Intravascular and interstitial fluid dynamics in rats treated with minoxidil

Edema is a major complication of vasodilatory therapy. However, the pathophysiologic mechanisms leading to the formation of vasodilator-mediated edema are insufficiently understood. The present study therefore examined the effect of the chronic administration of the potent arteriolar vasodilator, minoxidil (Mx), on extracellular fluid dynamics in rats. Extracellular volume (ECV), plasma volume (PV), interstitial fluid volume (IV), arterial pressure (AP), and interstitial fluid pressure (IP) were measured in rats treated for 10 days with Mx (1.5 mg/kg/day) and in control animals. In addition to a decreased AP, Mx-treated animals had diminished water and sodium excretion. ECV, PV, and IV and plasma renin concentration (PRC) were also increased in the Mx-treated rats. IP, which was subatmospheric in control rats (-2.6 +/- 0.04 mm Hg), was near zero in Mx-treated animals (-0.2 +/- 0.02 mm Hg, p less than 0.05). Saline ECV expansion (20 min, Ringer infusion, 3% body weight) or rat albumin injection (300 mg/2 ml) induced similar changes in the volume of the extracellular fluid compartments in both groups. However, changes in IP were blunted in Mx-treated rats. These results, therefore, show that Mx-treated rats have changes in interstitial fluid dynamics prior to any macroscopic evidence of edema accumulation. These alterations in the extracellular compartment dynamics may be a consequence of the sustained arteriolar vasodilation induced by Mx.

The extrarenal effects of atrial natriuretic peptide on body fluid distribution

To study the effects of atrial natriuretic peptide (ANP) on body fluid volume regulation, we estimated the changes in intra- and extravascular fluid volume by measuring hematocrit (Hct), plasma protein concentration and water balance, and the changes in intra- and extracellular fluid volume by the electrical impedance method during intravenous infusion of ANP. We did two studies, as follows: ANP was infused into 18 patients with essential hypertension, 29 with renal parenchymal hypertension and 15 normotensives at 0.025 microgram/kg/min for 40 min. Both hypertensive groups showed greater natriuretic responses to ANP than normotensives. ANP infusion into essential hypertensive patients increased the urinary excretion of water by 125%, Na by 205%, Hct by 4.2% and plasma total protein (TP) by 5.2% (each P less than .001). In 9 patients (1 with renal hypertension and 8 normotensives) who did not show a natriuretic response (-2.1%), the infusion of ANP also significantly increased Hct (3.8%) and plasma TP (3.1%, each P less than .01). The electrical impedance method was applied to 12 subjects to simultaneously detect the intracellular (Ri) and extracellular resistivities (Re), of which reciprocals reflect the fluid volume in the extra- and intracellular spaces, respectively. ANP infusion increased Re in all subjects (3.96 +/- 0.16 [SE] v 4.03 +/- 0.16 omega.m, P less than .05), but decreased Ri in 7. Changes in urinary Na excretion correlated positively with those in both Re (r = 0.62, P less than .05) and Ri (r = 0.75, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Control of pH of airway surface liquid of the ferret trachea in vitro

We measured the pH of airway surface liquid (ASL) secreted by the ferret trachea in vitro by using a catheter-tipped pH electrode implanted in a collecting cannula close to the airway epithelium. Mucus secretion was promoted by methacholine (0.02 mmol/l) in the organ bath. The pH of the ASL was 6.85 +/- 0.03 (SE) compared with a bath value of 7.39 +/- 0.01, when the bath was bubbled with 5.65% CO2. Changing the bath CO2 from 0 to 20.93% CO2 altered the bath pH from 8.06 to 6.96, but the ASL pH only varied from 6.92 to 6.85. This homeostasis of ASL pH was not the result of the buffering powers of the ASL, because ex situ buffer curves for secreted ASL were similar to those for Krebs-Henseleit solution. Changing the luminal CO2 content by blowing gases through the trachea changed ASL pH by values similar to that ex situ. However, when external organ bath CO2 was changed, the luminal CO2 changes were proportionately far smaller. Measurement of rates of diffusion of CO2 across the tracheal wall indicated that this was not a limiting factor in the results. Similarly, measurement of metabolic rate CO2 production in the tracheal lumen indicated that this did not significantly affect the results. We conclude that the pH of ASL is significantly on the acid side of the pH or interstitial fluid and plasma and that it is maintained relatively constant despite large changes in external pH.

Regional distribution of the cardiac output and renal responses to atrial natriuretic peptide infusion in rabbits with congestive heart failure

1. A biventricular, low-output congestive cardiomyopathy was induced in 19 rabbits by administering adriamycin (16 mg/kg). The effects of alpha-rat atrial natriuretic peptide (ANP) infused at 0.1, 0.2 and 0.4 micrograms/kg per min, were then examined in terms of (i) central haemodynamics (ii) regional blood flow (iii) renal function and (iv) plasma norepinephrine and plasma renin. 2. In this dose range, ANP produced progressive and significant falls in stroke volume, cardiac output and mean arterial pressure, owing to a fall in venous return. The heart rate response to this was blunted. 3. Using radiolabelled microspheres, significant falls in the perfusion of cutaneous, gastrointestinal and musculoskeletal tissues were observed, due to reduced vascular conductances in these beds. These changes were accompanied by activation of the sympathetic nervous system as evidenced by a progressive rise in plasma norepinephrine. A significant increase in plasma renin was only observed with the highest infusion of ANP. 4. Renal blood flow was maintained in the face of a falling mean arterial pressure and cardiac output, but diuretic and natriuretic effects were absent. 5. It was concluded that the dominant influence of ANP infusion in this model of heart failure appeared to be a reduction in cardiac preload with detrimental overall haemodynamic consequences.

Beneficial effects of erythropoietin on haematological parameters, aerobic capacity, and body fluid composition in patients on haemodialysis

Eleven patients on haemodialysis were treated with erythropoietin (EPO), 50-200 U kg-1 once to three times a week, for up to 1 year. After outset of EPO all patients became transfusion-independent. Four patients did not reach the target haemoglobin (Hb) level 100 g l-1 in 5 months. These patients had higher serum concentrations of aluminium (225 +/- 87 micrograms l-1, mean +/- SD) than the responding patients (55 +/- 56 micrograms l-1). Addition of desferrioxamine to treatment with EPO resulted in a rapid rise in Hb values in these patients. Thus, aluminium may inhibit EPO responsiveness. All patients were iron overloaded. Serum ferritin levels declined in all but one patient with secondary haemochromatosis. In exercise tests the aerobic capacity and oxygen uptake increased during EPO therapy. Peak oxygen consumption (Vo2 peak), oxygen pulse, oxygen uptake at anaerobic threshold (AT) and total work output (W max) increased 19%, 36%, 26% and 24%, respectively. Lean body mass (LBM) increased by 8%. Taken together, all clinical EPO effects measured appeared clinically favourable.

Inhibition by loperamide of mucus secretion in the rat colon in vivo

The effect of loperamide on mucus secretion and the net transport of fluid, sodium and potassium was investigated in the perfused rat colon in vivo. Prostaglandin E2 (PGE2, 1 mg/kg per h intraarterially) and deoxycholic acid (2 mM intraluminally) were used as secretagogues. Mucus secretion was determined as the total amount of protein-bound hexose in the effluent. Under basal conditions, loperamide (6 mg/kg subcutaneously) slightly decreased mucus secretion and increased the absorption of fluid and sodium. PGE2 and deoxycholic acid stimulated mucus secretion about 4- and 9-fold, respectively. Loperamide abolished the mucus secretory response to PGE2 and reduced the response to deoxycholic acid by 50%. It also reduced the fluid secretion following PGE2 but did not affect the diminished fluid absorption following deoxycholic acid. Potassium secretion was not significantly influenced by loperamide and therefore was independent of the secretion of mucus. The data suggest that loperamide is a potent inhibitor of colonic mucus secretion, a property that possibly contributes to the antidiarrheal effect of this opiate analogue.

Effects of furosemide on body water compartments in infants with bronchopulmonary dysplasia

We studied the effects of a single dose of intravenous furosemide on the body water compartments of nine infants with bronchopulmonary dysplasia. We measured total body water, extracellular water, and plasma volume using deuterium oxide, sodium bromide, and Evans blue dye, respectively. From the results of these measurements, we calculated cell water, interstitial water, red cell volume, and total blood volume. We performed these measurements on the first day of the study and again 28 h later, 4 h after an intravenous dose of furosemide (1 mg/kg). All infants had a brisk diuresis in the first hour after the dose, but urine output was no greater during the 24-h period after the dose than during the preceding 24-h period. Total body water, extracellular water, and interstitial water were significantly decreased 4 h after furosemide. There was no change in plasma volume, red cell volume, or total blood volume.

Estradiol-induced blockade of ovulation in the cow: effects on luteinizing hormone release and follicular fluid steroids

Administration of 10 mg estradiol valerate (EV) to nonlactating Holstein cows on Days 16 of the estrous cycle prevented ovulation in 7 of 8 cows for 14 days post-injection. In these 7 cows, the timing of luteolysis and the luteinizing hormone (LH) surge was variable but within the normal range. At 14 days post-treatment, each of these cows had a large (greater than 10 mm) follicle, with 558 +/- 98 ng/ml estradiol-17 beta, 120 +/- 31 ng/ml testosterone, and 31 +/- 2 ng/ml progesterone in follicular fluid (means +/- SE). A second group of animals was then either treated with EV as before (n = 22), or not injected (control, n = 17) and ovariectomized on either Day 17, Day 18.5, Day 20, or Day 21.5 (24, 60, 96, or 132 h post-EV). Treatment with EV did not influence the timing of luteolysis, but surges of LH occurred earlier (59 +/- 8 h post-EV vs. 100 +/- 11 h in controls). The interval from luteolysis to LH peak was reduced from 44 +/- 6 h (controls) to 6.9 +/- 1.5 h (treated). Histologically, the largest follicle in controls tended to be atretic before luteolysis, but nonatretic afterwards, whereas the largest follicle in treated animals always tended to be atretic. Nonatretic follicles contained high concentrations of estradiol (408 +/- 59 ng/ml) and moderate amounts of testosterone (107 +/- 33 ng/ml) and progesterone (101 +/- 21 ng/ml), whereas atretic follicles contained low concentrations of estradiol (8 +/- 4 ng/ml) and testosterone (12 +/- 4 ng/ml), and either low (56 +/- 24 ng/ml) or very high (602 +/- 344 ng/ml) concentrations of progesterone. This study suggests that EV prevents ovulation by inducing atresia of the potential preovulatory follicle, which is replaced by a healthy large follicle by 14 days post-treatment.

Effect of long-term nifedipine treatment on body fluid composition in essential hypertension

The antihypertensive efficacy and effects on body fluid composition of monotherapy with the calcium antagonist nifedipine were investigated in 15 patients with essential hypertension. The systolic as well as the diastolic blood pressure decreased significantly, by approximately 12%, during nifedipine treatment with a mean dose of 56 mg. Glomerular filtration rate, plasma volume, extracellular fluid volume, and the ratio plasma to interstitial fluid volume did not change significantly. The most frequently observed side-effects were flushing and peripheral oedema which occurred in four and three patients, respectively. These results indicate that sodium and water retention, which is often observed during long-term treatment with vasodilators, does not seem to be the explanation of the development of peripheral oedema seen with nifedipine.

Use of sodium dichloroisocyanurate granules for spills of body fluids

The use of chlorine-containing granules for disinfecting body fluid spills has been evaluated by hospital trials and laboratory tests. Hospital trials were carried out by nurses using 'Presept' disinfectant granules according to a protocol. In general they preferred using granules to bleach and, in 50 tests using granules on natural and artificial spills in wards, no organisms were recovered from the floor by contact plates after using the granules. Laboratory tests were carried out on 'Haz-Tab' granules, 'Biospot' disinfectant powder, 'Presept' disinfectant granules, 'Virusorb' absorbent powder and 'Titan' Sanitizer SU 357 using a standardized surface test. Available chlorine levels varied from 57.8% to 1.0% and the performance of products in the surface test varied with the chlorine level present. Granules containing a relatively high level of chlorine have the advantages that spilled material is contained and that a contact time of only 2-3 min is required before the spill can be safely removed.

Requirement for T cells and effect of lymphokines in successful chemotherapy for an intracellular infection. Experimental visceral leishmaniasis

Although directly microbicidal, pentavalent antimony has failed as treatment for visceral leishmaniasis in patients who also have AIDS or are receiving immunosuppressive therapy. To define the role of T cells in the successful host response to chemotherapy, we examined the efficacy of pentavalent antimony (sodium stibogluconate, Pentostam) in normal and T cell-deficient BALB/c mice infected with Leishmania donovani. In euthymic (nu/+) mice, single injections of 250 and 500 mg/kg of Pentostam induced the killing of 67% and 89% of intracellular liver amastigotes, respectively. In contrast, in athymic nude (nu/nu) mice, up to three injections of 500 mg/kg achieved no L. donovani killing and did not retard visceral parasite replication. Once nude mice were reconstituted with nu/+ spleen cells, however, Pentostam exerted strong leishmanicidal activity, an effect that appeared to be transferred by either L3T4+ or Lyt-2+ cells. Responsiveness to chemotherapy could also be induced by providing nude mice with either interferon-gamma or interleukin 2 alone. The absence of this T cell- and probably lymphokine-dependent mechanism is a likely explanation for treatment failures in immunocompromised patients infected with L. donovani and perhaps other systemic intracellular pathogens as well.

A comparison of hypochlorite and phenolic disinfectants for disinfection of clean and soiled surfaces and blood spillages

Suspension test methods were used to compare phenolic and hypochlorite disinfectants under conditions as recommended for use in hospitals. Using plasma to simulate soiled conditions, Clearsol (1% v/v) and Stericol (2% v/v) produced satisfactory disinfection, (i.e. 5 log reduction in 5 mins against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa in the presence of up to 50% v/v plasma (25 mg ml-1 plasma protein). Although sodium dichloroisocyanurate (NaDCC) at 2500 ppm AvCl2 was effective in the presence of up to 20% plasma, compared to 10% plasma for sodium hypochlorite 2500 ppm, sensitivity of NaDCC to inactivation was greater than for phenolics. In the presence of blood, both hypochlorites and phenolics were substantially inactivated, although here the effectiveness of NaDCC at 10,000 ppm was equivalent to the phenolics. Our results indicate that hypochlorites at 10,000 ppm, Clearsol 1% and Stericol 2% may be ineffective for treatment of blood spills unless applied at v:v ratios of 9 parts disinfectant to 1 part blood. In this situation, chlorine-releasing powder formulations, which produce higher AvCl2 concentrations and contain spilled material, offer an effective alternative.

Inositol 1,2-cyclic 4,5-trisphosphate is an order of magnitude less potent than inositol 1,4,5-trisphosphate in mobilizing intracellular stores of calcium in mouse pancreatic acinar cells

Semi-synthetic inositol 1,2-cyclic 4,5-trisphosphate is 1/16th as potent as inositol 1,4,5-trisphosphate in releasing Ca2+ from intracellular stores in permeabilized mouse pancreatic acinar cells. Competitive displacement studies in mouse pancreatic microsomes show that the affinity of inositol 1,2-cyclic 4,5-trisphosphate is 1/20th of that of inositol 1,4,5-trisphosphate at the latter's receptor, indicating that the lower potency of inositol 1,2-cyclic 4,5-trisphosphate in releasing Ca2+ can be accounted for by a weaker affinity at the receptor. These results suggest that inositol 1,2-cyclic 4,5-trisphosphate is unlikely to play any significant role in Ca2+ mobilization, at least in mouse pancreatic acinar cells.

Effect of DDE on ionic and fluid movement in rat colon in vitro

1. The effect of DDE on ionic (Na+ and K+) and fluid movement was studied in rat colon in vitro. 2. DDE (10(-7) M) increased net K+ secretion while inhibited the net flux of Na+ and fluid movement inducing net secretion. 3. DDE added before or after aldosterone caused an inhibition on the net influx of Na+ and fluid movement and potassium secretion. 4. DDE also inhibited (Na+ and K+)-ATPase from the same tissue suggesting that the inhibition of DDE is due to an action of this organochlorine compound on the sodium pump.

Control of anion and fluid secretion by apical P2-purinoceptors in the rat epididymis

1. Exogenous adenosine triphosphate (ATP) stimulated the short circuit current (SCC) in primary monolayer cultures of rat epididymal cells when added to the apical but not to the basolateral side of the monolayers. Half-maximal stimulation was achieved at 5 x 10(-8) M ATP. 2. The increase in SCC induced by ATP was dependent on the presence of extracellular Cl in the bathing solutions. 3. The effects of other adenosine derivatives, and purine and pyrimidine nucleotides were studied. Their orders of potency in stimulating SCC were: ATP greater than adenosine diphosphate much greater than adenosine monophosphate, adenosine, and ATP greater than inosine triphosphate greater than guanosine triphosphate greater than cytidine triphosphate. These results indicate that ATP interacts with a P2-purinoceptor at the apical membrane of the epididymal cells. 4. The SCC response to ATP was not blocked by 8-phenyltheophylline, a P1-purinoceptor antagonist or by propranolol. Although pretreatment of the cultures with piroxicam abolished the SCC response to bradykinin, it did not affect the response to ATP. This indicates that the SCC response to ATP was not mediated by an increase in the synthesis of prostaglandins. 5. Serosal to mucosal Cl flux (Js-m Cl) and net water flux were measured in the luminally perfused rat epididymis in vivo. ATP (1 microM) added to the luminal perfusion solution caused an increase in Js-m Cl and net water secretion by the epididymal duct. 6. Since spermatozoa contain a high concentration of ATP, it is proposed that ATP released from spermatozoa may affect anion and fluid secretion by the epididymis. The control of secretion via the apical purinoceptors offers a means by which spermatozoa regulate the fluidity of their own environment.

Trabecular meshwork cells grown on filters. Conductivity and cytochalasin effects

A system was developed to measure the hydraulic conductivity of cultured monolayers of human trabecular meshwork (HTM) cells. By optimizing the cell growth conditions and evaluating a number of filter supports, confluent HTM cells in single layers were obtained for measurement of hydraulic conductivity. The HTM monolayers had hydraulic conductivities of 0.3-2.0 microliters/min/mm Hg/cm2 measured at near-physiological flow rates. Evaluations of cytochalasin B (CB) effects on the hydraulic conductivity of our HTM monolayers revealed that CB (10(-6) to 10(-5) M) caused a dramatic dose-related increase in conductivity within 10 to 30 min, which parallels CB effects on outflow facility in vivo. Morphologic observations show that the increase in hydraulic conductivity was accompanied by a retraction of the trabecular cells and widening of the intercellular spaces. Our findings suggest that growth of HTM cells on filter supports can provide a useful in vitro system to study the regulation of aqueous outflow.

Effects of kassinin, a tachykinin of the skin of the African frog Kassina senegalensis, on body fluid homeostasis in rats

In Wistar rats loaded with SC hypertonic NaCl solution kassinin produces an inhibition of cell-dehydration drinking which lasts several hours. The long duration of the effect does not depend on a renal excretion of sodium but, hypothetically, on a redistribution of electrolytes between the extra- and the intra-cellular compartments of body fluids.

Effects of procaine on intracellular pH and its regulation: measurements with pH-selective micro-electrodes in Retzius neurones of the leech

The experiments were performed with double-barelled micro-electrodes in Retzius neurones of the leech in order to see if the tertiary amine local anesthetic procaine affects intracellular pH (pHi) and its regulation. Lasting about 20 min, exposures to procaine (3 mM) saline caused an intracellular alkalosis of about 0.2 pH units which gradually degradated; its removal initiated a fast decrease of pHi resulting in an acidosis, fron which the cells recovered. Detailed studies, involving CO2 or NH4+ acid loaded cells as well as inhibition of the pHi regulating exchange mechanism by various drugs or exposures to Na-free salines suggest, that neither the Na+ -H+, nor a probably Na+ -dependent HCO3-(-)Cl- exchange are affected by procaine. We propose a model for procaine action on pHi assuming that neutral procaine passes the membrane easily through lipophilic pathways. The degradation of alkalinity during procaine exposure hints on an entry of loaded procaine, some possible transport paths of which are discussed.

Body fluid homeostasis in the newborn infant with congestive heart failure: effects of diuretics

Congestive heart failure is characterized by extracellular fluid volume expansion, increased venous filling pressure, and paradoxal renal sodium retention. Although diuretics remain invaluable agents to lower venous pressure in congestive heart failure, they also carry the risk of further compromising cardiac output and inducing severe adverse effects. This article reviews the pathophysiology of body fluid homeostasis in neonates with congestive heart failure, and discusses the adverse effects associated with the use and abuse of diuretics.

Effects of ammonium metavanadate treatment upon macrophage glutathione redox cycle activity, superoxide production, and intracellular glutathione status

Female B6C3F1 mice were given intraperitoneal injections of ammonium metavanadate (2.5 or 10 mg V/Kg), ammonium chloride, or sodium phosphate buffer every 3 days for 6 weeks. Resident peritoneal macrophages were harvested, lysed by freeze-thawing, and the resulting cytolysate was assayed for total protein content and enzyme activities of glutathione reductase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase. In addition, peritoneal macrophages were assayed for superoxide production using nitroblue tetrazolium reduction, as well as for intracellular levels of oxidized and reduced glutathione. Exposure of mice to vanadium resulted in a dose-trend depression in the three macrophage enzyme activities as compared with the controls. Vanadium treatment resulted in a similar decrease in the production of superoxide anion, and an increase in levels of oxidized glutathione; however, the total glutathione pool (reduced plus oxidized forms) was not affected.

Na transport stimulation by novobiocin: intracellular ion concentrations and membrane potential

Microelectrodes and electron microprobe analysis were employed to study the effect of novobiocin on membrane potential and intracellular electrolyte concentrations in the frog skin epithelium. In both species investigated (Rana esculenta and Rana temporaria), novobiocin (1 mM, outer bath) caused a stimulation of transepithelial Na transport, a depolarization of apical membrane potential, a fall in the apical fractional resistance, and an increase in the intracellular Na concentration. The rise in the Na concentration was accompanied by an equivalent fall in the K concentration. All effects of novobiocin were fully reversible by subsequent application of amiloride. The depolarization as well as the Na increase suggests that the natriferic effect of novobiocin is due to a stimulation of the apical Na influx. Combining both measurements it was possible to calculate the effect of novobiocin on the Na permeability of the apical membrane directly. In Rana esculenta novobiocin increased the permeability from 4.5 to 23.2 nm/s. In Rana temporaria the increase was significantly smaller, from 8.7 to 16.9 nm/s. The transport rate as measured by the short-circuit current showed a non-linear dependence on the apical Na permeability. In the range of transport rates normally encountered, however, the current was a linear function of the Na permeability consistent with the view that the apical membrane is rate-limiting in transepithelial Na transport.

Extra- and intracellular calcium in vanadate-induced contraction of vascular smooth muscle

The effects of extracellular Ca and Ca antagonists on vanadate-induced contractions of vascular smooth muscles of aortae and mesenteric arteries from rabbits, guinea pigs, and Wistar-Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Vanadate-induced contractions of aortae were greatly diminished by extracellular Ca removal; the size of the remaining contraction was variable. Vanadate-induced contractions of mesenteric arteries, which were only observed in the presence of elevated K, were suppressed by the removal of Ca. Verapamil and nifedipine depressed vanadate-induced contractions of aortae from WKY and SHRSP, whereas they produced no or only slight inhibition of responses in guinea pig and rabbit aortae. Ca uptake into smooth muscle cell increased in the presence of vanadate, but the increase was much less than that induced by high K. In saponin-skinned smooth muscle, vanadate depressed the Ca-induced contraction. It is concluded that the vanadate-induced contraction utilizes both extracellular and intracellularly bound Ca, the relative contribution of which varies from preparation to preparation.

Involvement of prostaglandins in histamine-induced fluid and electrolyte secretion by rat colon

Histamine increased the transmural potential difference across rat colon in-vivo and induced a net secretion of fluid. Both effects were inhibited by indomethacin. Histamine increased the potential difference and short-circuit current, and reduced tissue resistance in colonic sheets in-vitro. This response was reduced in the absence of chloride in the bathing medium or in the presence of serosal frusemide, suggesting that histamine stimulated electrogenic chloride secretion by the colon. The rise in short-circuit current induced by histamine was calcium-dependent since it was reduced in the absence of serosal calcium or in the presence of serosal verapamil. Indomethacin, a cyclo-oxygenase inhibitor, and mepacrine, a phospholipase inhibitor, both caused a dose-dependent inhibition of the electrical response of colonic sheets to histamine, without affecting the rise in short-circuit current induced by prostaglandin E2. The stimulation of chloride secretion induced by histamine in rat colon therefore appears to be mediated by an increased production of prostaglandins.