Inhibition of carbonic anhydrase by plasma of dogs and rabbits.

Carbonic anhydrase (CA) activity was measured by the Bowes-Davis technique in diluted hemolysates of dog erythrocytes, rabbit erythrocytes, and dog lung tissue homogenates. Plasma (from the same animal) inhibited the CA activity in each case. For 1:16,700 dilution of dog erythrocytes, the CA catalyzed the CO2 hydration reaction by 5.3 +/- 0.4-fold above the uncatalyzed rate, and half that activity was inhibited by plasma concentrations of 0.44 +/- 0.05%. Similar rabbit CA concentrations were inhibited by plasma concentrations of 1.02 +/- 0.24%. CA from dog lung tissue homogenate is only partially inhibited by plasma even at high plasma concentrations, suggesting different isozymes, at least one of which is not inhibited by plasma. The results suggest that extrapolating from artificially perfused lungs or histological observations to in vivo conditions may not be valid, and the possibility of inhibition by plasma in at least some species should be considered.

Respiration and gene expression in germinating ascospores of Neurospora tetrasperma.

Cellular proteins were not synthesized by germinating ascospores of Neurospora tetrasperma until 90 min after spore activation. Nevertheless, immediately after activation these ascospores developed a cyanide-sensitive respiration which increased throughout this 90-min period. At 90 min the respiratory rates accelerated rapidly, protein synthesis was initiated, and transcripts for a subunit of the mitochondrial ATPase, employed here as a representative mRNA, began to accumulate.

Heat shock gene expression in germinating ascospores of Neurospora tetrasperma.

The activated ascospores of Neurospora tetrasperma were inactive in protein synthesis and did not accumulate transcripts for a constitutive protein until after 90 min of incubation. These spores were blocked even longer in the expression of a gene encoding a heat shock protein, hsp30, which could not be induced until after 300 min of spore germination. Early in germination the ascospores were highly susceptible to damage from moderately high temperatures. At the same time that spores became capable of expressing the hsp30 gene, there was a loss of cytosine methylation from the gene.

Occurrence of (Dirofilaria immitis) in gray fox (Urocyon cinereoargenteus) in Alabama and Georgia.

The occurrence of Dirofilaria immitis in gray fox (Urocyon cineroargenteus) was determined by gross examination, blood samples, and filtered tissue sediments in a sampling of 149 gray foxes taken from Alabama and Georgia during the 1977-78 trapping season. Microfilariae were not found in blood samples obtained from 24 of these gray foxes. Three of 82 male foxes (3.7%) and 1 of 67 female foxes (1.5%) were infected with heartworm. D. immitis rate of infection was 1 of 19 (5.3%) and 3 of 130 (2.3%), respectively, in juvenile and adult gray foxes. Single sex infections with D. immitis occurred in 4 of the 6 foxes, with a maximum nematode burden of approximately eight. Two other infected foxes were encountered separate from this study.

Brucella abortus in wildlife on selected cattle farms in Alabama.

Two studies of brucellosis in wildlife on farms where the brucellosis infection prevalence in cattle was known are reported. On a research farm, 233 feral animals of 22 mammalian species and 12 of seven avian species were trapped during three time periods. Sixty were studied before cattle were introduced, 128 were studied while 501 cattle infected with Brucella abortus were calving and aborting, and 60 specimens were collected 20 mo after the last infected cow calved. Selected tissues from 229 wild animals were cultured and sera from 138 were examined using the brucellosis card, standard tube agglutination (STA), 2-mercaptoethanol (2-ME) and rivanol (RIV) tests. Brucella abortus was not recovered from any animals sampled prior to cattle being introduced and all sera collected were negative. Brucella abortus was isolated from four opossums (Didelphis virginiana) and one raccoon (Procyon lotor) in the group of animals trapped during the calving period. Three serums were tested and had STA titers ranging from 1:100 to 1:200. Of 68 sera only one had antibodies. Brucella were not isolated from 59 animals trapped after the calving period and only one of 42 serums had antibodies. On regional cattle farms, 243 wild animals were trapped. Brucellae were not isolated from 223 animals which were cultured. No serums had significant titers. The data from this study suggest opossums and raccoons can be infected from cattle but are unlikely to maintain the infection.

Response of gray foxes to modified live-virus canine distemper vaccines.

Ten gray foxes seronegative for canine distemper virus were vaccinated with 1 of 3 commercial modified live-virus canine distemper vaccines. Of 5 foxes receiving vaccine A (chicken tissue culture origin), 4 developed significant titers (greater than or equal to 1:100) of neutralizing antibody to canine distemper virus and remained clinically normal after vaccination. Two of 3 foxes vaccinated with vaccine B (canine cell line origin) and both foxes receiving vaccine C (canine cell line origin) died of vaccine-induced distemper. Five unvaccinated control foxes died of distemper after a known occasion for contact transmission of virus from a fox vaccinated with vaccine B. The results suggested that the chicken tissue culture origin modified live-virus canine distemper vaccine is probably safe for normal adult gray foxes, whereas the canine cell origin vaccines are hazardous. The results of this study tended to corroborate anecdotal experiences of veterinarians who have observed that gray foxes frequently die from distemper soon after vaccination with modified live-virus canine distemper vaccines.

Effect of light on growth and sporulation of Aspergillus ornatus.

Aspergillus ornatus produces conidia when grown in continuous light but few, if any, when grown in continuous darkness. A minimum of 3 h of exposure to light is needed for induction. Light inhibits growth, glucose uptake and phosphorylation but does not inhibit the uptake of lysine. A low molecular weight substance produced or accumulating in the light inhibits the phosphorylation of glucose. It is suggested that the inhibition of glucose uptake and phosphorylation precedes conidiation and that conidiation may be the result of starvation caused by this light-induced inhibition.

Modest effect of temperature on the porcine oxygen dissociation curve.

It has been generally assumed that normally endothermic mammals have hemoglobins with greater temperature sensitivity than ectotherms or hibernating mammals. We found the pig to be an exception to this rule. We measured 101 dissociation curves using biotonometry on fresh heparinized blood from 9 pigs at 4 temperatures. The partial pressures of O2 at 50% saturation (P50 +/- SE) were 27.8 +/- 1.2, 30.0 +/- 1.3, 35.7 +/- 0.6 and 41.6 +/- 1.8 mm Hg at 30, 33, 37, and 41 degrees C, respectively. The temperature coefficient d log P50/dT was 0.016 +/- 0.002, about two-thirds that of human and dog blood. It was also saturation dependent, being significantly greater at lower saturations than at high saturations. This saturation dependence causes an increase in heme-heme cooperativity in binding oxygen at higher temperatures. The fixed acid Bohr coefficient was -0.441 +/- 0.005 at 37 degrees C and was not temperature sensitive. We conclude that the effect of temperature on the porcine dissociation curve is significantly lower than that reported for other endotherms, and is similar to that previously reported for hibernating mammals and some ectotherms.

CO2 diffusing capacity in isolated dog lung lobes and the role of carbonic anhydrase.

CO2 diffusing capacities (DmCO2) were measured at 22 degrees C on 12 isolated perfused dog lung lobes before and after inhibition of lung tissue carbonic anhydrase (CA) by acetazolamide (Diamox). The hypothesis is that CA in the alveolar-capillary tissue enhances overall transport of CO2 by converting CO2 to HCO-3 within aqueous portions of the tissue. HCO-3 diffuses simultaneously with molecular CO2, increasing the overall CO2 flux, and then converts back to molecular CO2 at the end of the aqueous pathway. To ensure at least partial diffusion limitation, lobes were perfused with phosphate buffer at high pH (7.7) and high flow rates. Plant CA (which is not inhibited significantly by Diamox) was added to the perfusate to provide rapid uptake of CO2 via conversion to HCO-3. After Diamox, DCO2 decreased 39.6%, indicating that CA does increase CO2 transport through lung tissue. Surprisingly, DCO2 exceeds CO diffusing capacity by only 9.3 +/- 2.1 times (without Diamox inhibition) rather than by the factor of 24 predicted by Graham's law on the basis of solubilities and molecular weights of the gases.

Effect of plasma carbonic anhydrase on ventilation in exercising dogs.

Recent studies suggest pH sampled by arterial chemoreceptors may not equal that sampled by external pH electrodes, because the uncatalyzed hydration of CO2 in plasma is a slow reaction (t 1/2 approximately 9 S). The importance of this reaction rate to ventilatory control (particularly during exercise) is not known. We studied the effect of catalyzing the CO2-pH reaction in three awake exercising dogs with chronic tracheostomies and carotid loops; the dogs were trained to run on a treadmill. Respiration frequency, tidal volume, total ventilation, and end-tidal partial pressure of CO2 (PCO2) were continuously monitored. Periodically, carotid artery blood was drawn and analyzed for partial pressure of O2 (PO2), PCO2, pH, and plasma carbonic anhydrase (CA) activity. Measurements were made during steady-state exercise (3 mph and 10% grade), during a control period, after injection of a 5 ml bolus of saline, and after injection of 5 mg/kg of bovine CA dissolved in 5 ml of saline. This dose of CA increased the reaction rate by more than 80-fold. Neither the control nor the CA injections significantly altered the ventilatory parameters. Saline and CA date differed by less than 5% in ventilation, 1 Torr in arterial PCO2, 0.01 in pH units, and 1.5 Torr in end-tidal PCO2. Thus the of CO2 hydration in plasma is not a significant factor in ventilatory control.

Carbon monoxide uptake and elimination in fetal and maternal sheep.

We studied the relation of carboxyhemoglobin concentration in the fetus, [HbCOf], to that of the pregnant mother, [HbCOm], and inspired CO concentrations in unanesthetized sheep. We exposed ewes with catheters chronically implanted in maternal and fetal blood vessels to varying inspired CO concentrations. At 30 parts per million (ppm) CO, [HbCOm] increased from base-line levels of about 1.1% to about 4.6% over a course of 8-10 h. [HbCOf] increased more slowly from base-line values of 1.8% to steady-state values of 7.4% by 36-48 h. At 50 ppm, steady-state [HbCOm] = 7.2% and [HbCOf] = 11.3%. At 100 ppm, steady-state [HbCOm] = 12.2%, [HbCOf] = 19.8%. The increase in [HbCOm] resembled a simple exponential process with a half-time of 1.5 h. The time for [HbCOf] to reach half its final value was 5 h. The decay curve for CO elimination showed similar reactions, with fetal washout occurring slower than in the mother. Elevated [HbCOf] significantly decreased the PO2 values in the fetal descending aorta and inferior vena cava. These decreases in PO2 values can cause hypoxia and fetal death.

Dynamics of maternal-fetal nutrient transfer.

Several mechanisms account for transfer of substances across the placenta, including passive diffusion, facilitated diffusion, active transport, solute drag, and pinocytosis. The rates at which these processes occur and the rates of equilibration of various substances between maternal and fetal circulation vary widely. In general, gases and some ions equilibrate rapidly while large molecules such as proteins exchange slowly. Some nutrients such as amino acids, calcium, iron, and possibly some vitamins are transported against a concentration gradient. This report compares equilibration rates for various nutrients and discusses the use of mathematical modeling to quantitate certain aspects of the processes, and to gain a better understanding of factors determining placental exchange.

Theoretical analysis of oxygen transport during hypothermia.

Oxygen transport and delivery to peripheral tissues during hypothermia are analyzed theoretically, taking into consideration various conditions observed both in nature and clinically. With decreasing temperature, P50 (the oxygen tension [PO2] at 50% hemoglobin saturation with oxygen) decreases, thereby leading to low mixed venous oxygen tension (PvO2) and thus low tissue PO2 values. On cooling from 37 degrees C to 25 degrees C at pH 7.4, the P50 decreases from a normal 26.8 mm Hg to 13.2 mm Hg. In the intact animal, as well as in a patient on cardiopulmonary bypass, oxygen consumption (Vo2) and cardiac output (QT, or recommended pump flow rate) decrease. If the ratio of Vo2/QT remains constant, then the arteriovenous O2 content difference, C(a-v)O2, must remain constant. If C(a-v)O2 is 5 ml/dl, we calculate that the PvO2 must decrease from a normal 40 mm Hg to 26.8 mm Hg at 25 degrees C. Clinically induced hypothermia is usually accompanied by hemodilution of the patient's blood to 50% normal hematocrit, which would reduce PvO2 to 13.7 mm Hg. Use of constant relative alkalinity (pH = 7.58 at 25 degrees C) further reduces the P50 to 10.8 mm Hg and the PvO2 to 10.9 mm Hg. Other clinical situations are also discussed. Sensitivity analysis predicts that during hypothermia PvO2 (and thus tissue PO2) is very dependent on P50, hemoglobin concentration, and QT, and less dependent on oxygen solubility and arterial PO2. We conclude that monitoring of mixed venous or tissue PO2 might be advisable, and that blood flow is the component of oxygen transport most amenable to manipulation by the clinician to ensure adequate tissue oxygenation during induced hypothermia.

Radiation dose reduction in pediatric CT.

The relationship between image noise and radiation dose was investigated in computed tomography (CT) images of a pediatric abdomen phantom. A protocol which provided a minimum absorbed dose consistent with acceptable image noise criteria was determined for a fourth generation CT scanner. It was found that pediatric abdominal CT scans could maintain diagnostic quality with at least a 50% reduction in dose from the manufacturers' suggested protocol.

Theoretical analysis of optimal P50.

A simple expression is derived to describe the partial pressure at 50% hemoglobin saturation with oxygen (P50) that maximizes venous oxygen tension (PO2) for a given arterial PO2 and oxygen consumption. That "optimal P50" also maximizes arteriovenous saturation differences for given arterial and venous PO2 values. The optimal P50 can be expressed as the square root of the product of arterial and venous PO2 values. Alternatively, it can be expressed as a simple function of the arterial PO2 and the arteriovenous saturation difference. Nomograms summarize the relationships between the variables, and published observations that suggest an observational basis for our theoretical analysis are reviewed. We conclude that for normoxia or moderate hypoxia a high P50 is advantageous, whereas for more severe hypoxia or increased metabolic demands, a low P50 is advantageous.

Rate of pH changes in blood plasma in vitro and in vivo.

The rate of pH decrease in dog blood after addition of CO2 (dissolved in saline) was measured in vitro with a combination pH electrode and fast-response amplifier. The pH change was found to have an apparent half time of 6.0 +/- 0.5 s at 38 degrees C, similar to that predicted by previous mathematical simulations on the basis of uncatalyzed CO2 hydration kinetics and the buffering characteristics of plasma. Measurements were also made in vivo in dogs by withdrawing blood rapidly from a carotid artery through a temperature-controlled chamber containing a pH electrode. When the flow was stopped, we measured the pH change which occurs in blood (after it leaves the lungs) as the slow dehydration of bicarbonate continues. The measured half time was 7.3 +/- 0.6 s, again agreeing well with predictions. Essentially the same half time was found when the direction of approach to chemical equilibrium was reversed by adding CO2 to the inspired air. The rate of the reactions could be increased markedly by hemolyzing the blood to release carbonic anhydrase into the plasma.

Decreased critical mixed venous oxygen tension and critical oxygen transport during induced hypothermia in pigs.

The effects of hypothermia on oxygen delivery and tolerance to hypoxia were studied in 8 normothermic (36.8 degrees C) and 10 hypothermic (29.3 degrees C) pigs that had been anesthetized and surgically implanted with instruments. Cardiac output (QT), VO2 [oxygen consumption, or QT X C(a-v)O2, where C(a-v)O2 is arteriovenous oxygen content difference], arterial and mixed venous blood gas values, and lactate concentrations were measured as the animals were made progressively hypoxic. Under control, normoxic conditions, mixed venous oxygen tension (PvO2) was 41.4 +/- 2.1 mm Hg (mean +/- SE) in the normothermic animals and 26.1 +/- 1.6 mm Hg in the hypothermic animals; these values are close to those predicted in our previous theoretical analysis. To study tolerance to hypoxia during hypothermia, critical PvO2 and critical total oxygen transport (TOT = QT X CaO2, where CaO2 is oxygen content of arterial blood) were determined by decreasing the inspired oxygen concentration (FIO2) in steps and measuring the point where VO2 and blood lactate levels became PO2 or TOT dependent. Again as predicted, the critical PVO2 was lower in the hypothermic animals (15.5 +/- 1.0 mm Hg at 29.3 degrees C compared with 22.0 +/- 1.4 mm Hg at 36.8 degrees C), but critical venous oxyhemoglobin saturation values were not statistically different at the two temperatures. Critical TOT was also decreased during hypothermia, as was the margin of reserve in both PVO2 and TOT (the difference between the normoxic and the critical values).

Impact of home infusion therapy on the Colorado Medicaid program budget.

The impact of home infusion therapies on the pharmaceutical services drug budget of the Colorado Medicaid program was evaluated retrospectively. Pharmacy billing claims and prior authorization forms for home infusion therapies submitted to the Colorado Department of Social Services during a 26-month period were reviewed to determine the costs of the drug or hydration solutions and ancillary products necessary for the preparation and administration of the solutions. A dispensing fee of +3.40 per dose was figured into calculations of total costs of home infusion therapies, and an estimated cost of +100-+150 per day for follow-up care was added. Equivalent costs of hospitalization were calculated using an average per diem charge of +315. A total of 61 patients received 1361 days of home infusion therapy during the study period. The majority of patients received home antimicrobial therapy; 752 days of hospitalization theoretically were avoided because of home administration of antimicrobial agents, which translates into a cost savings of +76,716-+114,316. Patients also received home parenteral nutrition therapy, analgesic therapy, and rehydration therapy that yielded cost savings of +48,374-+78,824 but in some cases resulted in higher costs than hospitalization would have. Home infusion therapies increased pharmaceutical services costs by +99,475, representing an important shift of costs from the hospital services budget to the pharmaceutical services budget. Home infusion therapies generally incur lower costs than would be incurred during an equivalent hospital stay. The Colorado Medicaid budget should be adjusted to compensate for the shift of costs from hospital to pharmaceutical services.