Characteristics of renin release from isolated superfused glomeruli in vitro.

1. A method is described for studying renin release from superfused rat glomeruli following their rapid isolation by a magnetic iron-oxide technique. 2. Microscopically selected glomeruli were free of tubular components. Some possessed vascular pole protrusions of up to 20 mum, unrelated to renin content. 3. Renin content of 102 batches, each of 400 glomeruli, was 1.34 plus or minus 0.08 times 10-4 Goldblatt hog units per 100 glomeruli (plus or minus S.E. of mean). Different osmolarities (305, 355 and 400 m-osmole/1.), sodium concentrations (110 and 135 mM) and buffer compositions of the preparation solution did not alter this value. Renin content per glomerulus in intact kidney was 100-fold higher. 4. At 30 degrees C the contained juxtaglomerular cells released renin at consistent but decreasing rates over 4-6 hr. Initial release rate in 110 mM sodium, 305 m-osmole/1. solutions were 0.86 plus or minus 0.068 times 10-6 units per 100 glomeruli per 30 min (plus or minus S.E. of mean, n = 42) or 0.546 plus or minus 0.046 percent of content per 30 min. In 135 mM sodium, 305 m-osmole/1. solutions, release was 2.4-fold higher (P less than 0.001) and remained elevated for at least 3 hr. When related to renin content per glomerulus resting release rate in vitro was higher by at most one order of magnitude than calculated in vivo values. 5. Release was augmented by gentle physical agitation of the glomeruli. 6. Release rate was inversely ralated to temperature. On reducing temperature from 30 degrees C, release increased 2.6-fold at 20 degrees C and 6.7-fold at 10 degrees C (P less than 0.001, n = 11). The response was reversible. 7. 3 mM sodium cyanide plus 3 mM sodium iodoacetate caused a variable release of renin associated with depletion of content within 4 hr. The response was progressive and reached a peak after 60 min. 8. Sensitivity of renin release to temperature and metabolic blockade indicates that energy is required for retention of renin by the cell. This, together with the release observed with increased sodium concentration at constant osmolarity, suggests a dependence of renin release upon the mechanism controlling the volume of the juxtaglomerular cell or its organelles.     

Studies on the mechanism of renin release from isolated superfused rat glomeruli: effects of calcium, calcium ionophore and lanthanum.

1. The effects of external medium calcium concentration, the ionophore A(23187) and lanthanum on the rate of renin release in vitro were studied with particular emphasis on results obtained from isolated superfused glomeruli of rat kidneys.2. The response to reduction in superfusate calcium concentration from 2 mM was a graded and reversible increase in the rate of renin release. An increase in release was detectable at 0.2 mM calcium; a threefold increase was found 36 min after a change from 2 mM calcium to calcium-free superfusate. A similar relative increase in release resulted from reductions from 0.1 mM to zero calcium, but the absolute amounts of renin released were greater in this latter series. Renin release from kidney cortical slices similarly increased in response to calcium-free incubation medium.3. The effects of A(23187) on renin release were modest. Changing from 2 mM calcium during control periods to calcium-free Ringer with A(23187) added caused an attenuated and more delayed increase in release than the change to calcium-free Ringer without ionophore. This difference in response was abolished when glomeruli were superfused with 0.1 mM calcium during the preceding 1 hr control period. There was no significant difference in renin release from glomeruli exposed to calcium-free EGTA-Ringer with and without A(23187) in the 2 mM calcium series; in the 0.1 mM calcium series the increase in release following a shift to calcium-free EGTA-containing superfusate with A(23187) added was significantly greater than in the absence of the ionophore.4. Addition of lanthanum (1 or 0.05 mM) to calcium-containing as well as calcium-free superfusate resulted in a significant depression of renin release. Subsequent removal of the lanthanum did not restore the rate of release unless EGTA was added; in the latter case a massive increase in renin release occurred resulting in a marked depletion of the remaining renin content of the glomeruli.5. It is concluded that calcium influences renin release by a direct action on the juxtaglomerular cells. The data support the previous suggestion that basal renin release is a function of active, calcium-dependent cell volume regulation - swelling causing an increase in the release; and further suggest that membrane-bound calcium has a direct effect on the cell membrane permeability to renin.6. The results exclude that calcium-stimulated exocytosis is responsible for basal renin release from the juxtaglomerular cells adhering to isolated glomeruli.     

Further studies on properties of renin granules isolated from rat kidney cortex

The properties of renin granules isolated from rat renal cortex were studied. Renin granules were thermolabile since in 10 min at 0°C twice as much renin was released as at +37°C. Addition of Ca++ (10^-6 M-10^-2 M) did not affect the spontaneous release at +37°C, pH 6.5, during 10 or 30 min incubation. However, when pH was elevated to above 7, renin release was significantly increased by Ca++ (10^-3 M). Additions of various amounts of KCl, NaCl or MgCl₂, which increased the osmolality less than 20 mOsm/kg, did not affect the stability of the renin granules. Mg-ATP (0.5 and 5 mM) as well as Mg-GTP (5 mM) stabilized renin granules at +37°C, pH 6.5, but the corresponding nitrogen analogues Mg-AMP-PNP and Mg-GMP-PNP (0.5 and 5 mM) were not effective. Neither did Mg-AMP (5 mM) nor ATP (5 mM) without Mg++ affect the renin release. No stabilization was observed by Mg-ATP and Mg-GTP in the purified granule preparations. The results suggest the importance of the cleavage of the terminal phosphate in the stabilization process. When the granules prepared at 300 mOsm/kg were first kept at hyperosmotic medium (range 300–1650 mOsm/kg) and then moved back to 300 mOsm/kg, the granules tend to lyse the more the greater was the reduction of the osmolality. The granules were more stable in isotonic sucrose than in isotonic ionic medium.     

Sensitive osmometer function of juxtaglomerular cells in vitro.

The rate of renin release from viable juxtaglomerular cells was studied during prolonged superfusion of isolated rat renal glomeruli with Ringer solutions of differing osmolarities. 2. Reduction in osmolarity from 305 to 285 m-osmole/l. by lowering sucrose concentration caused renin release rate to double. A rise in osmolarity of 30 m-osmole/l. by raising sucrose concentration halved release rate. 3. The response to osmolarity was graded. During the first 30 min following a 20 m-osmole/l. decrease in osmolarity, 1-57 +/- 0-22% (S.E. of mean) of cellular renin content was released; three times this amount was released with a decrease of 50 m-osmole/l. The effect persisted at lower release rates for 60-90 min. 4. The juxtaglomerular cells were four to five times more sensitive to changes in osmolarity through sucrose than sodium chloride concentration. Changes in potassium chloride concentration (7-57 mM) had little effect. 5. Sodium chloride had no direct ionic effect on renin release outside its osmotic properties. 6. The findings support a previous proposal that the rate of renin release in vitro relates directly to the volume of the juxtaglomerular cell. The hypothesis is developed that a similar mechanism may underlie renin secretion in vivo.     

Influence of bicarbonate on the sensitivity of renin release to sodium chloride

Juxtaglomerular cells in vitro are sensitive to changes in osmolality, but it is unknown whether volumeregulatory changes in cellular ion fluxes are important for the renin secretory process. The sensitivity of renin release to increases in osmolality by NaCl was therefore tested on superfused rat glomeruli treated with bicarbonate/chloride exchange inhibitor (DNDS), NaCl/KCl cotransport inhibitor (bumetanide), or Na⁺/H⁺ antiport inhibitor (amiloride) in the presence or absence of bicarbonate. In addition, the sensitivity to increases in osmolality by addition of sucrose was tested in the presence or absence of bicarbonate. Renin release from time controls superfused with a bicarbonatefree Ringer was identical to release from glomeruli superfused with a bicarbonate Ringer. DNDS (0.11 or 1.1 mM) had no effect on renin release in a bicarbonate Ringer. 30 mM sucrose inhibited renin release independently of bicarbonate. 15 mM NaCl stimulated renin release when bicarbonate was absent, while it caused an inhibition in the presence of bicarbonate. When bicarbonate/chloride exchange was inhibited, addition of NaCl stimulated renin release even when bicarbonate was present. The effect of NaCl on renin release was not affected by amiloride (1 mM) or bumetanide (10 M). Thus, volume regulatory mechanisms as known from other cells are not involved in the renin secretory response to small increases in NaCl concentration. Furthermore, the sensitivity of renin release to changes in NaCl concentration is modulated by bicarbonate in a way that depends on a functioning anion-exchange mechanism. The results are compatible with the existence in the membrane of the secretory granule of a Cl^–/HCO ₃ ^– exchange mechanism which mediates exit of Cl^–, and thereby attenuates granular swelling and exocytotic release.     

In mice aggressive behavior provokes vast increase in plasma renin concentration, causing only slight, if any, increase in blood pressure

In mice aggressive behaviour causes a vast release of renin, which can result in about 600-fold increase in plasma renin concentration, reaching 6 Goldblatt Units, corresponding to 15 microgram renin per ml. This increase is mainly due to release of submaxillary renin, but there is also a significantly increased renal renin release. The degree of renin release is influenced by the duration of the aggression and by previous contact with other mice. Contrasting with the vast increase in plasma renin the blood pressure is normal or only moderately increased. This disproportion is not due to the depletion of renin substrate, caused by the increased renin, as shown by the increased calculated renin activity, as well as by decrease in blood pressure elicited by blockade of the renin system. Nor is the disproportion due to change in the sensitivity of the vessels to angiotensin II, the cause of this lack of tachyphylaxis being unknown. By way of exclusion the lack of pronounced increase in blood pressure can be explained by homeostatic function of the cardiovascular reflexes, which may also account for the fact that the pressor response after injection of pure submaxillary renin is only short, contrasting with a prolonged marked increase in plasma renin concentration.     

In mice aggressive behaviour provokes vast increase in plasma renin concentration,causing only slight,if any,increase in blood pressure

In mice aggressive behaviour causes a vast release of renin, which can result in about 600-fold increase in plasma renin concentration, reaching 6 Goldblatt Units, corresponding to 15μg renin per ml. This increase is mainly due to release of submaxillary renin, but there is also a significantly increased renal renin release. The degree of renin release is influenced by the duration of the aggression and by previous contact with other mice. Contrasting with the vast increase in plasma renin the blood pressure is normal or only moderately increased. This disproportion is not due to the depletion of renin substrate, caused by the increased renin, as shown by the increased calculated renin activity, as well as by decrease in blood pressure elicited by blockade of the renin system. Nor is the disproportion due to change in the sensitivity of the vessels to angiotensin II, the cause of this lack of tachyphylaxis being unknown. By way of exclusion the lack of pronounced increase in blood pressure can be explained by homeostatic function of the cardiovascular reflexes, which may also account for the fact that the pressor response after injection of pure submaxillary renin is only short, contrasting with a prolonged marked increase in plasma renin concentration.     

Renin secretion from permeabilized juxtaglomerular cells requires a permeant cation

 The cytosolic concentration of chloride correlates directly with renin secretion from renal juxtaglomerular granular (JG) cells. In the present study, the mechanism by which chloride stimulates renin release was investigated in a preparation of permeabilized rat glomeruli with attached JG cells. An isosmotic increase in the concentration of chloride by 129 mM stimulated renin release 16- to 20-fold. Substitution of K⁺ by the impermeant cation N-methyl-d-glucamine (NMDG) abolished this response, while substitution with Na⁺ caused marginal inhibition. Substitution with Cs⁺ had no effect. Addition of sucrose, which permeates the secretory granules poorly, also abolished the stimulation of renin secretion by KCl. The response to KCl was not affected by K⁺-channel antagonists or by agonists of K⁺ channels. Chloride channel blockers were also without effect on the secretory response to KCl. When the ATP concentration was lowered from 1 to 0.1 mM renin release was stimulated, while an increase in the ATP concentration from 1 to 5 mM had no effect. Blockers of ATP-sensitive (K_ATP) channels did not modify the response to chloride. The present data suggest that chloride stimulates renin release after entry of KCl into the renin secretory granules which results in swelling and release of renin. Received: 3 July 1998 / Received after revision: 9 September 1998 / Accepted: 8 October 1998     

K(+)- and temperature-evoked taurine efflux from hypothalamic astrocytes

Hypothalamic astrocytes in culture released taurine, a suspected inhibitory amino acid neurotransmitter/neuromodulator/osmoregulator, in response to isoosmotically increasing extracellular K+ in a dose-dependent fashion. In the absence of added Ca2+, basal release levels rose to approach those obtained after exposure to 60 mM K+ in the presence of 2.5 mM Ca2+, and were only partially lowered by the addition of 10 mM Mg2+. Stimulation with K+ (60 mM) did not further increase taurine efflux above the high basal levels seen in the absence of Ca2+. Under standard conditions complete replacement of Na+ with choline Cl had little effect on basal taurine release, but reduced K(+)-evoked (60 mM) efflux by 60%. The temperature dependence of the basal levels of taurine released from hypothalamic astrocytes was similar to that seen for cultured cerebellar astrocytes and neurons over the range 5-50 degrees C. Taurine release increased from 5 to 15 degrees C, remained constant between 15 and 33 degrees C, decreased between 33 and 37 degrees C and increased thereafter. The infection point of increased basal taurine release seen around 37 degrees C (most prominent in astrocytes), may be of physiological significance. Results presented also show that the ion (Na+, Ca2+ and K+) sensitivities of taurine efflux for cultured hypothalamic astrocytes are similar to those previously reported for cultured astrocytes from the cerebellum.     

Studies on renin release in vitro

1) Measurements of renin secretion from single arterioles at time intervals down to 20 seconds showed that the renin secretion is episodic, the amount of renin released during each episode corresponding to the estimated content of one secretory granule. 2) A decrease in osmolality elicits episodic release of renin from single arterioles, stimulates renin release from isolated glomeruli transiently, and is associated with swelling of the secretory granules and formation of contacts between granules and the plasmalemma. 3) Increases in osmolality produce sustained inhibition of the renin secretion, and prevents swelling of the organelles of the juxtaglomerular epithelioid cells. 4) Treatment of isolated glomeruli with weak permeable bases has a biphasic effect on renin release: an initial transient stimulation, which can be blocked with sucrose, and a delayed inhibition which may be associated with an increase in intracellular pH. 5) Results with the monovalent cation ionophores nigericin and monensin, are similar to those obtained with weak permeable bases, and suggest that their effects are due to swelling and alkalinization of acidic cellular organelles. 6) A decrease in the extracellular calcium concentration results in sustained stimulation of renin secretion to a variable level dependent on the season. 7) After stimulation with a low extracellular calcium concentration, the sensitivity of secretion rate to osmotic stimuli is proportionally increased. A high extracellular osmolality blocks the stimulatory effect of a low calcium concentration. 8) Renin release is not correlated to the release of adenylate kinase.     

Effects of osmolality and calcium on renin release from superfused rat glomeruli treated with nigericin or monensin

Proton gradients may be important for the induction of swelling and exocytosis of secretory renin granules during basal renin release (RR). The sensitivity of renin release to changes in osmolality and to calcium was therefore tested on superfused rat glomeruli that had been pretreated with the monovalent cation/proton ionophores monensin and nigericin to dissipate granular proton gradients. Furthermore it was tested whether NH₄Cl stimulates RR by inducing waterfluxes. Pretreatment of glomeruli with 10 M nigericin or monensin inhibited RR, and suppressed the response to calcium removal, independently of the presence of 0.5 mM EGTA. In contrast, the stimulatory effect of a hypo-osmotic challenge (–20 mM sucrose) was unchanged after pretreatment with nigericin or monensin. The stimulation induced by 15 mM NH₄Cl was prevented by addition of 20 mM sucrose. The results suggest that dissipation of proton gradients with the ionophores inhibit RR late in the secretory pathways, independently of effects on the Golgiapparatus and intracellular calcium concentration. The results are consistent with the hypothesis that a low granular pH is important for driving JGC-granule swelling and exocytosis.Parts of the results were presented at 19th ASN Meeting, Washington DC, December 1986 and the 10th ISN Congress, London, July 1987     

Aggression-provoked renin release from extrarenal and extrasubmaxillary sources in mice.

In submaxillary sialoadenectomized and nephrectomized mice aggressive behaviour provoked 5 to 40-fold increases in plasma renin concentration. The changes in renin concentration with time were different in different groups of confronted mice with only partial correlation between the pattern and the observable degree of fight. The changes were similar in sialoadenectomized mice with untouched kidneys as in sialoadenectomized and nephrectomized, indicating that aggression causes no measurable, if any, renal renin release. Repeated aggression with 2 hourly intervals provoked repeated renin release from extrarenal and extrasubmaxillary sources. The renin concentrations of different organs showed the same mutual relationship as in other mammals, but were about 10-fold higher. Splenectomy was without effect on the aggression-provoked renin release. Antibodies against pure mouse renin neutralized the renin in plasma and organs, which contained only insignificant, if any, pepsin activatable inactive renin. Adrenaline, apomorphine, carbachol and dihydralazine were as isoprenaline and noradrenaline without effect on renin release in sialoadenectomized and nephrectomized mice.     

Aggression-provoked renin release from extrarenal and extrasubmaxillary sources in mice

In submaxillary sialoadenectomized and nephrectomized mice aggressive behaviour provoked 5 to 40-fold increases in plasma renin concentration. The changes in renin concentration with time were different in different groups of confronted mice with only partial correlation between the pattern and the observable degree of fight. The changes were similar in sialoadenectomized mice with untouched kidneys as in sialoadenectomized and nephrectomized, indicating that aggression causes no measurable, if any, renal renin release. Repeated aggression with 2 hourly intervals provoked repeated renin relase from extrarenal and extrasubmaxillary sources. The renin concentrations of different organs showed the same mutual relationship as in other mammals, but were about 10-fold higher. Splenectomy was without effect on the aggression-provoked renin release. Antibodies against pure mouse renin neutralized the renin in plasma and organs, which contained only insignificant, if any, pepsin activatable inactive renin. Adrenaline, apomorphine, carbachol and dihydralazine were as isoprenaline and noradrenaline without effect on renin release in sialoadenectomized and nephrectomized mice.     

The effect of isoprenaline infusion on renal renin and angiotensinogen gene expression in the anaesthetised rat

In this study, we investigated the ability of acute infusions of isoprenaline to alter renin and angiotensinogen gene expression in the kidney of rats anaesthetised with chloralose-urethane. Groups of rats received I.V. infusions of either saline or the beta-adrenoceptor agonist isoprenaline at 400 ng x kg(-1) x min(-1) for 4 h. The isoprenaline infusion caused a sustained decrease in mean blood pressure of approximately 20 mmHg (P < 0.01), an increase in heart rate of 50 beats x min(-1) (P < 0.01) and reductions in urine flow and sodium excretion of 80-90 % (both P < 0.01). Renal blood flow and glomerular filtration rate were transiently reduced by 21 % (P < 0.01) and 61 % (P < 0.001), respectively, in the first hour, recovering to baseline levels after 4 h of infusion. At the end of the study, plasma renin activity was raised approximately 6-fold (P < 0.01) while renal renin and angiotensinogen mRNA levels were 1.8- and 1.5-fold higher (both P < 0.05) compared to the control group (saline infusion). The isoprenaline-induced renin secretion could have been mediated via the activation of beta-adrenoceptors resulting in the exocytosis of renin-containing granules, with a smaller contribution being due to reduced renal haemodynamics. The increase in renal renin gene expression in response to isoprenaline was probably due primarily to the intracellular signalling processes acting directly on nuclear mechanisms. Similarly, the increased renal angiotensinogen gene expression most probably reflected a direct action of the isoprenaline. These findings provide evidence that catecholamines are involved in mechanisms that rapidly alter the expression of the genes of the renin-angiotensin system within the kidney.     

Ion and ion channel involvement in alpha-melanocyte-stimulating hormone secretion from superfused slices of rat hypothalamus

Release of alpha-melanocyte-stimulating hormone (alpha-MSH) from 250 micron frontal slices of rat hypothalamus superfused at 37 degrees C with oxygenated artificial cerebrospinal fluid (ACSF) was quantified in freeze-dried samples of ACSF by radioimmunoassay. Significant reproducible increases in alpha-MSH release were caused by 40-70 mM K+ in ACSF, maximum release being caused by 50 mM K+. Fifty mM K+-stimulated alpha-MSH release was abolished in the absence of Ca2+ from ACSF and by the presence of 10(-6) M tetrodotoxin. Tetrapentylammonium ions, 10(-4) M and 10(-3) M, stimulated dose-dependent increases in alpha-MSH release. The data support a putative neurotransmitter/neuromodulator role for alpha-MSH in the CNS.     

Influence of prehydration on the changes in renal tissue composition induced by water diuresis in the rat

1. The composition of renal tissue was determined in rats before and immediately after intravenous infusion of dextrose (2.5 g/100 ml.) in amounts sufficient to administer a positive fluid load of 4% body weight over 2 hr. The rats were classified into three groups, according to the preinfusion urine osmolality: hydropaenia, normal and moderately diuretic (over 2400, 800-1500 and below 800 mu-osmoles/g H(2)O, respectively).2. In non-infused rats, the steepness of the corticomedullary osmolal gradient varied, due to differences in both water and solute (sodium and urea) contents, and was related to urinary osmolality. Whereas differences in medullary and papillary solute contents occurred between all three groups, papillary water content was significantly higher only in the moderately diuretic animals.3. Dextrose infusion caused the induction of water diuresis, the lowest urinary osmolalities being produced in the previously moderately diuretic animals.4. Dextrose infusion caused a considerable reduction in the steepness of the corticomedullary osmolal gradient in all rats, particularly in the previously hydropaenic animals, due to changes in both solute (sodium and urea) and water contents. Whereas reductions in medullary and papillary solute contents occurred in all three groups, there was no further increase in papillary water content from the already high values seen in the noninfused diuretic animals.5. Thus, dextrose infusion largely abolished any previous differences in tissue water content, whereas significant, though small, differences in osmolal (particularly urea) content persisted.6. These data are discussed in terms of changes and differences in endogenous antidiuretic hormone (A.D.H.) release.7. Changes in the magnitude and direction of the urinary-papillary urea concentration difference are discussed in terms of passive transport, with probable A.D.H.-induced changes in nephron urea permeability.     

Temperature dependence of extracellular ionic changes evoked by anoxia in hippocampal slices

1. Extracellular [K] and [Ca] were measured with ion-selective microelectrodes in CA1 pyramidal cell layer of rat hippocampal slices in an interface chamber. 2. Near room temperature (21-22 degrees C), brief periods of anoxia (3- to 4-min substitution of 95% N2-5% CO2 for 95% O2-5% CO2) produced very small changes in [K]o [-0.022 +/- 0.10 (SE) mM] or [Ca]o (-0.030 +/- 0.0029 mM) and were associated with only minor depression of population spikes (-22.5 +/- 11%). 3. Stratum radiatum (SR) stimulation (0.2-5 Hz) could evoke substantial increases in [K]o (by 0.2-2 mM); although variable, they were consistent in any one slice. The same stimulation regularly caused only small depressions of [Ca]o (by less than 0.1 mM, typically). 4. Also at 21-22 degrees neither stimulation nor anoxia generated more than minimal reductions in extracellular space [by 2.3 +/- 0.94%, as measured by the tetramethylammonium (TMA) method], and spreading depression (SD) occurred in only 1 out of 20 slices. 5. At 33-34 degrees C, anoxia (also for 3-4 min) consistently produced more substantial increases in [K]o (0.83 +/- 0.18 mM); but the apparent changes in [Ca]o at 33 degrees C (0.058 +/- 0.12 mM) could not with certainty be distinguished from thermoelectric artifacts. There was a severe depression of population spikes (-76 +/- 10%). 6. Although electrical stimulation evoked greater reductions in [Ca]o, increases in [K]o were 50% smaller. 7. During anoxia at 33-34 degrees C, the extracellular space was significantly reduced, by 6.1 +/- 0.9%. Moreover, in 37% of the slices, either stimulation or anoxia triggered massive increases in [K]o (greater than 10 mM) and large reductions in [Ca]o (less than 1 mM), associated with SD-like swings in focal potential. 8. It is concluded that the extracellular ionic changes evoked by brief anoxia do not contribute in a major way to the depression of synaptic transmission.     

Involvement of renal alpha- and beta-adrenoceptors in release of renin by carotid baroreflex.

In anesthetized vagotomized dogs with renal arterial pressure constant, carotid sinus hypotension (BCO) caused a reflex rise in systemic arterial pressure, a fall in renal blood flow, and a similar increase in renin release from both kidneys. Unilateral alpha-adrenoceptor blockade with phenoxybenzamine resulted in an increase in basal renal blood flow, a depression of basal renin release, and an abolition of the responses to BCO in the treated kidney. The untreated kidney responsed to BCO as before. Nonblocked and alpha-blocked kidneys released similar amounts of renin when renal blood flow was mechanically reduced by aortic constriction. Administration of propranolol to the nonblocked kidney prevented the release of renin but not the hemodynamic changes resulting from BCO. The experiments demonstrated that under certain conditions carotid sinus hypotension produced alpha-adrenoceptor-mediated changes in the kidney sufficient to cause increased renin release. A step in the renin release mechanism subsequent to the alpha-adrenoceptor-mediated changes in sensitive to propranolol.     

Stimulus-secretion coupling in pancreatic acinar cells: inhibitory effects of calcium removal and manganese addition on pancreozymin-induced amylase release.

1. An experimental technique utilizing 'denervation diuresis' from one kidney with measurement of renin release from the contralateral innervated kidney was developed to study the sensitivity of renin secretion to volume depletion. 2. With urine excretion, release of renin increased progressively from the innervated kidney. The increase was significant at a sodium deficit of 0-23 mole.kg-1. At a sodium deficit of 0-6 m-mole.kg-1 renin release had doubled. 3. Bilateral vagotomy did not alter this response. 4. Precise replacement of sodium loss with isotonic saline but without replacement of other urinary components returned renin release to control levels. 5. Slow haemorrhage causing a rate of volume and sodium loss equivalent to urinary drainage did not alter the rate of renin release. 6. With a single denervated kidney and contralateral nephrectomy, renin release fell progressively to minimal levels despite sodium deficits up to 2-6 m-mole.kg-1. 7. It is concluded that renin secretion is sensitive to at most a 0-5% change in body fluid volume and should be considered a primary response to volume depletion. The sensitivity of the response depends upon normal renal innervation but is not mediated via vascular volume receptors nor via receptors innervated by the vagus. 8. It is proposed that the extreme sensitivity of the renin-secreting system in these experiments results from the combination of volume depletion and slight hypotonicity of extracellular fluid acting on the renal afferent arteriole without the mediation of the macula densa,     

Haemodynamic and ADH responses to central blood volume shifts in cardiac-denervated humans

Haemodynamic responses and antidiuretic hormone (ADH) were measured during body position changes designed to induce blood volume shifts in 10 cardiac transplant recipients to assess the contribution of cardiac and vascular volume receptors in the control of ADH secretion. Each subject underwent 15 min of a control period in the seated posture, then assumed a lying posture for 30 min at 6 degrees head-down tilt (HDT) followed by 30 min of seated recovery. Venous blood samples and cardiac dimensions (echocardiography) were taken at 0 and 15 min before HDT, 5, 15 and 30 min of HDT, and 5, 15 and 30 min of seated recovery. Blood samples were analysed for haematocrit, plasma osmolality, plasma renin activity (PRA) and ADH. Resting plasma volume (PV) was measured by Evans blue dye and per cent changes in PV during posture changes were calculated from changes in haematocrit. Heart rate (HR) and blood pressure (BP) were recorded every 2 min. In the cardiac transplant subjects, mean HR decreased (BP less than 0.05) from 102 b.p.m. pre-HDT to 94 b.p.m. during HDT and returned to 101 b.p.m. in seated recovery while BP was slightly elevated (P less than 0.05). PV was increased by 6.3% (P less than 0.05) by the end of 30 min of HDT but returned to pre-HDT levels following seated recovery. Plasma osmolality was not altered by posture changes. Mean left ventricular end-diastolic volume increased (P less than 0.05) from 90 +/- 5 ml pre-HDT to 105 +/- 4 ml during HDT and returned to 88 +/- 5 ml in seated recovery. Plasma ADH was reduced by 28% (P less than 0.05) by the end of HDT and returned to pre-HDT levels with seated recovery. PRA was also reduced by 28% (P less than 0.05) with HDT. These responses were similar to those of six normal cardiac-innervated control subjects and one heart-lung recipient. Therefore, cardiac volume receptors are not the only mechanism for the control of ADH release during acute blood volume shifts in man.