system in sodium and water excretion

There is considerable evidence that the renal nerves contribute to the regulation of salt and water excretion by a direct effect on tubular reabsorption, independent of changes in renal hemodynamics. Whereas the effect of the adrenergic nervous system on sodium reabsorption appears to be established in anesthetised animals, it has been suggested that the basal activity of the renal sympathetic nerves in conscious dogs is too low to have a significant effect on sodium reabsorption by the proximal tubules. However, denervation natriuresis and diuresis has recently been demonstrated in conscious euvolemic and conscious volume expanded rats. The effects of renal nerve stimulation on the handling of sodium and water by the proximal tubule can be mimicked by infusion of the alpha-adrenergic agonist norepinephrine and prevented by infusion of an alpha-adrenergic antagonist. This confirms that it is mediated by alpha-receptors. The adrenergic nervous system may have an independent role in the control of sodium excretion or may be complementary to other systems such as the renin-angiotensin-aldosterone system.

Regulation of sodium and water excretion by catecholamines

There is considerable evidence that the renal nerves contribute to the regulation of salt and water excretion by a direct effect on tubular reabsorption, independent of changes in renal hemodynamics. Whereas the effect of the adrenergic nervous system on sodium reabsorption appears to be established in anesthetized animals, it has been suggested that the basal activity of the renal sympathetic nerves in conscious dogs is too low to have a significant effect on sodium reabsorption by the proximal tubules. However, denervation natriuresis and diuresis have recently been demonstrated in conscious euvolemic and conscious volume-expanded rats. The effects of renal nerve stimulation on the handling of sodium and water by the proximal tubule can be mimicked by infusion of the alpha-adrenergic agonist norepinephrine and prevented by infusion of an alpha-adrenergic antagonist. This confirms that they are mediated by alpha-receptors. The adrenergic nervous system may have an independent role in the control of sodium excretion or may be complementary to other systems such as the renin-angiotensin-aldosterone system.

Prevention of kidney haemorrhagic necrosis of choline-deficient rats by alpha-methyldopa treatment

In a previous report from our laboratory we have shown a marked increase in the levels of renal catecholamines in choline-deficient rats in comparison to choline-supplemented animals, while the content of acetylcholine remained unchanged. Since the changes in tissue catecholamines occurred before kidney lesions developed, we have suggested that an imbalance between sympathetic and parasympathetic systems plays an important role in the pathogenesis of renal injury in choline-deficient rates, this imbalance being the result of an excess of catecholamines in the kidneys. A series of experiments was then planned to explore this theory further by administering adrenergic blocking agents in an attempt to prevent the development of the renal injury in choline deficiency. We report here our results on the administration of α-methyldopa, a drug that depletes the tissue stores of catecholamines, to choline-deficient and choline-supplemented rats. Young male Wistar rats were divided at random into 4 groups: Group CS, fed a choline-supplemented diet; Group CS + D, fed a choline-supplemented diet and treated with α-methyldopa; Group CD, fed a choline-deficient diet; and Group CD + D, fed a cholinedeficient diet and treated with α-methyldopa. The appropriate groups received daily i.p. injections of α-methyldopa (300 mg/kg body wt). The kidneys of all surviving rats were studied grossly and histologically, and the levels of noradrenaline and adrenaline determined. All animals from Control Groups CS and CS + D showed essentially normal kidneys on gross and light microscopic examination. On the other hand, CD rats showed marked renal injury, while the kidneys lesions of CD + D animals were significantly less pronounced than those of rats from Group CD. The total content of noradrenaline and adrenaline in the kidneys of CD + D and CD rats were not statistically different, although the CD + D animals tended to have lower levels of catecholamines. The content of noradrenaline and adrenaline of rats from Group CD was significantly higher than the corresponding values in CS rats. Also, the total content of renal noradrenaline of CD + D animals was found to be unaltered when compared to that of CS rats, while their content of adrenaline was found to be higher than the corresponding value in CS group. The noradrenaline levels of CS and CS + D rats were similar, but the latter group had a higher renal adrenaline content than the former. These findings, besides confirming our previous observations, clearly show that α-methyldopa afforded a protective effect against the renal injury of choline deficiency, thus giving strong additional support to the theory that the kidney haemorrhagic necrosis of choline deficiency in young rats is probably due to an autonomic imbalance.

Influence of renal nerve activity on arteriolar resistance, ultrafiltration dynamics and fluid reabsorption

In anaesthetized 300 g rats, the influence of sympathetic nerve activity on the renal hemodynamics, glomerular filtration and fluid reabsorption was studied with direct stimulation at frequencies of 2 Hz and 5 Hz. The single nephron plasma flow at control conditions was 164 nl/min decreasing to 138 nl/min during 2 Hz and 68 nl/min during 5 Hz, reaching complete glomerular ischemia at about 10 Hz. At 2 Hz, the pressure drop over the two arterioles remained essentially unchanged, indicating an equal response to sympathetic discharge. At higher frequencies the afferent tone showed a more marked increase. The glomerular ultrafiltration decreased in parallel to the blood flow. The filtration fraction remained thereby constant at about 0.33. The fractional proximal fluid reabsorption up to the puncture site in early distal tubules showed a clear increase; the Tf/P-Inulin increasing from 6.0 to 7.1 and 7.2 for 2 Hz and 5 Hz, respectively. The absolute reabsorption decreased, however, and indeed not far from the decrement in glomerular filtration. It is concluded that sympathetic nerve activity acts in the direction of fluid conservation, by reducing the glomerular filtration and increasing the fractional reabsorption. The hemodynamic effects will play the dominant role even at 2 Hz stimulation.

Adrenergic control of bicarbonate absorption in the proximal convoluted tubule of the rat kidney

The effects of norepinephrine and phenoxybenzamine on bicarbonate absorption in the rat proximal convoluted tubules were studied by simultaneous microperfusion of tubule and peritubular capillaries. Bicarbonate was determined by using a pH-sensitive membrane electrode system. The rates of bicarbonate absorption (JHCO3) were examined in the same proximal tubule before and after the addition of norepinephrine or phenoxybenzamine. When the proximal tubule was perfused with Ringer solution and peritubular capillaries were perfused with albumin Ringer solution, JHCO3 was 145 +/- 3.3 pEq/min X mm. Addition of 2 X 10(-6) mol/l norepinephrine to the capillary perfusate caused a 21% increase in JHCO3. Addition of 2 X 10(-6) mol/l phenoxybenzamine to the capillary perfusate caused a 12% decrease in JHCO3. Addition of both norepinephrine and phenoxybenzamine to the capillary perfusate caused a 19% decrease in JHCO3. However, there was no significant effect on JHCO3 observed when either norepinephrine or phenoxybenzamine was added to the luminal perfusate. These results suggest that adrenergic nerves participate in the regulation of renal tubular bicarbonate absorption through the direct action of norepinephrine on adrenergic receptors located at the basolateral side of the proximal tubule.

beta 1-Adrenergic receptors in kidney tubular cell membrane in the rat

We used a beta-adrenergic antagonist, (-) 3H-dihydroalprenolol, to demonstrate binding sites in purified rat kidney preparations that consistsed of plasma membranes of cells from tubules. The tubular origin of these plasma membranes was shown by electron microscopy and Na-K-ATPase enrichment. The binding was rapid (t1/2, 78 sec) and rapidly reversible (t1/2, 48 sec). The binding sites were saturable and bound 69.8 +/- (SD) 29.1 fmoles/mg of membrane protein. The binding was stereospecific with the isomers of beta-adrenergic agonists and beta-adrenergic antagonist propranolol, the (-) isomers being about 40 times more potent than the (+) isomers incompeting for these sites. (-) 3H-dihydroalprenolol had a high affinity for the binding sites, expressed by the mean equilibrium dissociation constant (KD) (KD, 7.1 nM). The beta-adrenergic antagonist (-) propranolol also showed high affinity (KD, 62.8 nM). The order of potency for inhibition of binding by beta-adrenergic agonists was: (-) isoproterenol (KD, 0.66 microM) greater than (-) epinephrine (KD, 4.3 microM) greater than or equal to (-) norepinephrine (KD, 13.5 microM). Conclusion. The (-) 3H-dihydroalprenolol binding sites in the rat kidney tubular cell membrane are beta-adrenergic receptor of the beta1 subgroup.

The clinical physiology of water metabolism. Part I: The physiologic regulation of arginine vasopressin secretion and thirst

Water balance is tightly regulated within a tolerance of less than 1 percent by a physiologic control system located in the hypothalamus. Body water homeostasis is achieved by balancing renal and nonrenal water losses with appropriate water intake. The major stimulus to thirst is increased osmolality of body fluids as perceived by osmoreceptors in the anteroventral hypothalamus. Hypovolemia also has an important effect on thirst which is mediated by arterial baroreceptors and by the renin-angiotensin system. Renal water loss is determined by the circulating level of the antidiuretic hormone, arginine vasopressin (AVP). AVP is synthesized in specialized neurosecretory cells located in the supraoptic and paraventricular nuclei in the hypothalamus and is transported in neurosecretory granules down elongated axons to the posterior pituitary. Depolarization of the neurosecretory neurons results in the exocytosis of the granules and the release of AVP and its carrier protein (neurophysin) into the circulation. AVP is secreted in response to a wide variety of stimuli. Change in body fluid osmolality is the most potent factor affecting AVP secretion, but hypovolemia, the renin-angiotensin system, hypoxia, hypercapnia, hyperthermia and pain also have important effects. Many drugs have been shown to stimulate the release of AVP as well. Small changes in plasma AVP concentration of from 0.5 to 4 muU per ml have major effects on urine osmolality and renal water handling.

[Acute combined alpha- and beta-adrenergic blockade in essential hypertension: effects on blood pressure, renal function, renin, and aldosterone]

In seven patients with uncomplicated essential hypertension the effects of an acute alpha-adrenergic blockade, alone and combined with a chronic beta-adrenergic blockade, on blood pressure, renal function as measured by standard clearance methods, plasma renin activity, and plasma aldosterone were evaluated. Acute alpha-adrenergic blockade with phentolamine (20 mg by intravenous infusion) significantly enhanced the antihypertensive effect of chronic beta-adrenergic blockade with slow-oxprenolol (160 mg/ day X 14 days) (- 14.5% verus - 7.4% for pulse pressure, - 12.4% versus - 6.0% for diastolic pressure, 2 alpha less than 0.05). Under combined adrenergic blockade renal plasma flow increased, glomerular filtration rate and filtration fraction decreased (2 alpha less than 0.05 each), whereas the fractional clearances of sodium, potassium, free water, and solute load remained unchanged. The activation of the renin-angiotensin-axis, elicited by alpha-adrenergic blockade alone, was suppressed by the preceding beta-adrenergic blockade. These findings demonstrate a favourable antihypertensive action of a combined blockade of alpha- und beta-adrenergic receptor sites without untoward side effects on renal function or the renin-angiotensin-axis.

Antidiuresis induced by beta1- and beta2-adrenergic agonists in ethanol-anesthetized rats

The beta1- and beta2-components in antidiuresis and sodium retention induced by beta-adrenergic agonists were analysed in ethanol-anesthetized, water-diuretic rats. Intravenous infusions of isoprenaline, salbutamol and carbuterol did not affect insulin clearance but increased plasma renin concentration to the same same extent. Propranolol completely blocked the decreases in urine volume (V) and urinary sodium excretion (UNaV) induced by isoprenaline; practolol (beta1-blocker) inhibited only the decrease in UNaV and butaxamine (beta2-blocker) inhibited only the decrease in V. The ratios of doses of beta-agonists which decreased UNaV and by 50% (ED50 UNaV decrease/ED50 V decrease) were 0.34, 0.68, 1.56 and 2.36 for isoprenaline, tretoquinol, salbutamol and carbuterol, respectively. This increasing order of the ratios coincided with the order reported for the preponderance of the beta2- over beta1-component of these agonists. These results indicate that the decrease in UNaV induced by beta-agonists is related to beta1 stimulation, while the decrease in V is related to beta2 stimulation.

The effect of an acute increase in renal perfusion pressure on sodium transport in the rat kidney

We used micropuncture techniques to examine the intrarenal response to an acute elevation of the renal perfusion pressure. In one series of studies (epinephrine, group I) the renal perfusion pressure was acutely increased by intravenous epinephrine infusion; in another series, by bilateral carotid occlusion and vagotomy. A third series of studies (epinephrine, group II) was performed identically to the epinephrine, group I, studies except that the renal perfusion pressure was held constant during the epinephrine infusion by suprarenal aortic constriction. After epinephrine infusion (group I) and following bilateral carotid occlusion and vagotomy the renal perfusion pressure increased, from 119 +/- 1.0 (SEM) to 166 +/- 1.85 mm Hg and from 122 +/- 5.9 to 168 +/- 3.1 mm Hg, respectively. Fractional sodium excretion rose from 2.31 +/- 0.34% to 5.09 +/- 0.58% (P less than 0.001) after epinephrine and from 1.80 +/- 0.71 to 6.40 +/- 1.0% (P less than 0.01) following carotid occlusion and vagotomy. In neither study, however, did we find that the increase in renal perfusion pressure changed the glomerular filtration rate (GFR) (both kidneys) or fractional sodium delivery from the superficial cortical late distal tubule. Furthermore, we found that epinephrine infusion at a constant renal perfusion pressure (epinephrine, group II) did not affect fractional sodium excretion, although a small, but significant, decrease in the GFR and sodium delivery from the superficial late distal tubule occurred. These data suggest that the natriuresis which follows an acute elevation of the renal perfusion pressure cannot be attributed to enhanced sodium delivery from superficial nephrons but must result from (1) inhibition of sodium reabsorption in inner cortical nephrons or (2) an effect on sodium transport in the collecting system.

Hormonal modulation of cyclic adenosine 3',5'-monophosphate-dependent protein kinase activity in rat renal cortex. Specificity of enzyme translocation

Many of the intracellular actions of cyclic adenosine 3',5'-monophosphate are expressed through phosphorylation reactions mediated by cAMP-dependent protein kinases, but little is known about hormonal control of endogenous protein kinase activity (PK) in kidney. In the present study, we examined the effects of parathyroid hormone, glucagon, and isoproterenol on cAMP and PK in slices of rat renal cortex. In the presence of 0.5 mM 1-methyl, 3-isobutyl xanthine, all three hormones activated PK in slices, as reflected by an increase in the ratio of enzyme activity assayable in homogenates of the slices without addition of cAMP to the kinase reaction mixture (cAMP-independent activity) over total enzyme activity (+2 uM cAMP in the reaction mixture). When enzyme activity was assayed in whole homogenates prepared from slices, the increase in the enzyme activity ratio (- cAMP/+cAMP) which followed hormonal stimulation was due entirely to an increase in cAMP-independent activity, with no change in total activity. In general, a good correlation existed between the alterations in tissue cAMP levels mediated by the hormones and/or 1-methyl, 3-isobutyl xanthine and concomitant alterations in PK. All three hormones increased PK activity ratios to near unity, suggesting complete enzyme activation. However, the concentrations of parathyroid hormone and glucagon which produced maximal activation of PK were much lower than those required for maximal cAMP responses. Studies with charcoal indicated that these hormonal actions on PK reflected intracellular events rather than representing activation of the enzyme during tissue homogenization, due to release of sequestered cAMP. Thus, homogenization of tissue in charcoal prevented activation of PK by subsequent addition of exogenous cAMP, but did not lower enzyme activity ratios in homogenates of hormone-stimulated cortical slices. When PK was determined in the 20,000 g supernatant fraction of renal cortical slices incubated with the hormones, enzyme activity ratios also increased, but total enzyme activity declined. Lost activity was recovered by extraction of particulate fractions with 500 mM KCl or NaCl, results which implied particulate binding of activated PK. Activated soluble PK from renal cortex was bound equally well by intact, heat- and trypsin-treated renal cortical pellets and by intact and heated hepatic pellets. Accordingly, the apparent translocation of enzyme in hormone stimulated cortex does not necessarily represent binding of the activated PK to specific acceptor sites in the particulate cell fractions or constitute a physiologic hormonal action. Activation of renal cortical PK by increasing concentrations of salts suggests that the enzyme in this tissue resembles the predominant type found in heart.

Control of renin release: a review of experimental evidence and clinical implications

Present knowledge of the mechanisms regulating release of renin is reviewed with particular emphasis on neural factors. Evidence is given for a direct effect of renal innervation on beta adrenergic receptors in juxtaglomerular cells, and for the involvement of reflex release of renin in conditions such as tilting and acute salt depletion. Participation of neural and nonneural mechanisms of control is also shown to occur in other conditions, such as aortic constriction and hemorrhage. The view is held that neural sympathetic factors might explain some of the renin disturbances found in essential hypertension. First, in patients with high renin hypertension part of the hypertension is renin-dependent, and these pressor levels of renin seem to be neurally induced since they can commonly be suppressed by beta adrenoreceptor blocking agents. Second, the hypothesis is presented that patients with low renin hypertension, at least those who have no volume disturbance, have a blunted sympathetic control of renin release. Therefore a sufficiently precise test of sympathetic activity, and possibly of body fluid volumes, should be associated with renin profiles for a better understanding of the pathophysiology of arterial hypertension and as a better guide to therapeutic management. Indeed, most of the available antihypertensive drugs act on sympathetic activity, body fluid volume or renin, and this multifaceted profile would provide more rational guidelines for treatment.

Catecholamine sensitive adenylate cyclase activity in different segments of the rabbit nephron

The sensitivity to catecholamines of the adenylate cyclase (AC) activity contained in single tubule samples was investigated on 10 different well defined segments, isolated by microdissection from collagenase treated rabbit kidneys. No responsiveness to isoproterenol (10(-6) M) was observed in the proximal tubule (convoluted and straight portions), the thin descending and thick ascending limbs of the loop of Henle, and the first ("bright") portion of the distal convoluted tubule (DCTb); in contrast high responses (stimulation factors: 4 to 6 fold) were obtained in the second ("granular") portion of the distal convoluted tubule (DCTg), as well as in both the "granular" (CCTg) and the "light" (CCTl) portions of the cortical collecting tubule. In absolute value, however, the CCTl response was definitely lower than those measured in DCTg and CCTg, as is its control activity. In the medullary portion of the collecting tubule, the AC response to isoproterenol was rather poor both in absolute and relative terms. Dose-response curves measured on DCTg samples indicated a threshold response with an isoproterenol concentration below 10(-8) M; half maximal effect corresponded to about 3 x 10(-8) M. CCTl sensitivity to isoproterenol was of the same order of magnitude. Isoproterenol as well as norepinephrine effects in DCTg and CCTl were completely suppressed by 10(-4) M propranolol, indicating that the observed AC stimulation was mediated via receptors of the beta type. In beta blocked CCTl, 10(-6) M norepinephrine did not inhibit vasopressin-induced AC stimulation; in the presence of 10(-6) M norepinephrine, 10(-4) M phentolamine resulted in no additional AC stimulation in DCTg and CCTl; these data suggest the absence of alpha receptors inhibiting AC activity in these structures. In DCTg, AC stimulation induced either by 10(-6) M isoproterenol or by 1 U/ml PTH were observed to be additive when the two hormones were given together. The presence of catecholamine-dependent AC activity in three distal portions of the rabbit nephron is discussed in relation to its possible physiological implications.

Effects of acute unilateral renal denervation in the rat

Studies were undertaken to characterize the renal responses to acute unilateral renal denervation and the mechanisms involved in these responses. Denervation was produced in anesthetized nondiuretic rats by application of phenol to the left renal artery. Studies were also performed in sham-denervated nondiuretic rats. Whole kidney and individual nephron studies were performed before and after denervation or sham denervation. Denervation increased urine volume from the left kidney to about twice its control value (P less than 0.001) and increased urinary sodium excretion from 332 neq min minus -1 to 1,887 neq min minus -1 (P less than 0.001). Glomerular filtration rate (GFR) and renal plasma flow (RPF) remained unchanged in both kidneys after the procedure. The innervated right kidney showed no changes in urine volume or in sodium excretion. After denervation, late proximal ratio of tubular fluid inulin concentration to that of plasma [(F/P)In] decreased from 2.23 to 1.50 (P less than 0.001) while single nephron GFR remained unchanged. Absolute reabsorption decreased from 16.5 to 9.9 n. min minus -1 (P less than 0.001). (F/P)In ratios were also decreased in early distal (from 6.21 to 3.18, P less 0.001) and late distal convolutions (from 16.41 to 8.33, P less than 0.001) during the experimental period. (F/P)Na ratios remained unchanged in the early distal convolutions, but increased from 0.18 to 0.38 (P less than 0.01) in late distal convolutions after denervation. Absolute Na reabsorption after denervation increased in the loop of Henle, distal convolution, and collecting ducts. Any changes in intrarenal hydrostatic pressures after denervation were always small. There were no changes in GFR, RPF, urine volume, urinary sodium excretion, or late proximal (F/P)In after sham denervation. We conclude that the diuresis and natriuresis seen after acute renal denervation were caused by a marked depression of sodium and water reabsorption in the proximal tubule with partial compensation in more distal nephron segments. These responses appeared to be unrelated to systemic or intrarenal hemodynamic changes. The results demonstrate an effect of the renal nerves on proximal tubular function.

Mechanism of antidiuretic effect of beta adrenergic stimulation

The effect of beta adrenergic stimulation on renal-diluting capacity was examined in the dog. Beta adrenergic stimulation with intravenous isoproterenol significantly increased urinary osmolality (U(Osm)) and decreased free water clearance (C(H2O)), and these effects were rapidly reversible with cessation of the infusion. This antidiuretic effect of systemic beta adrenergic stimulation was comparable in innervated and denervated kidneys and was not associated with alterations in glomerular filtration rate or renal vascular resistance. Renal perfusion pressure was maintained constant in all of the experiments. The same dose of isoproterenol, which produced the antidiuretic effect and markedly stimulated cardiac beta adrenergic receptors when infused intravenously, was not found either to increase U(Osm) or to decrease C(H2O) when infused directly into the renal artery. Removal of the source of production and release of antidiuretic hormone (ADH) was, however, found to abolish the effect of intravenous isoproterenol on U(Osm). A small effect on C(H2O) persisted and appeared to be related to an increase in arterial hematocrit. Thus, the results of the study exclude a major role of alterations in renal hemodynamics and renal innervation in the antidiuretic response to beta adrenergic stimulation with isoproterenol. They also provide no support for the hypothesis that beta adrenergic stimulation may directly alter the water permeability of the renal tubular epithelium. Rather the results suggest that the primary mechanism of the antidiuretic effect of beta adrenergic stimulation involves the integrity of the hypothalamoneurohypophyial system and the release of ADH.

Mechanism of increased sodium reabsorption during propranolol administration

The mechanism of diminished sodium excretion induced by propranolol was investigated in the dog. Propranolol (0.3 to 5 mg/kg) was given intravenously in a bolus to 16 dogs, eight of which had the renal perfusion pressure controlled by a suprarenal aortic clamp. In another group of six dogs propranolol (0.1 to 5 , µg/kg/min) was infused into one renal artery for 45 min. Cardiac output (dye dilution), mean arterial and right atrial pressures, heart rate, renal clearances of inulin, creatinine, and para-aminohippurate, and sodium excretion were measured. Total peripheral resistance, central blood volume, stroke volume, renal plasma flow, renal blood flow, renal vascular resistance, glomerular filtration rate, and filtration fraction were calculated.

Intravenous propranolol resulted in significant decreases in cardiac output (–25%) and heart rate (–14%) and increases in total peripheral resistance (28%) and renal vascular resistance (37%). Renal blood flow decreased by 25% and filtration fraction increased 21% as urinary sodium excretion diminished 36%. Glomerular filtration did not change significantly. Infusions of propranolol into one renal artery resulted in either no change in sodium excretion or bilateral changes; thus an intrarenal effect of the drug was not demonstrable.

The data suggest that the changes in renal hemodynamics associated with propranolol administration are secondary to alterations in systemic hemodynamics, particularly a decrease in cardiac output. These alterations in renal hemodynamics, including an increase in renal vascular resistance and filtration fraction, most likely account for the decrease in sodium excretion rather than a direct effect of propranolol on sodium reabsorption.

Renal effects of adenosine 3',5'-cyclic monophosphate and dibutyryl adenosine 3',5'-cyclic monophosphate. Evidence for a role for adenosine 3',5'-cyclic monophosphate in the regulation of proximal tubular sodium reabsorption

Stable water diuresis was produced in anesthetized, hydrocortisone-treated hypophysectomized dogs by infusion of 2.5% dextrose. Infusion of adenosine 3',5'-cyclic monophosphate (cyclic AMP) in the left renal artery decreased ipsilaterally glomerular filtration rate (GFR), cortical and non-cortical renal plasma flow, and tended to increase urine flow (V) and free-water clearance (C(H2O)) despite a decrease in mean arterial pressure. Infusion of dibutyryl adenosine 3',5'-cyclic monophosphate (dibutyryl cyclic AMP) in the left renal artery increased V and C(H2O) significantly (P<0.01) bilaterally with essentially no change in GFR, in total renal plasma flow or its cortical and non-cortical components. For each kidney the magnitude of the change in V was similar to the magnitude of the change in C(H2O) and the change in sodium excretion was trivial. Cyclic AMP probably produced its effects on renal hemodynamics and mean arterial pressure wholly or in part through the action of metabolites such as 5'-AMP and adenosine on the renal and systemic vasculature. The absence of an effect of dibutyryl cyclic AMP on renal hemodynamics and its bilateral effect may be explained by the resistance of this nucleotide derivative to metabolism. Dibutyryl cyclic AMP appears to decrease by direct cellular effect(s) proximal tubular sodium reabsorption but does not prevent virtually complete reabsorption of the increased load of sodium in the distal nephron. This effect on the kidney is qualitatively and quantitatively similar to the effect of renal arterial infusion of isoproterenol. The results suggest that synthesis of cyclic AMP in proximal renal tubule cells in response to stimulation of beta adrenergic or other receptors can mediate a decrease in the proximal tubular reabsorption of sodium.