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Biomedical subjects

J F Carroll

Publications and source records attributed to J F Carroll.

At least 37 records · Page 2Linked to original sources
PubMed1999

Notes on responses of blacklegged ticks (Acari: Ixodidae) to host urine.

In laboratory bioassays under conditions of high humidity, host-seeking female black-legged ticks, Ixodes scapularis Say, avoided urine of reproductively active male and nonestrous female white-tailed deer, Odocoileus virginianus (Zimmermann), the principal host species of the adult stage. At 50% RH, female I. scapularis did not avoid urine from male and female deer. Larval and nymphal I. scapularis did not exhibit an arrestment response to urine from male and female white-footed mice, Peromyscus leucopus (Rafinesque), a major host for immature blacklegged ticks. These results suggest that under some conditions, urine from 2 principal host species in certain physiological states does not provide kairomonal cues that aid I. scapularis in contacting these host species.

Animals↗
PubMed1999

Responses of three species of adult ticks (Acari: Ixodidae) to chemicals in the coats of principal and minor hosts.

In laboratory bioassays, host-seeking adult blacklegged ticks, Ixodes scapularis Say, lone star ticks, Amblyomma americanum (L.), and American dog ticks, Dermacentor variabilis (Say), were exposed to substances from the pelage of dogs and white-tailed deer, Odocoileus virginianus (Zimmermann). Male A. americanum exhibited an arrestant response to all samples of deer tarsal gland substances tested, whereas female A. americanum, female I. scapularis, and male and female D. variabilis responded to samples from certain deer and not others. Female I. scapularis, D. variabilis, and A. americanum of both sexes also showed an arrestant response to substances rubbed from the dorsal surface of dogs' ears. These findings suggest that, although these 3 species of ticks are associated with certain host species as adults (A. americanum and I. scapularis with white-tailed deer, D. variabilis with dogs), their repertoires of host-finding behaviors are broad, and use of minor host species may not be purely accidental.

Animals↗
PubMed1999

Diastolic compliance is reduced in obese rabbits.

Obesity often leads to symptoms of cardiopulmonary congestion associated with normal systolic but abnormal diastolic function. This study analyzed alterations in passive diastolic compliance in obesity using the rabbit model. New Zealand White rabbits were fed a normal (n=8) or 10% added fat diet (n=8). After 12 weeks, rabbits fed the high fat diet developed obesity (5.34+/-0.11 versus 3.68+/-0. 04 kg, P</=0.05) and left ventricular hypertrophy (1.37+/-0.07 versus 0.98+/-0.03 g dry weight, P</=0.05). Compliance was assessed with the isolated heart preparation by analyzing the passive end-diastolic left ventricular pressure-volume relationship. The pressure-volume relation was fit to an exponential function by regression analysis; results showed that the modulus of stiffness was greater in obese than in lean rabbits (1.21+/-0.16 versus 0. 83+/-0.05, P</=0.05), indicating that diastolic compliance was reduced. Computer simulation analyses suggested that an isolated reduction in diastolic compliance may contribute to elevated cardiac filling pressures and exercise intolerance. These data suggest that diastolic compliance is reduced early in the development of obesity and may be an important component in the reduction of cardiac reserve in obesity.

Animals↗
PubMed1999

Enhanced vascular reactivity and Ca2+ entry with low-salt diet: effect of obesity.

Salt moderation is often recommended as a nonpharmacological therapy for hypertension, particularly in overweight individuals; however, the effects of low dietary salt on the Ca(2+)-dependent mechanisms of vasoconstriction are unclear. The purpose of this study was to investigate the effect of low salt diet on vascular reactivity and Ca2+ mobilization mechanisms and the modulation of these effects with obesity. Active stress and (45)Ca2+ influx were measured in deendothelialized aortic strips isolated from lean (3.74 kg) and obese (5.51 kg) female rabbits on a normal (0.75%) or low (0.23%) salt (sodium chloride) diet for 18 weeks. Both phenylephrine (Phe, 10(-5) mol/L) and membrane depolarization by 96 mmol/L KCl caused extracellular Ca(2+)-dependent increases in active stress and (45)Ca2+ influx. In lean rabbits, the Phe- and KCl-induced stress and Ca2+ influx were significantly greater with the low-salt versus the normal-salt diet. The Phe-induced Ca2+ influx-stress relationship was significantly greater than that induced by KCl with low-salt diet. In obese rabbits on a normal-salt diet, the Phe- and KCl-induced stress and Ca2+ influx were significantly less than that in lean rabbits but the Ca2+ influx-stress relationship was not significantly altered. Feeding the obese rabbits a low-salt diet was associated not only with significant increases in Phe- and KCl-induced active stress and Ca2+ influx but also with significant enhancement in the Ca2+ influx-stress relationship. In Ca(2+)-free (2 mmol/L EGTA) Krebs solution, stimulation of intracellular Ca2+ release by Phe or caffeine (25 mmol/L) caused a transient contraction that was not significantly different in all groups of rabbits. Thus, with normal salt intake, obesity is associated with a reduction in Ca2+ entry and vascular reactivity. Low-salt diet is associated with an increase in Ca2+ entry and vascular reactivity in both obese and lean rabbits. The enhancement of the Ca2+ influx-stress relationship with low-salt diet, particularly in the obese rabbits, suggests activation of other contractile mechanisms in addition to Ca2+ entry.

Animals↗
PubMed1998

Renal size and composition in hypertensive, obese rabbits.

OBJECTIVE: To determine whether the renal growth associated with obesity is due to hypertrophy or hyperplasia. DESIGN: New Zealand white female rabbits were fed either standard rabbit chow (n=17) or chow fortified with 10% corn oil plus 5% lard (n=18) for 12-16 weeks. MEASUREMENTS: All rabbits were weighed, and intra-arterial blood pressures were successfully measured at the end of the study in 16 lean and 18 obese rabbits; percent water of entire kidneys (8 lean, 8 obese rabbits) and of defined regions of kidneys (8 lean, 10 obese rabbits) were obtained gravimetrically. Renal hemoglobin, protein and DNA was measured chemically (8 lean, 8 obese rabbits). RESULTS: Kidneys grew in size as the rabbits gained fat. In a series of 8 lean and 8 age-matched obese rabbits, weighing 3.7+/-0.1 kg and 5.4+/-0.4kg (P<0.05), the kidneys were 20% larger in the obese rabbits: 15.0+/-0.9 g vs 18.0+/-2.5 g (P<0.05). Kidney protein was also 20% greater in the obese rabbit: 1.38+/-0.06 g/kidney vs 1.66+/-0.06 g/kidney (P<0.05). While total renal DNA was 16% greater in the obese: 18.2+/-0.5 microg/kidney vs 21.1+/-0.61 g/kidney (P<0.05), no significant difference existed when the DNA was expressed as microg/mg protein. Fractional water content of the intact kidney declined with obesity: 78.7+/-1.1% vs 76.0+/-1.2% (P<0.05). Conversely, the hemoglobin content of the kidney at autopsy, an estimate of the unstressed vascular volume, increased with obesity: 55+/-19 mg/kidney vs 82+/-25 mg/kidney (P<0.05). By contrast, water content of renal parenchyma was constant: 80.8+/-1.0% vs 80.9+/-1.2% (cortex); 84.0+/-0.8% vs 83.6%+/-2.0% (outer medulla); and 85.7+/-0.8% vs 86.0+/-2.1% (inner medulla). CONCLUSION: The renal growth associated with obesity was predominantly hyperplastic and was associated with a partial exclusion of fluid from the renal sinus.

Animals↗
PubMed1998

Patterns of activity in host-seeking adult Ixodes scapularis (Acari: Ixodidae) and host-produced kairomones.

Adult blacklegged ticks, Ixodes scapularis Say, were confined to clay islands each surmounted with a vertical glass rod, and tick activities were videotaped continuously for 48 h. Some rods were treated basally or apically with substances rubbed from pelage associated with the tarsal or interdigital glands of white-tailed deer, Odocoileus virginianus (Zimmermann). Except for the activity immediately following their release, tick activity on both days was greatest during the period from 1700 to 2300 hours, which coincided with the onset of scotophase. Ticks were most active when rods had interdigital gland substances applied to their basal 2 cm, whereas they were least active when confined with rods treated with tarsal gland substances on their apical 2 cm. Overall, ticks spent more time on the apical 2 cm of the glass rods during the scotophase than during the photophase. The highest level of apical arrestment among treated and untreated rods occurred when the rod tips were treated with tarsal gland substances, with female ticks on the apical 2 cm of the rods 70-100% of every 3-h period beginning with the period from 2000 to 2300 hours on day 1. In contrast, when tarsal gland substances were applied to the basal 2 cm of the rods, the ticks spent < 40% of every period on day 2 on the rod tips.

Animals↗
PubMed1998

Attachment-site patterns of adult blacklegged ticks (Acari: Ixodidae) on white-tailed deer and horses.

The attachment site pattern of adult Ixodes scapularis Say on white-tailed deer and horses in Maryland was determined by whole-body examinations during fall and spring periods of tick host-seeking activity. On deer in the fall, both female and male I. scapularis attached largely to anterior dorsal body regions, with attachment to the ears (outside), head, neck, and brisket accounting for 87.9% of females and 86.6% of males. The attachment pattern of females differed between bucks and does during fall, but not in spring, and both females and males were more abundant on bucks than does during fall, but not in spring. Neither female nor male attachment patterns on deer differed between fall and spring seasons. In contrast to deer, the ears and neck of horses were largely devoid of blacklegged ticks, and 84% of the females were attached either on the chest, in the axillae of the fore and rear legs, or under the jawbone. The restricted attachment of female blacklegged ticks to ventral body regions of horses may reflect avoidance of light. An understanding of the attachment patterns of adult I. scapularis, an increasingly abundant and economically important species, enhances sampling of feeding ticks, deticking to limit host irritation or exposure to tick-borne pathogens, and identifies body areas that should be targeted for delivery of repellents or acaricides.

Animals↗
PubMed1997

Obese hypertensive rabbits develop concentric and eccentric hypertrophy and diastolic filling abnormalities.

We have developed a new small animal model of obesity in which rabbits fed a high diet develop abnormalities in common with obese humans, including left ventricular (LV) hypertrophy. Using M-mode and two dimensional Doppler echocardiography we examined the characteristics of LV hypertrophy and diastolic function in obese and lean rabbits. Obese rabbits had greater interventricular septum and LV posterior wall thickness and greater LV internal end-diastolic and end-systolic diameters. Functionally, obese rabbits had higher A/E ratios. Similarly to obese humans, obese hypertensive rabbits developed combined concentric and eccentric LV hypertrophy and diastolic filling abnormalities. Therefore, this model may be valuable in the study of the development and pathology of obesity-related LV hypertrophy.

Animals↗
PubMed1997

Cholesterol feeding does not alter renal hemodynamic response to acetylcholine and angiotensin II in rabbits.

Aortic ring studies have demonstrated a decrease in endothelium-dependent relaxation or an enhanced response to vasoconstrictors in rabbits fed a high-cholesterol diet. Whether such abnormalities exist in the renal circulation is unclear. The purpose of this study was to determine functional renal responses to acetylcholine (ACh) or angiotensin II (ANG II) infusion in anesthetized rabbits after 8-10 wk of either a control diet (ACh, n = 6; ANG II, n = 6) or a 1% cholesterol diet (ACh, n = 7; ANG II, n = 7). Mean arterial pressure (MAP), renal blood flow (RBF), and glomerular filtration rate (GFR) were measured. Renal vascular resistance (RVR) was calculated as MAP/RBF. For ANG II experiments, captopril (15 microg x kg(-1) x min(-1)) was infused to suppress endogenous ANG II production. After two control clearance periods, either ACh (1 microg x kg(-1) x min(-1)) or ANG II (0.5 ng x kg(-1) x min(-1)) was infused into the renal artery; RBF was allowed to stabilize before experimental clearances. RBF increased with ACh (control: 25 +/- 2 to 39 +/- 2 ml/min; cholesterol: 26 +/- 2 to 40 +/- 3 ml/min) and decreased with ANG II infusions (control: 40 +/- 4 to 25 +/- 3 ml/min; cholesterol: 36 +/- 3 to 24 +/- 2 ml/min). Nitrate/nitrite excretion also increased with ACh infusion (control: 2.3 +/- 1.0 to 5.2 +/- 1.8 nmol x kg(-1) x min(-1); cholesterol: 2.3 +/- 0.3 to 6.0 +/- 1.3 nmol x kg(-1) x min(-1)). However, there were no significant differences between control and cholesterol groups in either response. GFR was unaltered during ACh and ANG II infusions. MAP, RVR, and urinary sodium and potassium excretion did not differ between groups in response to either drug. These results suggest that, despite significant hypercholesterolemia and large-vessel atherosclerosis, both nitric oxideinduced vasodilation and endothelium-dependent modulation of ANG II vasoconstriction in the renal circulation are unaffected by cholesterol feeding.

Acetylcholine↗
PubMed1997

Reduced cardiac contractile responsiveness to isoproterenol in obese rabbits.

Although obesity is characterized by increased sympathetic nervous system activity, there is often a paradoxical reduction in cardiovascular end-organ response to sympathetic stimulation. Mechanisms involved in reduced sympathetic responsiveness in obesity have not been well characterized. Therefore, we determined cardiac contractile responsiveness to beta-stimulation in the obese rabbit model using both isolated heart (IH) and isolated papillary muscle (IPM) preparations. Female New Zealand White rabbits were fed control (IH: n=9; IPM: n=6) or 10% fat diets (IH: n=9; IPM: n=7) for 12 weeks. Contractile responsiveness in the IH was determined using a modified Langendorff preparation to evaluate the dose-response relationship between isoproterenol and 1) peak developed pressure/g of left ventricular wet weight and 2) maximal rate of pressure development (+dP/dt/P). Contractile responsiveness in the IPM was determined using right ventricular papillary muscles to evaluate the dose-response relationship between isoproterenol and (1) peak developed tension (T)/mm2 cross-sectional area (CSA) and (2) maximal rate of tension development (dT/dt/CSA). In the IH, baseline and maximum developed pressure/g were reduced in obese rabbits by 37% and 31%, respectively (P< or =.05). In the IPM, baseline and maximum T/CSA responses were reduced in obese rabbits by 59% and 33%, respectively (P< or =.05). Potency of isoproterenol as reflected by the EC50 did not differ between lean and obese animals in either preparation. These results demonstrate that left ventricular contractility in obesity is reduced at baseline and in response to stimulation with isoproterenol and suggest that decreased responsiveness to beta-stimulation may be a factor in the obesity-related systolic dysfunction.

Animals↗
PubMed1996

Relative heart rate, heart rate reserve, and VO2 during submaximal exercise in the elderly.

BACKGROUND: The purpose of this study was to examine the relationships among relative maximal heart rate (%HRmax), maximal heart rate reserve (%HRmax reserve), and maximal oxygen uptake (%VO2max) during submaximal exercise by elderly subjects. METHODS: VO2max and HRmax were determined on 36 women and 19 men, 60 to 80 yrs of age, by a maximal treadmill test to volitional exhaustion. On a separate day, subjects underwent a submaximal treadmill protocol consisting of three 6-min exercise stages at treadmill speeds and grades estimated to elicit 40%, 60%, and 80% of HRmax reserve. Cardiorespiratory responses were determined during mins 4-5 and 5-6 of each stage. RESULTS: Measured exercise intensities expressed by the three methods were: %HRmax reserve = 36, 55, and 79%; %HRmax = 65, 75, and 88%; %VO2max = 53, 69, and 88%. %HRmax was greater (p < .05) than %VO2max at 53 and 69% of VO2max. %HRmax reserve was less (p < .05) than %VO2max for all three intensities. Slopes and intercepts for the linear regression equations relating %VO2max with %HRmax and with %HRmax reserve differed between men and women (p < .05). The regression equation relating %VO2max and %HRmax was y = -22.8 + 1.2 (%HRmax) -13.0 (Gender) + 0.2 (%HRmax x Gender): standard error of the estimate (SEE) = 9.7% and R2 = .71. The regression equation relating %VO2max and %HRmax reserve was y = 32.4 + 0.7 (%HRmax reserve) -10.9 (Gender) + 0.2 (%HRmax reserve x Gender): SEE = 9.8% and R2 = .70 (Gender: F = 0; M = 1). CONCLUSIONS: The data indicate that there is considerable variability among methods of expressing exercise intensity and that %HRmax more closely represents %VO2max than does %HRmax reserve (p < .05) in older adults. These results are in contrast to what has been shown with younger subjects and with American College of Sports Medicine guidelines for exercise prescription.

Aged↗
PubMed1996

Dispersal of blacklegged tick (Acari:Ixodidae) nymphs and adults at the woods-pasture interface.

Marked nymphal and adult blacklegged ticks, Ixodes scapularis Say, were released in 4 host-exclusion cages and 4 similar control areas, all straddling the woods-pasture interface. Both nymphs and adults were recaptured by flagging at regular intervals outside the cages, having therefore actively dispersed > 4.5 m (i.e., without involvement of vertebrates). Nymphs were recaptured much more often ( > 90%) in the woods than pastures, whereas 62.8% of recaptured adults were taken in pastures. Females were recaptured in equal numbers in pastures and woods, but 75.4% of recaptured males were in pastures. Adults that dispersed into pastures were recaptured an average of 1.6 and 3.7 m from the woods edge in 1992 and 1993, respectively, and as far as 7-8 m from the woods edge. Nymphs dispersed shorter distances than adults with 66% of the recaptured nymphs found 2-3 m from their release points, and > 46% of recaptured adults found > 5 m from their release points. Twice as many nymphs were recaptured from the caged than uncaged sites. The lower numbers of nymphs recaptured from control sites compared with caged sites are probably the result of host acquisition; the absence of this discrepancy with the adults may reflect by their ability to move relatively quickly from the host-exclusion cages and become available for host contact.

Animals↗
PubMed1996

Field and laboratory responses of adult Ixodes scapularis (Acari: Ixodidae) to kairomones produced by white-tailed deer.

In a field test, adult blacklegged ticks, Ixodes scapularis Say, of both sexes exhibited an arrestant response to substances associated with external glands on the legs of white-tailed deer, Odocoileus virginianus (Zimmermann), their principal host. Substances rubbed from the pelage covering tarsal and interdigital glands were applied to artificial vantage points simulating vegetation on which I. scapularis adults wait for host contact. A combination of tarsal substances (applied to the apex of the simulated vantage point) and interdigital gland substances (applied to the horizontal base) elicited a greater response than either treatment alone. A minimal response was observed on untreated vantage points. In laboratory bioassays using glass tubing as vantage points, substances associated with preorbital glands of deer elicited a strong arrestant response among I. scapularis females, whereas samples rubbed from the forehead, back, and a nonglandular area on deer tarsi evoked weak arrestant responses. These results support the hypothesis that the kairomonal properties of host-generated residues, either in conjunction with or in lieu of the effects of carbon dioxide, help account for the prevalence of host-seeking ticks along animal trails.

Animals↗
PubMed1996

Silt fencing as a barrier to the dispersal of Ixodes scapularis (Acari:Ixodidae) into pastures.

Silt fence barriers were set along pasture fencelines and evaluated as a method of restricting the dispersal of blacklegged tick, Ixodes scapularis Say, adults and nymphs from woodlands into adjacent horse pastures. The barriers received no acaricidal treatment for the 1st cohort of adults. Thereafter the woods side of the barriers was sprayed with cyfluthrin at the onset of each season of host seeking activity of nymphs and adults. When high densities of adults were present, the barriers significantly limited the numbers of ticks in pastures. Nymphs, however, were not significantly fewer in numbers in pasture areas associated with the barriers compared with control areas. Marked adult ticks released in woodlands and ecotones were recaptured on mowed verges and pastures, but there was little dispersal from the woods edge into the woods.

Animals↗
PubMed1996

Occurrence of larval Ixodes scapularis (Acari:Ixodidae) on tree trunks.

Host-seeking larvae of blacklegged ticks, Ixodes scapularis Say, were found on the trunks of 7 species of trees in a mixed deciduous woodland in Maryland. Where larvae were present around the bases of trees, larvae were found on 45.8% of the tree trucks. Almost 15% of the larvae found on tree trunks were approximately 1-2 m above the ground. Larger trees harbored larvae more often than smaller trees. Trees having a circumference at breast height of > or = 1 m (0.96 m diameter) averaged 3.19 larvae. Because white-footed mice, Peromyscus leucopus (Rafinesque), the principal hosts of I. scapularis larvae, frequently nest in trees, it may not be detrimental to host-seeking larvae to ascend and remain on tree trunks.

Animals↗
PubMed1996

Hypertension, cardiac hypertrophy, and neurohumoral activity in a new animal model of obesity.

Although obesity is a major risk factor for morbidity and mortality, the mechanisms mediating cardiovascular abnormalities in response to weight gain are unclear. One reason for the paucity of information in this area is the lack of appropriate animal models for the study of human obesity. Therefore, the goal of the present study was to develop a small animal model of dietary-induced obesity that mimics many of the characteristics of human obesity. We studied female New Zealand White rabbits fed either a normal (n = 17) or high-fat diet (n = 15) and examined the cardiovascular consequences of obesity, including changes in blood pressure, humoral activation, and end-organ effects such as cardiac hypertrophy. After 12 wk, rabbits on the high-fat diet were 46% heavier than their lean counterparts (5.49 +/- 0.09 vs. 3.77 +/- 0.06 kg, respectively; P = 0.0001). Obese rabbits had higher resting heart rates than lean rabbits (220 +/- 7 vs. 177 +/- 6 beats/min; P = 0.0001) and developed hypertension (96 +/- 2 vs. 85 +/- 1 mmHg; P = 0.0001), hyperinsulinemia (32.5 +/- 3.4 vs. 15.5 +/- 1.0 microU/ml; P = 0.0001), hyperglycemia (162.4 +/- 2.9 vs. 141.9 +/- 2.7 mg/dl; P = 0.0001), and elevated triglycerides (102.3 +/- 9.1 vs. 48.5 +/- 4.0 mg/dl; P = 0.0001). Obese rabbits also developed cardiac hypertrophy, as evidenced by left ventricular (LV) dry weights that were 52% greater in obese than in lean rabbits (P = 0.0003). In addition, LV total protein was increased in proportion to the increase in LV weight. The results of this study suggest that rabbits fed a high-fat diet for a period of 12 wk develop many of the characteristics of human obesity. The obese rabbit should provide a small and relatively inexpensive animal model to investigate mechanisms of obesity-related cardiovascular abnormalities.

Animals↗
PubMed1996

Immunologic assessment of patients treated with bovine fibrin as a hemostatic agent.

Twenty-one cardiothoracic surgical patients have been treated with fibrin as a topical hemostatic/sealing agent, prepared from bovine fibrinogen clotted with bovine thrombin. Serum samples have been collected before treatment with fibrin and postoperatively between 1 and 9 days, 3 and 12 weeks, and 6 and 8 months. The titers of anti-bovine fibrinogen antibodies, measured by ELISA specific for immunoglobulins IgG or IgM, increased to maximal values after about 8 or 6 weeks, respectively. After 8 months, IgG titers were on average 20-fold lower than the mean maximal value, while IgM titers returned to the normal range. IgG was the predominant anti-bovine fibrinogen immunoglobulin as documented by ELISA, affinity chromatography and electrophoresis. Anti-bovine fibrinogen antibodies present in patients reacted readily with bovine fibrinogen, but did not cross-react with human fibrinogen as measured by ELISA or by immunoelectrophoresis. A significant amount of antibodies against bovine thrombin and factor V has been found, many cross-reacting with the human counterparts. No hemorrhagic or thrombotic complications, or clinically significant allergic reactions, occurred in any patient, in spite of antibody presence against some bovine and human coagulation factors. The treatment of patients with bovine fibrin, without induction of immunologic response against human fibrinogen, appeared to be an effective topical hemostatic/sealing measure.

Animals↗