American Association of Veterinary Parasitologists' review of veterinary fecal flotation methods and factors influencing their accuracy and use--is there really one best technique?

The principle of fecal flotation is based on the ability of a solution to allow less dense material (including parasite elements) to rise to the top. However, there are numerous factors that will influence the accuracy and use of such a theoretically simple technique. Whether or not centrifugation is used appears to have an impact on the ability to detect some parasites, but not others. Using a flotation solution with a relatively high specific gravity favors the simultaneous flotation of the diagnostic stages of many different parasites while, at the same time, making recognition of some more difficult because of distortion as well as the amount of debris in the preparation. Dilution methods tend to be less accurate because they require extrapolation; however, they are quicker to perform, in part, because of the cleaner preparation. Timing is a critical factor in the success of all flotation methods, as is technical ability of the personnel involved. Thus, simplicity, low costs and time savings have generally favored gravitational flotation techniques (including the McMaster technique and its modifications). How accurate the method needs to be is dependent upon the purpose of its use and choice of method requires an understanding of analytical sensitivity and expected levels of egg excretion. In some instances where the difference between, for example, 0 and 50 eggs per gram is insignificant with regards to management decisions, less accurate methods will suffice. In others, where the presence of a parasite means treatment of the animal regardless of the numbers of eggs present, methods with higher analytical sensitivities will be required, particularly for those parasites that pass few eggs. For other uses, such as the Fecal Egg Count Reduction Test, accuracy may become critical. Therefore, even though recommendations for standardized fecal flotation procedures have been promoted in the past, it is clear that the factors are too numerous to allow for the recommendation of one, or even a few, procedures for all purposes.

Efficacy of fipronil (9.8% w/w) + (S)-methoprene (8.8% w/w) and imidacloprid (8.8% w/w) + permethrin (44% w/w) against Dermacentor variabilis (American dog tick) on dogs

This study evaluated overall efficacy, percentage of dogs free of live ticks, retention of ticks, and efficacy against retained ticks of fipronil (9.8% w/w) + (S)-methoprene (8.8% w/w) and imidacloprid (8.8% w/w) + permethrin (44% w/w) spot-on topical solutions against Dermacentor variabilis-infested dogs. Tick control was significantly greater (P < .05) on dogs treated with fipronil + (S)-methoprene than on control dogs for the entire 30-day study period. Conversely, the combination product of imidacloprid + permethrin demonstrated activity significantly (P < .05) different from that seen on control dogs only up to day 23. Significantly (P < .05) more dogs treated with fipronil + (S)-methoprene were free of live ticks compared with controls on days 3, 9, and 16. There was never a significant difference (P > .05) between control and imidacloprid + permethrin-treated dogs in numbers of dogs free of live ticks. After the initial 10-minute tick exposure, lower numbers of ticks were retained on the imidacloprid + permethrin-treated dogs than on the fipronil + (S)-methoprene-treated dogs. However, when evaluating the effectiveness of the acaricides on "retained ticks," it appears that while some of the ticks were rapidly knocked down on the imidacloprid + permethrin-treated dogs, efficacy against ticks still retained at 10 minutes was never greater than 50%.

Efficacy of imidacloprid (8.8% w/w) plus permethrin (44% w/w) spot-on topical solution against Amblyomma americanum infesting dogs using a natural tick exposure model

This study evaluated the efficacy of an imidacloprid 8.8% w/w + permethrin 44% w/w spot-on topical solution (K9 Advantix, Bayer Animal Health) against Amblyomma americanum using a natural field exposure model. Sixteen beagles were divided into two groups of eight dogs each. One group of dogs was treated with K9 Advantix and the other group served as untreated controls. On day -1 and at 3, 7, 14, 21 and 28 days after treatment, the dogs were walked for 80 minutes in an A. americanum-infested habitat at the Konza Prairie Biological Station in Northeastern Kansas. Postexposure tick counts (efficacy evaluations) were conducted on each dog at 3 and 48 hours after exposure. At 3 days after treatment, the efficacy of K9 Advantix within 3 hours of natural tick exposure was 88.0% and declined slowly during the study. The 48-hour postexposure efficacy remained above 93.5% throughout the study.

Accurate diagnosis of Giardia spp and proper fecal examination procedures

A series of investigations evaluated the ability of different testing methods - a swing-head centrifugation technique using two flotation solutions (1.18-specific gravity zinc sulfate and 1.27-specific gravity Sheather's sugar solution), a passive commercial flotation technique, and the SNAP Giardia Test Kit from IDEXX Laboratories - to identify Giardia-positive dogs and recover the eggs of other intestinal parasites. It was determined that the SNAP Giardia test can improve a practice's ability to identify Giardia-infected dogs. Because of its higher specific gravity, the sugar solution was better for recovering heavy parasite eggs, such as Taenia spp, and thus is the flotation solution of choice when conducting routine centrifugation fecal examinations.

Evaluation of an imidacloprid (8.8% w/w)--permethrin (44.0% w/w) topical spot-on and a fipronil (9.8% w/w)--(S)-methoprene (8.8% w/w) topical spot-on to repel, prevent attachment, and kill adult Rhipicephalus sanguineus and Dermacentor variabilis ticks on dogs

This study evaluated the effectiveness of two topical spot-on formulations, imidacloprid (8.8% w/w)--permethrin (44.0% w/w) and fipronil (9.8% w/w)--(S)-methoprene (8.8% w/w), to repel, prevent the attachment of, and kill adult Rhipicephalus sanguineus and Dermacentor variabilis on dogs. Twelve purpose-bred beagles were distributed into three groups of four dogs each; one group served as untreated controls and each of the other two groups received one of the test products. Dogs were exposed to 25 adult ticks of each species for 10 minutes on posttreatment days 3, 7, 14, 21, and 28. Nonattached or repelled ticks were collected and evaluated for viability, and on-dog tick counts were conducted at 3, 24, and 48 hours after tick exposure. The imidacloprid-permethrin formulation provided significant repellency of R. sanguineus and D. variabilis for up to 3 and 4 weeks after treatment, respectively; and provided good overall control for R. sanguineus and D. variabilis during the study period. The fipronil--(S)-methoprene formulation provided good overall tick control during the study period.

Evaluation of an imidacloprid (8.8% w/w)--permethrin (44.0% w/w) topical spot-on and a fipronil (9.8% w/w)--(S)-methoprene (8.8% w/w) topical spot-on to repel, prevent attachment, and kill adult Ixodes scapularis and Amblyomma americanum ticks on dogs

This study evaluated the effectiveness of two topical spot-on formulations -- imidacloprid(8.8% w/w)-permethrin (44.0% w/w) and fipronil (9.8% w/w)-(S)-methoprene (8.8% w/w)--to repel, prevent the attachment of, and kill adult Ixodes scapularis and Amblyomma americanum on dogs. Twelve purpose-bred beagles were distributed into three groups of four dogs each; one group served as untreated controls, and each of the other two groups received one of the test products. Dogs were exposed to 25 adult ticks of each species for 10 minutes on posttreatment days 3, 7, 14, 21, and 28. Unattached or repelled ticks were collected and evaluated for viability, and on-dog tick counts were conducted at 3, 24, and 48 hours after tick exposure. The imidacloprid-permethrin formulation provided significant repellency against I. scapularis for up to 3 weeks after treatment, and both formulations provided good overall control of I. scapularis and A. americanum during the study period.

Comparative speed of kill of selamectin, imidacloprid, and fipronil-(S)-methoprene spot-on formulations against fleas on cats

The speed of kill of selamectin, imidacloprid, and fipronil-(S)-methoprene against Ctenocephalides felis infestations on cats for one month following a single treatment was evaluated. Eighty cats were randomly allocated so that there were 20 cats in four different treatment groups. On Days -2, 7, 14, 21, and 28, each cat was infested with 100 adult C. felis from the Kansas 1 flea strain. Following initial application only imidacloprid had caused a significant reduction in adult fleas on treated cats within 6 hours, but by 24 hours all three formulations had killed 96.7% of the fleas. At 7 days post treatment, all three formulations reduced flea populations within 6 and 24 hours by 68.4% and 99.4%, respectively. At 21 and 28 days after treatment, none of the formulations killed significant numbers of fleas as compared to controls within 6 hours of infestation. At 28 days after treatment, selamectin, fipronil-(S)-methoprene, and imidacloprid had killed 99.0%, 86.4%, and 72.6% of the fleas within 48 hours of infestation, respectively. This study demonstrates that the speed of kill of residual flea products on cats decreases throughout the month following application. It also demonstrated that selamectin provided the highest level of residual activity on cats against the Kansas 1 flea strain.

Comparison of common fecal flotation techniques for the recovery of parasite eggs and oocysts

A variety of procedures are available to detect parasite eggs or oocysts in feces. This study compared the efficacy of simple flotation, a commercial assay, and various centrifugation techniques and three common flotation solutions. Results indicate that centrifugation consistently recovered more eggs than other methods. Proper technique is critical, including ensuring that the specific gravity of the flotation solution is correct and allowing the sample to stand for a sufficient amount of time before examining the coverslip. Because of the zoonotic health risks of many companion animal parasites, veterinarian and their staff should better utilize fecal examinations in their routine diagnostic plan.

Effect of 0.29% w/w fipronil spray on adult flea mortality and egg production of three different cat flea, Ctenocephalides felis (Bouché), strains infesting cats

To evaluate the effect of fipronil spray on adult flea mortality and flea egg production of three different cat flea, Ctenocephalides felis (Bouché) strains, 30 domestic short hair cats were randomly allocated into six groups of five cats each. On day 0, cats in groups 2, 4 and 6 were treated with fipronil at 5-6ml/kg. Cats in groups 1, 3 and 5 served as untreated controls. On days -2, 7, 14, 21, and 28 each cat was infested with 50 adult cat fleas. Groups 1 and 2 were infested with fleas from the Kansas1 Colony (KS1) strain. Groups 3 and 4 were infested with a recently colonized cat flea strain from Florida (R6). Groups 5 and 6 were infested with fleas from the ARC strain. The adulticidal activity of fipronil was determined by flea comb counts 48h after treatment and then 48h after each reinfestation. Any flea eggs produced during the infestations were collected and counted prior to the 48h comb counts. Fipronil spray was > or = 99.5% effective against adults of all three cat flea strains when applied during an active infestation. Fipronil spray provided > or = 98.2 and > or = 99.5% control of adult fleas and egg production, respectively, for all strains through week 2. On days 23 and 30 control of R6 adults and egg production was significantly lower than either the ARC or the KS1 strain. On day 30, control of R6 adults and egg production was 77.3 and 87.3%, respectively. Control of KS1 adults and egg production on day 30 was significantly lower than the ARC strain. Fipronil provided > or = 99.5 and > or = 99.9% control of ARC fleas and egg production, respectively, throughout the entire study. The susceptibility to fipronil for the three strains was also evaluated on filter paper pesticide bioassays. The R6 strain was found to be less susceptible than the KS1 and ARC strains. The LC(95) estimates for the strains were 10.13, 4.77 and 2.62mg/m(2) for the R6, ARC and KS1 strains, respectively.

Evaluation of the CatanDog's tag to prevent flea infestations, inhibit flea reproduction or repel existing flea infestations on cats

To evaluate the ability of the CatanDog's tag to eliminate fleas, inhibit egg production and prevent flea infestations, six domestic shorthaired cats were randomly allocated to two treatment groups and housed individually in stainless steel metabolic cages. Three cats were each fitted with a CatanDog's tag; the other three cats were not fitted with tags and served as controls. Following a 42-day acclimation period, each of the six cats was infested with 100, 1-3 day post-emergence, adult Ctenocephalides felis felis (Bouché) on days 0, 7, 14, 21, and 27. Flea egg production was determined by collecting and enumerating eggs 2, 4 and 6 days after each infestation. Viability of eggs was determined by placing 100 eggs recovered from each cat in rearing media in an insect rearing chamber and determining adult emergence at 28 days. Adult fleas were recovered from cats 6 days post-infestation by thoroughly combing each cat to remove fleas. To determine if the tags provided protection from infestation, the six cats were placed into a 8.53mx4.36 m room with 400 cat fleas for 3h. Cats were then combed to remove and enumerate fleas. The CatanDog's tags had no significant effect upon egg production, egg viability, or adult fleas infesting cats. In addition there was no difference in the numbers of fleas recovered from the cats placed in the flea-infested room.

Strategic use of ivermectin during pregnancy to control toxocara canis in greyhound puppies

Twenty-one greyhound bitches were bred (Day 0) and housed throughout their pregnancies on three greyhound breeding farms in Kansas. These dogs were assigned randomly to one of four treatment groups. Group A dogs (6) were given ivermectin subcutaneously (300 microg/kg) on Day 0 (the first day the dogs were bred), and Days 30 and 60 of gestation. Group B dogs (6) were given ivermectin (300 microg/kg SQ) on Day 42. Group C dogs (3) were given ivermectin (300 microg/kg SQ) on Days 0, 30, and 60 plus 10 days after whelping. Group D dogs (6) served as controls and received no anthelmintic. Bitches and puppies were moved to the university on the day after birth and were maintained inside for 28 days. Weekly quantitative fecal exams were done on the bitches during this time. The puppies were euthanized humanely at 28 days of age. Intestinal parasites were recovered, identified, counted, sexed, and preserved in either 10% formalin or frozen at -70 degrees C. The geometric mean numbers of adult Toxocara canis in the small intestines for Group A puppies (n = 40) were 2.8, 8.5 for Group B puppies (n = 39), and 29.7 for Group D puppies (n = 28). No adults were found in the Group C puppies (n = 15). The geometric mean eggs per gram of feces from the pups in group A, B, and D were 1.3, 704, and 27, 134, respectively. No eggs were recovered from the Group C pups. The strategic use of ivermectin at 300 microg/kg in greyhound bitches on Days 0, 30, and 60 of gestation reduced the worm burden carried by the puppies by 90% and the actual number of eggs passed into the environment by 99.8%. The same dose on day 42 reduced the worm burden by 71.4% and the number of eggs passed into the environment by 97.4%. This dose given on days 0, 30, and 60 plus 10 days postwhelping, reduced the worm burden by 100%, and no eggs were passed into the environment.

A model of nurse-midwife and family physician collaborative care in a combined academic and community setting

Certified nurse-midwives and family physicians share a philosophy of family-centered maternity care. Collaboration between the two disciplines, however, has not been common. Collaboration can enhance the primary care and maternity care options available to clients of such collaborative practices. Advantages and barriers to collaboration for both types of practitioners, as well as suggestions for successful collaboration, are discussed.

Modelling of a photoacoustic probe designed for medical applications

A model is presented describing the thermoelastic photoacoustic interaction in a layered medium within a transparent fluid, where a polymer transducer is used for the detection of ultrasonic pulses. By taking the optical absorption coefficient and finite layer thickness into account, the amplitude and shape of photoacoustic transients are calculated for both forward and backward travelling directions. Additionally, photoacoustic transient interaction with the PVDF transducer has been characterised using a discrete-time algorithm for the transducer response. Good agreement with experimental waveforms are demonstrated, so that this may form the basis of system characterisation when miniature laser-ultrasound probes are used in various applications.

A new laser-ultrasound transducer for medical applications

A new type of probe is presented, which combines an ultrasound receiver constructed from piezoelectric polymer materials with a coaxial optical fibre for laser-induced ultrasound. The initial application of this probe, which may be further miniaturized, is in intra-arterial imaging and therapy. Overall diameters of the prototype probes presently range from 2.5 mm to 10.0 mm. Pulsed laser beams are introduced through the optical fibre to form a photoacoustic source within the material under investigation. Ultrasonic waves are induced in the material due to the photo-acoustic effect and received on return by a forward-looking piezoelectric polymer transducer. In principle, other high-power laser beams can also be introduced through the same optical fibre for therapeutic use. Initial development and characterization of this combined probe is reported in this paper, together with some results.

The use of fine-needle aspiration in the evaluation of persistent palpable dominant breast masses

OBJECTIVE

Our purpose was to determine if fine-needle aspiration can decrease the necessity for open surgical biopsy in the diagnosis of a persistent palpable dominant breast mass.

STUDY DESIGN

In a university obstetrics-gynecology resident physician training program, persistent palpable dominant breast masses seen in the Breast Diagnostic Center at Women's Hospital, Los Angeles County-University of Southern California Medical Center, were evaluated by fine-needle aspiration. When a cytologic diagnosis was obtained, the patients were treated, followed, or referred for treatment. Open surgical biopsy was reserved for those lesions that were not cytologically diagnosed or for which there was no concordance of the diagnostic triad of palpation, fine-needle aspiration, and mammography.

RESULTS

Resident physicians rotating through the Breast Diagnostic Center performed 568 fine-needle aspirations under staff supervision. The technique was readily learned by most of the resident physicians with equipment already available in most outpatient settings. Fine-needle aspiration was performed on the initial clinic visit, and the preliminary cytologic diagnosis was given to the patient on the same day. Forty-two cancers were cytologically diagnosed (7% of the fine-needle aspirations). Seventy-five (13%) other patients were referred for open surgical biopsy as the definitive diagnostic procedure. Twenty-four (4%) patients elected open surgical excision biopsy of fine-needle aspiration-diagnosed masses.

CONCLUSION

Fine-needle aspiration of persistent palpable dominant breast masses allows expeditious and potentially cost-effective management of most cases and decreases the necessity of open surgical biopsy for definitive diagnosis.

Correlates of hypnotizability in children: absorption, vividness of imagery, fantasy play, and social desirability

This study examined correlates of hypnotizability in children that had previously been reported for adults. Forty-two children (ages 7-14) completed the Fantasy Questionnaire (FQ), the Children's Social Desirability Questionnaire (CSDQ), the Zelter and LeBaron (1984) revision of the Stanford Hypnotic Clinical Scale for Children (SHCS:C-R), and the Children's Fantasy Inventory: Absorption and Vividness Scales (CFI: A & V). The nine-item SHCS:C-R yields separate scores for Observed Behavior (OB), and Realness (R), as well as a Total Score (TS). Results indicated significant correlations between SHCS:C-R scores and those for CFI: A & V, and the FQ (r = .42-.53) but not for the CSDQ. On the SHCS:C-R, correlations between R (involuntariness) scores and the above measures were not appreciably different from those found for OB scores. Observations suggested that attitudes towards hypnosis may influence children's hypnotic responsiveness.

Measurement of properties and function of skin

Dermatologists and skin biologists have traditionally approached the diagnosis of skin diseases by either a very gross measurement of its physical state, i.e. a skin pinch, or at the other extreme by being concerned with the cellular and sub-cellular organisation of the skin. Recently, using methods often borrowed from materials science, techniques have been developed and used to aid the investigation of the changes that occur with disease and ageing, for example. A review of these methods developed to study the structure and function of skin by the physical scientists working in close collaboration with dermatologists, pathologists and skin biologists is presented.

Transducers, sensors, and instrumentation in clinical biomechanics

Successful measurements in any field are dependent on the availability of appropriate transducer materials and the associated instrumentation. In recent years there has been a most welcome advance in both these areas. If we consider first the transducer developments that have recently taken place, these have much to do with the discovery and application of new materials such as electroactive polymers, fibre optic devices and many others. Instrumentation has largely benefitted from the microelectronics revolution. Our ability to process and ultimately display data has improved to a remarkable extent. Indeed, the designer of instrumentation is under enormous pressure to convert the data into the digital domain as early as possible simply because the resulting instrument will usually be easier to design and construct, more accurate, more reliable, smaller and possibly more important still, cheaper. This paper reviews some of these developments, gives a number of examples of applications in the clinical biomechanics area and makes some predictions for future developments.

Determination of ultrasonic velocity in human enamel and dentine

Acoustic velocity data have been obtained preparatory to investigation of high frequency ultrasound as a non-invasive imaging technique for dental hard tissues and their pathology. In vitro studies were conducted on extracted human permanent teeth. Pulse-echo ultrasound of 18 MHz centre frequency and approx. 150 ns pulse duration successfully detected the front and back surfaces of 0.45-1.07 mm thick sections of enamel and of dentine. Water was used as the coupling agent. The oscilloscope traces of the echoes from pure enamel and pure dentine were similar. The longitudinal ultrasonic velocities for pure enamel and dentine were experimentally determined for a number of teeth in different planes of section. For enamel in longitudinal and transverse sections, the mean ultrasonic velocities were 6150 +/- 140 and 6500 +/- 190 m/s respectively. For dentine in longitudinal section, the mean ultrasonic velocity was 4050 +/- 30 m/s.

An activated c-Ha-ras allele blocks the induction of muscle-specific genes whose expression is contingent on mitogen withdrawal

During myogenesis, induction of muscle-specific genes is subject to negative control by polypeptide mitogens and type-beta transforming growth factor. Since transduction of growth factor signals may require proteins encoded by cellular ras oncogenes, we have tested whether a mutationally altered Harvey ras expression vector, by itself, can prevent establishment of a differentiated phenotype in BC3H1 mouse myoblasts. Transfection with the valine-12 allele of the human Harvey ras gene, under the control of its own promoter, was sufficient to prevent the induction of both muscle creatine kinase activity and the nicotinic acetylcholine receptor following mitogen withdrawal but did not inhibit withdrawal from the cell cycle. The loss of creatine kinase activity resulted from a corresponding block to induction of muscle creatine kinase mRNA. Similarly, mitogen withdrawal elicited little or no alpha-actin mRNA in ras-transfected cells. These results suggest that an activated ras allele can inhibit myogenesis through a mechanism independent of cell proliferation and can preclude activation of genes whose up-regulation normally accompanies mitogen withdrawal.

Autonomous expression of c-myc in BC3H1 cells partially inhibits but does not prevent myogenic differentiation

Myogenic differentiation is obligatorily coupled to withdrawal of myoblasts from the cell cycle and is inhibited by specific polypeptide growth factors. To investigate the potential involvement of c-myc in the control of myogenesis, the BC3H1 muscle cell line was stably transfected with a simian virus 40 promoter:c-myc chimeric gene. In quiescent cells in 0.5% serum, the exogenous c-myc gene was expressed at a level more than threefold greater than the level of endogenous c-myc in undifferentiated, proliferating cells of the parental line in 20% serum. The transfected myc gene partially inhibited the expression of both muscle creatine kinase and the nicotinic acetylcholine receptor, but was not sufficient to prevent the induction of these muscle differentiation products upon mitogen withdrawal.

Dissociated expression of c-myc and a fos-related competence gene during cardiac myogenesis

Cardiac myocytes irreversibly lose their proliferative capacity soon after birth, and cardiac DNA synthesis becomes uncoupled from mitotic division. Therefore, we examined cardiac muscle for developmental down regulation of inducible proto-oncogenes associated with cell proliferation. c-myc mRNA decreased continuously from day 13 of embryonic development and was dissociated from expression of the fos-related gene r-fos, which decreased precipitously between days 3 and 7 after birth.

Intravenous acid infusion without lowering arterial pH stimulates breathing

The aim of this study was to determine whether increases in ventilation would occur during intravenous acid infusion even if systemic arterial pH was held constant. In six awake ponies, HCl (500 ml, approximately 0.312 M) was infused into the right atrium at a total dose of 1.0 meq/kg over 18 min while an equivalent dose of NaOH was infused into the left heart to restore systemic arterial pH to normal. Total ventilation increased at the onset of the infusion and remained elevated although systemic arterial pH was normal to slightly alkaline. The increase in ventilation during the initial 2 min of the infusion coincided with an increase in pulmonary arterial PCO2 and decrease in pulmonary arterial pH. As the infusion progressed, however, pulmonary arterial pH and PCO2 returned to near control values due to the recirculation of systemic arterial blood with an acid-base status that had been altered consequent to the hyperventilation. Pulmonary arterial blood pressure was increased significantly during the entire infusion. Infusion of equivalent doses of hypertonic saline led to only minor alterations in the variables that were measured. These experiments demonstrate that this dose of intravenous HCl can increase ventilation independent of reductions in systemic arterial pH. Because increases in ventilation and pulmonary arterial H+ were not well correlated throughout the entire infusion, and pulmonary arterial blood pressure was increased, it is not clear if the mechanism for this ventilatory response is due to stimulation of pulmonary chemoreceptors, pulmonary vascular mechanoreceptors, or some other mechanism unrelated to increases in systemic arterial H+ concentration.

Skin thickness measurement by pulsed ultrasound: its reproducibility, validation and variability

The reproducibility of the pulsed ultrasound technique for the determination of skin thickness was investigated, using two independent observers. No systematic difference was found and a high correlation was obtained. Studies were also undertaken to validate the pulsed ultrasound technique as a measure of true skin thickness. Skin thickness determined in vitro was found to be greater than when in vivo determinations were made by either the pulsed ultrasound or a xeroradiographic technique, probably due to the release of in vivo tension within the dermis after excision. Skin thickness was found to increase linearly with age up to the age of 20 years and to decrease linearly with age subsequently. Differences in skin thickness between the sexes and in different sites of the body were demonstrated.

The handling of immunoreactive vasopressin by the isolated perfused rat kidney

Using the isolated rat kidney perfused with an artificial medium containing glucose as the sole fuel, we studied the renal handling of immunoreactive arginine vasopressin (AVP) and determined the effect of various factors on the ability of the kidney to remove AVP. In control kidneys perfused with AVP at concentrations below 116 muU/ml, the organ clearance of AVP (OC(AVP)) was 1,145+/-47 (SE) mul/min, whereas glomerular filtration rate (GFR) averaged 515+/-37 mul/min. Filtration could thus account for up to 45% of the OC(AVP), the balance presumably being cleared from the peritubular circulation. Of the AVP filtered, only 38% could be recovered in the urine (urinary clearance AVP averaged 205+/-12 mul/min) suggesting that the balance was taken up by the tubular epithelium and degraded. Fractional excretion of filtered AVP rose significantly in the presence of anoxia and cold (10 degrees C) to 49 and 59%, respectively, but was not affected by ouabain or high levels of AVP (458+/-58 muU/ml). The OC(AVP) was not significantly altered by the absence of glucose in the perfusate, anoxia, or ureteral ligation, maneuvers that were associated with significant reductions in GFR. In these and the control experiments, there was a significant inverse correlation between GFR and peritubular clearance emphasizing the importance of the latter (r = -0.749; P < 0.001). Cold, ouabain, and high concentrations of AVP reduced the clearance of AVP by the kidneys. On the basis of these studies we conclude that the kidney clears AVP from the circulation via two pathways, glomerular clearance and peritubular clearance. This exposes both the luminal and contraluminal surfaces of the tubular cells to the hormone, allowing these cells to remove AVP from the filtrate and the peritubular compartment. Noteworthy is the observation that under several conditions when GFR falls reducing the glomerular clearance of AVP, peritubular clearance increases and the total clearance of AVP by the kidney remains constant.

Cardiovascular responses of men and women to lower body negative pressure

Changes in blood flow and blood redistribution were measured by impedance plethysmography in the pelvic and leg regions of six male and four female subjects during three 5-min exposures to -20, -40, and -60 mm Hg lower body negative pressure (LBNP). Female subjects demonstrated significantly higher mean heart rate and lower leg blood flow indices than the male subjects during the recumbent control periods. Men had slightly higher mean resting systolic and diastolic blood pressures and higher mean control pelvic blood flow indices. Women demonstrated significantly less blood pooling in the legs and slightly less in the pelvic region than the men. All of the 18 tests with male subjects at -60 mm Hg were completed without initial signs of syncope, while only two of the tests with women were completed successfully without the subject exhibiting presyncopal conditions. The results of this study indicate that impedance plethysmography can be used to measure segmental cardiovascular responses during LBNP and that females may be less tolerant to -60 mm Hg LBNP than males.

Physiological and biochemical effects of the mycotoxin patulin on Chang liver cell cultures

Patulin exhibits both cytotoxic and cytopathic effects on cultured Chang liver cells. The LD50 found was 1.85 mug per ml of patulin. Effects on growth were observed with as little as 0.1 mug per ml of patulin; a 50% reduction in growth was observed at 0.38 mug per ml of patulin. Using a challenge dose of 2.5 mug per ml of patulin, the cytotoxic effect was reversible after an exposure of 10 min, but was not reversible after 20 min. Protein synthesis was depressed after 60 min and RNA synthesis after 20 min of contact with patulin. Neither protein nor RNA synthesis was completely inhibited after 260 min.