Permeability and electrical properties of planar lipid membranes from thylakoid lipids

Electrical measurements were carried out on planar lipid membranes from thylakoid lipids. The specific capacitance of membranes formed from decane-containing monogalactosyldiacylglycerol (MGDG), which accounts for 57% of the total lipid content of thylakoids, showed that it adopted a bilayer structure. Solvent-free bilayers of MGDG were not formed, with very rare exceptions, indicating that decane is required to stabilize the planar conformation. However, this cone-shaped lipid produces bilayer structures in combination with other cylindrical thylakoid lipids even in the absence of organic solvent. We compared the properties of solvent-free and decane-containing bilayers from MGDG, soybean lecithin, and the quaternary mixture of lipids similar to that found in vivo. The conductance of decane-MGDG was 26 times higher than that of decane-lecithin. The flux through the decane-lecithin bilayer was found to be slightly dependent on pH, whereas the decane-MGDG membrane was not. The specific conductance of bilayers formed from the quaternary mixture of lipids was 5 to 10 times larger than lecithin (with alkane or not). Further experiments with bilayers made in the presence of a KCl gradient showed that decane-MGDG, decane-MGDG/DGDG/SQDG/PG, and solvent-free MGDG/DGDG/SQDG/PG were cation-selective. The permeability coefficient for potassium ranged from 4.9 to 8.3 x 10(-11) cm s-1. The permeability coefficient for protons in galactolipids, however, was determined to be about six orders of magnitude higher than the value for potassium ions. The HCl permeation mechanism through the lipid membranes was determined from diffusion potentials measured in HCl gradients. Our results suggest that HCl was not transported as neutral molecules. The data is discussed with regard to the function of galactolipids in the ion transport through thylakoid membranes.

Role of polymorphonuclear leucocytes and oxygen-derived free radicals in the formation of gastric lesions induced by HCl/ethanol, and a possible mechanism of protection by anti-ulcer polysaccharide

This study examined the role of oxygen-derived free radicals in the pathogenesis of gastric mucosal lesions induced by HCl/ethanol. Superoxide dismutase, and catalase, and their combination reduced gastric lesion formation in mice. Gastric lesions were also reduced in mice treated with cyclophosphamide or anti-neutrophils, but not in mice treated with allopurinol or desulphated-carrageenan. Cobra venom factor did not reduce lesion formation. These results suggested that oxygen-free radicals may contribute to the formation of gastric mucosal lesions induced by HCl/ethanol, and that oxygen radicals were generated from neutrophils but not from xanthine oxidase. Anti-ulcer pectic polysaccharide, bupleuran 2IIc, which was recently isolated from the roots of Bupleurum falcatum L., showed potent inhibition of HCl/ethanol-induced gastric lesions in mice. Bupleuran 2IIc seemed to scavenge hydroxyl radical effectively. It was suggested that this anti-ulcer polysaccharide may provide protection to the gastric mucosa by scavenging oxygen-free radicals.

Gastric branch vagotomy blocks nutrient and cholecystokinin-induced suppression of gastric emptying

A role for the vagus nerve in the emptying of intragastric nutrients and the gastric inhibitory actions of the brain-gut peptide cholecystokinin (CCK) has been proposed. To directly assess the role of the gastric vagal branches in these actions, we compared the emptying of 5-ml nutrient and nonnutrient gastric loads in male rats in which both branches of the gastric vagus nerves were cut (GVX, n = 7) with emptying in surgical control (n = 8) rats. Gastric emptying of saline was also examined in both groups after intraperitoneal administration of 8 micrograms/kg CCK. In control rats, high osmolarity, low pH, and caloric density all significantly decreased gastric emptying compared with the emptying of physiological saline. In addition, fat (oleic acid) and protein (peptone) loads emptied significantly more slowly than isocaloric carbohydrate (glucose) loads. Gastric branch vagotomy completely blocked the suppression of emptying produced by fat, protein, carbohydrate, and acid loads. In addition, GVX attenuated the ability of hyperosmotic nutrient and nonnutrient loads to inhibit emptying to the same degree, irrespective of their caloric content. Finally, in intact rats, CCK significantly inhibited the emptying of physiological saline, and gastric vagotomy abolished this suppression. Taken together, these results are consistent with the proposals that 1) the controlled emptying of caloric, hyperosmotic, and acidic solutions is dependent on gastric vagal branches, and 2) exogenous CCK relies on an intact vagal pathway in the control of gastric emptying.

Viscous fingering of HCl through gastric mucin

The HCl in the mammalian stomach is concentrated enough to digest the stomach itself, yet the gastric epithelium remains undamaged. One protective factor is gastric mucus, which forms a protective layer over the surface epithelium and acts as a diffusion barrier Bicarbonate ions secreted by the gastric epithelium are trapped in the mucus gel, establishing a gradient from pH 1-2 at the lumen to pH 6-7 at the cell surface. How does HCl, secreted at the base of gastric glands by parietal cells, traverse the mucus layer without acidifying it? Here we demonstrate that injection of HCl through solutions of pig gastric mucin produces viscous fingering patterns dependent on pH, mucin concentration and acid flow rate. Above pH 4, discrete fingers are observed, whereas below pH 4, HCl neither penetrates the mucin solution nor forms fingers. Our in vitro results suggest that HCl secreted by the gastric gland can penetrate the mucus gel layer (pH 5-7) through narrow fingers, whereas HCl in the lumen (pH 2) is prevented from diffusing back to the epithelium by the high viscosity of gastric mucus gel on the luminal side.

Testing for food-borne parasites, their metabolic products and symbionts

Microscopic animals associated with foods include free-living and saprophytic invertebrates, parasites of hosts other than humans, and parasitic animals specifically designated as food-borne that can infect a human host by the gastrointestinal route. The first general method used to screen for food-borne species was digestion with pepsin and hydrochloric acid at 36 degrees C, based on the "artificial stomach juice" technique for recovering larvae of the nematode Trichinella spiralis from muscle. This method selects for forms capable of surviving a mammalian digestive enzyme at mammalian temperatures. It has been used successfully to recover a variety of food-borne helminths, not only from mammalian flesh but also from fish, shellfish and molluscs, and can be adapted to greatly reduce the "background of living animals" associated with soils and the crops grown in them. However, not all animal forms that survive digestion are food-borne parasites, and all that succumb are not necessarily noninfectious. Methodology to test for food-borne parasites is, in general, not as efficient as that for food-borne bacteria. Recent developments in food parasitology indicate a need to identify not only the parasite, but also its metabolic products and associated symbionts.

Molecular cloning of a Pseudomonas paucimobilis gene encoding a 17-kilodalton polypeptide that eliminates HCl molecules from gamma-hexachlorocyclohexane

Pseudomonas paucimobilis UT26 is capable of growing on gamma-hexachlorocyclohexane (gamma-HCH). A genomic library of P. paucimobilis UT26 was constructed in Pseudomonas putida by using the broad-host-range cosmid vector pKS13. After 2,300 clones were screened by gas chromatography, 3 clones showing gamma-HCH degradation were detected. A 5-kb fragment from one of the cosmid clones was subcloned into pUC118, and subsequent deletion and gas chromatography-mass spectrometry analyses revealed that a fragment of ca. 500 bp was responsible for the conversion of gamma-HCH to 1,2,4-trichlorobenzene via gamma-pentachlorocyclohexene. Nucleotide sequence analysis revealed an open reading frame (linA) of 465 bp within the fragment. The nucleotide sequence of the linA gene and the deduced amino acid sequence showed no similarity to any known sequences. The product of the linA gene was 16.5 kDa according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

The importance of gastric secretion in the feedback control of interdigestive and postprandial pancreatic secretion in rats

Previous studies demonstrated that pancreatic enzyme secretion in rats is stimulated by the diversion of pancreatic juice from the duodenum or by the inhibition of pancreatic proteinases in the intestinal lumen but little attention has been paid to the role of gastric secretion in this stimulation. This study, carried out on conscious rats with large gastric (GF) and pancreatic fistulas, confirms that diversion of pancreatic juice in rats with the GF closed results in the progressive stimulation of pancreatic secretion reaching the maximum similar to that induced by exogenous CCK. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl (25-400 mumol/h) instilled intraduodenally (i.d.) in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice and this effect was completely abolished by the pretreatment with L-364,718, a specific CCK receptor antagonist. Pretreatment with omeprazole to suppress completely gastric acid secretion in the diverted state resulted in a decline in pancreatic secretion similar to that observed after opening the GF. Camostate given in graded doses (6-200 mg/kg) either i.d. or s.c. in rats with pancreatic juice returned to the duodenum caused a dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 50% while after L-364,718 it was abolished. This study provides evidence that gastric secretion plays an important role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteinases (but not to feeding) and the elimination of gastric acid reduces this response.

Redistribution of membranes and cytoskeletal proteins in chicken oxyntic cells during the HCl secretory cycle: ultrastructural and immunofluorescence study

Changes in ultrastructure and cytoskeletal organization by avian oxyntic cells, at the onset of HCl secretion, were analysed. Cells in resting state, induced by fasting and cimetidine, were compared with histamine stimulated secreting cells. Ultrastructural studies were done by transmission electron microscopy; the distribution of prekeratin, myosin, and filamin-like protein, by immunofluorescence; and that of F-actin using FITC-phalloidin. Resting cells show short pericellular clefts. These are increasingly deepened in secreting cells by a reorganization of the lateral cell borders involving displacement of the junctional complexes toward the cell base and incorporation of the tubular system to the luminal plasma membrane. In secreting cells, the processes of the secretory surface are concentrated in a pericellular groove. Histamine stimulation induces a drastic redistribution of cytoskeletal proteins. In chicken oxyntic cells, in addition to the F-actin cytoskeleton associated with the membranes of the secretory surface, there is a cytoskeletal ring containing F-actin, myosin, and a filamin-like protein, located at the level of the junctional complexes. In resting cells, filaments and masses of cytoskeletal matrix are associated with the zonula adherens. In secreting cells, the junctional complexes maintain their association with the filamentous ring, while the amorphous matrix is replaced by microfilaments that support the processes of the luminal surface. Intermediate filaments form a peripheral ring probably associated with the zonula adherens, and project from the ring toward the cell cytoplasm. Thus, with the onset of HCl secretion, the apical cytoskeletal ring of resting cells displaces toward the cell base. A role for this cytoskeletal ring in the changes in shape parallel to HCl secretion is discussed.

Interaction of calcium channel antagonists with parietal cell acid production, adenylate cyclase, intracellular-free Ca2+ and H+/K+-ATPase

The calcium channel antagonists verapamil, gallopamil and nifedipine were tested for their effects on acid secretion stimulated by histamine and dibutyryl-cyclic AMP in isolated and enriched guinea pig parietal cells, on adenylate cyclase activity mediated by histamine H2 receptors, on histamine-stimulated increase in cytosolic-free Ca2+ concentration [Ca2+], on gastric H+/K(+)-ATPase activity and on H+/K(+)-ATPase-mediated proton uptake in intact gastric membrane vesicles. Verapamil and gallopamil impaired all cellular and enzymatic test systems studied. Both drugs affected with highest potency the acid secretion in the parietal cell preparation (IC50: 1-2 mumol/l) and the H+/K(+)-ATPase-mediated H+ uptake in gastric membrane vesicles, whereas their inhibitory action was less pronounced on adenylate cyclase and on histamine-induced increase in cytosolic-free [Ca2+]. The type of interaction found in the gastric membrane vesicle preparation indicates that both drugs act as protonophores. Nifedipine was less effective as an inhibitor of acid secretion in the parietal cell preparation and in reducing proton concentration in isolated gastric membrane vesicles. The drug failed to block adenylate cyclase and H+/K+-ATPase activity. Since nifedipine is a more effective calcium channel blocking agent but a less lipophilic drug than verapamil and gallopamil, we conclude that the antisecretory activity of calcium channel antagonists in vitro is mediated by a nonspecific, i.e. a protonophoric, action. We suggest that verapamil exhibits its antisecretory activity in vivo partially by its protonophoric action at the secretory membrane of the parietal cell, whereas the decrease in acid secretion by nifedipine is not mediated by this mechanism.

Subepithelial tissue pH of rat gastric mucosa exposed to luminal acid, barrier breaking agents, and hemorrhagic shock

Tissue pH in the immediate subepithelial layer of rat gastric mucosa was measured using H+-selective microelectrodes. Exposure of the mucosa to luminal acid (50-150 mM) caused a significant acidification of the subepithelial tissue. Contrary to expectation, disruption of the mucosal barrier with taurocholate (10 mM), acetylsalicylic acid (10 mM), or ethanol (20% vol/vol) during acid (100 mM HCl) perfusion promoted no further acidification of the subepithelial tissue but rather caused an alkalinization of the primarily acidified subepithelial tissue. When hemorrhagic shock was induced during acid perfusion, a profound acidification of the subepithelial tissue occurred even though a much lower luminal acidity (10 mM HCl) was used. Also, taurocholate had no alkalinizing influence on subepithelial pH during hemorrhagic shock, but caused a rapidly progressing and irreversible drop of the subepithelial tissue pH. The findings suggest that in normal stomach with intact "mucosal barrier," H+ back-diffusion occurs during exposure to acid. However, disruption of the mucosal barrier seems to lead to alkali (HCO3-) efflux from the mucosa, which neutralizes the influxing H+, thus "masking" H+ back-diffusion and protecting the mucosa. Yet, when adequate supply of HCO3- to the mucosa is blocked during exposure to a barrier-breaking agent and acid, increased H+ back-diffusion becomes again "unmasked," leading to extensive acidification and ulceration of the mucosa.

Bile salt-induced injury of rabbit oesophageal mucosa measured by hydrogen ion disappearance

Oesophageal injury secondary to gastro-oesophageal reflux is unlikely to be due to the effects of hydrochloric acid alone. The present authors have investigated the development of acid and bile salt-induced oesophageal mucosal injury in a rabbit model. Solutions of hydrochloric acid and sodium taurocholate (ST) were perfused through an isolated oesophageal preparation and mucosal injury was determined by measuring the rate of H+ disappearance. Perfusion with acid alone in concentrations up to 10 mmol/l did not affect the H+ disappearance rate. Addition of 1 mmol/l ST to an acid perfusate resulted in loss of H+ from the system. The increase in H+ disappearance rate was associated with loss of ST from the perfusate. Sodium taurocholate was only lost from the system when in an acid medium. Increased rate of H+ disappearance occurred even after the bile salt had been washed out of the perfused oesophagus. The mechanism of bile salt-induced mucosal injury was unlikely to be due to mucosal disruption secondary to micelle formation since the critical micellar concentration of taurocholate was found to be greater than that used in the perfusate. These findings indicate that bile salts may be an important factor in hydrochloric acid-related damage to oesophageal mucosa, by acting through mechanisms unrelated to micelle formation.

Trimoprostil decreases acid disappearance from the human stomach

A double-blind, placebo-controlled, randomized crossover study involving 8 healthy volunteers was carried out to investigate the disposal of an acid load instilled into the stomach after oral administration of two doses of trimoprostil (0.125 and 1.5 mg). The results showed that trimoprostil reduced the disappearance of acid from the gastric lumen but did not influence the rate of gastric emptying of acid.

The role of extracellular mucus as a protective cap over gastric mucosal damage

Topical application of hypertonic saline to a chambered gastric mucosa (ex vivo) resulted in the formation of a cap of mucus, fibrin, plasma, and cellular debris over the damaged regions. The role of this 'mucoid cap' in protecting the underlying mucosa from subsequent challenges with hypertonic saline was studied. In the control group, the repeated challenges with 1 M NaCl in 0.05 M HCl caused macroscopically visible gastric damage involving only 2% of the total glandular mucosa. In the test group, in which the mucoid cap was peeled off the mucosa after the first challenge with NaCl, there was significantly more mucosal leakage of albumin (p less than 0.05), and the macroscopically visible gastric damage progressively increased to involve over 14% of the total glandular mucosa by the end of the experiment (p less than 0.005). Histological analysis showed that the mucoid cap provided a protective layer, allowing for restitution of the epithelium and protection of the mucosa from the damaging effects of hypertonic saline. In the absence of this protective layer, the repeated exposure to hypertonic saline resulted in deep mucosal necrosis. These studies support the hypothesis that mucus released in response to acute damage plays an important role in protecting the underlying mucosa so that restitution of the epithelium can proceed.

Cutaneous and renal responses to intravascular infusions of HCl and NH4Cl in the bullfrog (Rana catesbiana)

This study examined the ability of bullfrogs to correct a non-respiratory acidosis by renal and cutaneous mechanisms. Acidosis was induced by intravascular infusions of HCl (3 mmole/kg) or NH4Cl (4 mmole/kg). The acid load was removed primarily by increased renal excretion of NH4+, while urine pH and titratable buffer acid excretion changed little. Acid loading resulted in an increase in cutaneous permeability, shown by large ion losses and elevated water uptake across the skin. It is concluded that infused mineral acids were immediately buffered by the extracellular fluids, moved rapidly into the intracellular fluid compartment, and only later were slowly cleared.

Inhibition of gastric motor activity by 16,16-dimethyl prostaglandin E2. A possible explanation of cytoprotection

Effects of 16-dimethyl prostaglandin E2 (16-dmPGE2) and necrotizing agents on gastric motility and gastric mucosa were studied in conscious rats. Gastric motility was determined using a miniature balloon positioned in the glandular part of the stomach, which was connected to a pressure transducer and polygraph. Necrotizing agents, such as absolute ethanol, 0.6 N HCl, 0.2 N NaOH, or 4 M NaCl, were instilled into the stomach through a small fistula prepared in the forestomach. One milliliter of these agents produced streak lesions in the glandular part of the stomach within 1 hr, which were preceded by violent gastric contraction in every case. An intragastric administration of 16-dmPGE2 (0.3-3 micrograms/kg) by itself increased a tonus of the gastric wall but dose-dependently lessened the number and the amplitude of contractions. In those rats treated with 16-dmPGE2 (3 micrograms/kg), necrotizing agents failed to enhance the motility or to induce streak lesions. Pretreatment with 1 M NaCl as a mild irritant also inhibited gastric motility and lesion formation, but those actions were significantly antagonized by indomethacin (5 mg/kg). These results indicate that necrotizing agents induce a violent gastric contraction, followed by development of lesions in the stomach, and that the inhibition of gastric hypercontraction may be involved in a cytoprotective action of a prostaglandin against those induced gastric lesions in rats.

Parietal cell density in gastric biopsies from patients with and without duodenal ulcer disease

During gastroscopy biopsy specimens were taken from 4 different areas of gastric corpus mucosa in 51 patients with duodenal ulcer disease (DU) and 26 patients without ulcer disease and the patients underwent an acid stimulation test by injection of 6 micrograms 5-gastrin/kg bodyweight. A parietal cell density study was carried out, using a direct counting of cell nuclei in a standardized lattice. The method was found fully acceptable when compared with stereological analysis of parietal cell density per unit volume (Nv) and was found having a low variation in and between observers. There was no significant variation of parietal cell density locally or regionally in the oxyntic mucosa. No correlation was found in DU group between Basic Acid Output (BAO), Peak Acid Output (PAO) and the parietal cell density, but in the non-DU group a rather poor, but significantly positive correlation was demonstrated. We conclude that the parietal cell mass is not exactly correlated to acid production and that the term "Parietal cell mass" have to include acidogenic area and the secretory ability of the parietal cells.

Redistribution of gastric K+-NPPase in vertebrate oxyntic cells in relation to hydrochloric acid secretion: a cytochemical study

Gastric K+-NPPase represents a partial reaction of the (K+-H+)ATPase system, which is considered to be the proton pump in mammalian parietal cells. In the present paper, K+-NPPase activity was cytochemically studied by the method of Mayahara et al. (1980) in gastric glands of birds, amphibia, and mammals, either in the resting state induced by cimetidine or after stimulation of HCl secretion by histamine. The gastric K+-NPPase cytochemical reaction was localized only in oxyntic cells of the gastric mucosa in the three species tested. The subcellular distribution of the K+-NPPase reaction product drastically changes with the secretory state of HCl. In resting cells, the K+-NPPase staining is associated with the membranes of the endocellular tubular system while in HCl-secreting cells, it is associated with the plasma membrane of the elaborate secretory surface characteristic of this functional state. The above results demonstrate that the same enzymatic activity, which is associated with the gastric proton pump, is present in both membranous systems of the oxyntic cell secretory pole. This fact supports the proposal that the tubular system represents a membrane reserve that inserts the proton pump into the luminal plasma membrane in vertebrate oxyntic cells under the action of HCl secretagogues.

Hyperchloremic metabolic acidosis after chlorine inhalation

Chlorine gas inhalation is usually accompanied by pulmonary toxicity and hypoxemia; the associated acidemia, when present, has been attributed to lactic acidosis. This case report describes the development of hyperchloremic metabolic acidosis following accidental chlorine gas exposure. The mechanism postulated for the production of this acidosis is the absorption of hydrochloric acid following the reaction of chlorine gas with tissue water. This may be the first case of chlorine toxicity in which the mechanism of the acidosis has been determined.

Effect of sleep on swallowing, esophageal peristalsis, and acid clearance

Recent studies have shown that impaired esophageal clearance of refluxed material during the sleeping interval plays a major role in the pathogenesis of esophagitis. The present investigation compares esophageal responses to both acid and water infusions during sleep in asymptomatic subjects. Fourteen healthy individuals were studied. The subjects were studied for two nights in the sleep laboratory. Each night involved four to six infusions of 15 ml of either sterile water or 0.1 N HCl. A similar infusion was conducted during the presleep waking interval. Acid clearance time was shown to decrease as a function of increasing wakefulness during the acid clearing interval. Arousal responses were significantly greater with acid infusions during sleep (p less than 0.05). Awakenings from sleep with acid infusions were associated with significantly greater swallowing rates than those associated with water infusions (p less than 0.01). Peristaltic parameters of amplitude, velocity, and duration were not differentially affected by acid versus water infusions or by sleep versus waking.

Biosynthesis of radiolabeled phomopsin by Phomopsis leptostromiformis

[14C]phomopsin and [36Cl]phomopsin were synthesized by Phomopsis leptostromiformis in liquid cultures containing various labeled compounds. [U-14C]isoleucine, [U-14C]phenylalanine, and [U-14C]proline were the best precursors in terms of labeling efficiency, whereas [36Cl]hydrochloride was much less efficient. When each of the four precursors was used, a large proportion of recovered label was associated with phomopsin. The specific activities of phomopsin produced with labeled isoleucine, phenylalanine, proline, and hydrochloride were 150, 120, 90, and 17 muCi/mmol, respectively. 14C label from acetate, malate, propionate, sucrose, or tryptophan was neither specifically nor efficiently incorporated into phomopsin.

The kinetics of acid adsorption by crosslinked casein

A rate law for the diffusion-controlled adsorption of monoprotic mineral acids by crosslinked casein has been determined. From the temperature dependence of the rate constant, the activation energy for the process was found to be 22 kJ mol-1.

The role of the esophageal body in the antireflux mechanism

The competency of the cardia depends on the interaction of the distal esophageal sphincter (DES) pressure and the length of the DES exposed to the positive-pressure environment of the abdomen. These two components were measured in 20 normal control volunteers and 126 patients with objectively proved gastroesophageal reflux. The results, when plotted on a grid with the horizontal bar representing the length of the abdominal esophagus and the vertical bar representing the DES pressure, indicated that factors in addition to the mechanical components of the cardia were important in the antireflux mechanism. The 24-hour esophageal pH records from the patients and the antireflux mechanism. The 24-hour esophageal pH records from the patients and normal subjects were analyzed as to the number of reflux episodes that occurred per hour while the patients were in the supine position and the ability to clear the refluxed acid by the propulsive "P"pump" of the body of the esophagus. It was concluded that the antireflux mechanism of the esophagus consists of a valvular cardia and a propulsive "pump" action of the body of the esophagus. The failure of either may lead to abnormal acid exposure but can be compensated by one or the other in normal subjects. Failure of both invariably leads to abnormal acid exposure. The cardia can fail either mechanically (i.e., having inadequate valvular components) or functionally (i.e., having normal valvular component but abnormal number of reflux episodes per hour). The latter suggests gastric pathology. Precise diagnosis of the reason for abnormal acid exposure is needed to develop a rational basis for therapy.

Independence of the acute acid-buffering response from endogenous parathyroid hormone

Two recent reports have made the provocative suggestion that parathyroid hormone (PTH) and, by implication, bone play a critical role in the early phase of acid buffering. The purpose of the present study was to investigate the effect of PTH on the acute buffering process by examining the influence of thyroparathyroidectomy (TPTX) on acid-base parameters in nephrectomized rats following infusion of hydrochloric acid at two differing doses. To ensure hemodynamic and physiologic stability of the animals, the required surgical procedures were staged over several days. Additionally, the experimental protocol was carried out in awake and unrestrained animals. Non-TPTX (sham) animals underwent a sham operation to equalize the surgical stresses between the two groups. The decrements in plasma [HCO-3] observed following infusion of 3.5 mmol/kg HCl over 1 h did not differ between TPTX vs. sham animals at 1 h (-9.4 vs. -9.9 meq/liter), 3 h (-8.6 vs. 8.6 meq/liter), or 6 h (-8.6 vs. -8.5 meq/liter) from the start of the infusion. Similarly, virtually identical falls in plasma [HCO-3] were observed between TPTX vs. sham rats after infusion of 5 mmol/kg HCl over 30 min at 30 min (-13.6 vs. -14.2 meq/liter) and 3 h (-10.9 vs. -11.4 meq/liter) after the start of the infusion. At both doses, the resultant changes in plasma [H+] and PaCO2 were not different in the two groups. The observed mortality was comparable in both TPTX and sham groups. The data demonstrate that endogenous PTH is not necessary in the early phase of buffering of a mineral acid load.