The status of ORT (oral rehydration therapy) in Bangladesh: how widely is it used?

During 1980-1990 BRAC, a Bangladeshi non-governmental organization, taught over 12 million mothers how to prepare oral rehydration therapy (ORT) at home with lobon (common salt) and gur (unrefined brown sugar). This was followed by a strong promotion and distribution of prepackaged ORS by various agencies including the government. In 1993 we assessed knowledge of ORT preparation, its local availability and its use for the management of diarrhoea. Over 9000 households in 90 villages were revisited; 306 government outreach health workers, 296 drug sellers, and 237 village doctors were interviewed; 152 government facilities and 495 pharmacies/shops were visited. ORT prepared by mothers in a sub-sample of the households was analyzed for chloride content and interviewers collected information on use of ORT for diarrhoeal episodes occurring in the preceding two weeks. The data quality was assessed through a resurvey of sample respondents within two weeks of the first interview. Over 70% of the mothers could prepare a chemically 'safe and effective' ORS. A significant proportion of these mothers were very young at the time of the mass campaigns using house to house teaching, implying an intergenerational transfer of the knowledge on ORT. ORT was found to be used in 60% of all diarrhoeal episodes, but the rate varied with the type of diarrhoea, being highest for daeria (severe watery diarrhoea) and lowest for amasha (dysentery). Drug sellers and village doctors now recommend ORT much more frequently than before. Members of the medical profession (qualified and unqualified) still lag behind in prescribing the use of ORT. The availability of pre-packaged ORS in rural pharmacies has improved enormously. There is convincing evidence that the widescale promotion in the past of ORS for dehydration in diarrhoea has led to this marked improvement today. Nevertheless the use of rice-based ORS, culturally appropriate messages and the promotion of ORS with food offer opportunities to further improve the utilization of ORT.

Role of 5-hydroxytryptamine3 (5-HT3) antagonists in the prevention of emesis caused by anticancer therapy

Most anticancer drugs are cytotoxic and produce various side-effects, among which nausea and vomiting are almost ubiquitous and usually extremely distressing to the patient. Cancer chemotherapy elicits two main phases of vomiting: an intense, acute phase of vomiting that occurs almost immediately following anti-cancer therapy and a milder, delayed phase of nausea and vomiting of longer duration. The mechanisms underlying the induction of nausea and vomiting after cancer chemotherapy are poorly understood but may be mediated by serotonin (5-hydroxytryptamine or 5-HT), particularly in the acute phase. Serotonin activates 5-HT3 receptors, which function as ligand-gated ion channels located either in the periphery and/or in the central nervous system to produce emesis, among other effects. The peripheral 5-HT3 receptors may be pharmacologically distinct from the central 5-HT3 receptors and may exhibit some association with GTP-binding proteins. In addition, different populations may exist as distinct subtypes of the same receptor. The 5-HT3 receptor antagonist ondansetron (GR 38032F) is effective in preventing the emesis induced by cytotoxic agents currently used in the treatment of many forms of cancer. Ondansetron has, comparatively, a much higher efficacy in the treatment of acute emesis following cancer chemotherapy than it does in the delayed phase, suggesting that the late phase of emesis may be mediated by other distinct mechanisms.

Spinal morphine/clonidine antinociceptive synergism: involvement of G proteins and N-type voltage-dependent calcium channels

When morphine and clonidine are coadministered into the spinal cord (intrathecally) the resulting antinociception is greater than would be expected if the drug responses were additive; thus, a synergistic interaction. The mechanism for this synergistic interaction was investigated using agents which alter calcium channel function and G protein function. Drugs were administered intrathecally to mice and antinociception was measured using the tail flick test. The L-type calcium channel antagonists nifedipine (15 micrograms) and verapamil (15 micrograms) and the N-type antagonist omega-conotoxin GVIA (3 and 30 ng) decreased ED50 values for both morphine and clonidine three-to five-fold. The L-type calcium channel activator Bay K 8644 had a biphasic effect; 1.7 ng increased, although 170 ng decreased, morphine and clonidine ED50 values. None of the calcium channel modifiers affected the morphine/clonidine synergism. In mice pretreated with pertussis toxin (PTX, one, 10-ng dose 21 days previously), the morphine ED50 value increased two-fold, although the clonidine ED50 value was not changed. PTX pretreatment did not alter the morphine/clonidine synergism. Also, in PTX-pretreated mice, nifedipine and 1.7 ng Bay K 8644 did not alter the morphine/clonidine synergism. However, in PTX-pretreated animals omega-conotoxin GVIA (3 ng) changed the morphine/clonidine synergism to an additive interaction. Thus, both N-type calcium channels and PTX-sensitive G proteins are likely involved in spinal morphine/clonidine synergism.

Loss of tramtrack gene activity results in ectopic R7 cell formation, even in a sina mutant background

We have screened a collection of transposable-element-induced mutations for those which dominantly modify the extra R7 phenotype of a hypomorphic yan mutation. The members of one of the identified complementation groups correspond to disruptions of the tramtrack (ttk) gene. As heterozygotes, ttk alleles increase the percentage of R7 cells in yan mutant eyes. Just as yan mutations increase ectopic R7 cell formation, homozygous ttk mutant eye clones also contain supernumerary R7 cells. However, in contrast to yan, the formation of these cells in ttk mutant eye tissue is not necessarily dependent on the activity of the sina gene. Furthermore, although yan mutations dominantly interact with mutations in the Ras1, Draf, Dsor1, and rolled (rl) genes to influence R7 cell development, ttk mutations only interact with yan and rl gene mutations to affect this signaling pathway. Our data suggest that yan and ttk both function to repress inappropriate R7 cell development but that their mechanisms of action differ. In particular, TTK activity appears to be autonomously required to regulate a sina-independent mechanism of R7 determination.

Regional differences in the negative inotropic effect of acetylcholine within the canine ventricle

1. Regional differences in the effects of ACh on sub-epicardial, mid-wall and sub-endocardial cells of the dog left ventricle have been studied. 2. ACh produced a dose-dependent, atropine-sensitive negative inotropic effect that was greatest in sub-epicardial cells and small or absent in sub-endocardial cells. 3. In sub-epicardial (but not sub-endocardial) cells, ACh also resulted in a dose-dependent decrease in action potential duration. The inotropic effect of ACh on sub-epicardial cells was primarily the result of the decrease of action potential duration, because during trains of voltage clamp pulses the inotropic effect of ACh was reduced or abolished. At a holding potential of -80 mV, 10(-5)M ACh decreased L-type Ca2+ current by approximately 8% and this is thought to be responsible for the small inotropic effect during trains of pulses. 4. Although 4-AP, a blocker of the transient outward current (I(to)), abolished the "spike and dome' morphology of the sub-epicardial action potential, it had little or no effect on the actions of ACh on sub-epicardial cells. ACh had no effect on I(to) in sub-epicardial cells in voltage clamp experiments. 5. ACh activated a Ba(2+)-sensitive outward current (IK,ACh) in sub-epicardial cells, but little or no such current in sub-endocardial cells. In sub-epicardial cells, ACh also inhibited the inward rectifier current, IK,1. 6. It is concluded that in left ventricular sub-epicardial cells, ACh activates IK,ACh. This results in a shortening of the action potential and, therefore, a negative inotropic effect. In subendocardial cells, ACh activates little or no IK,ACh and, therefore, it has little or no negative inotropic effect. This may result from a regional variation in the expression of the muscarinic K+ channel.

The role of adenosine in functional hyperaemia in the coronary circulation of anaesthetized dogs

1. The aim of this investigation was to determine the contribution of adenosine to coronary active hyperaemia in the dog denervated heart by using adenosine deaminase. 2. Beagles were anaesthetized with thiopentone sodium (500 mg, I.V.) and chloralose (100 mg kg-1, LV.) and artificially ventilated. The hearts were denervate by bilateral cervical vagotomy and cardiac sympathectomy. Blood samples were collected from the coronary sinus via a cannula passed through the right external jugular vein. The anterior descending or circumflex branch of the left coronary artery was cannulated and perfused with blood from the left subclavian artery under systemic blood pressure through an electromagnetic flow probe and a perfusion circuit. The heart was paced (3 V, 0.2 ms and a suitable frequency) via two electrodes attached to the right atrium from 109 +/- 7.3 to 170 +/- 9.8 beats min-4 (means +/- S.E.M.) for 3-4 min, first during an infusion of the solvent, and then during an infusion of a solution of adenosine deaminase (5 U kg-1 min-1) into the circuit. 3. In seventeen tests in eight dogs, infusion of adenosine deaminase did not cause a significant change in the basal coronary blood flow nor in the immediate increase (within 10s) in blood flow induced by pacing the heart from its basal rate to 170 beats min-1. However, adenosine deaminase did cause a significant attenuation by 58 +/- 5.2% (P < 0.05) of the increase in coronary blood flow induced at 3-4 min of pacing from 31 +/- 4.6 to 43 +/- 5.8 ml min-1 (100 g cardiac tissue)-1. Concomitantly, the pacing-induced increase in coronary vascular conductance (from 0.41 +/- 0.08 to 0.54 +/- 0.12 ml min-1 (100 g)-1 mmHg-1) was reduced by 75 +/- 6.6% (P < 0.02) and the increase in myocardial O2 consumption (from 13 +/- 3.5 to 21 +/- 4.2 ml min-1 (100 g)-1) was reduced by 50 +/- 12% (P < 0.05) but without significant changes in oxygen extraction or myocardial contractility. 4. The results show that although adenosine is unlikely to play a significant role in the regulation of the basal coronary blood flow, it can play a major role in the coronary active (functional) hyperaemia induced by atrial pacing to a high rate in the denervated heart of anaesthetized dogs.

Early repair of inguinal hernia in preterm infants with oxygen-dependent bronchopulmonary dysplasia

Despite inguinal hernia being both common and problematic in a significant proportion of preterm infants with bronchopulmonary dysplasia (BPD), there has been a reluctance to intervene surgically for fear of exacerbating the underlying lung disease. We report our experience of early operation in 12 consecutive infants with varying degrees of oxygen-dependent BPD and investigate the effect of general anaesthesia and herniotomy on pulmonary function by measuring oxygen requirements prior to and following operation. Two infants who required oxygen in a concentration in excess of 95% failed to improve and died from the pulmonary disease 6 and 8 weeks following their operation. The remaining infants all showed a reduction in mean oxygen requirements in the weeks following operation. We conclude that, in the short term, hernia repair performed under general anaesthesia in infants with BPD of varying severity had no adverse effects on respiratory function, as determined by oxygen requirements. We suggest that in certain infants early repair may have been beneficial--potential mechanisms are explored.

Primary neural involvement in renal haemodynamic and functional responses to prolonged stimulation of atrial receptors in anaesthetized dogs

To determine the precise contributory role of neural and humoral factors in the efferent mechanism of the atrial receptor-renal reflex, we have examined the effects of prolonged (45 min) stimulation of left atrial receptors on renal haemodynamics and function simultaneously in both kidneys (right kidney intact and left kidney denervated) of anaesthetized dogs. Aortic pressure in these dogs was held constant by means of an arterial reservoir connected to the aorta; heart rate changes were prevented by blocking beta 1-adrenoceptor activity with atenolol (2 mg kg-1 i.v.). Localized stimulation of atrial receptors in six dogs increased renal blood flow (6 +/- 2%), creatinine clearance (11 +/- 4%), urine flow (9 +/- 3%), sodium excretion (14 +/- 7%) and osmolal excretion (10 +/- 4%), and decreased free water clearance (14 +/- 7%) in intact kidneys, but led to no changes in denervated kidneys. In an additional four dogs, cooling the vagus nerves to 6-7 degrees C or cutting them in the neck abolished the renal responses to stimulation of atrial receptors in these stabilized preparations. These data clearly demonstrate that the renal responses to prolonged stimulation of atrial receptors are primarily mediated via myelinated vagal afferents and renal sympathetic efferents.

Modification of carotid chemoreceptor-induced changes in renal haemodynamics and function by carotid baroreflex in dogs

1. Mongrel dogs were anaesthetized with thiopental sodium and chloralose and artificially ventilated. The carotid sinus regions were vascularly isolated and perfused either with arterial or mixed (arterial and venous) blood (PO2, 44.2 +/- 3.3 mmHg, mean +/- S.E.M.) to stimulate the chemoreceptors. Cervical vagosympathetic trunks were ligated and atenolol (2 mg kg-1, I.V.) was given in all dogs and gallamine triethiodide (3 mg kg-1 h-1, I.V.) was given in two dogs. Renal blood flow was measured by an electromagnetic flowmeter, glomerular filtration rate by creatinine clearance, sodium excretion by flame photometry and solute excretion by osmometry. The viability of the preparations was tested by recording total vascular capacitance responses to stimulation of carotid baro- and chemoreceptors. 2. In eleven tests in seven dogs at a constant aortic pressure of 88.9 +/- 2.6 mmHg stimulation of carotid chemoreceptors at a high carotid sinus pressure (194.0 +/- 3.6 mmHg) resulted in significant increases in urine flow of 22.8 +/- 3.0%, urinary sodium excretion of 30.7 +/- 5.2%, fractional sodium excretion of 35.3 +/- 18.6%, osmolar excretion of 17.5 +/- 4.1% and a decrease in free water clearance of 30.8 +/- 3.1% without significant changes in urinary sodium concentration, renal blood flow, glomerular filtration rate, and filtration fraction. 3. In seventeen tests in these seven dogs at a constant aortic pressure of 94.0 +/- 2.2 mmHg, stimulation of carotid chemoreceptor at a low carotid sinus pressure (72.0 +/- 1.3 mmHg) resulted in significant decreases in renal blood flow of 10.6 +/- 2.5%, glomerular filtration rate of 19.6 +/- 6.8%, filtration fraction of 13.2 +/- 5.5%, urine flow of 23.4 +/- 4.1%, urinary sodium concentration of 20.3 +/- 4.1%, urinary sodium excretion of 38.5 +/- 4.6%, fractional sodium excretion of 20.2 +/- 7.7%, osmolar excretion of 23.9 +/- 4.0% and an increase in free water clearance of 23.1 +/- 2.5%. 4. The results show that moderate stimulation of carotid chemoreceptors at a low carotid sinus pressure, when the activity in renal nerves is high and blood volume is low, can produce significant reflex decreases in renal haemodynamic and functional variables. However, at a high carotid sinus pressure when the renal sympathetic activity is low and blood volume is high, carotid chemoreceptor stimulation produces diuresis and natriuresis but no change in renal haemodynamics.

The formalin test in the naked mole-rat (Heterocephalus glaber): analgesic effects of morphine, nefopam and paracetamol

The present experiments were initiated to study the effects of morphine, nefopam and paracetamol in the naked mole-rat, a hairless rodent that lives in subterranean colonies of up to 300, following the inability to demonstrate morphine analgesia in the hot-plate test in the rodent. The formalin test was used. Injection of 20 microliters 10% formalin produced two periods of high licking and pain behaviour, the early (0-5 min) and the late phase (15-60 min). Morphine (10 or 20 mg/kg), nefopam (10 or 20 mg/kg) and paracetamol (200 mg/kg) significantly inhibited the two phases. Paracetamol (400 mg/kg) produced significant analgesia only during the late phase. It is concluded that, unlike in the hot-plate test, it is possible to demonstrate the analgesic effects of morphine in the naked mole-rat, in the formalin test.

Effects of codeine, naproxen and dexamethasone on formalin-induced pain in the naked mole-rat

A dilute solution of formalin (20 microliters of 10% formalin) was injected subcutaneously in the dorsal right hind paw of the naked mole-rat. The injection of the dilute formalin produced two periods of pain behaviour, the early (0-5 minutes) and the late phase (25-60 minutes). These were quantified as the total time spent licking the injected paw. Codeine phosphate (10, 25 or 50 mg kg-1) significantly reduced pain behaviour in both the early and late phase. Codeine administration also induced aggressive, hyperactive behaviour and motor impairment that was naloxone (2 mg kg-1) reversible. Naproxen (200 mg kg-1) and dexamethasone phosphate (30 mg kg-1) significantly reduced licking activity in the late phase only.

Effects of left atrial receptor stimulation on carotid chemoreceptor-induced renal responses in dogs

1. Dogs were anaesthetized with thiopentone sodium and alpha-chloralose and artificially ventilated. The carotid sinus regions were vascularly isolated and perfused with arterial or venous blood to stimulate the chemoreceptors. Left atrial receptors were stimulated by distending four balloons, three in the left pulmonary vein-atrial junctions and one in the left atrial appendage. Mean aortic pressure was held constant by means of a pressure control device. Atenolol and atropine (2.0 and 0.5 mg kg-1, respectively), and gallamine triethiodide (3.0 mg kg-1 h-1) were given I.V. Renal blood flow was measured by an electromagnetic flowmeter, glomerular filtration rate by creatinine clearance, urinary sodium by flame photometry and solute excretion by osmometry. 2. In fifteen tests in eight dogs (in one dog responses of both left and right kidneys were determined), at a constant aortic pressure (AoP) of 92.0 +/- 3.2 mmHg, and carotid sinus pressure (CSP) of 95.0 +/- 2.0 mmHg, stimulation of left atrial receptors with balloon inflation resulted in significant increases in renal blood flow (RBF) by 8.3 +/- 0.9 from 255.0 +/- 14.6 ml min-1 (100 g kidney weight)-1 (n = 9), in glomerular filtration rate (GFR) by 4.1 +/- 0.6 from 21.2 +/- 1.9 ml min-1 (100 g)-1, in filtration fraction (FF) by 0.04 +/- 0.003 from 0.20 +/- 0.01, in urine flow rate (V) by 0.08 +/- 0.02 from 0.33 +/- 0.05 ml min-1 (100 g)-1, in sodium excretion (UNaV) by 4.4 +/- 0.9 from 27.7 +/- 4.2 mumol min-1 (100 g)-1, in osmolar excretion (UosmV) by 62.0 +/- 5.6 from 303.0 +/- 28.3 mu osmol min-1 (100 g)-1, and in a decrease in free water clearance (CH2O) by 0.13 +/- 0.03 from -0.63 +/- 0.04 ml min-1 (100 g)-1. Left atrial pressure (LAP) and heart rate (HR) did not change significantly from 6.9 +/- 0.3 cmH2O, and 133.0 +/- 3.4 beats min-1 respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Primary effects of carotid chemoreceptor stimulation on gracilis muscle and renal blood flow and renal function in dogs

1. In chloralose-anaesthetized and artificially ventilated dogs, the carotid sinus regions were vascularly isolated and perfused either with arterial or mixed (arterial and venous) blood (partial pressure of O2 (PO2) 43.8 +/- 2.4 mmHg, mean +/- S.E.M. n = 14) to stimulate the carotid chemoreceptors. The carotid sinus pressure was held constant at 142.0 +/- 2.8 mmHg. Measurements were made of renal and gracilis muscle blood flow by wrap-round electromagnetic flow probes placed around the renal and gracilis arteries, glomerular filtration rate by creatine clearance, urinary sodium excretion by flame photometry and solute excretion by osmometry. 2. In ten dogs, with intact cervical vagosympathetic trunks, carotid chemoreceptor stimulation produced significant increases in aortic pressure (AoP) of 12.7 +/- 1.1% (n = 10, P < 0.001), in glomerular filtration rate (GFR) of 14.7 +/- 4.1% (P < 0.001), urine flow rate (V) of 16.5 +/- 3.5% (P < 0.002), in urinary sodium excretion (UNaV) of 17.5 +/- 2.5% (P < 0.005) and in urinary osmolar excretion (UosmV) of 13.2 +/- 2.2% (P < 0.001), but a significant decrease in renal blood flow (RBF) of 5.8 +/- 1.8% (P < 0.02). In six of these dogs in which gracilis muscle blood flow (MBF) was also recorded, carotid chemoreceptor stimulation caused significant increases in AoP of 12.8 +/- 1.4% (n = 6, P < 0.001) and in MBF of 10.0 +/- 1.6% (P < 0.002), and a small but significant decrease in RBF of 3.6 +/- 1.5% (P < 0.02). 3. In fourteen dogs, with sectioned cervical vagosympathetic trunks, carotid chemoreceptor stimulation produced increases in AoP of 22.0 +/- 2.6% (n = 14, P < 0.001), in GFR of 36.9 +/- 4.2% (P < 0.001), in V of 30.1 +/- 4.4% (P < 0.001), in UNaV of 31.4 +/- 5.3% (P < 0.001), and in UosmV of 25.7 +/- 5.8% (P < 0.001). However, it produced a greater decrease in RBF of 10.5 +/- 1.9% (P < 0.001). In ten of these dogs, where MBF was recorded, carotid chemoreceptor stimulation caused greater increase in AoP of 22.4 +/- 3.0% (n = 10, P < 0.001) and in MBF of 32.8 +/- 3.7% (P < 0.001), and a greater decrease in RBF of 9.8 +/- 1.9% (P < 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of discrete stimulation of carotid body chemoreceptors on atrial natriuretic peptide in anaesthetized dogs

1. In seven chloralose-anaesthetized and artificially ventilated beagles, the carotid sinus regions were vascularly isolated and perfused with either arterial or mixed (arterial and venous) blood (PO2 46.4 +/- 1.5 mmHg, mean +/- S.E.M.) to stimulate the chemoreceptors at constant flow and pressure. Cervical vagosympathetic trunks were ligated in all dogs, and gallamine triethiodide (2.0 mg kg-1 h-1, I.V.) was given in five dogs. Right atrial pressure was measured in all dogs, and left atrial pressure in four dogs. Mean aortic pressure was held constant (91.0 +/- 3.0 mmHg) by means of a reservoir connected to the animal via the common carotid and femoral arteries. Plasma atrial natriuretic peptide (ANP) was measured by radioimmunoassay and urinary sodium by flame photometry. 2. In seven dogs with mean carotid sinus pressure maintained at 96.0 +/- 4.3 mmHg, stimulation of the carotid chemoreceptors for 25 min produced significant increases in left atrial pressure of 41.2 +/- 3.3% (n = 4; P less than 0.005) from 5.4 +/- 0.6 cmH2O and of 30.9 +/- 4.5% (n = 7; P less than 0.002) in ANP from 31.6 +/- 2.1 pg ml-1. However, chemoreceptor stimulation produced significant decreases in urine flow rate of 26.1 +/- 1.9% (n = 9; P less than 0.001) from 0.29 +/- 0.03 ml min-1 (100 g kidney weight)-1 and sodium excretion of 29.0 +/- 2.3% (P less than 0.001) from 8.5 +/- 1.7 mumol min-1 (100 g kidney weight)-1 but right atrial pressure and heart rate did not change significantly. In three of the dogs, beta-adrenoceptor blockade by atenolol (2 mg kg-1, I.V.) greatly reduced the effects of chemoreceptor stimulation on plasma levels of ANP. 3. The results show, for the first time, that discrete stimulation of the carotid chemoreceptors caused an increase in plasma ANP levels, probably due to the reflex increase in atrial pressure that results from an inhibition of the cardiac sympathetic nerves, and an increase in venous return from a reduction of peripheral vascular capacitance.

Attenuation of exercise vasodilatation by adenosine deaminase in anaesthetized dogs

1. In dogs anaesthetized with sodium pentobarbitone and artificially ventilated, the gracilis muscles were vascularly isolated and perfused at a constant flow of 28.4 +/- 4.6 ml min-1 (100 g muscle tissue)-1 (99.8 +/- 4.5% of maximum free flow, means +/- standard error of the mean (S.E.M.), n = 9). 2. Three to five minutes of electrical stimulation of the cut peripheral end of the obturator nerve (4 Hz, 6 V, 0.2 ms) resulted in muscle contraction (0.61 +/- 0.14 kg (100 g)-1 during solvent infusion and 0.56 +/- 0.10 kg (100 g)-1 during intra-arterial adenosine deaminase infusion (50 U min-1) and an immediate decrease in arterial perfusion pressure from 184.5 +/- 8.1 mmHg to 148.2 +/- 5.7 mmHg (18.7 +/- 3.4% decrease) during solvent infusion, and from 193.5 +/- 7.16 to 142.0 +/- 10.2 mmHg (25.4 +/- 6.1% decrease) during adenosine deaminase infusion 10 s after the commencement of muscle stimulation. After about 5 min of muscle contractions, the arterial perfusion pressure decreased to 120.8 +/- 7.8 mmHg (32.9 +/- 5.8% decrease) during solvent infusion, and to 152.8 +/- 11.2 mmHg (20.9 +/- 5.3% decrease) during adenosine deaminase infusion (i.e. 37.9 +/- 6.2% attenuation of the fall in arterial perfusion pressure). The time taken for 90% recovery of the arterial perfusion pressure was 72.1 +/- 10.9 s during solvent infusion, and 51.5 +/- 9.3 s during adenosine deaminase infusion (P less than 0.05). 3. Adenosine (2 x 10(-3) mol l-1) infusion in the resting muscle during solvent infusion (final concentration in arterial blood 1.3 x 10(-4) +/- 6.0 x 10(-5) mol l-1) resulted in a 34.8 +/- 7.2% fall in arterial perfusion pressure but a fall of only 7.2 +/- 1.8% during adenosine deaminase infusion (50 U min-1; P less than 0.05; n = 5) indicating that adenosine deaminase infused at 50 U min-1 was more than adequate to metabolize endogenous adenosine produced during muscle contractions. 4. These data suggest that adenosine contributes about 40% to the sustained-exercise vasodilatation under constant high-flow conditions and also in post-exercise vasodilatation, but does not contribute to the initiation of exercise vasodilatation.

The renal response to electrical stimulation of renal efferent sympathetic nerves in the anaesthetized greyhound

1. The effect of direct electrical stimulation of the renal efferent nerves upon renal haemodynamics and function was studied in greyhounds anaesthetized with chloralose and artificially ventilated. The left kidney was neurally and vascularly isolated, and perfused with blood from one of the femoral arteries at a constant pressure of 99 +/- 1 mmHg. Renal blood flow was measured with a cannulating electromagnetic flow probe placed in the perfusion circuit, glomerular filtration rate by creatinine clearance, urinary sodium excretion by flame photometry and solute excretion by osmometry. Beta-Adrenergic receptor activation was blocked by the infusion of dl-propranolol (17 micrograms kg-1 min-1). The peripheral ends of the ligated renal nerves were stimulated at 0.5, 1.0, 1.5 and 2.0 Hz. 2. At 0.5 Hz frequency only osmolar excretion was significantly reduced (10.3 +/- 3.2%, P less than 0.05, n = 6). Reductions in sodium excretion (53.6 +/- 8.5%, P less than 0.01, n = 6) and water excretion (26.9 +/- 8.0%, P less than 0.05, n = 6) and further reductions of osmolar excretion (20.7 +/- 3.7%, P less than 0.01, n = 6) were observed at 1.0 Hz; however, these were observed in the absence of significant changes in renal blood flow and glomerular filtration rate. Significant reductions were observed in glomerular filtration rate at 1.5 Hz (16.3 +/- 4.1%, P less than 0.02, n = 5) and in renal blood flow at 2.0 Hz (13.1 +/- 4.0%, P less than 0.05, n = 5). Further reductions in urine flow and sodium excretion were also observed at these higher frequencies. 3. These results clearly show that significant changes in renal tubular function can occur in the absence of changes in renal blood flow and glomerular filtration rate when the renal nerves are stimulated electrically from a zero baseline activity up to a frequency of 1.5 Hz. Higher frequencies caused significant changes in both renal haemodynamics and function.

Oral rehydration therapy: a community trial comparing the acceptability of homemade sucrose and cereal-based solutions

Sugar-based oral rehydration therapy (ORT) for diarrhoea is promoted in many countries of the world. One programme in Bangladesh has instructed more than 13 million mothers in the preparation of a sugar-salt solution in the home; despite very high rates of correct mixing and knowledge, subsequent application was found in only some 20% of all diarrhoea episodes. Since rice is far more available in rural homes (95%) than any type of sugar (30%) and rice gruel is a widely accepted food during illness, a field trial was conducted in three areas (total population, 68,345) to compare the acceptability and use of rice-based ORT with that of sugar-based ORT. Although the mothers unanimously agreed that the rice-based solutions "stopped" the diarrhoea more quickly, they used the sugar-based solutions twice as often (in 40% of severe watery episodes) as the rice-based solutions (in 18%), because the rice-ORT was much more time-consuming and difficult to prepare. The observed reduced utilization of home-made rice-ORT makes it a poor substitute for sugar-ORT at the community level in rural Bangladesh.

Inhibition of atrial receptor-induced renal responses by stimulation of carotid baroreceptors in anaesthetized dogs

1. Dogs were anaesthetized with chloralose and artificially ventilated. The receptors at three pulmonary vein-atrial junctions and in the left atrial appendage were stimulated by distension of small balloons. The carotid sinuses were vascularly isolated and perfused with arterial blood. A volume reservoir was connected to the aorta via the common carotid and femoral arteries to keep the mean aortic pressure constant (78.8 +/- 2.9 mmHg at low and 87.1 +/- 4.3 mmHg at high carotid sinus pressure, CSP). Propranolol and atropine were infused (i.v.) at 17 and 13 micrograms kg-1 min-1 respectively in order to block beta-adrenergic and cholinergic receptor activities. The renal blood flow was measured by an electromagnetic flow meter (wrap-round probe), glomerular filtration rate by creatinine clearance, urinary sodium excretion by flame photometry and osmolar excretion by osmometry. 2. In twelve tests in eight dogs, stimulation of the left atrial receptors for 13 min, at a mean CSP of 68.6 +/- 2.3 mmHg, resulted in significant increases in renal blood flow from 216 +/- 20.0 to 230 +/- 22.1 ml min-1 (100 g renal mass)-1 (P less than 0.005), glomerular filtration rate from 33.9 +/- 3.2 to 42.1 +/- 4.1 ml min-1 100 g-1 (P less than 0.005), filtration fraction from 0.23 +/- 0.02 to 0.26 +/- 0.02 (P less than 0.005), urine flow rate from 0.21 +/- 0.03 to 0.26 +/- 0.03 ml min-1 100 g-1 (P less than 0.001), sodium excretion from 12.9 +/- 4.0 to 16.4 +/- 4.8 mumol min-1 100 g-1 (P less than 0.01), osmolar excretion from 196 +/- 27.8 to 246 +/- 32.9 muosmol min-1 100 g-1 (P less than 0.005), whilst free water clearance decreased from -0.39 +/- 0.07 to -0.50 +/- 0.09 ml min-1 100 g-1 (P less than 0.005). However, the fractional excretion of sodium did not change. 3. In nine tests in seven dogs, stimulation of the left atrial receptors at a constantly high CSP (161 +/- 11.3 mmHg) did not produce significant change in any of the renal variables. 4. The results show that high level excitation of carotid baroreceptors can completely inhibit the reflex renal haemodynamic and functional responses to atrial receptor stimulation.

Lack of interaction between adenosine-induced vasodilatation and carotid baroreflex-induced changes in sympathetic activity in dog hindlimb artery

In anaesthetized dogs, a hindlimb was vascularly isolated and perfused at a constant flow rate of 7.7 +/- 1.9 ml min-1 100 g-1 (mean +/- S.E.M.; n = 5) through the femoral artery. The carotid sinuses were isolated and perfused at high (greater than 145 mmHg) or low (less than 75 mmHg) pressure to enable reflex sympathetic tone on the hindlimb vessels to be controlled. Both vagi were sectioned in the neck and mean aortic blood pressure was held constant by connection of the aorta to a reservoir. The responses to infusion of three doses of adenosine at high and low carotid sinus pressures were not significantly different: infusion of 0.60 +/- 0.16 microM-adenosine reduced femoral arterial perfusion pressure (FAPP) by 11.6 +/- 3.2% (n = 6) at high carotid sinus pressure and by 12.6 +/- 5.1% (n = 4) at low carotid sinus pressure, while 4.71 +/- 0.49 microM-adenosine reduced FAPP by 20.8 +/- 4.8% (n = 6) at high carotid sinus pressure and by 20.7 +/- 4.8% (n = 6) at low carotid sinus pressure; 50.1 +/- 7.3 microM-adenosine reduced FAPP by 36.7 +/- 5.5% (n = 6) at high carotid sinus pressure and by 27.7 +/- 7.8% (n = 5) at low carotid sinus pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of small changes in carotid sinus pressure on renal haemodynamics and function in dogs

1. In dogs anaesthetized with chloralose and artificially ventilated, the carotid sinuses were vascularly isolated and perfused with arterial blood. Mean aortic pressure was held constant at 111 +/- 2 mmHg (mean +/- S.E.M., n = 18) by means of a pressure bottle connected to the aorta and a Starling resistance. Both vagus nerves were sectioned in the neck and propranolol hydrochloride (1 mg kg-1 h-1) or atenolol (0.5-4 mg kg-1 h-1) was administered. The left and right renal blood flows were measured by electromagnetic flowmeters (wrap-round probes), glomerular filtration rate by creatinine clearance, urinary sodium by flame photometry and solute excretion by osmometry. 2. In six dogs decreasing pressure in the isolated carotid sinuses from 119 +/- 4 to 78 +/- 3 mmHg (n = 9) resulted in significant decreases in renal blood flow by 18 +/- 3% (P less than 0.01), glomerular filtration rate by 41 +/- 9% (P less than 0.01), filtration fraction by 30 +/- 11% (P less than 0.05), urine flow by 46 +/- 6% (P less than 0.001), sodium excretion by 46 +/- 9% (P less than 0.001) and osmolar excretion by 44 +/- 6% (P less than 0.001). Fractional sodium excretion did not change significantly. Increasing carotid sinus pressure back to 120 +/- 4 mmHg (n = 6) resulted in increases in all the variables to values not significantly different from those at initial high carotid pressure. 3. Ligation of left renal nerves at low carotid sinus pressure (83 +/- 3 mmHg, n = 5) caused significant increases in all of the variables in the left kidney. After ligation, changes in carotid sinus pressure produced no effect on the denervated left kidney, but in the three dogs in which the responses of the right kidney were also tested, the usual responses after denervation of the left kidney were seen. 4. The results show that changes in carotid sinus pressure around the normal range can result in significant reflex effects on renal haemodynamics and function and that these effects are mediated solely by renal sympathetic nerves. The influence of any extrarenal humoral factors seems to be minimal.

Sympathetic nerves in the mediation of renal response to localized stimulation of atrial receptors in anaesthetized dogs

1. Dogs were anaesthetized with chloralose and artificially ventilated. Localized stimulation of left atrial receptors for 23-25 min was achieved by distension of three small balloons at the pulmonary vein-atrial junctions and one in atrial appendage. Renal blood flows were measured by electromagnetic flow probes, glomerular filtration rate by creatinine clearance, urinary sodium excretion by flame photometry and solute excretion by osmometry. The mean aortic pressure was held constant at 92.2 +/- 2.4 mmHg (mean +/- S.E.M., n = 27) by means of a pressure bottle connected to the aorta and beta-adrenergic receptor activity was blocked by continuous infusion of propranolol (17 micrograms kg-1 min-1, I.V.). 2. In twelve dogs stimulation of left atrial receptors resulted in significant increases of 11.8 +/- 2.4% (P less than 0.001) in renal blood flow; 32.5 +/- 7.2% (P less than 0.001) in glomerular filtration rate; 19.5 +/- 5.0% (P less than 0.005) in filtration fraction: 36.3 +/- 9.0% (P less than 0.001) in urine flow: 32.7 +/- 9.2% (P less than 0.005) in sodium excretion: 36.6 +/- 9.9% (P less than 0.005) in osmolar excretion and a decrease of 31.3 +/- 11.2% (P less than 0.025) in free water clearance. Left atrial pressure and heart rate did not change significantly. In eight of the dogs ligation of the renal nerves resulted in similar changes in all of the renal variables; subsequent stimulation of atrial receptors did not cause significant changes in the renal variables. 3. In five additional dogs, in which heart rate and aortic pressure were allowed to change, stimulation of left atrial receptors for the same period resulted in significant increases in heart rate (4.3 +/- 0.7%. P less than 0.001) and mean aortic pressure (2.0 +/- 0.6%, P less than 0.025). Under this condition both the intact right kidneys and the denervated left kidneys showed significant responses in urine flow, sodium excretion, osmolar excretion and free water clearance. 4. The results show that the renal sympathetic nerves mediate the primary renal responses to atrial receptor stimulation, at least in the short term. The influence of any humoral factor in this reflex seems to be secondary to changes in heart rate and systemic blood pressure, possibly via arterial baroreceptors.

The influence of blood flow rate on adenosine release from contracting dog skeletal muscle

The dependence of adenosine release on blood flow was investigated in greyhounds anaesthesized with sodium pentobarbitone and artificially ventilated. The gracilis muscles were neurally and vascularly isolated, and perfused at constant flow rates of 42% (low), 89% (medium) or 132% (high) of their maximum free flow during contraction induced by stimulation of the motor nerve. Stimulation produced contractions whose force declined from 716 +/- 60 to 464 +/- 46 g (100 g)-1 over 10 min. Resting perfusion pressure increased in line with the flow rate, but the fall in resistance accompanying contractions varied reciprocally with the flow (57 +/- 2.9, 39.6 +/- 6.6 and 15.3 +/- 5.6% at low, medium and high flows respectively). Venous PO2 decreased during contraction to 26.6 +/- 6.2 mmHg at 'low', 31.5 +/- 5.1 mmHg at 'medium' and 37.2 +/- 1.7 mmHg at 'high' flows. Venous plasma adenosine concentration increased significantly above resting levels during contraction at all flow rates. Adenosine release at low flow (12.0 +/- 2.7 nmol min-1 (100 g)-1) was significantly greater than that at medium or high flows (5.6 +/- 1.3 and 4.1 +/- 1.3 nmol min-1 (100 g)-1 respectively), but the latter were not different from each other. There was no correlation between adenosine release and either venous oxygen tension during muscle contraction or the ratio of oxygen supply to free-flow oxygen consumption. These data suggest that the mechanism underlying adenosine release during muscle contraction may be independent of oxygen lack.

Teaching ORT to women: individually or in groups?

Programmes to promote the widespread use of oral rehydration therapy (ORT) for diarrhoea used a variety of methodologies to carry the message to mothers. The Bangladesh Rural Advancement Committee (BRAC) sent its health workers to individual households, and mothers were trained through a one-to-one approach. The cost of training a mother was 72 US cents. Recently, an alternative approach was tried. Instead of individually, mothers were trained in groups which halved the cost. Outcome indicators, such as usage, knowledge and safety of ORT solution, were looked at for each type of approach and were not found to be significantly different.

Changes in adenosine release and blood flow in the contracting dog gracilis muscle

Ischaemic contraction of skeletal muscle increases the venous concentration of adenosine. The present investigation was undertaken to determine changes in blood flow and the release of adenosine into venous blood resulting from 5 min of free flow contractions of the isolated gracilis muscle in dogs anaesthetised with pentobarbitone sodium (42 mg.kg-1) and artificially ventilated. Arterial and venous concentrations of adenosine were measured by high performance liquid chromatography. Five-minute-contractions (induced electrically, 6 V, 1.8 ms, 4 Hz) caused significant increases in blood flow (to 304 +/- 33% of control; mean +/- SEM, n = 9) and venous plasma adenosine concentration (from 126 +/- 18 nM to 293 +/- 76 nM, equivalent to an average increase in release of 7.28 +/- 1.89 nmol.min-1 100 g-1 wet weight of muscle). The venous oxygen tension decreased from 8.33 +/- 0.48 to 3.39 +/- 0.31 kPa (62.5 +/- 3.6 to 25.4 +/- 2.3 mm Hg). This small but significant increase in venous adenosine concentration within the vasoactive range, in the face of a concomitant increase in blood flow, suggests that an increase in the interstitial adenosine concentration during free-flow exercise may contribute to the total dilatation of the resistance vessels to increase blood flow and keep its own concentration low. A significant correlation between venous adenosine concentration and vascular conductance is therefore absent. The results suggest that adenosine may contribute to sustained active hyperaemia in skeletal muscle.

The effects of stimulating carotid chemoreceptors on renal haemodynamics and function in dogs

1. Dogs were anaesthetized with chloralose and artificially ventilated. The carotid chemoreceptors were stimulated by changing the perfusion of vascularly isolated carotid sinus regions from arterial to venous blood. The mean carotid sinus pressure and the mean arterial blood pressure were held constant at 124 +/- 3 and 122 +/- 3 mmHg, respectively. Both vagosympathetic trunks were sectioned in the neck and propranolol (17 micrograms kg-1 min-1 I.V.) and gallamine triethiodide (0.2-2.0 mg kg-1 30 min-1 I.V.) were infused. Renal blood flow was measured by an electromagnetic flow probe, glomerular filtration rate by creatinine clearance, sodium excretion by flame photometry and solute excretion by osmometry. 2. In sixteen tests in thirteen dogs perfusion of the carotid sinus regions with venous blood resulted in significant decreases in renal blood flow from 271 +/- 24 to 198 +/- 21 ml min-1 100 g-1 renal mass; glomerular filtration rate from 41.0 +/- 4.8 to 22.1 +/- 3.1 ml min-1 100 g-1; filtration fraction from 0.25 +/- 0.02 to 0.19 +/- 0.02; urine flow from 0.48 +/- 1.0 to 0.21 +/- 0.03 ml min-1 100 g-1; sodium excretion from 18.1 +/- 4.1 to 12.9 +/- 4.2 mumol min-1 100 g-1; and osmolar excretion 327 +/- 42 to 171 +/- 26 mu osmol min-1 100 g-1. The right atrial pressure did not change significantly from 4.6 +/- 1.2 cmH2O. 3. In seven dogs, tying renal sympathetic nerves abolished all the responses except that of sodium excretion which was now reversed; sodium excretion increased from 68 +/- 19 to 116 +/- 38 mumol min-1 100 g-1 without significant change in right atrial pressure from 7.4 +/- 1.9 cmH2O. Crushing the carotid bodies, however, abolished all the responses. 4. The results show that carotid chemoreceptor stimulation can cause significant reflex effects on renal haemodynamics and function which are mediated via renal sympathetic nerves. They also show that the chemoreceptor stimulation can cause natriuresis in the absence of haemodynamic changes, in the denervated kidney, presumably via a humoral factor.

Venous adenosine content and vascular responses in dog hind-limb skeletal muscles during twitch contraction

In dogs anaesthetized with pentobarbitone sodium and chloralose and artificially ventilated, the skeletal muscles of a hind limb were vascularly and neurally isolated and perfused at a constant flow of 150% of the resting blood flow (5.8 +/- 0.3 ml.min-1.100g-1 muscle tissue, mean +/- S.E.M., n = 6) obtained after denervation of the limb. Electrical stimulation of the cut peripheral ends of the femoral and sciatic nerves for 20 min resulted in muscle contraction and a decrease in arterial perfusion pressure to a new steady level (59.7 +/- 8.6% decrease in vascular resistance) within 2 min; the pressure remained constant throughout the remaining 20 min. Similarly venous oxygen tension decreased from 38.2 +/- 1.3 (control) to 16.4 +/- 1.7 mmHg (n = 5) during contractions. The concentration of adenosine in arterial plasma did not change significantly during muscle contraction (122.5 +/- 28 nM, n = 8). However, the adenosine concentrations in venous plasma increased significantly (P less than 0.05) from a control value of 94.8 +/- 33 nM (n = 8) to 256 +/- 82 nM (n = 8) after 10 min and 235 +/- 31 nM (n = 8) after 20 min of muscle contraction. During infusion of adenosine into the femoral artery to give a range of arterial plasma concentrations between 0.17 and 90 microM, 89.2 +/- 2.8% (n = 20) of the infused adenosine was removed (taken up by tissues) from the blood before it reached the vein. Infusion of adenosine caused dose-dependent decreases in vascular resistance ranging between 7 and 79%; 5.58 +/- 1.50 microM adenosine caused a decrease in resistance of 36.1 +/- 7.1% (n = 10) and 51.7 +/- 7.4 microM adenosine caused a decrease of 51.2 +/- 4.1% (n = 9). Comparison of venous plasma adenosine concentrations during adenosine infusions with those seen during contractions suggests that the released adenosine can contribute about 60% of the total vasodilatation seen during contractions of the muscle. These results show that adenosine appears in the venous blood during muscle contraction and is likely to contribute to exercise hyperaemia.

Appearance of adenosine in venous blood from the contracting gracilis muscle and its role in vasodilatation in the dog

1. In dogs anaesthetized with sodium pentobarbitone and artificially ventilated, the gracilis muscles were vascularly isolated and perfused at a constant flow rate of 51.2 +/- 9.8 ml min-1 100 g-1 muscle tissue (183 +/- 17.8% of resting blood flow; mean +/- S.E.; n = 13). 2. Electrical stimulation of the cut peripheral end of the obturator nerve (6 V, 4 Hz) resulted in muscle contraction (658 +/- 118 g 100 g-1 force after 5 min), and an immediate decrease in arterial perfusion pressure from 179 +/- 15.7 mmHg to 87 +/- 10.0 mmHg (51.4 +/- 4.5% decrease in vascular resistance after 2 min of contraction). Venous oxygen tension decreased from 69.2 +/- 5.1 mmHg to 18.5 +/- 1.4 mmHg (n = 6). These values did not significantly alter during the remaining period of stimulation (10-20 min). 3. The concentration of adenosine in arterial plasma did not change significantly during muscle contraction (137 +/- 23 nM; n = 10). However, the adenosine concentrations in venous plasma showed a significant (P less than 0.01) increase from a control value of 164 +/- 55 nM to 455 +/- 77 nM (n = 9) after 5 min of muscle contraction and remained high during the rest of the 20 min contraction. In six of the dogs adenosine concentrations were determined after 1 and 3 min of contraction and showed a smaller but statistically significant (P less than 0.05) rise in venous concentration. 4. During infusion of adenosine into the artery to give plasma concentrations between 0.3 microM and 1 mM, 72.6 +/- 2.1% (n = 29) of the infused adenosine was taken up by the tissues before it reached the vein. Comparison of vasodilatation and venous adenosine concentrations during adenosine infusion and muscle contractions showed that the released adenosine could contribute about 15% to the total vasodilatation after 1 min and about 40% between 5 and 20 min of contractions. Released adenosine could contribute about 80% to the vasodilatation that remained 5 min after the withdrawal of stimulation. Arterial perfusion pressure took 22 min to return to control, whereas adenosine release had fallen to zero within 10 min. 5. These data suggest that the released adenosine could contribute to exercise hyperaemia, but is unlikely to be the main factor, particularly in the initial stage.

The reflex effects of changes in carotid sinus pressure upon renal function in dogs

In chloralose-anaesthetized and artificially ventilated dogs, the carotid sinuses were vascularly isolated and perfused with arterial blood. Mean aortic pressure was held constant at 100 +/- 2 mmHg (mean +/- S.E. of mean, n = 19) by means of a pressure bottle connected to the aorta. Both vagus nerves were sectioned in the neck and propranolol hydrochloride (0.5 mg kg-1) was administered every 30 min. The left renal blood flow was measured by an electromagnetic flowmeter (wrap-round probe), glomerular filtration rate by creatinine clearance and urinary sodium by flame photometry. Decreasing pressure in the isolated carotid sinuses from 186 +/- 10 to 63 +/- 5 mmHg resulted in significant decreases in renal blood flow from 281 +/- 35 to 177 +/- 30 ml min-1 100 g-1 renal mass; glomerular filtration rate from 40.0 +/- 7.8 to 12.3 +/- 4.4 ml min-1 100 g-1; urine flow from 0.31 +/- 0.05 to 0.12 +/- 0.03 ml min-1 100 g-1 and sodium excretion from 21.7 +/- 7.2 to 8.2 +/- 3.0 mumol min-1 100 g-1. Increasing carotid sinus pressure back to 188 +/- 11 mmHg resulted in increases in all the variables to values not significantly different from their initial values. Tying renal sympathetic nerves at low carotid sinus pressure (73 +/- 11 mmHg) caused an increase in all of the variables. After denervation there was no response to changes in carotid sinus pressure. These results show that changes in carotid sinus pressure can result in significant reflex effects on renal function and that these effects are mediated by renal sympathetic nerves.

Hind-limb vascular-capacitance responses in anaesthetized dogs

In anaesthetized dogs a hind limb was vascularly isolated, perfused through the femoral artery at either constant flow or constant pressure and drained from the femoral vein at constant pressure. Inflow and outflow were recorded. Vascular-resistance changes were calculated from changes in pressure or flow and volume changes from the differences between inflow and outflow. During constant-flow perfusion, both changes in carotid sinus pressure and direct stimulation of efferent sympathetic nerves resulted in large resistance responses. However, changes in carotid sinus pressure did not result in changes in limb blood volume and only small decreases were obtained in response to direct stimulation. During constant-pressure perfusion, both reflex and direct stimulation resulted not only in significant changes in resistance but also in significant volume changes which were much larger than those obtained during constant-flow perfusion. Similar responses were obtained when the flow rate was changed by altering the pump speed. These results indicate that changes in pressure to carotid baroreceptors do not result in active capacitance responses in the limb circulation and that only very small responses are obtained even to electrical stimulation of sympathetic nerves. The larger responses occurring during constant-pressure perfusion are thought to be secondary to changes in blood flow.

Effects of combined carotid chemoreceptor and atrial receptor stimulation on renal blood flow in anaesthetized dogs

In dogs anaesthetized with chloralose and artificially ventilated, carotid chemoreceptors were stimulated by changing the perfusate of the vascularly isolated carotid bifurcations from arterial to venous blood. Left atrial receptors were stimulated by distending balloons in two pulmonary vein-left atrial junctions and in this left atrial appendage. The left renal blood flow was measured by an electromagnetic flow meter at a constant systemic (renal) arterial pressure in preparations in which heart rate changes were prevented by administration of propranolol hydrochloride (0.5 mg kg-1) and atropine sulphate (0.4 mg kg-1). Muscular movement was prevented by gallamine triethiodide (0.2 mg kg-1). Stimulation of left atrial receptors resulted in a significant increase (P less than 0.001) in renal blood flow of 5.6 +/- 0.88 ml min-1 100 g-1 renal mass from a control of 223 ml min-1 100 g-1 renal mass. The responses were abolished by cooling the cervical vagus nerves to 6-8 degrees C. Stimulation of carotid chemoreceptors, by perfusion of the carotid bifurcations by venous blood, caused a decrease in renal blood flow of 20 +/- 6.9 ml min-1 100 g-1 renal mass from 224 ml min-1 100 g-1 renal mass. Stimulation of left atrial receptors during venous perfusion of carotid chemoreceptors resulted in an increase in renal blood flow of 10.9 +/- 1.82 ml min-1 100 g-1 renal mass from 208 ml min-1 100 g-1 renal mass. These results show that atrial receptors and chemoreceptors can interact in their effects on renal blood flow.

Responses of abdominal vascular resistance and capacitance to stimulation of carotid chemoreceptors in anaesthetized dogs

1. In anaesthetized dogs the regions of the carotid bifurcations were isolated vascularly and perfused at constant non-pulsatile pressures. The abdominal circulation was isolated vascularly, perfused at constant flow and drained through the inferior vena cava at constant pressure. Vascular resistance and capacitance responses were determined from the changes in perfusion pressure and changes in venous outflow. 2. Stimulation of carotid chemoreceptors with venous blood resulted in an increase in arterial perfusion pressure of 38% (S.E. +/- 4.6) and a decrease in vascular capacitance of 24.4 +/- 2.5 ml. (1.05 +/- 0.24 ml. kg-1). 3. When carotid perfusion pressure was higher than 17 kPa, stimulation of chemoreceptors resulted in significantly (P less than 0.05) smaller resistance responses but significantly (P less than 0.05) greater capacitance responses than those obtained at lower carotid pressures. 4. These results show that abdominal resistance and capacitance vessels constrict in response to stimulation of carotid chemoreceptors. We suggest that the larger responses of capacitance and the smaller responses of resistance obtained at higher carotid sinus pressures may be due to different sensitivities of resistance and capacitance vessels to efferent sympathetic nerve activity.

Effects of stimulation of aortic chemoreceptors on abdominal vascular resistance and capacitance in anaesthetized dogs

1. Dogs were anaesthetized with chloralose, ventilated artificially, and the regions of the aortic arch and carotid sinuses were isolated vascularly and perfused with blood. The abdominal circulation was isolated vascularly, perfused at constant flow and drained from the inferior vena cava at constant venous pressure. Changes in vascular resistance were determined by calculating changes in abdominal aortic perfusion pressure, and changes in capacitance by integrating the changes in venous outflow. 2. Stimulation of aortic body chemoreceptors, either by changing the aortic arch perfusate from arterial to venous blood at constant perfusion pressure or by injection of sodium cyanide into the aortic arch, resulted in an increase in abdominal vascular resistance and a decrease in abdominal vascular capacitance. 3. After both cervical vagosympathetic trunks had been cut, stimulation of aortic chemoreceptors no longer resulted in resistance or capacitance responses. 4. These results indicate that stimulation of aortic chemoreceptors, like carotid chemoreceptors, results in reflex constriction of both resistance and capacitance vessels in the abdominal circulation.

Effect of stimulating right atrial receptors on renal blood flow

This investigation was undertaken to determine the effect of stretching the superior vena caval--right atrial (SVC-RA) junction and the right atrial appendage on blood flow to the kidney (RBF) and to establish whether any changes observed were influenced by the input from the baroreceptors in the carotid sinus. The experiments were performed on seven dogs, anaesthetized with alpha-chloralose. The systemic arterial (i.e., renal perfusion) pressure was held constant. At a carotid sinus pressure (CSP) of 59.0 +/- 1.2 mmHg (1 mmHg = 133.322 Pa), the RBF increased from 218 +/- 16.1 to 231.7 +/- 18.4 mL/min per 100 g renal mass (p less than 0.025). At a CSP of 88.0 +/- 3.5 mmHg, the RBF increased from 230.1 +/- 19.2 to 237.1 +/- 19.2 mL/min per 100 g renal mass (p less than 0.05). At a CSP of 137 +/- 3.7 mmHg there were no significant changes in RBF. These responses were abolished by cutting (four dogs) or cooling the vagi (one dog only). In a subsidiary investigation it was shown that stretching the SVC-RA junction activated receptors in the endocardial surface of the right atrium which discharged into myelinated fibres in the vagi, having an average conduction velocity of 8.1 m/s (range 3.8-15). It is concluded that stimulation of right atrial receptors increases the RBF and that this response is influenced by the input from the baroreceptors in the carotid sinus.

Influence of carotid sinus pressure on atrial receptors and renal blood flow

Stimulation of the atrial receptors results in an increase in renal blood flow. The present investigation was undertaken to determine whether this response was modulated by the input from the baroceptors in the carotid sinus. The experiments were performed on dogs anesthetized with chloralose. The systemic arterial pressure was held constant. The carotid sinuses were perfused at 62 +/- 1.3, 95 +/- 2.7, and 145 +/- 8.3 mmHg. The atrial receptors were stimulated by distension of small balloons positioned at the left pulmonary vein-atrial junctions and the left atrial appendage. At a carotid sinus pressure of 62 +/- 1.3 mmHg, the blood flow increased from 182 +/- 8.5 to 199 +/- 8.9 ml . min-1 . 100 g-1 renal mass. At a carotid sinus pressure of 95 +/- 2.7 mmHg, the blood flow increased from 202 +/- 9.6 to 209 +/- 10.4 ml . min-1 . 100 g-1 renal mass. At a carotid sinus pressure of 145 +/- 8.3 mmHg, the blood flow increased from 237 +/- 13.0 to 239 +/- 12.5 ml . min-1 . 100 g-1 renal mass. The first two responses alone were statistically significant. The response at a carotid sinus pressure of 62 +/- 1.3 mmHg was abolished by cutting or cooling the cervical vagi to 8--10 degrees C. It is concluded that stimulation of the left atrial receptors produces a reflex increase in blood flow to the kidney, and this response is modulated by the input from the carotid sinus baroceptors.

Effects of adenosine and its analogues on the perfused hind limb artery and vein of anaesthetized dogs

1. The effects of infusion of adenosine and its analogues on arterial and venous resistance have been studied in the vascularly and sympathetically isolated hind limb of chloralose-anaesthetized dogs. Resistance changes have been assessed by monitoring changes in perfusion pressures at constant flow through the femoral artery and metatarsal vein.2. With sympathetic stimulation (10 V, 2 msec, 0.5-2 Hz applied to the cut peripheral end of the lumbar sympathetic trunk), continuous infusion of adenosine, to produce a concentration of approximately 2 x 10(-5)m, resulted in a near maximal sustained decrease in arterial perfusion pressure of 35.3+/-3.6%, and a decrease of about half this in venous perfusion pressure.3. Bolus injections of adenosine into the artery, to produce a concentration of about 7 x 10(-5)m, caused a transient decrease in resistance similar to that observed with continuous infusion. However, the venous response was smaller than that induced by continuous infusion.4. Withdrawal of sympathetic stimulation to the limb had little effect on adenosine-induced vasodilatation in the artery, but abolished the small response of the vein.5. Less than 5% vasodilatation was produced in the artery and vein by 2-deoxyadenosine, inosine, guanosine, xanthosine, cytidine or uridine when infused in amounts up to ten times, or by sodium phosphate (pH 7.4) in amounts one hundred times the maximal amounts of adenosine given.6. These results suggest that adenosine caused vasodilatation, at least in arterioles, largely by acting directly on vascular muscle rather than via presynaptic inhibition of noradrenaline release.

Reflex inotropic responses of the heart from lung inflation in anaesthetized dogs

In anaesthetized dogs a tracheal divider was inserted to allow inflation of one lung with various pressures. Left ventricular inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) using a preparation in which aortic pressure, carotid sinus pressure and heart rate were held constant. Heart responses to lung inflation were variable. In five dogs there was a consistent tachycardia, in three bradycardia and in six there was no change. In the dogs in which heart rate increased, inflation of one lung with pressures between 0.5 and 2.0kkPa (5 and 20 cm H2O) resulted in no significant change in dP/dt max. In the remaining dogs there was a decrease in dP/dt max which was more pronounced at the higher inflation pressures. The negative inotropic response was shown to be a reflex with afferent nerve endings in the lung and with the efferent pathway in the sympathetic nerves.

The influence of perfusate temperature on the responses of a superficial vein in the carotid baroreceptor reflex in dogs

In chloralose-anaesthetised dogs, both vagus nerves were cut and both carotid sinuses vascularly isolated and perfused with blood. The left hind limb was vascularly isolated and the femoral artery and the central end of a superficial metatarsal vein were perfused at constant flows with blood from an oxygenator. Femoral venous pressure was held constant. Arterial and venous responses were determined by measuring changes in arterial perfusion pressure and in the pressure gradient between the superficial metatarsal and femoral veins. Large step increases in carotid sinus pressure resulted in an average decrease in venous gradient of 5.6% when the temperature of the venous perfusate was 38 degrees C and a significantly (P less than 0.01) greater response (8.8%) when the perfusate was at 31 degrees C. When the venous perfusate was cooled from 38 to 31 degrees C, venous gradient increased by averages of 89% when carotid pressure was low, 64% when carotid pressure was high and 32% after lumbar sympathectomy. These responses are significantly different from each other (P less than 0.05). It is concluded that the reflex responses of the superficial vein to maximal stimulation of the baroreceptors were small but they were significantly protentiated by cooling the perfusate. The venous constriction in response to cooling was reduced by raising the carotid pressure and further reduced by surgical sympathectomy.

Responses of the heart to stimulation of aortic body chemoreceptors in dogs

We stimulated the aortic chemoreceptors in dogs that were anesthetized with chloralose and artificially ventilated by perfusing the isolated aortic arch with venous blood. Inotropic responses were determined by measuring the maximum rate of change of left ventricular pressure (dP/dt max) with aortic pressure and heart rate held constant. Stimulation of the aortic chemoreceptors resulted in an average increase in heart rate of 14 +/- 2.0 beats/min (mean +/- SE) from 166 +/- 7.7 beats/min and an increase in dP/dt max of 501 +/- 85 mm Hg/sec from 3508 +/- 154 mm Hg/sec. These changes were statistically significant (P less than 0.001). The afferent pathway of the reflex was shown to be in the vagus nerves and the efferent pathway in the cardiac sympathetic nerves. In some of the dogs, the carotid chemoreceptors were also stimulated. This resulted in decreases in heart rate and dP/dt max of 48 +/- 24 beats/min and 795 +/- 142 mm Hg/sec. Thus we have shown that stimulation of aortic chemoreceptors evokes chronotropic and inotropic responses opposite to those evoked from stimulation of carotid chemoreceptors.

Left ventricular inotropic responses to stimulation of carotid body chemoreceptors in anaesthetized dogs

1. Dogs were anaesthetized with chloralose and artificially ventilated. The regions of both carotid bifurcations were vascularly isolated and perfused at constant pressure with arterial blood or with venous or hypoxic blood. 2. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dtmax) with aortic pressure and heart rate held constant. 3. Stimulation of the chemoreceptors with venous blood from the inferior vena cava resulted in a decrease in dP/dtmax from 510 +/- 27 kPa.s-1 to 418 +/- 21 kPa.s-1 (mean +/- S.E.): a change of 17.9 +/- 1.0% 4. In experiments in which the oxygen tension of the blood perfusing the carotid chemoreceptors was decreased in steps between 10 and 3 kPa, by use of an oxygenator, graded responses of dP/dtmax were obtained at each step. 5. The inotropic responses to chemoreceptor stimulation were abolished by raising carotid pressure. 6. The inotropic responses were abolished either by crushing both carotid bodies or both ansae subclaviae, indicating that the reflex originates from the carotid bodies and that the efferent pathway is in the cardiac sympathetic nerves.

Reflex responses of abdominal vascular capacitance from aortic baroreceptors in dogs

The vascularly isolated abdominal circulation of chloralose-anesthetized dogs was perfused at constant flow through the aorta and drained at constant pressure from the inferior vena cava. Changes in resistance were calculated from changes in perfusion pressure and changes in capacitance were calculated by integrating changes in venous outflow. While carotid sinus pressure was constant, a decrease in pressure in the vascularly isolated aortic arch, over the whole range of baroreceptor sensitivity, decreased abdominal vascular capacitance by 2.9 ml-kg-1 (mean, SE +/- 0.42) and increased the abdominal vascular resistance by 35 +/- 7.1%. Decreases in pressure in the vascularly isolated carotid sinuses, while aortic pressure was constant, decreased capacitance by 5.0 +/- 0.62 ml-kg-1 and increased resistance by 72 +/- 15.9%. Responses of capacitance and resistance to changes in aortic pressure were greatest when carotid pressure was held near threshold levels and least when it was held at levels that would maximally excite carotid baroreceptors. The responses to changes in aortic pressure were abolished when the venous nerves were cooled or the splanchnic nerves were cut.