The Effect of Emergency Financial Assistance on Healthcare Use

Does providing financial assistance to people who have just experienced an income shock affect their healthcare use? To address this question, we examine healthcare outcomes in a setting where people at risk of homelessness due to an income shock were offered or denied referral to financial assistance quasi-randomly. Among callers who have been screened as eligible for assistance at Chicago's Homelessness Prevention Call Center (HPCC), some are denied assistance because the availability of funding varies. Conditional on some observable characteristics, funding availability is as-good-as-randomly assigned to callers. We link callers to healthcare utilization records and observe their inpatient hospital stays and emergency department visits. We find that referral to financial assistance has little effect on overall healthcare use-we can reject increases in total utilization greater than 7% of the base rate and decreases of more than 4%. This null effect can be explained, in part, by the fact that the income shock does not significantly change overall healthcare use among those not receiving assistance, suggesting that these individuals can insure health and healthcare demand against these shocks in other ways.

What questions do patients with curable prostate cancer want answered?

PURPOSE

To determine the questions that recently diagnosed early-stage prostate cancer patients think should be addressed with patients like themselves.

STUDY POPULATION

56 patients diagnosed as having early-stage prostate cancer within the previous year.

METHODS

Surveys distributed to the patients included 93 questions that might be considered important. Respondents judged the importance (essential/desired/no opinion/avoid) of addressing each question, and indicated why those "essential" or "desired" were important.

RESULTS

38 patients (68%) responded. Agreement on question importance, overall, was rather poor (mean 41.6%, kappa 0.17). There were, however, 20 questions that at least 67% of the respondents agreed were essential to address and 12 that they agreed were not essential. No question was relevant to the treatment decisions of more than 50% of respondents, but 91 questions were relevant to at least one respondent's decision.

CONCLUSIONS

Although there was enough agreement to define a core set of questions that should be addressed with most patients, each of the remaining questions was also considered essential to some people. The core set, therefore, would not be adequate to satisfy any one patient's essential information needs. Whereas most questions would be needed to cover all patients' decision needs, only some are needed for any given patient. Such variability in information needs means that the subjective standard is the only viable legal standard for judging the adequacy of provision of information for the treatment decision.

Retention of nociceptor responses during deep barbiturate anesthesia in frogs

Bullfrogs (Rana catesbeiana) anesthetized with a large dose of thiopental (42.8 mg/kg) retained movement responses to nociceptor stimuli despite an average plasma drug level of 51 mg/l, of which 63% was bound to plasma proteins. This concentration, when corrected to include only unbound and uncharged drug, was 2-fold greater than those reported to abolish nociceptor response (NR) during surgical anesthesia in man. The median anesthetic dose (AD50) for loss of the righting reflex was 11.2 mg/kg by s.c. injection into the abdominal lymph sac; however, at 54.0 mg/kg, all frogs retained NRs, although otherwise deeply anesthetized. The ratio of NR-blocking dose to light AD was thus > 4.8, as compared to < 2 in mammalian studies. Whole body levels of thiopental determined at 3 h after intralymphatic injection showed that about half the injected drug had been eliminated by this time and that termination of anesthesia was chiefly due to drug elimination. Even though the pharmacokinetics of thiopental appears to differ markedly in frogs and men, the poor analgesia seen in the present study frequently has been reported during clinical barbiturate anesthesia. Since this deficiency is much more pronounced in the bullfrog than in man, its neurophysiological basis might profitably be studied using the bullfrog as a model; however, the high mortality associated with deep thiopental anesthesia in the frog should preclude its use as a practical anesthetic in amphibia.

What prostate cancer patients should know: variation in professionals' opinions

PURPOSE

This study was designed to determine what questions health-care professionals think should be addressed with curable prostate cancer patients before treatment decisions are made.

METHOD

A survey was distributed to radiation oncologists, urologists, medical oncologists, nurses and radiation therapy technologists (RTTs) involved in treating prostate cancer patients. Participants were asked to judge the importance of addressing each of 78 questions (essential/important/no opinion/avoid) with a described hypothetical patient prior to the treatment decision. Eighty participants were later selected at random for a retest.

RESULTS

The overall response rate was 55% (284/518) on the initial survey and 56% (45/80) on the retest. The relative importance of the various questions was similar across groups (r(76) ranged from 0.75 to 0.91, all P<0.001). Despite the between-group similarity, opinions within each group varied widely. For example, among oncologists, the number of questions deemed essential by individual respondents ranged from five to 69, with >90% respondent agreement on only 15 of the 78 questions. The extent of agreement was similar in the other groups. The retest showed that essential and important responses were reasonably stable, i.e. 92% of questions judged essential at one time were judged either essential (58%) or important (34%) at the other time.

CONCLUSIONS

Although the relative importance of addressing the various questions appears similar across the professional groups involved in the care of prostate patients, within each profession there seems to be little agreement. The lack of agreement includes both how many questions are essential to address and whether or not most individual questions are essential.

Contrasting effects of anesthetics in tadpole bioassays

The median anesthetic concentrations (AC 50 values) in the bath solution for loss of righting reflex (RR) or nociceptor response (NR) were determined in larval Rana catesbeiana. The AC50 (NR)/AC50(RR) ratios were between 1.6 and 1.9 for ethanol, ether and diazepam. Comparable ratios for hexobarbital and thiopental were 9.8 and 6.2, which indicated a marked lack of "analgesic" effect. The tadpole AC50 values were consistently higher than AC50 values reported for nonionized and unbound drug in mammalian blood water. The tadpole/mammal ratio for loss of NR during thiopental anesthesia was approximate 8, and analysis of ventricular blood showed that the ultrahigh bath concentrations of thiopental were in equilibrium with those in tadpole serum. The tadpole/mammal ratio for diazepam was approximate 110, and its effect in the tadpole was not reversed by flumazenil. Tadpole/mammal ratios for ethanol and ether were approximate 2. Ethanol and ether showed additive effects when tested in combination, and ethanol-tolerant tadpoles showed a similar tolerance to ether. In contrast, hexobarbital and ethanol showed supra-additive effects, and ethanol-tolerant tadpoles showed a greater tolerance to hexobarbital than to ethanol or ether. These studies show marked differences in effect between barbiturates and the ethanol-ether group, high-concentration benzodiazepine effects presumably independent of a specific receptor, and marked differences in drug potency between amphibia and mammals.

CHEB, a convulsant barbiturate, evokes calcium-dependent spontaneous glutamate release from rat cerebrocortical synaptosomes

CHEB [5-(2-cyclohexylidene-ethyl)-5-ethyl barbituric acid] is a potent convulsant barbiturate that causes direct neuronal excitation by an unknown mechanism. We have analyzed the effects of CHEB on the release of endogenous glutamate from rat cerebrocortical synaptosomes using an on-line enzyme-coupled fluorimetric assay. CHEB evoked spontaneous Ca(2+)-dependent glutamate release with an EC50 = 14.2 microM and an Emax = 3.2 mumol/min/mg. The non-convulsant barbiturates pentobarbital and phenobarbital evoked significantly less glutamate release at high concentrations. CHEB (30 microM) increased intrasynaptosomal [Ca2+] by 58 +/- 4 nM (p < 0.01; n = 4) above baseline compared to an increase of 5 +/- 4 nM (NS; n = 4) produced by pentobarbital (30 microM). CHEB-evoked glutamate release was inhibited by pentobarbital, phenobarbital, EGTA, CoCl2/CdCl2 and flunarizine, but not by local anesthetics, tetrodotoxin, nitrendipine or omega-conotoxin GVIA. These results demonstrate that CHEB acts as a potent and effective secretogogue for glutamate by a pre-synaptic mechanism that does not require activation of Na+ channels or of L-type or N-type Ca2+ channels. Stimulation of spontaneous glutamate release may contribute to the convulsant properties of CHEB.

Forebrain ischemia increases GLUT1 protein in brain microvessels and parenchyma

Glucose transport into nonneuronal brain cells uses differently glycosylated forms of the glucose transport protein, GLUT1. Microvascular GLUT1 is readily seen on immunocytochemistry, although its parenchymal localization has been difficult. Following ischemia, GLUT1 mRNA increases, but whether GLUT1 protein also changes is uncertain. Therefore, we examined the immunocytochemical distribution of GLUT1 in normal rat brain and after transient global forebrain ischemia. A novel immunocytochemical finding was peptide-inhibitable GLUT1 immunoreactive staining in parenchyma as well as in cerebral microvessels. In nonischemic rats, parenchymal GLUT1 staining co-localizes with glial fibrillary acidic protein (GFAP) in perivascular foot processes of astrocytes. By 24 h after ischemia, both microvascular and nonmicrovascular GLUT1 immunoreactivity increased widely, persisting at 4 days postischemia. Vascularity within sections of brain similarly increased after ischemia. Increased parenchymal GLUT1 expression was paralleled by staining for GFAP, suggesting that nonvascular GLUT1 overexpression may occur in reactive astrocytes. A final observation was a rapid expression of inducible heat shock protein (HSP)70 in hippocampus and cortex by 24 h after ischemia. We conclude that GLUT1 is normally immunocytochemically detectable in cerebral microvessels and parenchyma and that parenchymal expression occurs in some astroglia. After global cerebral ischemia, GLUT1 overexpression occurs rapidly and widely in microvessels and parenchyma; its overexpression may be related to an immediate early-gene form of response to cellular stress.

Muscle weakness during tricaine anesthesia

An isolated preparation of tadpole tail muscle was used to assess the peripheral effects of tricaine (3-aminobenzoic acid ethyl ester) at anesthetic concentrations and under physiological conditions. The drug effect on the electrically-evoked twitch was tested using short-pulse durations that elicited synaptically mediated effects or longer-duration pulses that stimulated the muscle directly. Tricaine reduced both types of response anesthetic and even subanesthetic concentrations. At steady state concentrations that produced surgical anesthesia in vivo, tricaine reduced the directly evoked response by about half. It is concluded that tricaine anesthesia has a pronounced peripheral effect on neuromuscular function and that direct effect(s) on muscle are a major component.

Progressive hippocampal loss of immunoreactive GLUT3, the neuron-specific glucose transporter, after global forebrain ischemia in the rat

Brain damage after global forebrain ischemia is worsened by prior hyperglycemia and ameliorated by antecedent hypoglycemia. To assess whether GLUT3, the neuron specific glucose transporter and its mRNA, are affected by cerebral ischemia, we investigated the hippocampal pattern of GLUT3 immunoreactivity and GLUT3 gene expression 1, 4 and 7 days after global forebrain ischemia in a rat 2-vessel occlusion model. We used a newly generated, specific, C-terminally directed polyclonal antiserum against GLUT3 to stain coronal frozen sections. Thionin staining and the microglial marker, OX42, indicated the extent of ischemic damage in hippocampus and correlated with GLUT3 loss. One day after ischemia, no significant change in hippocampal GLUT3 immunoreactivity was observed; by 4 days however, there was consistent and pronounced loss; and at 7 days the loss of GLUT3 staining was maximal. The greatest loss of GLUT3 staining was in the CA1 region, especially the strata oriens and radiatum of Ammon's horn. By contrast, GLUT3 staining was undiminished in the stratum lacunosum moleculare, in the mossy fibers of the lateral aspect of CA3 and in all but the inner-most portion of the molecular layer of the dentate gyrus, immediately adjacent to the granule cells. GLUT3 mRNA levels were not significantly altered at 24 hours and significantly declined at 4 and 7 days after ischemia in the CA1 pyramidal layer. These data are consistent with the pattern of neuronal loss and microglial activation in hippocampus. Loss of GLUT3 may affect the availability of glucose, and possibly the viability of ischemically damaged neurons.

Binding of thiopental in neonatal serum

Protein binding of thiopental was studied in 21 samples of neonatal serum (from placental blood) and compared with protein binding in ten healthy volunteers. These infants ranged between 32 and 43 weeks of gestational age (mean, 37.7 weeks) and the adult age range was from 27 to 54 years (mean, 35.4 years). Because the unbound fraction of the drug is responsible for its pharmacologic effect, a marked difference in the protein binding between neonates and adults may be relevant to the clinician. Blood obtained from freshly delivered placentas or from adult volunteers was allowed to clot and the serum separated from the sample. A portion of the serum was sent for protein and bilirubin analysis and the remainder retained for study. This latter serum was combined with four concentrations of thiopental. These specimens were then ultrafiltered and the amount of thiopental in the ultrafiltrate (unbound) compared with the prefiltered amount (total), as measured by reverse-phase high-performance liquid chromatography. The binding studies were repeated at pH 7.2, 7.4, and 7.6 in both the adult and neonatal serum. Total protein and albumin are significantly less in neonatal serum, whereas bilirubin (total and direct) is significantly higher in neonatal serum than in adult serum (P less than 0.01). Neonatal serum was associated with significantly more unbound thiopental than adult serum at all levels of pH studied (P less than 0.005). Increasing the pH resulted in less free drug in both groups, but this reached statistical significance only in the adult group (P less than 0.025). Drug concentration had no effect on binding in the range examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of in vitro drug responses in airways of atopic dogs with and without in vivo airway hyperresponsiveness

For comparison with previous studies in greyhounds and in the Basenji-Greyhound dog model of asthma (BG), basenji dogs were studied under identical conditions with respect to airway responsiveness to inhaled methacholine, cutaneous responses to intradermal antigen injection, and the sensitivity of isolated trachealis muscle to methacholine and isoproterenol. The relaxant effect of isoproterenol was assessed in trachealis muscle precontracted with methacholine (ED50). The basenji dogs resembled the BG dogs in that they showed multiple positive skin tests. Further, trachealis muscle showed a markedly reduced sensitivity to methacholine (pD2 6.64 +/- 0.10) (+/- S.E.) in vitro. However, basenji dogs resembled the greyhounds in requiring high concentrations of methacholine aerosols to produce a 2-fold increase in pulmonary resistance (1.68 mg/ml +/- 1.21). Thus, there were no significant correlations between sensitivity to methacholine in vitro and airway responsiveness to methacholine in vivo; however, the reduced sensitivity to methacholine in vitro in both basenji and BG dogs may be related to the marked atopy characteristic of both groups. In vitro sensitivity to isoproterenol was correlated (r = 0.82) with the concentration of methacholine needed to elicit the test contraction, but isoproterenol sensitivity in BG dogs was significantly less (p = .0027) than that predicted by the common regression line. This deficit in beta adrenergic function in trachealis muscle unrelated to atopy may be important in the in vivo airway hyperresponsiveness of BG dogs.

Cyclic nucleotide function in trachealis muscle of dogs with and without airway hyperresponsiveness

We examined basal adenosine 3',5'-cyclic monophosphate (cAMP) levels, isoproterenol (ISO)-stimulated cAMP responses, basal cAMP, and guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterase (PDE) activities and protein-kinase (PK) activities in trachealis muscle from five Basenji-greyhound (BG) and four greyhound dogs to determine whether the inverse relationship between in vivo and in vitro airway responsiveness could be due to altered cyclic nucleotide metabolism. Basal cAMP levels were not significantly different (PNS) in muscle from BG (11.6 +/- 0.53 pmol/mg protein) and greyhound dogs (10.30 +/- 1.60 pmol/mg protein). The cAMP responses to stimulation with ISO were enhanced in BG compared with greyhound dogs. The low Michaelis constant (1) for Km-cAMP PDE activity (Km = 0.63 microM) was significantly less (P less than 0.005) in BG dogs (1.54 +/- 0.28 pmol.min-1.mg protein-1) than greyhounds (11.76 +/- 2.48). Endogenously active PK activity was significantly greater (P less than 0.005) in BG (54.74 +/- 5.39 pmol.min-1.mg protein-1) than in greyhound dogs (15.50 +/0 2.20). Increases in PK activity with 5 microM cAMP added were not significantly different between BG (14.79 +/- 6.00) and greyhound dogs (7.04 +/- 2.14). Approximately 90% of both endogenous PK activity and cAMP-activated PK activity in BG and greyhound dogs was inhibited by a cAMP-dependent PK inhibitor (PKI'). These data suggest that decreased cyclic nucleotide degradation due to decreased cyclic nucleotide PDE activity with increased PK could account for the in vitro hyporesponsiveness of airway smooth muscle in BG dogs as a protective adaptive mechanism.

Large-volume ventilation results in bronchoconstriction of Basenji-Greyhound dogs

We compared the effects of large-volume ventilation on airway responses to aerosolized histamine in anesthetized mongrel dogs with its effects in Basenji-Greyhound crossbred (B-G) dogs. Before bronchoconstriction, large inflations resulted in only small changes of dynamic compliance (Cdyn) and pulmonary resistance (RL) in both groups of dogs. After the induction of a moderate degree of bronchoconstriction with aerosolized histamine, large inflations had a more substantial effect; Cdyn increased by 7.5 +/- 2.3% (mean +/- SE; P less than 0.05), and RL decreased by 32 +/- 3.4% (P less than 0.001) in the mongrel dogs. In the B-G group, Cdyn increased by only 0.2 +/- 1.8% (NS), and RL increased by 29.3 +/- 9.2% (P less than 0.05); these changes differed significantly (P less than 0.05) from those observed in the mongrel dogs. Large-volume ventilation following the administration of indomethacin (10 mg/kg iv) and histamine increased Cdyn by 11.4 +/- 1.8% (NS vs. without indomethacin) and decreased RL by 43.9 +/- 3.4% (P less than 0.05) in the mongrel group. In the B-G group large-volume ventilation increased Cdyn by 7.6 +/- 1.7% (P less than 0.01) and decreased RL by 15.7 +/- 8.1% (P less than 0.05). Thus indomethacin enhanced the bronchodilator effects of large-volume ventilation in mongrel dogs and reversed the bronchoconstrictor effect of this maneuver on RL in B-G dogs.

Inhibition of d-tubocurarine-induced histamine release by halothane

To determine whether anesthetics modify mediator release, the authors measured the amount of histamine released by d-tubocurarine (dTC) in human foreskin preparations in the presence of high (2.0%) and low (0.5%) halothane concentrations and nitrous oxide (10%). Freshly excised human foreskins were divided into four matched pieces. Two matched pieces were aerated with oxygen, and the other two with an oxygen-anesthetic gas mixture. One chamber of each served as a control, while the other was stimulated with 3 X 10(-5) M d-tubocurarine for 30 min. Supernatant histamine concentrations were measured by automated fluorometry. Percent histamine release was determined by dividing the experimentally released histamine concentration by the total histamine released after the tissue was sonicated and boiled. Neither halothane nor N2O alone altered spontaneous histamine release. Histamine release by d-tubocurarine was significantly reduced by 2% halothane compared to d-tubocurarine alone (2.8% +/- 0.9 vs. 13.9% +/- 3.7, mean + SEM) (P less than 0.05) in the in vitro preparation. Histamine release was reduced in the preparations pretreated with 0.5% halothane group, but this was not statistically significant (P greater than 0.05) when compared to d-tubocurarine alone. N2O (10%) did not reduce d-tubocurarine-induced histamine release. The authors conclude that halothane, in clinically used concentrations, significantly impairs histamine release from human neonatal foreskin preparations.

Comparison of drug responses in vivo and in vitro in airways of dogs with and without airway hyperresponsiveness

Basenji-greyhound (BG) dogs demonstrate marked nonspecific airway hyperresponsiveness. To assess the possible contribution of an abnormal sensitivity of airway smooth muscle to this phenomenon, we studied the in vitro contractile responses to methacholine and histamine and the relaxant response to isoproterenol in trachealis muscle from five BG dogs with airway hyperresponsiveness in vivo and from five greyhound dogs that served as a control population. Isoproterenol responses were determined against a half-maximal methacholine contraction. Aerosol methacholine concentrations required to produce a 2-fold increase in pulmonary resistance were 0.07 +/- 0.02 (+/- S.E.) mg/ml in BG dogs and 0.67 +/- 0.26 mg/ml in greyhounds; pD2 values for methacholine-induced contraction of cervical trachealis muscle were 7.03 +/- 0.11 in BG dogs and 7.50 +/- 0.11 in greyhounds. A significant (P less than .01) negative correlation was found between methacholine sensitivity in vivo and in vitro. Aerosol concentrations of histamine required to produce a 2-fold increase in pulmonary resistance were 0.19 +/- 0.06 mg/ml in BG dogs and 1.44 +/- 0.43 mg/ml in greyhounds; pD2 values for histamine were identical in BG dogs (4.95 +/- 0.08) and greyhounds (5.05 +/- 0.19). Isoproterenol pD2 values were less in the trachealis muscle (cervical) of BG dogs (6.76 +/- 0.10) than in that of greyhounds (7.93 +/- 0.16), but this is probably a consequence of the higher concentration of methacholine needed to contract BG muscles. We conclude that the airway hyperresponsiveness of BG dogs does not reflect an increased sensitivity of airway smooth muscle per se.

Airway responses to methacholine and histamine in basenji greyhounds and other purebred dogs

To investigate whether airway hyperresponsiveness is a general characteristic of either the basenji or the greyhound ancestry of the basenji-greyhound (BG) dog and to determine whether airway hyperresponsiveness of the BG dogs in specific for methacholine, we compared pulmonary responsiveness to increasing doses of aerosols of histamine and methacholine in 17 BG dogs, 5 unrelated purebred basenjis and 5 unrelated greyhounds. BG dogs were hyperresponsive to both methacholine and histamine compared to basenjis and greyhounds. There was a significant correlation between histamine compared to basenjis and greyhounds. There was a significant correlation between histamine and methacholine responsiveness (r = 0.70, P less than 0.0001) in the dog population. We conclude that airway hyperresponsiveness characteristic of the BG dog is not a general characteristic of the basenji or greyhound breed and occurs to histamine as well as to methacholine.

Mechanisms of intrinsic tone in bullfrog lung: relaxant effects of indomethacin, ouabain and potassium

Bullfrog hemilungs showed minimal relaxation (9 +/- 2% of the maximal relaxant effect of theophylline, Imax) after a 16 h incubation in 10(-5) M indomethacin, indicating that prostaglandin synthesis plays little or no role in the high intrinsic tone characteristic of this preparation. A higher concentration of indomethacin (10(-4) M) produced greater relaxation (23 +/- 3% of Imax), but also markedly potentiated isoprenaline-induced relaxation. The interaction with isoprenaline was similar to that previously found for papaverine, a phosphodiesterase inhibitor. Ouabain (10(-5) and 10(-4) M) produced an initial contraction followed by marked relaxation (50% of Imax), indicating that a ouabain-sensitive mechanism is of major importance in the maintenance of intrinsic tone. Ouabain-treated hemilungs showed reversal (relaxation) of the normal contractile response to 26 mM potassium and marked impairment of the contractile response to calcium in calcium-depleted preparations. These effects suggest that ouabain-induced relaxation reflects a drug action on calcium movements. The marked relaxation (30 to 40% of Imax) produced by 26 mM potassium in ouabain-treated hemilungs is of particular interest in that it indicates a mechanism of potassium-induced relaxation distinct from stimulation of sodium-potassium ATPase.

Calcium chelators increase airway responsiveness

To test the effect of calcium chelation on airway responsiveness to methacholine, purebred Basenji dogs were pretreated with a calcium-chelating aerosol (edetate disodium, Na2EDTA) or a placebo aerosol (saline or CaNa2-EDTA) and then challenged with methacholine bromide aerosols. The lowest dose of methacholine (0.15 mg/ml) produced no change in pulmonary resistance (RL) following pretreatment with the placebo aerosols, but RL increased (P less than 0.05) by 5.1 +/- 1.2 (SE) cmH2O X l-1 X s following pretreatment with Na2EDTA. The highest dose of methacholine (1.5 mg/ml) increased RL in all animals, but the increase was greater (P less than 0.01) following pretreatment with Na2EDTA (9.5 +/- 1.9 cm H2O X l-1 X s) than following pretreatment with a placebo aerosol (6.4 +/- 1.5 cmH2O X l-1 X s). These studies show that calcium-chelating aerosols significantly increase airway responsiveness and suggest that a localized calcium deficit may contribute to hyperresponsive airway disease.

Antigen sensitization and methacholine responses in dogs with hyperreactive airways

Antigen sensitization was induced in six Basenji-Greyhound (BG) dogs by weekly aerosol exposure to Ascaris suum. The effects on airway responsiveness to inhaled methacholine were studied before and at least 2 wk following Ascaris sensitization. All dogs developed detectable serum levels of Ascaris-specific immunoglobulin E (IgE), and five out of six dogs developed airway responsiveness to antigen over the 4- to 6-mo period. This was accompanied by a decrease rather than an increase in airway responsiveness to inhaled methacholine. When dogs were challenged with methacholine 30 min after Ascaris antigen aerosol challenge, however, dogs reactive to Ascaris became hyperresponsive to methacholine. The magnitude of the response to antigen correlated (r = 0.85) inversely with the dose of methacholine increasing pulmonary resistance 200%. These data show that in BG dogs airway responsiveness to methacholine is increased by acute antigen exposure but that sensitization of previously unsensitized dogs does not increase nonspecific airway responsiveness.

Airway responses in offspring of dogs with and without airway hyperreactivity

We examined airway responsiveness to aerosols of Ascaris suum, citric acid, and methacholine chloride in the offspring of two highly allergic breeds of dogs: Basenji-greyhounds (BG) and Basenjis (B). The BG parents had airway hyperresponsiveness to citric acid and methacholine, whereas the B parents did not. Both BG and B offspring were allergic as measured by many positive skin tests. BG offspring, like their parents, were hyperresponsive to citric acid and methacholine, whereas B offspring were not. We conclude that familial rather than environmental factors are important for the development of nonspecific airway hyperresponsiveness as well as allergy in the BG dog model of asthma. Allergic asthma in these animals represents a combination of two discrete processes: allergy and nonspecific airway hyperresponsiveness.

Effect of stimulation of non-adrenergic inhibitory nerves on cyclic nucleotide levels in bullfrog lung

Carbachol in the presence of atropine and propranolol was employed to stimulate a non-adrenergic neural inhibitory system in the hemilung of the bullfrog (Rana catesbeiana). Tissue levels of cGMP were elevated 95% by carbachol whilst cAMP levels were unchanged. The phosphodiesterase inhibitor papaverine did not affect either cAMP or cGMP levels, but did selectively increase the carbachol-induced increase in lung cGMP to 220% of control levels. Papaverine did not potentiate the relaxant effects of carbachol. The results suggest that cyclic nucleotides may not be directly involved in the relaxation produced by stimulation of the non-adrenergic neural inhibitory system in this preparation.

Importance of calcium in citric acid-induced airway constriction

In previous studies, a 5-min inhalational challenge with 10% citric acid aerosol (0.52 M) elicited bronchoconstriction in Basenji-Greyhound (BG) dogs with hyperreactive airways but not in mongrel dogs. This response was independent of vagal reflexes because it was not attenuated by atropine. Citric acid might elicit bronchoconstriction because of acidity, calcium chelation, or some other effect of the citrate molecule. To assess these factors, barbiturate-anesthetized BG dogs were challenged (5 min) with aerosols of 10% acetic acid or a citric acid (0.48 M)/Na3citrate (0.04 M) mixture of equivalent pH, 6% Na2-ethylenediaminetetraacetic acid (EDTA), or 6% CaNa2EDTA. Each challenge was delivered in a separate week. The acidity alone was not an adequate stimulus, since pulmonary resistance (RL) was unaltered by 10% acetic acid, although markedly increased by the citric acid-Na3citrate mixture [2.2 +/- 0.4 (SE) cmH2O X l-1 X s prechallenge, 10.0 +/- 2.2 postchallenge]. Aerosols of Na2EDTA provoked a similar increase in RL (2.1 +/- 0.4 cmH2O X l-1 X s prechallenge, 9.0 +/- 1.8 postchallenge). Neither effect was attenuated by intravenous atropine (0.2 mg/kg). CaNa2EDTA caused no changes in RL. We conclude that it is the calcium chelating action of citric acid rather than its acidity that is responsible for bronchoconstriction in BG dogs with hyperreactive airways.

Pulmonary uptake of mannitol as an index of changes in lung epithelial permeability

To develop a simple, inexpensive, and nontoxic test for changes in bronchial permeability we have employed a specific gas chromatographic assay to measure the uptake of mannitol from the lung after administration of an intratracheal aqueous bolus (8 ml of 5% solution). We have tested the ability of our method to detect the known increase in lung epithelial permeability elicited by challenge of previously sensitized animals with aerosols of Ascaris suum antigen. In Ascaris-sensitive Basenji-Greyhound dogs, antigen challenge significantly increased the rate of appearance and peak plasma level of mannitol after administration of the intratracheal bolus. Peak plasma mannitol levels averaged 25 +/- 3 (SE) micrograms/ml in dogs challenged with Ascaris antigen aerosols, and 14 +/- 2 micrograms/ml in the same animals in separate control experiments employing saline aerosols. The method presented could be readily applied to animal and human studies as a simple, inexpensive, and nontoxic indicator of lung epithelial permeability.

Citric acid airway constriction in dogs with hyperreactive airways

To understand the mechanisms underlying the bronchoconstrictor response to 10% citric acid administered for 5 min in Basenji-Greyhound (BG) dogs, we evaluated the protection afforded by atropine (0.2 and 0.4 mg/kg iv) and by aerosols of isoproterenol (1 mg/ml) and cromolyn sodium (20 mg/ml). In untreated dogs, citric acid increased pulmonary resistance by 4.6- to 11.5-fold and decreased dynamic compliance (Cdyn) to 45-55% of the control response. Isoproterenol and cromolyn sodium significantly reduced the response, whereas atropine did not. Moreover we have demonstrated in the arterial plasma of these dogs a slow-reacting substance (SRS) after, but not before, citric acid challenge. This SRS exhibits both pharmacologic properties and chemical characteristics similar to leukotrienes. We conclude that mediators of immediate-type hypersensitivity rather than reflex mechanisms play a dominant role in the production of airway constriction during citric acid (5-min) challenge in BG dogs.

Role of mediators in allergic and nonallergic asthma in dogs with hyperreactive airways

Basenji-Greyhound crossbreed dogs, with nonspecific airway hyperreactivity, release histamine into the plasma after aerosol challenge with Ascaris antigen and a slow reacting substance (SRS) after aerosol challenge with citric acid or Ascaris antigen. The appearance of SRS in the plasma after citric acid aerosol challenge, without an increase in histamine, closely parallels the changes in pulmonary mechanics. The pulmonary response to citric acid, in contrast to Ascaris antigen, is totally prevented in vivo by FPL 55712, an SRS antagonist. SRS exhibits both pharmacologic properties and chemical characteristics similar to leukotrienes. These studies suggest that SRS may be an important mediator in nonallergic airway constriction in vivo.

Comparison of local anesthetics as bronchodilator aerosols

Lidocaine aerosols have been ineffective at preventing airway constriction provoked by non-reflex stimuli. To determine if there were any advantages to using more potent amide-type local anesthetics or local anesthetics from other chemical classes, the authors compared the protection afforded by pretreatment with aerosols of lidocaine, bupivacaine, hexylcaine, and procaine against a subsequent prolonged challenge (5 min) with 10% citric acid aerosols in barbiturate-anesthetized Basenji-Greyhound dogs. The local anesthetics were administered as aerosols (4% solutions) for 10 min immediately preceding the citric acid challenge. In control experiments, that employed pretreatment with aerosols of isotonic saline rather than local anesthetics, the citric acid challenge aerosol increased pulmonary resistance by an average of 3.3 +/- 0.8 (+/- SE) cmH2O X 1(-1) X s during the first 15-min postchallenge, and reduced dynamic compliance by one-third during this time. None of the local anesthetics prevented citric-acid-induced changes in pulmonary mechanics. The average increases in pulmonary resistance (0-15 min postchallenge) elicited by citric acid aerosols in dogs pretreated with lidocaine, hexylcaine, bupivacaine, and procaine were 2.1 +/- 0.6, 2.1 +/- 0.6, 3.2 +/- 1.3, and 3.3 +/- 1.0 cmH2O X 1(-1) X s, respectively. The authors concluded that local anesthetic aerosols have little or no effect against other than reflex bronchoconstriction, and none of those tested were more effective than lidocaine.

Distinctive pharmacological profile of a nonadrenergic inhibitory system in bullfrog lung

1 Bullfrog hemilungs, pretreated with atropine, are markedly relaxed on addition of carbachol. Since the relaxant effect is inhibited by tetrodotoxin or hexamethonium, it is neurally mediated and involves stimulation of nicotinic receptors with release of an unknown inhibitory transmitter.2 Carbachol-induced relaxation is nonadrenergic since: (a) it considerably exceeds the maximal effects of isoprenaline or the effect of 10(-3)M adrenaline or noradrenaline; (b) it elicits marked further relaxation in preparations already relaxed by high concentrations of catecholamines; (c) it is not attenuated by low concentrations of propranolol (10(-6) and 3 x 10(-6)M) that competitively antagonize isoprenaline-induced relaxation.3 Carbachol-induced relaxation has multiple distinguishing characteristics, which serve as a fingerprint for the unknown inhibitory transmitter. These include an exceptionally rapid onset of action, a ceiling effect at 50% of maximal relaxation, and minimal retardation by concentrations of procaine that block or markedly retard relaxant responses to all other agonists.4 This distinctive pharmacological profile cannot be reproduced by addition of exogenous catecholamines, 5-hydroxytryptamine, adenosine triphosphate (ATP) or adenosine, or by addition of ATP or adenosine following pretreatment with indomethacin. Furthermore, addition of carbachol to preparations previously relaxed with 10(-3)M concentrations of these agents produced marked, additional relaxation.5 Maximally effective concentrations of vasoactive intestinal peptide produced a barely detectable relaxant response equivalent to 8% of maximal relaxation. The response was totally prevented by pretreatment with procaine.6 Carbachol-induced relaxation was not impaired by pretreatment with 10(-4)M indomethacin.7 Carbachol-induced relaxation of bullfrog lung therefore involves a postganglionic inhibitory transmitter that in nonadrenergic, non-5-hydroxytryptaminergic, and nonpurinergic, and whose effects are not dependent on prostaglandin synthesis. Although a peptide may function as the inhibitory transmitter, it is not vasoactive intestinal peptide.

Bronchodilator mechanisms in bullfrog lung: differences in response to isoproterenol, theophylline and papaverine

The effects of bronchodilators and smooth muscle relaxants on mechanical responses and lung cyclic nucleotide levels in the isolated hemilung of Rana catesbeiana demonstrate striking differences in intensity and time course of drug action in an unstimulated preparation of airway smooth muscle. Isoproterenol, nitroprusside and nitroglycerin elicit a fast onset relaxation (minutes) with ceiling effects at 20, 22 and 43%, respectively, of maximal relaxation. Theophylline, dibutyryl cyclic AMP and papaverine produce maximal or near maximal relaxation, but require 8 to 32 hr for peak effect. Papaverine-induced relaxation is accompanied by a slow increase in lung cyclic AMP and cyclic GMP and is markedly accelerated by isoproterenol. Theophylline (10(-3) M) produces no change in cyclic nucleotide levels and its relaxant effect is not accelerated by isoproterenol. The hierarchy of relaxant responses suggests drug action at discrete loci in a highly compartmentalized effector chain, with cyclic AMP-dependent mechanisms separable into at least two components. The first is activated by isoproterenol and elicits a rapid, limited response, presumably reflecting an increase in cyclic AMP in a relatively restricted pool. The second is activated by papaverine and elicits a very slow, but complete relaxation, presumably reflecting a more pervasive or diffuse accumulation of cyclic AMP secondary to phosphodiesterase inhibition. The major portion of theophylline-induced relaxation in this preparation appears to be independent of changes in cyclic nucleotide metabolism.

A potent, structurally specific stimulant action of procaine in bullfrog lung

1. Local anesthetics with a procaine-like structure are exceptionally potent smooth muscle stimulation in Rana catesbeiana. 2. Procaine completely reverses the relaxant effect of 1 mM theophylline, an action that cannot be duplicated with carbachol, histamine or 5-hydroxytryptamine. 3. Stimulant activity is related to the procaine-like structure rather than local anesthetic potency, and is independent of pH between 7.0 and 8.4. 4. The high potency and structural specificity of this effect suggests an action at a specific receptor site rather than a diffuse action on membrane structure.

Basenji-greyhound dog model of asthma: pulmonary responses after beta-adrenergic blockade

To understand the mechanism underlying bronchial hyperreactivity in the Basenji-Greyhound (BG) dog, the effects of propranolol (2 mg/kg) and hexamethonium (5 mg/kg) on base-line pulmonary mechanics and on the bronchial response to aerosol challenges of citric acid and methacholine were studied in five BG dogs. Both propranolol and hexamethonium increased base-line pulmonary resistance (RL) from 0.69 +/- 0.05 (means +/- SE) cmH2O.l-1.s to 1.67 +/- 0.10 (P less than 0.05) and 2.22 +/- 0.45 cmH2O.1-1.s (P less than 0.05) and decreased dynamic compliance (Cdyn) from 190 +/- 10 ml/cmH2O to 154 +/- 9 (P less than 0.05) and 140 +/- 9 (P less than 0.05) ml/cmH2O, respectively. Both propranolol and hexamethonium potentiated the pulmonary response to 10% citric acid given for 5 min (P less than 0.05). RL postchallenge was 4.4 +/- 0.23, 8.1 +/- 0.81, and 7.8 +/- 0.31 cmH2O.l-1.s, and Cdyn was 78 +/- 5, 58 +/- 6, and 51 +/- 3 ml/cmH2O in untreated, propranolol-pretreated, and hexamethonium-pretreated animals. In untreated BG dogs, methacholine (0.075 mg/ml) increased RL from 0.94 +/- 0.25 to 2.2 +/- 0.21 cmH2O.l-1.s (234%) and decreased Cdyn from 223 +/- 39 to 141 +/- 14 ml/cmH2O (63%). In the same animals pretreated with propranolol, methacholine (0.075 mg/ml) increased RL from 1.9 +/- 0.66 to 4.8 +/- 1.37 cmH2O.l-1.s (253%) and decreased Cdyn from 144 +/- 35 to 81 +/- 15 ml/cmH2O (56%). We conclude that propranolol produces airway constriction in BG dogs, as in asthmatic humans and that the effects of propranolol on airways in BG dogs are not due to parasympathetic or alpha-adrenergic predominance.

Mechanism of tracheal constriction by succinylcholine

The purpose of this study was to identify the mechanism by which succinylcholine produced large increases in endotracheal tube cuff pressure in barbiturate-anesthetized dogs (n = 7). Cuff pressure was measured in vivo by a transducer connected to a fluidfilled, high-volume, low-pressure cuff. Intravenous succinylcholine, 0.5 and 1 mg/kg, produced mean increases in cuff pressure of 12 +/- 2 (+/-SE) and 27 +/- 5 cm H2O, respectively, which reached peak effect in 1 to 3 min and declined slowly over the next 10 min. Bilateral vagotomy, intravenous administration of atropine (0.2 mg/kg) and hexamethonium (5 mg/kg) prevented or terminated succinylcholine-induced increases in cuff pressure. Isolated preparations from an additional three dogs were employed to study the direct actions of succinylcholine on trachealis muscle in vitro. In organ baths, succinylcholine (10(-6) to 10(-3) M) did not contract canine trachealis muscle, and concentrations of 10(-5) M and above significantly relaxed carbamylcholine-induced contractions. The authors conclude that succinylcholine elicits contraction of trachealis muscle by a stimulant action on parasympathetic pathways rather than by a direct action on airway smooth muscle. Since vagotomy prevented the succinylcholine response, the site of stimulant action is not at autonomic ganglia.

Basenji-Greyhound dog model of asthma: influence of atropine on antigen-induced bronchoconstriction

To test the relative importance of cholinergic effects on the Basenji-Greyhound (BG) model of asthma, we administered Ascaris antigen to Ascaris-sensitive BG dogs without other treatment, and following intravenous atropine. Pulmonary resistance (RL) increased from 1.4 +/- 0.43 cmH2O . l-1 . s (mean + SE) to 26.0 +/- 5.21 after Ascaris antigen exposure in seven untreated dogs. In the same dogs pretreated with 0.2 mg/kg atropine, RL increased from 1.5 +/- 0.31 to 18 +/- 5.00. Atropine 0.4 and 1.0 mg/kg did not result in increased protection. Although 0.2 mg/kg atropine markedly inhibited the airway responses to both inhaled citric acid and methacholine, it only slightly prevented antigen-induced airway constriction. We conclude that in BG dogs, cholinergic pathways elicit bronchomotor responses to irritants but that the major component of antigen-induced bronchoconstriction is not cholinergically mediated.

Dyphylline aerosol attenuates antigen-induced bronchoconstriction in experimental canine asthma

This study compared the bronchodilator effect in experimental canine asthma of dyphylline administered by aerosol and intravenous routes in doses producing equivalent concentrations of the drug in the plasma. Pulmonary resistance (RL) was calculated from simultaneous measurements of pressure and flow during fixed-volume controlled ventilation at the same peak flow and corrected for elastic recoil pressure. Dynamic compliance (Cdyn) was calculated by dividing tidal volume by the change in pressure measured between points of zero flow. Concentrations of dyphylline in the plasma were measured using high-performance liquid chromatographic techniques. Rates of infusion of dyphylline were determined from values for clearance observed in preliminary experiments with intravenous injection. Prior to exposure to antigen, RL and Cdyn were not significantly different in control and dyphylline-treated dogs. Following challenge, with antigen RL increased by 8.3 +/- 2.6 times (mean +/- SE) in untreated dogs but only by 2.4 +/- 0.4 times in dyphylline treated dogs. Levels of dyphylline in the plasma averaged 4.2 micrograms/ml +/- 0.6 micrograms/ml at the end of the ten-minute period of aerosol administration and remained at that level for 60 minutes. At equivalent plasma levels (4.3 micrograms/ml +/- 0.3 micrograms/ml), infusion of dyphylline did not significantly after the response to Ascaris antigen, whereas dyphylline administered by the aerosol route markedly attenuated the response.

Lidocaine aerosols do not prevent allergic bronchoconstriction

To test the effectiveness of local anesthetic aerosols in asthma, we compared the protection afforded by lidocaine and saline aerosols to bronchoconstriction provoked by inhalation of Ascaris antigen aerosols in five previously sensitized, anesthetized Basenji-Greyhound, crossbred dogs. Pulmonary resistance (RL) was determined by the method of Von Neergaard and Wirz, and blood lidocaine levels were determined by gas chromatography. Lidocaine, 4%, was administered as an aerosol for 10 minutes before challenge with Ascaris antigen and again during the 10-minute challenge with Ascaris antigen. Lidocaine aerosols frequently elicited a slight increase in RL before antigen challenge, whereas saline aerosols did not alter RL. Despite a large dose (approximately 10 mg/kg), which produced blood levels of 0.6 to 3.3 micrograms/ml, lidocaine afforded no protection against antigen challenge: RL increased from a control mean of 4.2 +/- 1.7 (SEM) cm H2O/liters/sec to 26.9 +/- 9.3 after challenge in lidocaine-treated dogs, and from 2.9 +/- 0.6 to 22.8 +/- 5.1 in saline-treated dogs. In contrast, lidocaine aerosols prevented the 7-fold increase in RL elicited by challenge with citric acid aerosols, demonstrating an adequate block of irritant reflexes. The failure of lidocaine aerosols to protect against antigen-induced bronchoconstriction indicates that the concentrations achieved in lung by this route are inadequate to relax smooth muscle directly.

Basenji-Greyhound dog model of asthma: reactivity to Ascaris suum, citric acid, and methacholine

Bronchial inhalation challenges to Ascaris suum, citric acid, and methacholine were performed in eight Basenji-Greyhound (BG) crossbreed dogs, five of which were reactive to Ascaris antigen aerosols (AAA). Responses to aerosol challenges were measured as changes in pulmonary resistance (RL) and dynamic compliance (Cdyn) and were compared to responses obtained in five mongrel dogs. Responses to methacholine and citric acid were similar in BG dogs whether Ascaris-sensitive or not, but BG dogs were clearly more reactive than mongrels to both types of nonspecific challenge. Methacholine responses were elicited at 10-30 times lower concentrations in BG dogs than in mongrels; 10% citric acid, which failed to elicit any response in mongrels, increased RL 5- to 10-fold in BG dogs. We conclude that the BG dog demonstrates nonspecific bronchial hyperreactivity, as in human asthma.

I.V. lignocaine in reflex and allergic bronchoconstriction

The protection against bronchospasm afforded by infusions of lignocaine was tested in dogs anaesthetized with thiamylal by challenge with aerosols of citric acid (CAA) or ascaris antigen (AAA). During the infusion of lignocaine, the response to CAA was blocked or markedly attenuated, but AAA still elicited a large increase in pulmonary resistance (RL). In untreated dogs, CAA increased RL from 0.14 +/- 0.05 (mean +/- SEM) kPa litre-1 s to 1.09 +/- 0.18, whereas in dogs treated with lignocaine, RL was 0.19 +/- 0.09 before challenge with CAA and 0.44 +/- 0.13 after challenge. AAA increased RL from 0.14 +/- 0.06 kPa litre-1 s to 3.01 +/- 0.65 in untreated dogs, and from 0.34 +/- 0.10 kPa litre-1 to 1.85 +/- 0.69 in dogs treated with lignocaine. Blood concentrations of lignocaine were 1.5 +/- 0.3 and 2.5 +/- 0.6 microgram ml-1 during challenge with CAA and AAA, respectively. We conclude that lignocaine, at blood concentrations which will reduce the risk of cardiac arrhythmia, markedly reduces reflex bronchonconstriction, but has relatively little effect on that initiated by allergic mediators.

Ketamine block of bronchospasm in experimental canine asthma

Experimental asthma was induced in dogs previously sensitized to ascaris antigen by ventilation with ascaris antigen, in an aerosol, for 10 min. Before the administration of antigen, there was no significant difference in pulmonary airways resistance (RL) during thiopentone and ketamine anaesthesia. In dogs anaesthetized with thiopentone, RL increased significantly from a pre-antigen control of 0.36 +/- 0.13 (mean +/- SEM) kPa litre-1 s to 1.56 +/- 0.38 at 5 min after administration of antigen. In dogs anaesthetized with ketamine, RL before (0.30 +/- 0.10) and 5 min after antigen (0.47 +/- 0.18) was not significantly different. Beta adrenergic blockade with propranolol abolished the protective effect of ketamine so that there was no significant difference in the maximal increase (5 min after antigen) in RL in dogs anaesthetized with ketamine (2.92 +/- 0.74) or thiopentone (3.28 +/- 1.16). Beta adrenergic blockade also increased pre-antigen RL in both groups (ketamine 0.87 +/- 0.24; thiopentone 0.77 +/- 0.32).

Conjugate lateral gaze nystagmus and free phenytoin concentrations in plasma: lack of correlation

Electrooculographic recordings during left and right conjugate lateral gaze fixation from 10 degrees to 50 degrees were made in 29 patients being treated with phenytoin. At the time of electrooculographic recordings, venous blood samples were drawn for analysis of total and free phenytoin plasma concentrations. Rhythmic horizontal nystagmus occurred in 7 patients, and only at extreme (40 degrees, 50 degrees) later gaze in 6 of these. Measurable free phenytoin levels in the 29 patients ranged from 0.2 to 3.2 mug/ml, and in the 7 patients with nystagmus were 0.6, 0.8, 1.0, 1.0, 1.7, 1.8, and 3.2 mug/ml. Neither the occurrence of nystagmus nor the degree of lateral gaze at onset could be correlated with free phenytoin concentrations in plasma.

Calcium-dependent, iproveratril-resistant contractions of aortic strips induced by a convulsant barbiturate

At 3 X 10(-5) M concentratons, 5-(2-cyclohexylideneëthyl)-5-ethyl barbituric acid (CHEB) causes a contraction of rabbit aortic strips that is equivalent to about half of the maximal response to norepinephrine. If a calcium-free medium is substituted for normal bathing solution and drug is added immediately thereafter, there is no response to the convulsant barbiturate but a nearly normal response to norepinephrine. When calcium is replaced in stepwise increments, the contractor response to CHEB appears in corresponding increments. The prompt influence of changes in external calcium-concentration suggests that CHEB-induced contraction occurs as a result of calcium influx into cells rather than a release of free calcium from previously accumulated intracellular stores. CHEB effect, like that of potassium, is prevented by pretreatment with lanthanum (5 X 10(-3)M). CHEB differs from potassium in that its effects are even more sensitive to changes in extracellular calcium concentration. Nevertheless, CHEB can contract aortic strips in the presence of iproveratril at a concentration (10(-4)M) that blocks all response to potassium (100 mM).

Studies on the comparative pharmacology and selective toxicity of tricaine methanesulfonate: metabolism as a basis of the selective toxicity in poikilotherms

Tricaine methanesulfonate, administered at a dose of 150 mg/kg i.p., produced a flaccid paralysis and loss of the righting reflex in a number of poikilothermic species including the frog. Leopard frogs (Rana pipiens) given 150 mg/kg i.p. regained the righting reflex at 113 +/- 28 (S.D.) minutes after injection. A similar dose administered i.p. to mice produced no apparent pharmacological response. The biological half-life (T1/2) of tricaine in frogs (R. pipiens) was about 70 minutes at temperatures of 23 and 37.5 degrees C; at 7 degrees C the T1/2 was 309 minutes. In contrast, in the mouse the drug was metabolized so rapidly that 5 minutes after i.p. administration of 5 mg of tricaine methanesulfonate (250 mg/kg) none of the unchanged drug could be recovered from the animal. It was, however, recovered quantitatively as Bratton-Marshall reacting metabolites, including m-aminobenzoic acid. Incubations of tricaine with serum from bullfrogs, mice and humans indicated that the drug was metabolized to m-aminobenzoic acid with an apparent Km of 3 X 10(-3) M for the reaction. The Vmax for incubations of the drug with bullfrog and human serum was 40 nmol/min/ml of serum, whereas in mouse serum it was 93 nmol/min/ml of serum. In vitro studies with liver homogenates showed that mouse liver metabolized tricaine 39 times more rapidly than frog liver. We conclude, therefore, that the liver is the major site of tricaine hydrolysis in mammals and that the selective toxicity of tricaine for poikilotherms is a consequence of their slower rate of hepatic biotransformation of tricaine.