Seed coat cell turgor in chickpea is independent of changes in plant and pod water potential

Turgor pressure in cells of the pod wall and the seed coat of chickpea (Cicer arietinum L.) were measured directly with a pressure probe on intact plants under initially dry soil conditions, and after the plants were irrigated. The turgor pressure in cells of the pod wall was initially 0.25 MPa, and began to increase within a few minutes of irrigation. By 2-4 h after irrigation, pod wall cell turgor had increased to 0.97 MPa. This increase in turgor was matched closely by increases in the total water potential of both the pod and the stem, as measured by a pressure chamber. However, turgor pressure in cells of the seed coat was relatively low (0.10 MPa) and was essentially unchanged up to 24 h after irrigation (0.13 MPa). These data demonstrate that water exchange is relatively efficient throughout most of the plant body, but not between the pod and the seed. Since both the pod and the seed coat are vascularized tissues of maternal origin, this indicates that at least for chickpea, isolation of the water relations of the embryo from the maternal plant does not depend on the absence of vascular or symplastic connections between the embryo and the maternal plant.

Insulin resistance, impaired glucose tolerance and non-insulin-dependent diabetes, pathologic mechanisms and treatment: current status and therapeutic possibilities

Impaired glucose tolerance and non-insulin-dependent diabetes (NIDDM) are the pathologic consequence of two co-incident and interacting conditions, namely insulin resistance and relative insulin deficiency. Recognised by the World Health Authority as a global health problem there are at 1995 estimates at least 110 million diagnosed diabetics world wide with at least the same number undiagnosed. Diabetes is the 4th leading cause of death in developed countries and its management exerts a vast economic and social burden. Insulin resistance is established as the characteristic pathologic feature of patients with glucose intolerance and NIDDM describing a state in which insulin stimulated glucose uptake and utilisation in liver, skeletal muscle and adipose tissue is impaired and coupled to impaired suppression of hepatic glucose output. Although the biochemical mechanisms underpinning both defects are becoming better understood, the genetic and molecular causes remain elusive; and whether insulin resistance or relative insulin deficiency represents the primary defect in patients with NIDDM is the matter of some debate. In this article we review the biochemical and molecular nature of the defects in insulin sensitivity and glucose uptake, and discuss some of the potential causative mechanisms. The genetic and environmental basis of insulin resistance is reviewed and presented, and potential therapeutic targets including thiazolidinediones are discussed.

Potential benefit of inhibitors of advanced glycation end products in the progression of type II diabetes: a study with aminoguanidine in C57/BLKsJ diabetic mice

Prolonged hyperglycemia in type II diabetic patients is linked both with diabetic complications and with further impairment of glucose homeostasis, possibly due to glucose toxicity of the beta cell. While the connection between the accumulation of extracellular advanced glycation end products (AGEs) and the development of complications is well established, it has only recently been suggested that intracellular glycation may be equally adverse and could be involved in the pathogenesis of glucose toxicity in vitro. Aminoguanidine is a recognized inhibitor of the formation of both extracellular and intracellular AGEs. In this study, we show that the development of diabetes, measured by increased water intake and concomitant midday blood glucose levels in type II genetically diabetic mice, is reduced by treatment with aminoguanidine at a dosage of 500 mg/kg/d for 12 weeks in the diet. In addition, at the end of the study, aminoguanidine reduced the decline in serum and pancreatic insulin levels and the degree of pancreatic islet morphological degeneration, all of which are associated with pancreatic insufficiency following prolonged hyperglycemia in this animal model. These results suggest that AGEs may be involved in the aggravation of type II diabetes in vivo and aminoguanidine may be beneficial in its treatment.

Peroxisome proliferator-activated receptor-gamma agonist, rosiglitazone, protects against nephropathy and pancreatic islet abnormalities in Zucker fatty rats

Rosiglitazone (BRL 49653), a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist and potent insulin action-enhancing agent, was given in the diet (50 micromol/kg of diet) to male Zucker rats ages 6-7 weeks for 9 months (prevention group). In this treatment mode, rosiglitazone prolonged the time to onset of proteinuria from 3 to 6 months and markedly reduced the rate of its subsequent progression. Progression was also retarded when treatment was commenced (intervention group) after proteinuria had become established (4 months; ages 24-25 weeks). In either treatment mode, rosiglitazone normalized urinary N-acetyl-beta-D-glucosaminidase activity, a marker for renal proximal tubular damage, and ameliorated the rise in systolic blood pressure that occurred coincidentally with the development of proteinuria in Zucker fatty control rats. The renal protective action of rosiglitazone was verified morphologically. Thus in the prevention group there was an absence of the various indexes of chronic nephropathy that were prominent in the Zucker fatty control group, namely, glomerulosclerosis, dilated tubules containing proteinaceous casts, a loss of functional microvilli on the tubular epithelium, and varying degrees of chronic interstitial nephritis. An intermediate pathology was observed in the intervention group. Also, pancreatic islet hyperplasia, ultrastructural evidence of beta-cell work hypertrophy, and derangement of alpha-cell distribution within the islet were prominent features of Zucker fatty control rats, but these adaptive changes were ameliorated (intervention group) or prevented (prevention group) by rosiglitazone treatment. These data demonstrate that treatment of Zucker fatty rats with rosiglitazone produced substantial protection over a prolonged period against the development and progression of renal injury and the adaptive changes to pancreatic islet morphology caused by sustained hyperinsulinemia.

Elevated renal endothelin-I clearance and mRNA levels associated with albuminuria and nephropathy in non-insulin-dependent diabetes mellitus: studies in obese fa/fa Zucker rats

1. The obese fa/fa Zucker rat is a genetic model of obesity and insulin resistance which develops a number of metabolic and endocrine features of non-insulin-dependent diabetes, including hypertension, proteinuria and glomerular sclerosis. 2. We have investigated the urinary excretion of the metabolites of thromboxane (thromboxane B2) and prostacyclin (6-keto prostaglandin F1 alpha), and of endothelin and cyclic GMP as markers for changes in the balance of renal haemodynamic factors in the obese Zucker rat. 3. Obese fa/fa Zucker rats were hypertensive compared with their lean counterparts (161 +/- 3 and 138 +/- 3 mmHg respectively, P < 0.01); obese animals were also markedly proteinuric (16.7 +/- 6.7 versus 1.1 +/- 0.1 mg/ml) and albuminuric (8.3 +/- 2.9 versus 0.4 +/- 0.25 mg/ml) and excreted less creatinine than lean animals (all P < 0.01). Urinary excretion of endothelin was greater in obese rats (123 +/- 24 versus 62 +/- 10 pg/15 h, P < 0.05) as was the level of pre-proendothelin mRNA, but excretion of cyclic GMP was depressed (12.5 +/- 1.6 versus 27.2 +/- 3.1 nmol/ 15 h, P < 0.01). Histological examination of kidneys from obese animals showed evidence of focal glomerulosclerosis and cortical tubular damage. 4. These results show that increased urinary endothelin is associated with proteinuria and early stage nephropathy in this animal model of non-insulin-dependent diabetes mellitus. This finding, coupled with a decreased excretion of cyclic GMP, suggests that these increased renal vasoconstrictor/vasodilator forces might contribute to the renal functional changes in non-insulin-dependent diabetes mellitus.

Effects of the glucocorticoid II receptor antagonist mifepristone on hypertension in the obese Zucker rat

We have investigated the possible involvement of endogenous corticosteroids in the maintenance of hypertension in aged lean and obese Zucker rats using the type II corticosteroid antagonist mifepristone. At 8 mo of age, the start of the study, obese Zuckers had been hypertensive for at least 2 mo (systolic blood pressure; 153 +/- 4 vs. 136 +/- 5 mmHg; n = 8-9; P < .05) and were hyperinsulinemic (756 +/- 98 vs. 193 +/- 61 microU x ml(-1)) and hypercorticosteronemic (524 +/- 83 vs. 260 +/- 97 ng x ml(-1)) compared to their lean littermates. There were no differences in plasma renin activity between lean and obese animals and plasma renin activity was unaffected by any treatment. Oral treatment of obese rats with mifepristone (40.0 mg x kg(-1) day(-1) for 9 days) resulted in a gradual reduction in SBP to lean levels by day 9. Mifepristone treatment did not affect plasma insulin or corticosterone levels but resulted in a significant reduction in plasma aldosterone concentration. Mifepristone was without significant effect on systolic blood pressure in lean rats. Oral treatment of lean rats with corticosterone-21-acetate (3.0 mg x kg(-1) day(-1) for 9 days) resulted in a rise in systolic blood pressure to levels similar to obese Zuckers after 9 days. Plasma insulin levels were unchanged but corticosterone immunoreactivity was significantly reduced. Plasma aldosterone levels were increased from 564 +/- 3 to 802 +/- 68 pg x ml(-1). Our data suggest that raised glucocorticoids and aldosterone may be factors contributing to hypertension in obesity.

Effects of streptozotocin-induced diabetes on vascular reactivity in genetically hyperinsulinaemic obese Zucker rats

Although the fa/fa Zucker rat shows many of the features of type II diabetes, the absence of consistent cardiovascular complications in this model may be due to the absence of significant hyperglycaemia. We studied the consequences of streptozotocin (STZ)-induced insulin deficiency and hyperglycaemia on vascular reactivity in the fa/fa Zucker rat. Hyperinsulinaemic obese Zucker rats were rendered diabetic by injection of STZ (50-60 mg/kg intraperitoneally, i.p.), and vascular tissue was removed for study 10-12 weeks later. In isolated aorta, there was no difference in the phenylephrine (PE) concentration-response relation between lean and obese control animals, but the concentration-response curve was shifted to the left in diabetic animals, (pD2 7.56 +/- 0.04 in STZ diabetic animals, n = 8; 7.4 +/- 0.04 in obese control, n = 9, p < 0.05). The maximum response was also enhanced in both aorta and perfused mesentery of STZ-treated animals. In contrast, the potency of serotonin (5-HT) in inducing contractions of isolated aorta were enhanced in tissues from obese as compared with lean animals (pD2 6.63 +/- 0.06, n = 9; 6.17 +/- 0.07, n = 7 respectively; p < 0.01) and was attenuated in animals with STZ-induced diabetes (pD2 6.31 +/- 0.09, n = 8, p = 0.05). The differential effects of hyperglycaemia on PE-and 5-HT-induced vasoconstriction suggest that the long-lasting modulation of vasoconstrictor responses induced by increases in blood glucose level may be specific for some agonists.

Plant and soil influences on estimating biomass of wheat in plant breeding plots using field spectral radiometers

Field spectral radiometers were used to estimate the biomass of wheat at early growth stages, as wheat breeders require a rapid, non-destructive technique to rank wheat genotypes for early vigour. Under experimental conditions, good relationships were obtained between reflectance and biomass prior to the wheat crop achieving a green area index of 1.5. When used above different soil types, good results were achieved on very uniform dark and light soils under experimental conditions, but greater differentiation between plots differing in biomass was achieved on darker soils. Similarly, under operational conditions in wheat breeders' plots, the best results were achieved against a dark soil background. Structural differences between plants also influenced solar radiation reflectance. At the Merredin site with the dark soil background, where the best correlation between reflectance and biomass was achieved, the relationship was much stronger for the more uniform genotypes at the second stage of selection than for the more heterogeneous genotypes at the first stage of selection. On these plots, the vegetation spectral indices NDVI (normalised difference vegetation index) and TSAVI (transformed soil-adjusted vegetation index) had a coefficient of determination 90-95% as good as the best regression using two wavebands. To optimise the field spectroradiometry technique for estimating early biomass, it should be applied at a weed-free site, with a uniform dark soil background and on material that is relatively homogenous in structure. We conclude that, unless these precautions are taken, the technique will have limited utility in breeding programs.

Effects of genetic hyperinsulinaemia on vascular reactivity, blood pressure, and renal structure in the Zucker rat

The association between insulin resistance, obesity, and hypertension is well recognised. We examined the hypothesis that hypertension in the obese Zucker rat is related to changes in vascular reactivity. Systolic blood pressure (SBP) in conscious Zucker rats was significantly greater in obese as compared with lean animals (157 +/- 9 and 117 +/- 8 mm Hg). Obese animals also had marked proteinuria and reduced urinary creatinine excretion in 24 h as compared with their lean counterparts. The reactivity of isolated aorta to phenylephrine (PE) and 5-hydroxy-tryptamine (5-HT) was modestly (twofold) increased in obese animals (EC50 13.8 nM as compared with 29.4 nM in lean animals and 0.19 nM as compared with 0.46 nM in lean animals, respectively). In the perfused mesenteric vascular bed, basal perfusion pressure was the same in both phenotypes, as was the pressor response to PE and depressor response to acetylcholine (ACh) and sodium nitroprusside (SNP). In the isolated aorta, from obese animals, insulin attenuated the contractile response to PE but markedly enhanced the vasoconstrictor potency of 5-HT. It had no significant effect on pressor or depressor responses in the perfused mesenteric bed. The data suggest that increased reactivity of central arteries to spasmogenic agents may be involved in the development of systolic hypertension in the hyperinsulinaemic Zucker rat.

Eicosanoid release in allergen-induced bronchoconstriction in dogs. Its relationship to airways hyperreactivity and pulmonary inflammation

In vitro studies have demonstrated the release of histamine, PGD2, TXB2, PGE2, PGF2 alpha, 6-keto-PGF1 alpha and the peptidoleukotrienes from sensitized lung. We have assessed the release of these mediators following antigen challenge in vivo. Antigen challenge of allergic dogs resulted in an acute bronchoconstriction and an increase in bronchial reactivity to histamine and an increase in neutrophil and eosinophil numbers recovered by bronchoalveolar lavage (BAL), 2 and 24 h later. The acute response was associated with histamine and PGD2 release but there was no increase in the levels of other eicosanoids in recovered BAL. Bronchial hyperreactivity and pulmonary inflammation, 2 and 24 h post-challenge was not associated with a concommitant (antigen specific) increase in BAL fluid eicosanoid levels. We conclude that although PGD2 is released during the acute response to antigen the subsequent changes (hyperreactivity and inflammation) are not characterised by a maintained elevation in eicosanoid levels detectable by BAL.

Superoxide generation by guinea-pig peritoneal macrophages is inhibited by rolipram, staurosporine and mepacrine in an agonist-dependent manner

Platelet-activated factor (PAF) (EC50 -7.9 +/- 0.6 M), formyl-methionyl-leucyl-phenylalanine (fMPL) (EC50 -7.7 +/- 0.1M), phorbol 12-myristate 13 acetate (PMA) (EC50 -8.4 +/- 0.3 M), opsonized zymosan (OPZ) (0.01-1 mg/ml) were potent stimuli to superoxide generated by guinea-pig peritoneal macrophages. Superoxide generation by low (< or = -8M) concentrations but not high (> or = -7M) concentrations of PAF or fMLP were attenuated by rolipram (100 microM) in the presence of 1 microM prostaglandin E2 (PGE2). That stimulated by PMA or OPZ, however, was unaffected. At 1 microM, staurosporine was a potent inhibitor of superoxide generation stimulated by both fMLP and PAF but was without effect on that stimulated by OPZ. Superoxide generation stimulated by fMLP, PAF and OPZ was inhibited by 100 microM mepacrine. We conclude that superoxide generation stimulated by the chemoattractants fMLP and PAF involves a cyclic AMP regulated and cyclic AMP independent process. The cyclic AMP independent process is mediated by protein kinase C. Although protein kinase C seems a central element in the respiratory burst stimulated by fMLP, PAF and PMA that stimulated by OPZ bypasses this mechanism. Phospholipase A2 however, represents a common stage in the signal transduction pathway.

Leaf growth, photosynthesis and tissue water relations of greenhouse-grown Eucalyptus marginata seedlings in response to water deficits

Leaf growth, rate of leaf photosynthesis and tissue water relations of shoots of Eucalyptus marginata Donn ex Sm. (jarrah) seedlings were studied during a soil drying and rewatering cycle in a greenhouse experiment. Rates of leaf growth and photosynthesis were sensitive to water deficits. The rate of leaf growth decreased linearly with predawn leaf water potential to reach zero at -1.5 MPa. Rate of leaf growth did not recover completely within the first three days after rewatering. Midday photosynthetic rates declined to 40% of those of well-watered seedlings at a predawn leaf water potential of -1.0 MPa and reached zero at -2.2 MPa. Photosynthetic rate recovered rapidly following rewatering and almost fully recovered by the second day after rewatering. All tissue water relations parameters, except the bulk modulus of elasticity, changed significantly as the soil dried and recovered completely by the third day after rewatering. Changes in osmotic pressure at full turgor of 0.4 MPa indicated considerable capacity for osmotic adjustment. However, because there was little osmotic adjustment until predawn leaf water potential fell below -1.5 MPa, this capacity would not have enhanced seedling growth, although it may have increased seedling survival. The sensitivity of photosynthesis and relative water content to water deficits suggests that greenhouse-grown E. marginata seedlings behave like mesophytic plants, even though E. marginata seedlings naturally grow in a drought-prone environment.

Effects of PAF, FMLP and opsonized zymosan on the release of ECP, elastase and superoxide from human granulocytes

Platelet-activating factor (PAF) is a potent chemoattractant for human eosinophils and neutrophils and causes eosinophil and neutrophil recruitment into animal airways. Since eosinophils and eosinophil cationic proteins are thought to play an important role in the pathophysiology of asthma, we have examined the hypothesis that PAF may also stimulate eosinophil cationic protein (ECP) release from human granulocytes. Granulocytes (93% neutrophils, 3% eosinophils) were isolated from the blood of normal volunteers, using metrizamide density gradients, and stimulated in vitro with PAF, L-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) or opsonized zymosan (OPZ). Superoxide generation was measured colorimetrically, granulocyte degranulation by a fluorimetric assay for elastase, and eosinophil activation by specific radioimmunoassay (RIA) for ECP. Granulocyte chemotaxis was also measured. Whilst both PAF and FMLP were potent chemoattractants for human mixed granulocytes (concentrations producing half the maximal effect (EC50s) ca 10 nM), PAF at concentrations below 10 microM was a poor stimulus to superoxide generation, elastase release or ECP release from the same cell population. In contrast, FMLP was a potent stimulus to both superoxide generation (EC50 48 nM) and ECP (EC50 ca 100 nM) and elastase release (EC50 ca 1 microM). OPZ was a potent stimulus to superoxide generation, but was a poor stimulus to ECP or elastase release. Thus, although PAF is a potent chemoattractant for human granulocytes, our results suggest that it alone may not stimulate their subsequent activation and release of cytotoxic products.

Effects of PAF, FMLP and opsonized zymosan on the release of ECP, elastase and superoxide from human granulocytes

Platelet-activating factor (PAF) is a potent chemoattractant for human eosinophils and neutrophils and causes eosinophil and neutrophil recruitment into animal airways. Since eosinophils and eosinophil cationic proteins are thought to play an important role in the pathophysiology of asthma, we have examined the hypothesis that PAF may also stimulate eosinophil cationic protein (ECP) release from human granulocytes. Granulocytes (93% neutrophils, 3% eosinophils) were isolated from the blood of normal volunteers, using metrizamide density gradients, and stimulated in vitro with PAF, L-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) or opsonized zymosan (OPZ). Superoxide generation was measured colorimetrically, granulocyte degranulation by a fluorimetric assay for elastase, and eosinophil activation by specific radioimmunoassay (RIA) for ECP. Granulocyte chemotaxis was also measured. Whilst both PAF and FMLP were potent chemoattractants for human mixed granulocytes (concentrations producing half the maximal effect (EC50s) ca 10 nM), PAF at concentrations below 10 microM was a poor stimulus to superoxide generation, elastase release or ECP release from the same cell population. In contrast, FMLP was a potent stimulus to both superoxide generation (EC50 48 nM) and ECP (EC50 ca 100 nM) and elastase release (EC50 ca 1 microM). OPZ was a potent stimulus to superoxide generation, but was a poor stimulus to ECP or elastase release. Thus, although PAF is a potent chemoattractant for human granulocytes, our results suggest that it alone may not stimulate their subsequent activation and release of cytotoxic products.

Relaxation of guinea-pig trachea by cyclic AMP phosphodiesterase inhibitors and their enhancement by sodium nitroprusside

1. The effects of agents that elevate either cyclic AMP (the phosphodiesterase (PDE) III inhibitor siguazodan, salbutamol) or cyclic GMP (sodium nitroprusside (SNP)) on the relaxant activity of the PDE IV inhibitor, rolipram, were investigated in carbachol (0.1 microM) precontracted guinea-pig tracheal sheets. 2. Rolipram, siguazodan and SNP caused concentration-related reductions in tone of tissues precontracted with 0.1 microM carbachol (EC50 values 12.5; 2.73 and 0.35 microM respectively). Whilst the concentration-response relationship for the PDE III inhibitor, siguazodan, was monophasic that of the PDE IV inhibitor, rolipram, was biphasic. 3. The relaxant activity of rolipram was markedly enhanced in the presence of 10 microM siguazodan (EC50 < 0.01 microM), 0.1 microM salbutamol (EC50 0.03 microM) and 0.3 microM SNP (EC50 0.03 microM). In contrast, the relaxant activity of siguazodan was unaffected by SNP and only modestly enhanced by rolipram (10 microM) and salbutamol (0.1 microM). 4. The relaxant activity of SNP was enhanced by the PDE V inhibitor SK&F 96231 (30 microM: EC50 0.06 microM) and rolipram (30 microM, EC50 0.08 microM) but was unaffected by 30 microM siguazodan. 5. At concentrations up to 10 microM, neither siguazodan nor rolipram elevated tracheal cyclic AMP levels. However, the combination of 10 microM rolipram and siguazodan caused a two fold increase in the cyclic AMP content (from 2.19 to 4.36 pmol cyclic AMP mg-1 protein). SNP (0.1-10 microM) failed to produce a significant increase in tracheal cyclic AMP levels. At 0.1 microM the effect of SNP on tracheal cyclic AMP levels was significantly (P < 0.05) increased in the presence of rolipram but not siguadozan. 6. The results indicate that the relaxant effects of rolipram are markedly enhanced by agents that inhibit PDE III activity or elevate cyclic GMP. They support the hypothesis that SNP potentiates the effects of rolipram via the inhibitory action of cyclic GMP on hydrolysis of cyclic AMP by PDE III. The findings also suggest that whilst PDE III may be more significant in regulating basal smooth muscle tone in the absence of any exogenous stimulus to cyclic AMP accumulation, PDE IV activity may be more tightly coupled to the pool of adenylyl cyclase stimulated by beta2-adrenoceptor agonists.

Pulmonary effects of type V cyclic GMP specific phosphodiesterase inhibition in the anaesthetized guinea-pig

1. We have investigated the bronchodilator potential of type V phosphodiesterase (PDE V) inhibitors in anaesthetized ventilated guinea-pigs using the potent and selective PDE V inhibitor, SK&F 96231. We have compared its activity to that of salbutamol, the PDE III inhibitors, siguazodan and SK&F 95654 and to the PDE IV inhibitor rolipram. 2. Administered as an i.v. infusion SK&F 96231 (0.6 and 1 mg kg-1 min-1, i.v.) caused a slowly developing inhibition of histamine (100 nmol kg-1, i.v.)-induced bronchoconstriction and elevated tracheal cyclic GMP levels in the anaesthetized guinea-pig. SK&F 96231 (0.1 and 0.3 mg kg-1 min-1, i.v.) was without effect on histamine-induced bronchoconstriction. In the presence of a sub-threshold infusion of SNP (0.1 mumol kg-1 min-1, i.v.) there was a marked enhancement of SK&F 96231-induced inhibition of histamine responses such that at infusion rates that were ineffective alone, SK&F 96231 caused a > 50% inhibition of histamine responses. The stimulation of tracheal cyclic GMP accumulation by SK&F 96231 was also potentiated. 3. Administered directly into the airway, SK&F 96231 (300 micrograms in 5 mg lactose carrier) was largely without effect on histamine-induced bronchoconstriction (4.9 +/- 1.9% inhibition). In the presence of SNP (0.1 mumol kg-1 min-1, i.v.) or isosorbide dinitrate (200 micrograms administered by insufflation into the trachea) there was a marked potentiation of the inhibitory activity of SK&F 96231 (40 +/- 4% and 62 +/- 1.8% respectively). 4. Salbutamol and rolipram (3-300 microg by insufflation) caused a dose-related inhibition of histamine responses with a maximum of 91 +/- 2% and 59 +/- 10% respectively. The PDE III inhibitor, siguazodan,was without effect on histamine responses but they were reduced (27.7 +/- 4.8% at 300 microg) by SK&F95654. There was a marked enhancement of the inhibitory activity of rolipram in the presence of SK&F 95654.5. We conclude that SK&F 96231 has weak anti-spasmogenic activity in the guinea-pig in vivo, we suggest that this is primarily a consequence of a low endogenous guanylate cyclase activity in the airway. The potentiation of the anti-spasmogenic activity of SK&F 96231 by SNP suggests that a combination of PDE V inhibitor and guanylate cyclase agonist might provide significant bronchodilator activity.6. We have established that PDE IV inhibitors are bronchodilators when administered directly into the airway of anaesthetized guinea-pigs but that PDE III inhibitors are only weakly active. The marked enhancement of the inhibitory activity of rolipram by the PDE III inhibitor, SK&F 95654, indicates that inhibitors of both PDE III and PDE IV might offer greater potential as bronchodilators than inhibitors of either isoenzyme alone.

The effect of cyclic AMP and cyclic GMP phosphodiesterase inhibitors on the superoxide burst of guinea-pig peritoneal macrophages

1. The cyclic nucleotide phosphodiesterase (PDE) activity of guinea-pig peritoneal macrophages was partially characterized and the effects of selective and non-selective inhibitors of adenosine 3':5'-cyclic monophosphate (cyclic AMP PDE) and guanosine 3':5'-cyclic monophosphate (cyclic GMP PDE) phosphodiesterases on superoxide generation were investigated using peritoneal macrophages from horse-serum pretreated guinea-pigs. 2. The non-selective PDE inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and the PDE I/V selective inhibitor, zaprinast, inhibited spontaneous superoxide generation with IC50s of 30.7 +/- 11.3 microM and 145 +/- 17 microM respectively (n = 6 and 5). The concentration-response curves for the PDE IV selective inhibitors rolipram and Ro20-1724 were biphasic; mean maximum inhibitions were 56.9 +/- 5.9% and 66.8 +/- 10.5% respectively at 300 microM, but in 2 out of 6 (rolipram) and 2 out of 5 (Ro20-1724) experiments inhibition was < 50%. The PDE III inhibitor SK&F 94120 was without effect. Spontaneous superoxide generation was reduced 57 +/- 10% by 1 microM prostaglandin E2 (PGE2) and 62.6 +/- 3.76% by 1 microM salbutamol. 3. The increase in superoxide generation elicited by FMLP (10(-9)-10(-5)M) was unaffected by any of the PDE inhibitors studied. Inhibition of FMLP-stimulated superoxide generation by PGE2 was enhanced in the presence of 10 microM IBMX. 4. Macrophages were found to contain a predominantly membrane bound cyclic AMP PDE (90% of total activity) which was unaffected by cyclic GMP or calcium/calmodulin. The cyclic AMP PDE activity in the cytosolic fraction was enhanced in the presence of calcium/calmodulin. Selective inhibitors of PDE IV inhibited the particulate cyclic AMP PDE activity (IC50s rolipram 1.5 +/- 0.3 microM, Ro 20-17244.1 +/- 0.6 microm) as did the non-selective inhibitor IBMX (IC50 22 +/- 8 microM). The macrophage particulate PDE activity was resistant to inhibition by the PDE III inhibitor SK&F 94836 and the PDE I/V inhibitor, zaprinast. The cytosolic calcium/calmodulin stimulated cyclic AMP hydrolytic activity was inhibited by zaprinast (IC50 - calcium/calmodulin 123 +/- 39 microM; + calcium/calmodulin IC50 17.7 +/- 6.3 microM).5. The results indicate that guinea-pig peritoneal macrophages contain a type IV cyclic AMP PDE which is predominantly membrane associated and a predominantly cytosolic calcium/calmodulin stimulated cyclic AMP PDE. Functional studies suggest that both of these PDE activities contribute to cyclic AMP hydrolysis and regulation of superoxide generation in these cells. Inhibition of spontaneous superoxide generation, but not that stimulated by FMLP, suggests that the activity of PDE inhibitors is subject to functional antagonism but that this can be overcome by enhancing cyclic AMP formation.

Evaluation of chemical desiccation as a selection technique for drought resistance in a dryland wheat breeding program

Previous studies have shown that some chemical desiccants and senescing agents, when applied to adequately watered cereals 10 to 14 days after anthesis, can be used to select lines with stable grain size (kernel weight) under post-anthesis water deficits. The present study evaluated the potential of one of these chemicals, potassium iodide (KI), to select for this character in a dryland wheat breeding program. Ninety-six F2-derived lines grown in the F6and F7 generations and 11 cultivars of wheat (Triticum aestzvum L.) were grown in two experiments at two medium-rainfall sites in 1988 and 1989 and sprayed with a 0.3% solution of KI when the grains had developed one-third in the lemma. Reductions in grain yield and thousand kernel weight due to treatment with KI were greater in 1988 than in 1989, probably due to the higher growing-season rainfall in that year. The reduction in grain yield as a result of desiccation was greater than the reduction in thousand kernel weight, but the correlation between the two was low (0.09 to 0.58) and non-significant in five out of the eight comparisons. There were considerable differences among genotypes in response to the desiccation treatment in the wetter 1988. Genetic coefficients of variation ranged from 5.6 to 12.9% for yield and 2.5 to 9.5% for thousand kernel weight. The ratio of the variance component estimates for the interaction between genotypes and desiccation treatment to the variance component estimates for genotypes was generally less than one. However, genetic differences in response to the desiccation treatment could be demonstrated in some experiments, particularly at one site and in the wetter of the two years. We conclude that the chemical desiccation technique can be used to select for post-anthesis drought resistance in a dryland breeding program. However, there are some limitations to the technique, and selection needs to be confined to wetter sites and seasons.

Potential of using field spectroscopy during early growth for ranking biomass in cereal breeding trials

The use of field spectroscopy for the non-destructive ranking of cereal breeding plots at the early stages of crop growth was investigated using measurements of spectral reflectance over 222 wavebands between 400 and 2500 nm using the single beam GEOSCAN Portable Field Spectroradiometer (PFS). Measurements were made on 54 barley plots at the 5- and 7-leaf stages of growth with biomass varying between 10 and 96 g/m2. The optimal multiple linear regression relationship between reflectance and biomass included wavebands from the near-infrared (NIR) and mid-infrared (MIR) with a standard deviation of 4.8 g/m2. The ranking of plots according to biomass by this optimal relationship or the Simple Ratio of NIR to visible (VIS) reflectance, which is a common index of greeness, agreed closely with actual ranking. Tested against an independent set of wheat plots at the 4-leaf stage with biomass ranging from 3 to 32 g/m2, the barley-derived relationship, but not the Simple Ratio, performed poorly in ranking plots according to biomass. However, at the 7-leaf growth stage, when the biomass range had increased to 48-117 g/m2, both the Simple Ratio and the barley-derived relationship agreed closely with the actual ranking. To apply these results in practice, the accuracy of the simpler CROPSCAN portable field radiometer (PFR) was found to be greater than the GEOSCAN PFS for comparable NIR and VIS wavebands. It was therefore concluded that it is practically feasible to use field spectroscopy to rank cereal plots for biomass at early growth stages where the difference between plots is of the order of 5-7 gm/m2. Such biomass differences were more apparent at the 7-leaf than 4-leaf stage of growth.

Characterization of the antagonist activity of the PAF antagonists RP 59227 and WEB 2086 on elicited guinea pig peritoneal macrophages. Evidence for variable affinities and kinetics

The pharmacological selectivity and affinity of the two PAF antagonists RP 59227 and WEB 2086 for macrophage platelet activating factor (PAF) receptors have been investigated. PAF produced a dose-related increase in superoxide generation from elicited guinea pig peritoneal macrophages (IC50 41 +/- 16 nM, n = 9). After a 5 min preincubation time RP 59227 (0.1, 1.0 and 10 microM) produced a dose-related rightward displacement of the PAF dose-response curve, the Schild plot gave a pA2 of 7.39 +/- 0.07 (n = 5) with a slope of 1.17 +/- 0.11, indicating competitive antagonism. WEB 2086 over the same concentration range was without effect at the lower two concentrations, but at 10 microM, the displacement of the PAF dose-response curve was similar to that obtained with 10 microM RP 59227. Increasing the preincubation time to 30 min increased the affinity of RP 59227 (apparent pA2 8.76 +/- 0.28, n = 5). This was associated with a reduction in the slope of the Schild plot to 0.67 +/- 0.11, suggesting noncompetitive kinetics. The affinity of WEB 2086 could not be determined, but the antagonism appeared noncompetitive in nature. The results indicate that PAF antagonists can show variable affinities for macrophage PAF receptors depending on the experimental conditions, as well as competitive or noncompetitive kinetics depending on the contact time.

Crop production on duplex soils: an introduction

Duplex or texture-contrast soils occur over about 60% of the agricultural areas of south-west Western Australia. Annual crops of wheat, barley, oats, and lupins predominate on these soils, grown in rotation with annual pastures. The climate is characterised by cool, wet winters and hot, dry summers. Crop production is restricted to the winter and spring and is limited by waterlogging in the wet winter months and by water shortage during grain filling in spring. Research on crop production on duplex soils has been undertaken for the past 8 years by a collaborative team from the CSIRO Dryland Crops andyoils Program and the Western Australian Department of Agriculture. This research has been focussed on 3 sites at which processes limiting crop production on duplex soils have been highlighted. This special issue was initiated to summarise that research and to put it in its regional and national perspective. Additionally, opportunity was taken to compare and contrast experiences both within Western Australia and throughout Australia, and to draw out management options for crop production on duplex soils.

Potential for increasing early vigour and total biomass in spring wheat. II. Characteristics associated with early vigour

Increased early growth and total dry matter production have been suggested as useful traits to improve yield in Mediterranean-type environments. In Part I, genotypic variation for early growth and total dry matter production was identified among cultivars and some introduced lines. In this part, characteristics associated with early vigour in five of these introduced lines and ten Australian cultivars were examined in a field study at Wongan Hills in Western Australia. Differences in dry matter production were observed at all sampling times during the season, with three of the introduced lines (CEP 8058, Kansu No. 32 and V979-28) having consistently higher dry matter production than the standard cultivars during the early growth period. Those genotypes with a higher dry matter production at 54 days after sowing had higher relative growth rates and green area indices than those with low dry matter production. Both genotypes with large leaves on few tillers and genotypes with small leaves on many tillers had higher green area indices and higher dry matter production. While high dry matter production was associated with a large degree of ground cover and high light interception, it was not associated with the earlier commencement of reproductive development. Incorporation of early vigour and high dry matter production into locally adapted cultivars is required to demonstrate its benefit in these environments.

Characterization of guinea-pig eosinophil phosphodiesterase activity. Assessment of its involvement in regulating superoxide generation

Experiments have been performed to characterize guinea-pig peritoneal eosinophil cyclic nucleotide phosphodiesterase (PDE) activity and establish whether it is involved in regulating superoxide (.O2-) generation. Eosinophils were found to contain a predominantly membrane-bound cAMP PDE(s) (92.5 +/- 2.4% of total activity) which was resistant to solubilization with Triton X-100 (1%). This particulate PDE exhibited complex kinetics (Km = 1.3 and 31.4 microM) and was unaffected by cGMP (IC50 greater than 100 microM) or CaCl2 (2 mM) + calmodulin (10 units/mL). Little cGMP PDE activity was detected in either the soluble or particulate fractions. Inhibitors of the Ro-20-1724-inhibited (Type IV) cAMP PDE, namely Ro-20-1724 (IC50 = 0.92 +/- 0.43 microM), rolipram (IC50 = 0.20 +/- 0.04 microM) and denbufylline (IC50 = 0.20 +/- 0.01 microM), potently inhibited the particulate cAMP PDE, as did the non-selective inhibitors trequinsin (IC50 = 0.11 +/- 0.02 microM) and AH-21-132 (IC50 = 2.57 +/- 0.02 microM). Eosinophil cAMP PDE was resistant to SK&F 94120 (IC50 greater than 1000 microM), the cGMP-inhibited (Type III) cAMP PDE inhibitor, and the cGMP PDE (Type I) inhibitor, zaprinast, was only weakly active (IC50 = 35.33 +/- 10.74 microM). .O2- release from resting cells was potently inhibited by rolipram (IC50 = 0.05 +/- 0.03 microM) and denbufylline (IC50 = 0.06 +/- 0.04 microM) but surprisingly, in view of its potent cAMP PDE inhibitory activity, was only weakly decreased by trequinsin (IC50 = 8.0 +/- 2.7 microM). AH-21-132 (IC50 greater than 10 microM), SK&F 94120 (IC50 greater than 10 microM) and zaprinast (IC50 greater than 10 microM) were without effect. Rolipram and denbufylline alone exerted little effect on cAMP in intact cells but, in the presence of 10 microM isoprenaline, potently increased intracellular accumulation (EC50 = 0.45 +/- 0.16 and 0.28 +/- 0.08 microM, respectively). Trequinsin and AH-21-132 only weakly enhanced isoprenaline-stimulated cAMP accumulation. Although it induced a marked rise in cAMP only in the presence of isoprenaline, rolipram (50 microM) alone was able to increase the activity ratio of cAMP-dependent protein kinase from 0.24 to 0.84. The results suggest that Ro-20-1724-inhibited cAMP PDE plays a role in regulating eosinophil .O2- generation. The poor correlation between the PDE inhibitory actions of certain compounds and their effectiveness in elevating cAMP and inhibiting .O2- suggests the existence of a barrier impeding access to the enzyme.

Water deficits change dry matter partitioning and seed yield in narrow-leafed lupins (Lupinus angustifolius L.)

lrrigation treatments were imposed in the field on an indeterminate cultivar of narrow-leafed lupins (Lupinus angustifolius L., cv. Danja) and on a breeding line with reduced branching (75A/329) so that they experienced no water-deficits (frequently irrigated), a transient mild water-deficit or a transient severe water-deficit during early reproductive growth, or continuous severe water-deficit during reproductive growth (unirrigated). Both leaf water potential and leaf conductance declined in all treatments in which a water-deficit was imposed. Differences in leaf conductance were apparent before differences in leaf water potential: conductance declined to 40% and 30% of the frequently irrigated controls in the transient mild and severe water-deficit treatments, respectively. Leaf water potential declined to -1 - 1 MPa and -1.6 MPa, respectively, in the transient mild and severe water-deficit treatments, compared to between -0 - 65 and -0 - 95 MPa for the frequently irrigated controls. Seed yield and total dry weight were reduced in the transient severe water-deficit and unirrigated treatments, but were no different from the frequently irrigated treatment when the water-deficit was transient and mild. However both transient water-deficit treatments produced more main-stem seed yield than the frequently irrigated treatment, especially in the reduced-branching line 75A/329. The transient mild water-deficit treatment also produced more first-order apical axis yield than the frequently irrigated treatment. These yield increases were mainly due to a greater yield of seed per pod, although on the first-order apical axes there was also a tendency to set more pods. The greater seed yield per pod in the transient water-deficit treatments was due to an apparent redirection of assimilate from vegetative to reproductive growth. This was not due to a smaller reduction in reproductive growth rates than in vegetative growth rates, but to an acceleration of reproductive growth that was maintained after stress relief. The same early acceleration of reproductive growth was also observed in unirrigated treatments, but the severe stress which persisted throughout later reproductive growth reduced pod growth rates and negated the early advantage.

Effects of nonsteroidal anti-inflammatory drugs on the bronchial hyperresponsiveness of middle-aged male smokers

Bronchial hyperresponsiveness (BHR) in smokers is believed to be a consequence of airway wall inflammation. We have examined the effects of treatment with nonsteroidal anti-inflammatory drugs (NSAID) on BHR to inhaled histamine, measured as the provocative concentration reducing forced expiratory volume in one second (FEV1) by 20% (PC20), in middle-aged male cigarette smokers in two separate double-blind, placebo-controlled, cross-over trials. Baseline FEV1 in these smokers ranged from 41-117% predicted values. In the first study 15 men (mean age 58 yrs, FEV1 2.20 l) were examined before and one hour after a single dose of 1.2 g aspirin. There was no significant change in PC20 (geometric mean 1.88 mg.ml-1 pre-aspirin, 1.89 mg.ml-1 post-aspirin) or baseline FEV1 and we observed no tachyphylaxis to the effects of inhaled histamine at one hour after placebo. In the second study 10 men (mean age 60 yrs, FEV1 2.53 l) were examined before and after three days' treatment with the NSAID flurbiprofen 50 mg t.d.s. Baseline PC20 was higher in this group than in the first study. There was no relationship between the excretion of urinary thromboxane metabolites and the intensity of BHR under baseline conditions; flurbiprofen greatly reduced the urinary excretion of thromboxane metabolites, but baseline FEV1 was not altered. Analysis of change in PC20 was complicated by a difference in baseline PC20 before the two treatments, but treatment with flurbiprofen did not significantly attenuate BHR. The results suggest that thromboxane or other cyclo-oxygenase products of arachidonic acid metabolism do not play an important role in the short-term maintenance of BHR to histamine in middle-aged male cigarette smokers.

Effects of nonsteroidal anti-inflammatory drugs on the bronchial hyperresponsiveness of middle-aged male smokers

Bronchial hyperresponsiveness (BHR) in smokers is believed to be a consequence of airway wall inflammation. We have examined the effects of treatment with nonsteroidal anti-inflammatory drugs (NSAID) on BHR to inhaled histamine, measured as the provocative concentration reducing forced expiratory volume in one second (FEV1) by 20% (PC20), in middle-aged male cigarette smokers in two separate double-blind, placebo-controlled, cross-over trials. Baseline FEV1 in these smokers ranged from 41-117% predicted values. In the first study 15 men (mean age 58 yrs, FEV1 2.20 l) were examined before and one hour after a single dose of 1.2 g aspirin. There was no significant change in PC20 (geometric mean 1.88 mg.ml-1 pre-aspirin, 1.89 mg.ml-1 post-aspirin) or baseline FEV1 and we observed no tachyphylaxis to the effects of inhaled histamine at one hour after placebo. In the second study 10 men (mean age 60 yrs, FEV1 2.53 l) were examined before and after three days' treatment with the NSAID flurbiprofen 50 mg t.d.s. Baseline PC20 was higher in this group than in the first study. There was no relationship between the excretion of urinary thromboxane metabolites and the intensity of BHR under baseline conditions; flurbiprofen greatly reduced the urinary excretion of thromboxane metabolites, but baseline FEV1 was not altered. Analysis of change in PC20 was complicated by a difference in baseline PC20 before the two treatments, but treatment with flurbiprofen did not significantly attenuate BHR. The results suggest that thromboxane or other cyclo-oxygenase products of arachidonic acid metabolism do not play an important role in the short-term maintenance of BHR to histamine in middle-aged male cigarette smokers.

Oral N-acetylcysteine or S-carboxymethylcysteine inhibit cigarette smoke-induced hypersecretion of mucus in rat larynx and trachea in situ

Two weeks exposure of rats to cigarette smoke (CS) significantly (p less than 0.05) increased the secretion of fucose-containing glycoconjugates above normal in an in situ preparation of larynx and trachea. After equilibration mean basal secretion in CS-exposed rats was 24 micrograms (per 30 min collection) which was 8 times higher than that of unexposed animals (p less than 0.01). N-acetylcysteine (NAC) or S-carboxymethylcysteine (SCMC) given as 1% of the drinking water, before and after daily exposure to CS, significantly inhibited the development of the CS-induced increase in fucose secretion reducing the mean for basal secretion in each group to 7 and 5 micrograms, respectively (p less than 0.05). Neither NAC nor SCMC had significant effects on baseline glycoconjugate secretion in control animals. Albumin was inconsistently present in the secretions of both control and CS-exposed animals, whereas in those exposed to CS and also given one of the two cysteine derivatives there was a consistent increase in albumin transudation.

Oral N-acetylcysteine or S-carboxymethylcysteine inhibit cigarette smoke-induced hypersecretion of mucus in rat larynx and trachea in situ

Two weeks exposure of rats to cigarette smoke (CS) significantly (p less than 0.05) increased the secretion of fucose-containing glycoconjugates above normal in an in situ preparation of larynx and trachea. After equilibration mean basal secretion in CS-exposed rats was 24 micrograms (per 30 min collection) which was 8 times higher than that of unexposed animals (p less than 0.01). N-acetylcysteine (NAC) or S-carboxymethylcysteine (SCMC) given as 1% of the drinking water, before and after daily exposure to CS, significantly inhibited the development of the CS-induced increase in fucose secretion reducing the mean for basal secretion in each group to 7 and 5 micrograms, respectively (p less than 0.05). Neither NAC nor SCMC had significant effects on baseline glycoconjugate secretion in control animals. Albumin was inconsistently present in the secretions of both control and CS-exposed animals, whereas in those exposed to CS and also given one of the two cysteine derivatives there was a consistent increase in albumin transudation.

Endothelin-induced contractions of tracheal smooth muscle and identification of specific endothelin binding sites in the trachea of the rat

1. The presence of specific binding sites and the contractile activity of the novel peptide, endothelin have been investigated in rat trachea. 2. Endothelin (10(-8)-10(-5) M) induced long-lasting contraction of rat tracheal rings superfused with Krebs solution (EC50 5.4 x 10(-6) M). Contractions of the tissue to 10(-6) M endothelin were attenuated in Ca2+-free medium containing 0.1 mM EGTA but unaffected by nicardipine (10(-7) M). 3. After equilibration in Ca2+-free medium (without EGTA) a return to normal Ca2+ concentrations (2.5 mM), 30 min or 60 min following endothelin (10(-6) M), produced a sustained contraction of the tissue. 4. Specific binding sites for endothelin were identified on rat tracheal smooth muscle (KD 1.34 x 10(-10) M, maximal binding 1.2 fmol mm-2). Specific binding sites were also identified on nerve trunks. Endothelin binding was unaffected by co-incubation with nicardipine (10(-7) M) or verapamil (10(-7) M). 5. The discrepancy between the apparent KD for endothelin binding and the EC50 for endothelin-induced contraction suggests that the endothelin binding sites identified in this study may not be associated with the receptors mediating contraction. 6. These results indicate that endothelin binding sites are present on tracheal smooth muscle. The mechanism of endothelin-induced contraction, whilst being dependent on extracellular calcium, does not appear to involve binding to the dihydropyridine- or verapamil-sensitive sites on the voltage-dependent Ca2+ channel. Its long duration of action may be associated with a sustained increase in Ca2+ permeability.

Endothelin-1-induced contractions of vascular and tracheal smooth muscle: effects of nicardipine and BRL 34915

Endothelin-1 (ET-1) produced concentration-dependent contractions of rat aorta and rat trachea. These contractions were dependent on the presence of extracellular calcium but unaffected by nicardipine. Contractions of aorta could be attenuated with the potassium channel activator BRL 34915. BRL 34915 also elicited dose-related relaxations of rat aorta and trachea precontracted with ET-1. We conclude that although the increase in calcium permeability elicited by ET-1 may not involve dihydropyridine-sensitive calcium channels, its reversal by BRL 34915 suggests that smooth muscle contraction by ET-1 may involve a voltage-linked mechanism.

Release of arachidonic acid metabolites and histamine from sensitized guinea-pig lung following antigen challenge

1. The time course of mediator release and the hypothesis that the ratio of eicosanoids to histamine might alter with the intensity of stimulus or its route of administration has been explored in isolated perfused lung from sensitized guinea-pigs challenged with ovalbumin. 2. Histamine and prostaglandin release was rapid in onset and virtually complete within 10 min. Thromboxane B2 (TXB2) and leukotriene D4 (LTD4) release, however, was more sustained. Release of the major prostanoid metabolites was relatively delayed compared to that of the parent compounds and was more sustained. 3. Mediator release was antigen-dose dependent and TXB2, prostaglandin D2 (PGD2) and LTD4 release linearly related to histamine concentrations (P less than 0.05). However, the ratio of the percentage maximum release of eicosanoids relative to histamine was greatest with low doses of ovalbumin. 4. At a low antigen dose (10 micrograms ovalbumin), histamine and prostanoid release was greatest when the challenge was via the airway rather than into the pulmonary artery and the greatest differences were in PGF2 alpha levels. At near maximal challenge (1 mg ovalbumin) there was little difference in concentrations of PGD2, TXB2, 6-oxo-PGF1 alpha and LTD4 by either route, but PGF2 alpha levels remained greater. 5. The results indicate that biologically active amounts of prostanoids may be released from sensitized lung at low degrees of mast cell activation and that differences in mediator release following antigen administration to the airway or into the pulmonary vasculature simply reflects its accessibility to sensitized cells.

Single-step procedure for the extraction and purification of leukotrienes B4, C4 and D4

A rapid and simple method for the on-line concentration and high-performance liquid chromatographic (HPLC) purification of the leukotrienes in good yield from biological fluids is described. Readily available antisera are used in conjunction with this system to give a specific and sensitive assay for leukotrienes B4, C4 and D4 with sub-nanogram limits of detection. Tritium-labelled leukotrienes are used as internal standards, both to locate the leukotrienes post-HPLC and to accurately determine recoveries.

Cigarette smoke-induced 'chronic bronchitis': a study in situ of laryngo-tracheal hypersecretion in the rat

Mucous secretion and mucosal permeability by the larynx and trachea, isolated in situ, was investigated in normal rats and in those in which 'chronic bronchitis' was induced by daily exposure to cigarette smoke for 2 weeks. Fucose was used as a specific marker for the secretion of mucus glycoprotein, and hexose and protein were markers both for mucus and plasma-type glycoproteins present in tissue fluid transudate. Albumin was used as an indicator of the contribution of serum to the secretions. After equilibration, the mean basal secretion of fucose (microgram/30 min collection) was significantly higher in 'bronchitic' rats than in the controls (P less than 0.01). Mean values for controls were: fucose 3 (SEM 1: n = 9), hexose 41 (SEM 9; n = 8), protein 1082 (SEM 385; n = 8), albumin less than 2 (n = 8); for 'bronchitic' rats the values were: 24 (SEM 6; n = 7), 101 (SEM 26; n = 8), 2000 (SEM 520; n = 8) and less than 2 micrograms (n = 7) respectively. In control and bronchitic animals acute administrations of cigarette smoke, blown directly through the laryngo-tracheal segment after equilibration, caused significant (P less than 0.05) transient increases in the secretion of fucose, hexose and protein, but not of albumin.

The influence of native porcine gastric mucus gel on hydrogen ion diffusion: the effect of potentially ulcerogenic agents

Experiments were carried out to investigate the ability of native gastric mucus gels to retard hydrogen ion diffusion. Mucus held between two polycarbonate membrane filters in a diffusion cell, separating equimolar solutions of NaCl and HCl, significantly reduced the rate of hydrogen ion diffusion and increased the time for the mean hydrogen ion front to traverse the mucus compartment (lag time) when compared to an unstirred layer of saline (P less than 0.01). N-acetylcysteine, sodium taurodeoxycholate and acetylsalicylic acid significantly increased the diffusion rate (P less than 0.025); the lag time was significantly reduced by N-acetylcysteine (P less than 0.001). In addition mucus gels were found to have buffering capacity at a pH greater than 2. These observations suggest that native gastric mucus gels can retard hydrogen ion diffusion and that this retardation of diffusion is reduced by agents which are potentially damaging to the gastric mucosa.

Influence of Osmotic Adjustment on Leaf Rolling and Tissue Death in Rice (Oryza sativa L.)

Osmotic adjustment, measured by the lowering of the osmotic potential at full turgor, and its influence on leaf rolling and leaf death was assessed in the lowland rice (Oryza sativa L.) cultivar IR36 in both the greenhouse and field. The degree of osmotic adjustment varied with the degree and duration of stress, but was usually 0.5 to 0.6 megapascal (maximally 0.8 to 0.9 megapascal) under severe stress conditions. In leaves in which osmotic adjustment was 0.5 to 0.6 megapascal, leaf rolling and leaf death occurred at lower leaf water potentials in adjusted than in nonadjusted leaves. We conclude that osmotic adjustment aids in the drought resistance of rice by delaying leaf rolling, thereby maintaining gas exchange, and by delaying leaf death.

Comparison of water potentials measured by in situ psychrometry and pressure chamber in morphologically different species

Leaf water potentials measured by in situ psychrometry were compared with leaf water potentials measured by the pressure chamber technique at various values of water potential in Helianthus annuus, Helianthus nuttallii, Vigna unguiculata, Nerium oleander, Pistacia vera, and Corylus avellana. In V. unguiculata, the leaf water potentials measured by the in situ psychrometer oscillated at the same periodicity as, and proportional to, the leaf conductance. In all species, potentials measured by in situ psychrometers operating in the psychrometric mode were linearly correlated with potentials measured with the pressure chamber. However, the in situ psychrometers underestimated the leaf water potential in the two Helianthus species at low water potentials and overestimated the water potential in P. vera, N. oleander, and C. avellana. The underestimation in the two Helianthus species at low water potentials resulted from differences in water potential across the leaf. The overestimation in P. vera, N. oleander, and C. avellana was considered to arise from low epidermal conductances in these species even after abrasion of the cuticle. Pressure-volume studies with Lycopersicon esculentum showed that less water was expressed from distal than proximal leaflets when the whole leaf was slowly pressurized. The implication of this for water relations characteristics obtained by pressure-volume techniques is discussed. We conclude that in situ psychrometers are suitable for following dynamic changes in leaf water potential, but should be used with caution on leaves with low epidermal conductances.

Correction of flow resistances of plants measured from covered and exposed leaves

The difference in water potential between an enclosed nontranspiring leaf and an adjacent exposed transpiring leaf, and the transpiration rate of a similarly exposed leaf, were used to calculate the change in hydraulic resistance of sorghum (Sorghum bicolor [L.] Moench) and sunflower (Helianthus annuus L.) leaves throughout the day and at various rates of transpiration. Since cotton (Gossypium hirsutum L.) leaves enclosed in aluminum foil alone had enclosed leaf water potentials about 0.06 megapascals lower than similar leaves enclosed in a polyethylene bag shielded with aluminum foil, the sorghum and sunflower leaves were enclosed in polyethylene bags shielded with aluminum foil. Enclosing the exposed leaf in a plastic sheath just prior to excision led to the water potential measured by the pressure chamber technique being 0.3 to 0.4 megapascals higher at rapid transpiration rates than in exposed leaves not sheathed just prior to excision. This error, previously shown to arise from rapid water loss after excision, led to an overestimation of the leaf hydraulic resistance in both species. Correction of the error reduced the resistance by 40 to 90% in irrigated sorghum and by about 40% in irrigated and unirrigated sunflower. After correction, the hydraulic resistances were still flow-dependent, but the dependency was markedly reduced in sorghum.

Comparison of the agonist activity of impromidine (SK & F 92676) in anaesthetized rabbits and on the rabbit isolated fundic mucosa

1 The actions of impromidine in vivo and in vitro have been compared on gastric acid secretion. In both preparations impromidine was more potent than histamine. 2 There were no statistically significant differences between the maximum responses to impromidine and histamine in vivo or in vitro although in vitro the maximum response to impromidine was only 67% of that to histamine. In vivo the maximum response to impromidine was significantly less than the maximum response to histamine plus mepyramine. 3 The results are discussed in the light of recent findings.

Histamine H1- and H2-receptors in the gastric vasculature of the rabbit

The histamine receptors in the rabbit blood perfused gastric vasculature were analysed pharmacologically. Histamine elicited a monophasic increase in perfusion pressure which was antagonized by mepyramine and enhanced by metiamide. The maximum observed response was enhanced by metiamide to that produced by a specific H1-receptor agonist. It is concluded that the gastric vasculature responds to histamine with an H1-receptor mediated vasoconstriction and an H2-receptor mediated dilatation. In this preparation the H1-effect predominates in response to injection of histamine.

The involvement of histamine receptor subtypes in gastric acid secretion and mucosal blood flow in the anaesthetized rabbit

1. The involvement of histamine receptor subtypes in the gastric acid secretory and mucosal blood flow responses of the pentobarbitone-anaesthetized rabbit to histamine were investigated. 2. Histamine produced a dose-related increase in gastric acid secretion and mucosal blood flow. Maximal effects were stimulated further by mepyramine and inhibited by metiamide. Mepyramine had no effect on methacholine- or impromidine-stimulated gastric acid secretion or mucosal blood flow. 3. Impromidine also produced a dose-related increase in gastric acid secretion and mucosal blood flow. The maximal effect produced depended on the method of administration. The H1-receptor agonist 2-TEA inhibited impromidine-stimulated blood flow but not gastric acid secretion. 4. It is concluded that, in addition to stimulating acid secretion by an action on H2-receptors, histamine also exerts an inhibitory effect which is mediated by H1-receptors and that this inhibitory effect operates via reduced blood flow resulting from vasoconstriction in the stomach.

Concurrent comparisons of stomatal behavior, water status, and evaporation of maize in soil at high or low water potential

Concurrent measurements of evaporation, leaf conductance, irradiance, leaf water potential, and osmotic potential of maize (Zea mays L. cv. Pa602A) in soil at either high or low soil water potential were compared at several hours on two consecutive days in July. Hourly evaporation, measured on two weighing lysimeters, was similar until 1000 hours Eastern Standard Time, but thereafter evaporation from the maize in the dry soil was always less than that in the wet soil; before noon it was 62% and by midafternoon, only 35% of that in the wet soil. The leaf water potential, measured with a pressure chamber, was between -1.2 and -2.5 bars and between -6.8 and -8 bars at sunrise (about 0530 hours Eastern Standard Time) in the plants in the wet and dry soil, respectively, but decreased quickly to between -8 and -13 bars in the plants in the wet soil and to less than -15 bars in the plants in the dry soil by 1100 to 1230 hours Eastern Standard Time. At this time, the leaf conductance of all leaves was less than 0.1 cm sec(-1) in the maize in the dry soil, whereas the conductance was 0.3 to 0.4 cm sec(-1) in the leaves near the top of the canopy in the wet soil. The osmotic potential, measured with a vapor pressure osmometer, also decreased during the morning but to a smaller degree than leaf water potential, so that by 1100 to 1230 hours Eastern Standard Time the leaf turgor potential was 1 to 2 bars in all plants. Thereafter, leaf turgor potential increased, particularly in the plants in soil at a high water potential, whereas leaf water potential continued to decrease even in the maize leaves with partly closed stomata. Evidently maize can have values of leaf conductance differing 3- to 4- fold at the same leaf turgor potential, which suggests that stomata do not respond primarily to bulk leaf turgor potential. Evidence for some osmotic adjustment in the plants at low soil water potential is presented. Although the degree of stomatal closure in the maize in dry soil did not prevent further development of stress, it did decrease evaporation in proportion to the decrease in canopy conductance.

Changes in Alfalfa Stem Conductance Induced by Corynebacterium insidiosum Toxin

A toxin involved in bacterial wilt of alfalfa (Medicago sativa L.) has been isolated from cultures of the pathogen, Corynebacterium insidiosum, as well as from diseased plants (S. M. Ries and G. A. Strobel. 1972. Physiological Plant Pathology 2: 133-142). The influence of this toxin, a glycopeptide with a molecular weight of 5 x 10(6), on the water relations of alfalfa was examined. It was found that very small amounts of the toxin (2 mug) significantly reduced stem conductance through 15-cm long stems. This decrease in stem conductance caused by the toxin best explains the rapid decrease in transpiration and stomatal conductance and the resultant wilting after alfalfa cuttings have been in 200 mug ml(-1) toxin for 2 hours. Membrane damage resulting in water leakage was ruled out as a factor in the wilting during the 2-hour period. It is postulated that the toxin acts by interfering with water movement through pit membranes.

Water uptake, diameter change, and nonlinear diffusion in tree stems

A diffusion model for phloem swelling and contraction is proposed in which the rate of water movement changes markedly with moisture content. Good agreement between the actual swelling of the phloem of cotton stems and that predicted by the model was obtained. This result implies that water moves more readily into the phloem when it becomes wetter. This model also explains the lag of shrinkage of pine stems behind the water potential of the foliage and predicts that the lag is related to the thickness of the phloem.

Influence of a Ceratocystis ulmi Toxin on Water Relations of Elm (Ulmus americana)

Water-soluble glycopeptides isolated from cultures of Ceratocystis ulmi have been reported to be toxins involved in Dutch elm disease. The influence of the glycopeptides on the water relations of Ulmus americana seedlings was tested by placing cut stems in glycopeptide preparations. After 4 hours in 200 micrograms per milliliter toxin the stem conductance of the seedlings was reduced by 79% and the leaf water potential was reduced by 3 bars to that at which the seedlings wilted, the stomata closed, and transpiration decreased. Decrease in stem conductance as the mode of action of the toxin was further confirmed by forcing toxin through the stem and petiole of elm and measuring the effects on stem conductance. High molecular weight dextrans were found to mimic the action of toxin on stem and petiole conductance, and their ability to do so was found to be correlated with their molecular weight. As low as 4 micrograms of toxin or dextrans were found to measurably decrease the stem and petiole conductance of elms. Disruption of the water-conducting system of elms and other plants by small quantities of high molecular weight compounds may be a factor in diseases with wilting symptoms.

Stomatal Behavior and Water Status of Maize, Sorghum, and Tobacco under Field Conditions: II. At Low Soil Water Potential

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), leaf resistance (r(1)), leaf water potential (psi), osmotic potential (pi), and turgor potential (P) were followed concurrently in crops of maize (Zea mays L. cv. Pa602A), sorghum (Sorghum bicolor [L.] Moench cv. RS 610), and tobacco (Nicotiana tabacum L. cv. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were low. The r(1), measured with a ventilated diffusion porometer, of the leaves in the upper canopy decreased temporarily after sunrise [ approximately 0530 hours Eastern Standard Time] as I increased, but then r(1) increased again between 0700 and 0830 hr Eastern Standard Time as the psi, measured with a pressure chamber, decreased rapidly from the values of -7, -4 and -6 bars at sunrise to minimal values of -18, -22 and -15 bars near midday in the maize, sorghum, and tobacco, respectively. The pi, measured with a vapor pressure osmometer, also decreased after sunrise, but not to the same degree as the decrease in psi, so that a P of zero was reached in some leaves between 0730 and 0800 hours. The lower (more negative) pi of leaves in the upper canopy than those in the lower canopy gave the upper leaves a higher P at a given psi than the lower leaves in all three species; leaves at intermediate heights had an intermediate P. This difference between leaves at the three heights in the canopy was maintained at all values of psi. The r(1) remained unchanged over a wide range of P and then increased markedly at a P of 2 bars in maize, -1 bar in sorghum, and near zero P in tobacco: r(1) also remained constant until psi decreased to -17, -20, and -13 bars in leaves at intermediate heights in maize, sorghum, and tobacco, respectively. In all three species r(1) of leaves in the upper canopy increased at more negative values of psi than those at the base of the canopy, and in tobacco, leaves in the upper canopy wilted at more negative values of psi than those in the lower canopy.

Toxicity of Leaf and Stem Extracts to Tylenchorhynchus dubius

Plant extracts, made by grinding 2 g of fresh tissue in 5 ml of water, were toxic to Tylenchorhynchus dubius and Hoplolaimus spp. Such extracts from leaves and stems of bean (Phaseolus vulgaris L.) and leaves of tobacco (Nicotiana tabacum L.) were most toxic; those from leaves of corn (Zea mays L.), tomato (Lycopersicon esculentum Mill.) and rhododendron (Rhododendron catawbiense L.) were less toxic; and extracts of bean roots were nontoxic. Nematode movement slowed markedly within 1 hr in tobacco leaf extract, and within 4 hr in bean leaf extract; both extracts completely inactivated or killed 95% of the nematodes in 24 hr. Heating leaf extract 10 min at 80 C eliminated toxicity. Absorption of fusicoccin, a phytotoxin produced by Fusicoccum amygdali Del., increased the toxicity of tomato leaf extracts, whereas water extracts of acetone-extracted powder preparations of leaves were about 15-fold more toxic than water extracts of fresh tissue. Addition of homogenized leaves of bean, tobacco and tomato to soil significantly reduced nematode populations within 3 days.