A dimethylnitrosamine-induced model of cirrhosis and portal hypertension in the rat

A method of producing cirrhosis consistently in rats by the administration of dimethylnitrosamine (DMNA) is described. Two weeks following the cessation of DMNA treatment there was distortion of the lobular architecture of the liver and some focal nodule formation. This 'pre-cirrhotic' state was accompanied by portal hypertension, biochemical abnormalities and the development of ascites. The mortality 2 weeks after cessation of DMNA was 42%. Twenty-four weeks after DMNA treatment cirrhosis had developed with diffuse nodularity and fibrosis, marked portal hypertension, and accumulation of ascites. There was also a deterioration in liver function, with hypoproteinaemia and jaundice. The overall mortality 24 weeks after the cessation of DMNA treatment had risen to 52%. This model of cirrhosis in the rat may be useful in evaluating the efficacy of drugs in the long-term management of portal hypertension in man.

Cell growth, cell division and cell size homeostasis in Swiss 3T3 cells

By separating large and small 3T3 cells we show here that cell growth (in volume) after stimulation from quiescence is not 'autocatalytic'. Rather, large cells grow significantly more slowly, in relative terms, than small cells. It follows that 3T3 cells do not require a size control mechanism operating at the level of division timing in order to achieve cell size homeostasis.

The effect of vasopressin and hepatic artery ligation on the blood supply to normal and metastatic liver tissue

The effect of low (0.08 microU g-1 body wt min-1) and high (0.16 microU g-1 body wt min-1) rates of vasopressin infusion on blood flow to normal liver tissue and to liver metastases derived from azoxymethane induced colorectal carcinomas was studied in 36 male Wistar rats. Portal venous flow was measured by electromagnetic flowmetry and blood flow to normal and metastatic liver tissue by the clearance of xenon-133 injected directly into the liver parenchyma or metastasis. The low rate of vasopressin infusion decreased portal venous flow but increased blood flow to normal and metastatic liver tissue while at the higher rate of infusion these effects were reversed. Hepatic artery ligation (HAL) immediately following a low rate of vasopressin infusion abolished the observed increase in blood flow to both normal liver tissue and metastases. HAL immediately following the higher rate of vasopressin infusion further reduced blood flow to metastases but did not further alter blood flow to normal liver tissue. HAL prior to the infusion of the vasoactive drug significantly reduced blood flow to metastatic liver tissue, increased portal venous flow and was without effect on blood flow to normal liver tissue. Following HAL, blood flow to metastatic liver tissue was not further altered by either the low or high rates of vasopressin infusion. However, blood flow to normal liver tissue after HAL was reduced by a low rate of infusion of vasopressin and increased by the higher rate of infusion. The results of this study indicate that blood flow to normal or metastatic liver tissue can be increased or decreased by differential rates of infusion of vasopressin. These observations may have important implications in the treatment of liver metastases in man where different rates of vasopressin infusion may potentiate the effects of hepatic artery ligation or cytotoxic therapy.

The effect of vasopressin on hepatic artery flow in the rat

The effects of vasopressin infusion on hepatic artery flow was studied in rats. Hepatic artery ligation followed by the infusion of vasopressin (0.08 microU/g body weight per min) decreases portal venous flow and liver blood flow. Vasopressin infusion results in an increase in hepatic artery flow and liver blood flow both of which are abolished by subsequent hepatic artery ligation. The increase in hepatic artery flow and the decrease in portal venous flow following the infusion of vasopressin is discussed in relation to the management of patients presenting with bleeding oesophageal varices.

Circulating levels of arginine vasopressin before and during the infusion of the hormone in patients presenting with bleeding oesophageal varices

Circulating levels of antidiuretic hormone (ADH) were measured in patients presenting with bleeding oesophageal varices before and during treatment with arginine vasopressin. There was no significant difference in the circulating levels of ADH before and during treatment with arginine vasopressin in patients in which the hormone successfully controlled haemorrhage and those in which it did not. It is concluded that the failure of vasopressin to control variceal haemorrhage in approximately 40% of patients presenting for treatment cannot be attributed to higher circulating levels of the hormone in these subjects.

Radioenzymatic assay for measurement of tissue concentrations of histamine: adaptation to correct for adherence of histamine to mechanical homogenizers

Because adherence of histamine to glass is well-known, we tested for its adherence to a mechanical homogenizer commonly used in the extraction of histamine from tissue samples. During 60 sec of homogenization, 15% to 17% of the histamine originally present in the samples "disappeared," and the reason for the disappearance was reversible binding of histamine to the homogenizer. Adding trace amounts of [14C]histamine to each sample before homogenization and measuring the disappearance of radioactivity during homogenization permitted correction for binding to the homogenizer. This technique for correction was validated by the measurement of endogenous concentrations of histamine in the tracheal posterior membranes of six dogs (range of mean concentrations: 0.63 to 1.51 ng/mg wet weight) followed by the measurement of known amounts of exogenous histamine added before homogenization to tracheal tissue samples from the same dogs. In the latter samples, 96 +/- 13% (mean +/- SEM) of the histamine added was measured by our technique. We conclude that binding of histamine to mechanical homogenizers may be an important cause of inaccuracy of the enzymatic assay for the measurement of histamine concentrations in tissue but that such binding may but that such binding may be easily corrected for.

Use of fungicides in plant tissue culture

We have examined a number of antifungal agents which might prove useful in plant tissue culture. We find that carbendazim, fenbendazole and imazalil can be used relatively safely and also have a broad spectrum of antifungal activity. Fungicides in clinical use do not prove to be as effective.

Effect of vasopressin on liver blood flow in the hypophysectomised rat

Liver blood flow (xenon-133 clearance method) and portal venous flow were measured in hypophysectomised rats following the infusion of vasopressin at a range of infusion varying from 0.0125 to 0.8 microU/g b.w./min over the range 0.0125-0.1 microU/g b.w./min, portal venous flow was reduced, the reduction being linearly related to the logarithm of the dose (r = -0.88). Following the infusion of 0.8 microU/g b.w. of vasopressin, portal venous flow significantly increased above pre-infusion levels (p less than 0.05). Liver blood flow was increased significantly (p less than 0.05) when vasopressin was infused over the range 0.0125-0.2 microU/g b.w. At higher rates of infusion, liver blood flow was progressively reduced, and at 0.8 microU/g b.w./min liver blood flow was less than pre-infusion levels (p less than 0.05). These data suggest that the effects of vasopressin on hepatic haemodynamics is related to the rate of infusion with a reversal of effects at higher rates of infusion. The implications of these findings in relation to the use of vasopressin in the management of portal hypertension and bleeding oesophageal varices is discussed.

Augmentation of alpha-adrenergic contractions in the trachealis muscle of living dogs

Discrepancies exist between reported effects of histamine on the alpha-adrenergic responsiveness of the canine trachealis muscle. Therefore, using an in situ preparation described recently (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 49: 84-94, 1980), we tested the effects of histamine and other agents on alpha-adrenergic responses in the trachealis muscle of 34 anesthetized dogs. Under basal conditions, maximum alpha-adrenergic responses were small [3 +/- 1 (SE) g/cm] compared with those induced by a supramaximal parasympathetic stimulus (45 +/- 3 g/cm). After exposure of the muscle to histamine, responsiveness increased markedly to alpha-adrenergic stimuli, which included tracheal arterial injections of norepinephrine and phenylephrine or electrical stimulation of sympathetic nerves. Augmented alpha-adrenergic responsiveness persisted for 20 min after the end of contractions induced by histamine. Serotonin and long-acting, but not short-acting, cholinergic agonists also potentiated alpha-adrenergic responsiveness. We concluded that exposure of the trachealis muscle in living dogs to a variety of constrictor stimuli potently augmented its alpha-adrenergic responsiveness.

Technetium-99m labelled bran: a new agent for measuring gastric emptying

Bran was labelled with 99mTc-pertechnetate, ingested as part of a normal meal and used to measure gastric emptying in 15 normal subjects and in 15 patients with ulcerative colitis. There was no significant difference between the gastric emptying curves of the normal subjects and the patients, suggesting that rapid gastric emptying does not contribute to diarrhoea in ulcerative colitis.

The toxicity of antibiotics to plant cell cultures

We have examined the toxicity of over twenty antibiotics to protoplast-derived cells of Nicotiana plumbaginifolia. The least toxic antibiotics are the betalactams: ampicillin, carbenicillin and the cephalosporins can be used to provide broad spectrum antimicrobial activity without significant toxicity to plant cells. Similar broad spectrum activity can also be obtained by combining rifampicin and trimethoprim. Other antibiotics which may be useful are erythromycin and colistin. The aminoglycosides are not recommended.

Characterization of tracheal mast cell reactions in vivo. Inhibition by a beta-adrenergic agonist

In 12 anesthetized dogs, we tested the effects of pharmacologic beta-adrenergic stimulation on the severity of tracheal mast cell reactions in vivo (Am Rev Respir Dis 1979; 119:62). In control dogs, tracheal arterial injections of compound 48/80 produced arteriovenous differences in histamine concentrations across the trachea (35 +/- 15 ng/ml), but not the lung; this finding suggested selective degranulation of tracheal mast cells. Tracheal arteriovenous histamine differences correlated (r = 0.70) with tracheal contractions (12 +/- 4 g/cm) induced by compound 48/80 in these animals. In other dogs, injections of isoproterenol (10 micrograms/kg) before compound 48/80 prevented the development of both tracheal arteriovenous differences and contractions. We concluded that pharmacologic beta-adrenergic stimulation inhibited degranulation of tracheal mast cells. The preparation appears suitable for examining the effects of endogenous stimuli on the severity of mast cell reactions in the central airways of anesthetized dogs.

Parasympathetic innervation of the cervical trachealis muscle in living dogs

In 34 anesthetized dogs, we characterized the pathways by which parasympathetic fibers were carried to the cervical trachealis muscle. Nerves were stimulated electrically, and tracheal tension was monitored in segments of the posterior membrane in vivo as described previously (J.K. Brown et al.; J. Appl. Physiol: Respirat. Environ. Exercise Physiol. 49: 84-94, 1980). Stimulation of superior laryngeal nerves contracted 34 of 34 cranial cervical segments and 2 of 4 caudal cervical segments. Recurrent laryngeal nerves contributed to innervation of 34 of 34 cranial, as well as 4 of 4 caudal, segments. Stimulation of pararecurrent nerves contracted 11 of 34 cranial and 4 of 4 caudal segments. Mechanical effects of esophageal contraction, induced by stimulating pararecurrent nerves, did not alter tension in tracheal segments. Tracheal contractions induced by stimulation of all three pathways simultaneously were significantly less than the sum of contractions produced by stimulating each set individually; this was probably due to anastomoses between terminal neurons, overlap in their anatomic distribution, or intercellular nexuses in trachealis muscle. We conclude that parasympathetic innervation of the canine trachea is by three different neuroanatomic pathways.

A rapid quantitative method for the preparation of 123I-iodo-hippuric acid

The labelling of o-iodo-hippuric acid (hippuran) with 123I by several methods was investigated with a view to producing a simple one-step kit preparation. The requirements for the final product are high labelling efficiency and high radiochemical purity. A method which incorporates CuSO4 . 5H2O as a catalyst was found which gave promising preliminary results. Such variables as pH, mass of CuSO4 . 5H2O, volume of 0.02 N NaOH containing the 123I, reaction temperature and time were investigated in detail and optimum values obtained. The results have led to the production of a kit which can be stored for up to 3 months in liquid form and up to 9 months if freeze-dried. The kit has been used in several thousand patients and has yielded consistently good clinical results.

The effect of increased motility on absorption from the canine colon

The absorption of water and electrolytes and intraluminal pressure were measured from Thirty-Vella loops in 4 dogs under basal conditions and during electrical stimulation of the colonic smooth muscle. Pulse wave electrical stimulation via serosal silver/silver chloride electrodes gave rise to significant increases in both intraluminal pressure and percentage motility. Absorption of water, sodium and chloride was significantly increased during stimulation but the transport of ammonia, bicarbonate and potassium was not significantly affected. It is suggested that motility changes result in altered absorption irrespective of transit time.

Capillary blood flow in the canine colon and other organs at normal and raised portal pressure

Capillary blood flow in the canine colon and other organs has been assessed over a wide range of portal pressures using radio-labelled microspheres. The proximal colon received a greater proportionate flow than the distal region. At both normal and raised pressures, the mucosa received 90% of the total colonic capillary flow. A highly significant negative correlation (P less than 0.001) was found between colonic capillary blood flow and portal pressure. A highly significant positive correlation (P less than 0.001) was found between colonic capillary blood flow in the superior mesenteric artery.

Fibrinogen in the 'hepato-renal syndrome': an experimental study

The pathogenesis of renal failure in jaundice is controversial. Several factors have been incriminated, including intravascular coagulation. We have investigated this hypothesis by by studying the deposition of radioactive fibrinogen in the kidney of jaundiced rats. Fibrinogen labelled with 125I was injected into rats whose bile duct was subsequently ligated. The radioactivity in the kidney was compared to that in blood and the renal uptake ratio calculated. This ratio (mean +/- s.e.mean) rose from 0.24 (+/- 0.04) to 2.93 (+/- 0.43) after ligation of the common bile duct. In contrast, in control rats who underwent a sham operation, the uptake ratio rose from 0.31 (+/- 0.03) to 0.96 (+/- 0.08). This deposition of 125I fibrinogen in the kidneys of jaundiced rats was significantly greater (P < 0.001) than that in control rats. The deposition was specific to the kidney compared with that in the heart, bowel, muscle and liver. In the control animal the uptake of 125I fibrinogen by the kidney was not different from that by other viscera.

Effects of wide variations in portal pressure on mesenteric blood flow and absorption from the canine colon

Splanchnic blood flow was studied over a wide range of portal pressures in five dogs. An inverse linear relationship between flow and pressure was found in the range from 6 to 42 mmHg. The colonic absorption of ammonia, water, sodium, potassium, bicarbonate, and chloride was measured in four dogs over a similar range of portal pressures. Absorption of ammonia, water, sodium, and chloride was significantly reduced by increasing portal pressure, and this reduction was abolished when portal pressure was allowed to return to the basal level. It is suggested that splanchnic decompression by portasystemic shunt gives rise to increased mesenteric flow and increased colonic ammonia absorption, which may contribute to portasystemic encephalopathy.

Zinc absorption in Crohn's disease

Zinc deficiency is a potential complication of Crohn's disease and we have searched for evidence of this and assessed the possibility that malabsorption of zinc might be a cause. Serum zinc concentrations in 33 patients suffering from Crohn's disease were significantly lower than in 58 normal control subjects (9 . 18 +/- 2 . 3 mumol compared with 13 . 6 +/- 1 . 73 mumol, P < 0 . 0005). Serum zinc correlated well with serum albumin concentrations and the low serum zinc may simply reflect the low serum albumin. Thus its value as an indicator of zinc deficiency is poor. We studied zinc absorption in seven patients with Crohn's disease and compared it with the results obtained previously in five normal subjects using a new technique involving a short-lived isotope of zinc (69mZn). Plasma appearance curves, constructed after an oral dose of isotope, and disappearance curves, after an intravenous dose, were used in a deconvolution computer programme to calculate zinc absorption. Compared with normal subjects, zinc absorption was considerably impaired in patients with Crohn's disease (range 9--45%, compared with 38--75%). This abnormality is a potential cause of zinc deficiency in patients with Crohn's disease.