Resprouting as a key functional trait: how buds, protection and resources drive persistence after fire.

Resprouting as a response to disturbance is now widely recognized as a key functional trait among woody plants and as the basis for the persistence niche. However, the underlying mechanisms that define resprouting responses to disturbance are poorly conceptualized. Resprouting ability is constrained by the interaction of the disturbance regime that depletes the buds and resources needed to fund resprouting, and the environment that drives growth and resource allocation. We develop a buds-protection-resources (BPR) framework for understanding resprouting in fire-prone ecosystems, based on bud bank location, bud protection, and how buds are resourced. Using this framework we go beyond earlier emphases on basal resprouting and highlight the importance of apical, epicormic and below-ground resprouting to the persistence niche. The BPR framework provides insights into: resprouting typologies that include both fire resisters (i.e. survive fire but do not resprout) and fire resprouters; the methods by which buds escape fire effects, such as thick bark; and the predictability of community assembly of resprouting types in relation to site productivity, disturbance regime and competition. Furthermore, predicting the consequences of global change is enhanced by the BPR framework because it potentially forecasts the retention or loss of above-ground biomass.

The effect of hormone replacement therapy of the age-related rise of factor VIIc, and its activity state.

Although hormone replacement therapy (HRT) appears to protect women from ischaemic heart disease (IHD), its use is associated with increased factor clotting activity (VIIc), an independent risk factor for IHD. The nature of this factor VII rise was therefore examined in a cross-sectional study of 279 women aged between 40 and 65 years. Ninety-four were pre-menopausal, 44 were post-menopausal and taking HRT, whilst 141 were post-menopausal non-users. For those women on oestrogen-only HRT, the mean factor VIIc was 144%, compared to 130% for post-menopausal non-users, and 116% for those on combined HRT. These differences were significant (p = 0.01). Oestrogen-only users also had significantly higher mean levels of factor VIIa (3.3 ng/ml) compared to non-users (2.2 ng/ml) and those on oestrogen-progestogen HRT (2.2 ng/ml-p = 0.015). In contrast for factor VII antigen the mean values of the three groups were similar. Analysis of the age-regression slopes showed a significant age-related rise in factor VIIc of 1.2% per annum (p < 0.01) for post-menopausal non-users. There was a similar increase in factor VII antigen (2.1%) but no rise in factor VIIa. For all HRT users there was no change with age for any of the factor VII measures. Thus the age-related rise in factor VIIc appears to be due to an increase in factor VII zymogen alone, and taking HRT seems to abolish such a rise. In contrast, the increased factor VIIc seen with oestrogen-only HRT appears to be secondary to factor VII activation.

In vitro assessment of the efficacy of erythromycin in combination with oxytetracycline or spectinomycin against Pasteurella haemolytica.

The effects of combining erythromycin (Ery) with oxytetracycline (Oxy) or spectinomycin (Sp) on Pasteurella haemolytica were evaluated in vitro using the chessboard (checkerboard) technique. These combinations were selected because all are drugs widely used in bovine respiratory disease treatment, and they represent possible sequential or complementary mechanisms of action. Using the recommended breakpoints of greater than 4 micrograms/ml for Ery, 16 micrograms/ml for Oxy, and 32 micrograms/ml for Sp, of the 33 P. haemolytica isolates, 32 were resistant to Oxy, 27 to Sp, and 14 to Ery. Based on the fractional inhibitory concentration index, Ery and Oxy in combination were synergistic or additive against 32 of 33 isolates. The combination of Ery and Sp was synergistic or additive against 27 of 33 isolates. No instances of antagonism were seen. When the effects were considered within the context of therapeutically achievable serum/tissue concentrations, the effects of Ery and Oxy in combination were only marginal. Thus, against P. haemolytica isolates, Ery and Sp appeared to represent an effective antimicrobial combination, whereas Ery and Oxy were only of marginal efficacy as a combination.

Microdilution antimicrobial susceptibilities of selected gram-negative veterinary bacterial isolates.

Gram-negative bacterial isolates (635) obtained from routine submissions to the Oklahoma Animal Disease Diagnostic Laboratory during 1983-1987 were tested for antimicrobial susceptibility. Minimal inhibitory concentrations (MICs) were determined for the following antimicrobials using commercially prepared microdilution assay materials: ampicillin, cephalothin, chloramphenicol, erythromycin, gentamicin, kanamycin, oxytetracycline, penicillin G, spectinomycin, sulfachlorpyridazine, sulfadimethoxine, and tylosin. Results for isolates from cattle, dogs, horses, and pigs are presented. In only a few instances were differences in MICs apparent among bacterial isolates from different tissues. Aminocyclitol MICs for equine uterine isolates of Klebsiella pneumoniae differed from MICs for isolates from other tissues, and ampicillin, kanamycin, and spectinomycin MICs for bovine fecal isolates of Escherichia coli differed from MICs for isolates obtained from other tissues. In several instances, bimodal distribution of susceptibilities was apparent for ampicillin, kanamycin, and/or oxytetracycline. There was also a bimodal distribution pattern for erythromycin against Pasteurella haemolytica of bovine origin.

Hypotension produced by rapid intravenous administration of chloramphenicol in anaesthetised dogs.

Rapid intravenous administration (60 mg s-1) of chloramphenicol (50 mg kg-1) in a 40 per cent w/v polyethylene glycol (400 to 600), 30 per cent ethyl alcohol, 2 per cent benzyl alcohol and 28 per cent distilled water vehicle produced a transient but significant decrease in systemic arterial blood pressure and heart rate with no effect on central venous pressure in sodium pentobarbital anaesthetised dogs. The vehicle alone had no significant effect on any of the parameters studied. Various approaches including the use of anticholinergic, antihistaminergic, antiadrenergic and ganglion blocking drugs failed to attenuate chloramphenicol induced hypotension and bradycardia. However, the hypertensive response to bilateral carotid arterial occlusion was significantly attenuated by rapid intravenous administration of chloramphenicol. The results clearly indicate that chloramphenicol itself, but not its vehicle, is responsible for the severe hypotension and bradycardia. These results also suggest that chloramphenicol-induced hypotension and bradycardia might be mediated peripherally via vasodilation due to its direct effect on vascular smooth muscle and centrally via interruption of the baroreceptor reflex pathway.

Experimental chloramphenicol intoxication in neonatal calves: intravenous administration.

Chloramphenicol was administered intravenously for eight to 17 days to five newborn calves at a daily dosage of 100 mg kg-1. Haemodynamic, haematological, blood chemistry, serum enzyme, urinalysis and clinical responses were evaluated. High levels of serum chloramphenicol were observed throughout the study although a marked increase in elimination rate was seen with increasing age. The most severe adverse effects were severe hypotension following rapid intravenous administration and severe gastrointestinal dysfunction with diarrhoea accompanying prolonged high dosage. There appeared to have been a haematological effect in one calf, but it was of minor significance compared with the other effects.

Antipyrine, erythromycin and oxytetracycline disposition in experimental fasciolosis.

The effects of fasciolosis on drug disposition were studied by administration of antipyrine, erythromycin and oxytetracycline to sheep and cattle. Fasciolosis was produced by administration of 200 or 400 metacercariae (MC) of Fasciola hepatica to sheep and 500 MC to cattle. The disease was subsequently confirmed by determination of plasma glutamate dehydrogenase and gamma-glutamyl transferase and identification and quantitation of mature flukes in the liver at necropsy. Acute or subacute fasciolosis in sheep was accompanied by a significant decrease in the elimination rate constant (beta) and increase in the elimination half-time (t 1/2) for antipyrine and erythromycin when compared with controls or infected sheep which had been treated with the anthelmintic luxabendazole. An increase in apparent volume of distribution (Vd) was seen only for erythromycin in sheep given 400 MC. There were no changes in the disposition of oxytetracycline in sheep with either acute or subacute infection and no effects on disposition of the three test drugs in chronically infected sheep. With early chronic disease in calves, only the disposition of oxytetracycline was affected; not that of antipyrine or erythromycin.

Endotoxaemia in the horse.

Endotoxins are non-protein fragments of the cell wall of Gram-negative bacteria. They must be absorbed into the circulation to produce disease and systemic effects are similar, regardless of bacterial source. Absorption of endotoxins occurs in obstructive bowel disease and may play a significant part in determining the severity of the disease. Many of the responses to experimentally administered endotoxin are identical to those of bowel diseases or the horse and include circulatory, haematological and metabolic alterations. Therapeutic approaches are indirect and include many drugs currently employed in equine practice. The agents are directed toward mediators of the disease rather than the endotoxins themselves and include fluids, corticosteroids, anti-inflammatory drugs, energy sources and vasoactive drugs. The rationale for use and dosages are discussed.

Interactions between chloramphenicol, acepromazine, phenylbutazone, rifampin and thiamylal in the horse.

The potential for interactions between chloramphenicol, phenylbutazone, acepromazine and thiamylal and chloramphenicol, rifampin, and phenylbutazone were evaluated in two groups of experiments. In the first, five horses were given thiamylal intravenously (iv) (6.6 mg/kg) after pretreatment with acepromazine, and the time of recumbency was determined. Administration of chloramphenicol iv (25 mg/kg) 1 h prior to anaesthesia significantly lengthened the recumbency time from 21.8 +/- 4.8 mins to 36.0 +/- 8.3 mins. There was an apparent but not statistically significant decrease in recumbency time when phenylbutazone (4.4 mg/kg) was administered iv daily for 4 days prior to anaesthesia. In the second series of experiments, phenylbutazone (4.4 mg/kg), chloramphenicol (25 mg/kg) and rifampin (10 mg/kg) were administered in various sequences to five different horses. Chloramphenicol pretreatment produced a significant decrease in the elimination rate and rifampin a significant increase in the elimination rate of phenylbutazone. The half-life of elimination of phenylbutazone alone was about 4 h. Following four days pretreatment with rifampin it was approximately 2.7 h, it was approximately 5.6 h and 9.5 h, respectively, when chloramphenicol was administered in one dose 1 h before or two doses 12 h and 1 h before phenylbutazone.

The prophylactic effect of corn supplementation on experimental nitrate intoxication in cattle.

Sodium nitrate was administered through rumen cannulae to produce NO-3 intoxication in four cows (382 to 445 kg body wt) fed prairie grass hay and a protein-mineral supplement. The cows were fed 0, 1.6 or 3.2 kg of dry rolled corn daily for 10 d prior to sodium nitrate administration. Sodium nitrate administration was followed by a marked increase in intraruminal NO-2 and NH3 and blood NO-2 and methemoglobin. Six of eight cows fed 0 and 1.6 kg of corn were given methylene blue to treat severe methemoglobinemia, while none of the cows fed 3.2 kg corn required such therapy. Feeding of 3.2 kg of corn protected against nitrate poisoning by reducing intraruminal nitrite and blood methemoglobin (P less than .05).

Antibiotic disposition in experimental pneumonic pasteurellosis: gentamicin and tylosin.

The effects of severe respiratory disease on the disposition of antibiotics were evaluated using two drugs chosen because of their widely differing solubility characteristics. The experiments were carried out in series, using five calves for each drug. The drugs were given to seven week old calves before and after induction of pneumonia by bilateral intrapulmonary administration of 3 mL of 5 X 10(7) colony forming units of Pasteurella haemolytica. Following inoculation, the calves developed clinical signs of pneumonia and were given gentamicin (5 mg/kg) or tylosin (10 mg/kg) 48, 60 and 72 hours after Pasteurella administration. There was a statistically significant decrease in distribution rate but not elimination rate of gentamicin. For tylosin, there was a significant increase in elimination rate. These results indicate the kinetics of tylosin but not gentamicin are sufficiently altered as to support a need for increased frequency of administration with severe respiratory disease in calves.

Effects of experimentally induced Pasteurella haemolytica pneumonia on the pharmacokinetics of erythromycin in the calf.

Pneumonic pasteurellosis was produced experimentally in 3- to 4-month-old Holstein bull calves by bilateral intrapulmonary administration of 5 X 10(7) to 10(9) colony-forming units of Pasteurella haemolytica. Of 8 calves, 4 developed minor pulmonary changes, 1 died of an apparent bacteremia within 24 hours, and 3 developed extensive pneumonic changes. At 1 week before (1 dose) and at 48, 60, and 72 hours (3 doses) after Pasteurella administration, the calves were given erythromycin at a dosage of 15 mg/kg, and the pharmacokinetic values were determined. There were statistically (P less than or equal to 0.05) significant increases in the distribution and elimination rates associated with pneumonia. The elimination half life decreased from 132.7 +/- 9.6 minutes in prepneumonic calves to 111.1 +/- 13.8 minutes and 99.7 +/- 2.6 minutes in calves with minor and with moderate pneumonic changes, respectively. There also was a decrease in apparent volume of distribution with pneumonia. Erythromycin tissue concentrations were determined 2 hours after the last dose was given to the calves with pneumonia. Tissue concentrations in the pneumonic lung areas were as high or higher than those in nonaffected lung tissues in the same animals. Because of the increased rate of elimination from serum in pneumonic calves, it may be advisable to use shorter dosage intervals in calves with severe respiratory tract disease.

Equine Escherichia coli endotoxemia: comparison of intravenous and intraperitoneal endotoxin administration.

Certain physiologic and hematologic data were determined in ponies given Escherichia coli endotoxin by three routes: single IV dose, single intraperitoneal (IP) dose, and multiple IP boluses. In all ponies, the reaction was characterized by weakness, depression, peripheral circulatory abnormalities, and pyrexia. The pyrexia was more severe and was sustained in the ponies given multiple IP bolus endotoxin. Changes in packed cell volume, peripheral blood neutrophil, lymphocyte, and thrombocyte counts, and blood glucose were noticed in the three groups. Blood lactate and beta-glucuronidase values were determined and increases occurred only in the two IP endotoxin administration groups. A fibrinogen increase was observed in only the multiple IP bolus group. Attempts were made to correlate the lactate and beta-glucuronidase values with the severity and prognosis of the endotoxemia response. In general, the single IV bolus and, to a lesser extent, the single IP bolus endotoxin produced abrupt but transient responses. The multiple IP bolus endotoxin administration produced a more gradual and sustained response, which was more closely comparable with a clinical gastrointestinal disease problem than the other routes of administration produced.

Therapeutic effect of phenylbutazone on experimental acute Escherichia coli endotoxemia in ponies.

Phenylbutazone (PBZ), a classic anti-inflammatory and prostaglandin-synthesis inhibitor drug, was used to determine the role of prostaglandins and other mediators on the development and perpetuation of the response to intraperitoneal Escherichia coli endotoxin administration. The PBZ (15 mg/kg of body weight) was administered IV 30 minutes after endotoxin administration and was repeated later at 6 and 12 hours at a dose of 10 mg/kg. A variety of evaluation measurements (hematologic, blood glucose, pyruvate, lactate and fibrinogen, serum beta-glucuronidase, prothrombin time, blood gases, hepatic glycogen, plasma esterase, capillary refill time, and rectal temperature) were utilized. Marked alterations were noted for all evaluators following endotoxin administration except for blood fibrinogen, prothrombin time, and plasma esterase activity. The PBZ therapy blocked the hemoconcentration, hyperglycemia, increased blood lactate, decreased bicarbonate, decreased blood pH, pyrexia, and prolonged capillary refill time responses associated with endotoxin administration. Despite the significant blocking effects of PBZ on endotoxin responses, the eventual survival rate was unaffected in these experiments.

Cyanide intoxication in sheep: therapeutic value of oxygen or cobalt.

The combination of cobalt salts and oxygen with the traditional sodium nitrite-sodium thiosulfate antidote may have value as cyanide antidotes. Results reported previously in mice were extended to sheep in the present experiments. Cobaltous chloride (15 mg/kg of body weight) or oxygen with or without sodium nitrite and sodium thiosulfate were compared with respect to the median lethal dose of oral sodium cyanide. Although cobaltous chloride or oxygen used alone did result in a significant increase in the median lethal dose of sodium cyanide in sheep, the protection was minor compared with the overall protection provided by the classic antidotal combination of sodium nitrite and sodium thiosulfate. Cobaltous chloride combined with sodium nitrite and sodium thiosulfate did not provide any increase in protection more than that observed with sodium nitrite and sodium thiosulfate alone. Oxygen used in combination with sodium nitrite and sodium thiosulfate did significantly increase the protection. However, the increase in protection was not of sufficient magnitude to recommend it as a practicable addition to the present therapeutic regimen.

Experimental lead toxicosis in ponies: comparison of the effects of smelter effluent-contaminated hay and lead acetate.

Grass hay produced in the Coeur d'Alene River Basin of northern Idaho was fed to a group of 4 ponies. The hay contained Pb in concentration of 423 +/- 82 mg/kg and Cd in concentration of 10.8 +/- 1.4 mg/kg, resulting in daily exposures of the ponies to approximately 7.4 mg of Pb/kg and 0.19 mg of Cd/kg/day. The results in this group of ponies were compared with those from a group fed noncontaminated grass hay and given a daily dose of 10 mg of Pb/kg of body weight, in the form of lead acetate. Clinical toxicologic signs, hematologic changes, and blood and tissue Pb concentrations were similar in the 2 groups. However, the severity of the disease process appeared to be greater in the ponies fed the Pb- and Cd-contaminated hay. This was shown clearly by the shorter interval between onset of clinical changes and death in the ponies fed contaminated hay. The possibility of multiple heavy metal effects is discussed. Clinical toxicologic signs observed include incoordination, labial paresis, pharyngeal paresis, CNS depression, anorexia, and body weight loss. Anemia or marginal anemia was common and was often accompanied by the appearance of nucleated RBC and Howell-Jolly bodies in peripheral blood. Neither the hematologic response nor the blood Pb concentrations were reflective of the severity of poisoning, although blood Pb concentrations were greater than 0.35 micrograms/ml once clinical signs of toxicity were observed. Liver, kidney, spleen, brain, and bone Pb concentrations and liver, kidney, and brain Cd concentrations were increased in both the ponies fed contaminated hay and the ponies given lead acetate.

Cyanide intoxication in sheep: enhancement of efficacy of sodium nitrite, sodium thiosulfate, and cobaltous chloride.

For treatment of cyanide intoxication of ruminants, the present recommended doses of sodium nitrite (5 mg/kg of body weight) and sodium thiosulfate (25 to 50 mg/kg) are smaller than those recommended for other animals; the decrease is partially attributed to the greater susceptibility of ruminants to the toxic effects of sodium nitrite. Based on the high tissue concentration and activity rate of rhodanese in ruminants, sulfur donors such as sodium thiosulfate could be utilized more efficaciously. Doses of sodium nitrite and sodium thiosulfate (up to 22 and 660 mg/kg, respectively) were evaluated in the present studies. Adjustment of the antidotal combination provided almost three times the protection afforded by the previously recommended doses. Moreover, under the conditions tested, the newly adjusted dose levels of sodium thiosulfate alone were more effective than the previously used antidotal combination of sodium nitrite and sodium thiosulfate and this protective effect was enhanced by cobaltous chloride (10.6 mg/kg) or sodium nitrite. The present recommended therapeutic approach to cyanide intoxication in sheep should be based primarily on administration of a much higher dose of sodium thiosulfate in combination with sodium nitrite or cobaltous chloride (or both).

Serum and tissue concentrations of erythromycin in calves with induced pneumonic pasteurellosis.

The effects of pneumonia on the pharmacokinetics of erythromycin administered IM and the tissue concentration changes with time were evaluated in 2-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures through the thoracic wall into each lung. Six days prior to induction of pneumonia, erythromycin (15 mg/kg) was administered in a single IM dose. Erythromycin was administered again 48, 72, and 96 hours after injection of P haemolytica. On the third day of erythromycin administration (96 hours), the calves were serially euthanatized in groups of 4 calves each at 2, 5, 8, 12, 18, and 24 hours after the final dose was given. Tissue concentrations of erythromycin in kidney, liver, lung, muscle, CSF, and serum were determined. Neither the serum concentrations nor the overall pharmacokinetic values were significantly (P less than or equal to 0.05) changed by pneumonia. The concentrations of erythromycin were maximal at 5 hours for liver, muscle, and serum and at 8 hours for CSF, kidney, and lung. Serum and muscle concentrations were similar, whereas concentrations in CSF were lower than in serum and higher in kidney, liver, and lung. The lung/serum ratios were approximately 2.5 to 3 at 8 through 24 hours after IM administration. The peak concentration in lung was approximately 6 micrograms/g at 8 hours.

Response of Pasteurella haemolytica to erythromycin and dexamethasone in calves with established infection.

A subcutaneous soft tissue infection model in calves was used to study the in vivo response of Pasteurella haemolytica to erythromycin and dexamethasone. Two tissue chambers were implanted SC in each of 12 calves. At 45 days after implantation, all tissue chambers were inoculated with an erythromycin-sensitive strain of P haemolytica. Starting 24 hours after inoculation, calves were allotted to 4 groups of equal size and a 2 x 2-factorial arrangement of treatments was applied: 3 calves were given erythromycin (30 mg/kg of body weight, IM, for 5 days), 3 calves were given dexamethasone (0.05 mg/kg, IM, for 2 days), 3 calves were given erythromycin and dexamethasone, and the remaining calves served as nontreated controls. Chamber fluids were tested daily, and the response to treatment was measured. Neither erythromycin nor dexamethasone affected viability or growth of bacteria within tissue chambers. Dexamethasone had no effect on the influx of neutrophils into infected chambers. Despite repeated administration of a high dose of erythromycin and attainment of adequate concentration in serum, erythromycin concentration in chamber fluids did not exceed the minimal inhibitory concentration established in vitro. These results indicate that the clinical efficacy of erythromycin against P haemolytica sequestered in consolidated pneumonic lesions may not be well correlated with predictions based on serum pharmacokinetic and in vitro susceptibility data.

Comparative pharmacokinetics of antibiotics in newborn calves: chloramphenicol, lincomycin, and tylosin.

The pharmacokinetics of 3 antibiotics--chloramphenicol, lincomycin, and tylosin--were determined in newborn calves. The kinetic determinations, using 2-compartment open models, were made at increasing ages from 1 day to 42 days and compared with those made from 9-month-old calves. Although all 3 antibiotics require a degree of hepatic metabolism, there were marked differences in the development of elimination processes for the individual drugs. Elimination of tylosin, which was slow in the calves at birth, increased rapidly and was equal to that in older calves by the end of 1 week. Lincomycin elimination was not markedly reduced in calves at birth. Chloramphenicol elimination was slow in calves at birth and only by 4 to 6 weeks attained the rate found in older calves. Dosage adjustments would not be required for the antibiotics tylosin or lincomycin when given to newborn calves, but may be necessary for chloramphenicol given to calves before they are 4 to 6 weeks old.