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H L Collins

Publications and source records attributed to H L Collins.

At least 37 records · Page 2Linked to original sources
PubMed2000

Post-exercise elevations in sympathetic nerve activity and baroreflex function in normotensive rabbits.

We tested the hypothesis that a single bout of dynamic exercise reduces post-exercise arterial pressure, heart rate, and renal sympathetic nerve activity and attenuates the arterial baroreflex control of heart rate and renal sympathetic nerve activity in normotensive New Zealand White rabbits. Animals were chronically instrumented with right jugular venous and left femoral arterial catheters, and electrodes around the renal sympathetic nerve. Arterial pressure, heart rate, and renal sympathetic nerve activity were recorded for two hours pre-exercise and two hours after a single bout of treadmill exercise (post-exercise). Post-exercise heart rate, arterial pressure, and renal sympathetic nerve activity were elevated above pre-exercise values (71+/-3 bpm, 13+/-1 mmHg, and 80+/-21%, respectively). These data demonstrate that normotensive rabbits do not exhibit post-exercise hypotension, due in part to elevations in sympathetic nerve activity. In addition, arterial baroreflex regulation of heart rate and renal sympathetic nerve activity were determined pre- and post-exercise. Exercise shifted the baroreflex function curve for heart rate and renal sympathetic nerve activity upward and to the right without a change in gain. These data suggest that post-exercise elevations in sympathetic nerve activity are due, in part, to an elevation of the operating point of the arterial baroreflex to a higher pressure. These responses in normotensive rabbits contrast sharply with the responses in hypertensive individuals and animals. Understanding the mechanisms contributing to the differences between hypertensive and normotensive subjects may lead to measures designed to lower arterial pressure in hypertensive individuals.

Animals↗
PubMed2000

Daily exercise attenuated the sympathetic component of the spontaneous arterial baroreflex control of heart rate in hypertensive rats.

The influence of daily spontaneous running on the sympathetic and parasympathetic components of the spontaneous arterial baroreflex control of heart rate was examined in 22 female spontaneously hypertensive rats [12 sedentary and 10 daily spontaneous running]. Following 8 weeks of sedentary control or daily spontaneous running, animals were chronically instrumented with an arterial catheter. Daily spontaneous running resulted in an increased heart weight/body weight ratio (5.2 +/- 0.27 vs 4.3 +/- 0.01 g/kg) and a resting bradycardia (321+/- 8 bpm vs 360 +/- 6). The spontaneous changes in arterial pressure and the reflex responses of heart rate were examined under three experimental conditions: 1) pre-blockade, 2) following beta1-adrenergic receptor blockade, and 3) following muscarinic-cholinergic receptor blockade. Daily spontaneous running attenuated the spontaneous gain of the arterial baroreflex control of heart rate (56%). After muscarinic-cholinergic receptor blockade, the spontaneous gain remained reduced in daily spontaneous running rats (57%). In contrast, after beta1-adrenergic receptor blockade the spontaneous gain was not different between sedentary control and daily spontaneous running animals. Results demonstrate that daily spontaneous running decreased the sympathetic component resulting in an apparently greater influence of the parasympathetic component on the spontaneous arterial baroreflex control of heart rate.

Adrenergic beta-Antagonists↗
PubMed2000

Autonomic and endothelial dysfunction in experimental diabetes.

The effect of streptozotocin induced diabetes on autonomic regulation of heart rate and endothelial function was examined in Sprague-Dawley rats. Weanling rats (3-4 weeks of age) of either sex were randomly assigned to a non-diabetic (male 5, female 6) or diabetic (male 4, female 5). Diabetes was induced with a single intraperitoneal (IP) injection of streptozotocin (STZ, 100 mg/kg). Nondiabetic rats received an IP injection of saline. Eight weeks after injection, rats were chronically instrumented with a left jugular venous catheter and a left carotid arterial catheter. After recovery (5 days) cardiac sympathetic tonus, parasympathetic tonus and intrinsic heart rate were determined. On an alternative day, the pressor response to nitric oxide synthase inhibition (NOS-X) was determined in areflexic rats. Cardiac sympathetic tonus (72 +/- 13 vs. 41 +/- 7), parasympathetic tonus (-51 +/- 10 vs. -22 +/- 7), and intrinsic heart rate (368 +/- 6 vs. 292 +/- 9), were reduced in diabetic rats. Furthermore, diabetic rats had a smaller pressor response (A33 +/- 7 vs. A66 +/- 5) to NOS-X. These results document impaired autonomic control of heart rate and endothelial dysfunction in 8-week streptozotocin induced diabetic rats.

Adrenergic beta-Antagonists↗
PubMed2000

Development and characterization of diamondback moth resistance to transgenic broccoli expressing high levels of Cry1C.

A field-collected colony of the diamondback moth, Plutella xylostella, had 31-fold resistance to Cry1C protoxin of Bacillus thuringiensis. After 24 generations of selection with Cry1C protoxin and transgenic broccoli expressing a Cry1C protein, the resistance that developed was high enough that neonates of the resistant strain could complete their entire life cycle on transgenic broccoli expressing high levels of Cry1C. After 26 generations of selection, the resistance ratios of this strain to Cry1C protoxin were 12,400- and 63,100-fold, respectively, for the neonates and second instars by a leaf dip assay. The resistance remained stable until generation 38 (G38) under continuous selection but decreased to 235-fold at G38 when selection ceased at G28. The Cry1C resistance in this strain was seen to be inherited as an autosomal and incompletely recessive factor or factors when evaluated using a leaf dip assay and recessive when evaluated using Cry1C transgenic broccoli. Saturable binding of (125)I-Cry1C was found with brush border membrane vesicles (BBMV) from both susceptible and Cry1C-resistant strains. Significant differences in Cry1C binding to BBMV from the two strains were detected. BBMV from the resistant strain had about sevenfold-lower affinity for Cry1C and threefold-higher binding site concentration than BBMV from the susceptible strain. The overall Cry1C binding affinity was just 2.5-fold higher for BBMV from the susceptible strain than it was for BBMV from the resistant strain. These results suggest that reduced binding is not the major mechanism of resistance to Cry1C.

Animals↗
PubMed2000

Who wants to be a physician? An educational tool for reviewing pulmonary physiology.

Traditional review sessions are typically focused on instructor-based learning. However, experts in the field of higher education have long recommended teaching modalities that incorporate student-based active-learning strategies. Given this, we developed an educational game in pulmonary physiology for first-year medical students based loosely on the popular television game show Who Wants To Be A Millionaire. The purpose of our game, Who Wants To Be A Physician, was to provide students with an educational tool by which to review material previously presented in class. Our goal in designing this game was to encourage students to be active participants in their own learning process. The Who Wants To Be A Physician game was constructed in the form of a manual consisting of a bank of questions in various areas of pulmonary physiology: basic concepts, pulmonary mechanics, ventilation, pulmonary blood flow, pulmonary gas exchange, gas transport, and control of ventilation. Detailed answers are included in the manual to assist the instructor or player in comprehension of the material. In addition, an evaluation instrument was used to assess the effectiveness of this instructional tool in an academic setting. Specifically, the evaluation instrument addressed five major components, including goals and objectives, participation, content, components and organization, and summary and recommendations. Students responded positively to our game and the concept of active learning. Moreover, we are confident that this educational tool has enhanced the students' learning process and their ability to understand and retain information.

Blood Flow Velocity↗
PubMed2000

Arterial baroreflex regulation of regional vascular conductance at rest and during exercise.

We tested the hypothesis that dynamic exercise resets the operating point and attenuates the spontaneous gain of the arterial baroreflex regulation of mesenteric and hindlimb vascular conductance in hypertensive rats. Eleven adult male spontaneously hypertensive rats were chronically instrumented with left carotid arterial catheters and Doppler ultrasonic flow probes around the superior mesenteric and left common iliac arteries. After the rats recovered, arterial baroreflex function was examined by recording reflex changes in conductance in response to spontaneous changes in mean arterial pressure before exercise and during steady-state treadmill running at 6 and 18 m/min. Dynamic exercise reduced the spontaneous baroreflex gain of mesenteric conductance (by 51 and 36%) and maximum mesenteric conductance (by 24 and 32%) at 6 and 18 m/min, respectively. In sharp contrast, dynamic exercise increased the spontaneous maximum iliac conductance (by 32 and 47%) without changing the spontaneous gain. Sinoaortic denervation eliminated the relationship between mean arterial pressure and conductance by reducing the mesenteric (92%) and iliac (68%) vascular conductance gain. These results demonstrate that dynamic exercise has differential effects on the regulation of mesenteric and iliac vascular conductance in hypertensive rats.

Animals↗
PubMed2000

Assessment of insecticide resistance after the outbreak of diamondback moth (Lepidoptera: Plutellidae) in California in 1997.

During an outbreak of the diamondback moth, Plutella xylostella (L.), in California in 1997, nine populations were collected from the major broccoli areas throughout the state. Populations were assayed for their susceptibility to currently used materials (Bacillus thuringiensis subsp. kurstaki, permethrin, and methomyl) and to newer materials that had not yet been commercially used in California (spinosad, emamectin benzoate, and chlorfenapyr). For the currently used insecticides, elevated levels of resistance were seen only with permethrin and seven of the nine populations had tolerance ratios (TR) of > 100. With the newer chemistries, TR values were all < 15. To compare potential cross-tolerance, TR values of the currently used insecticides were compared with TR values of the newer insecticides. There were significant relationships found between: methomyl and emamectin benzoate, methomyl and spinosad, and permethrin and spinosad. Further biochemical studies are needed to confirm the actual mechanisms that lead to these relationships and field tests are needed to determine what impact, if any, such TR levels would have on control in the field. These data indicate that resistance to at least one of the commonly used insecticides (permethrin) may have played a role in the outbreak during 1997. However, other factors may have been at least equally important. The winter of 1996-1997 was warmer than normal, and during the period from February through August of 1997 the amount of rainfall was < 50% of normal. Hot and dry conditions are known to be conducive to outbreaks of P. xylostella. These data add to an overall knowledge about the geographic variation of resistance in P. xylostella populations within the United States. They also serve as a baseline for monitoring changes in susceptibility to these newer insecticides and can also help explain the occurrence of outbreaks caused by factors other than insecticide resistance.

Animals↗
PubMed1999

Apolipoprotein B mRNA and lipoprotein secretion are increased in McArdle RH-7777 cells by expression of betaine-homocysteine S-methyltransferase.

The cDNA encoding rat betaine-homocysteine S-methyltransferase (BHMT) was isolated through production of monoclonal antibodies against protein fractions enriched with apolipoprotein B (apo B)-mRNA-editing complexes. BHMT mRNA was expressed predominantly in liver, and also in kidney, but not in small intestine. In stable McArdle RH-7777 (McA) cell lines expressing differing levels of BHMT, the editing efficiency of apo B mRNA was unchanged. Evaluation of apo B-mRNA expression revealed that steady-state levels were increased significantly and in parallel with BHMT protein expression. The highest levels of BHMT mRNA and BHMT enzyme activity expressed in stably transfected McA cells were comparable with those found in rat hepatocytes. In contrast to the changes in apo B-mRNA abundance, levels of other apolipoprotein-encoding mRNAs and several liver-specific and ubiquitously expressed mRNAs were unchanged by BHMT expression. In the cell line expressing the highest level of BHMT, apo B-containing lipoprotein secretion was increased, indicating utilization of increased endogenous message. Results suggest that apo B-mRNA abundance in McA cells is related to the expression of BHMT, an enzyme important in homocysteine metabolism.

Amino Acid Sequence↗
PubMed1999

An inquiry-based teaching tool for understanding arterial blood pressure regulation and cardiovascular function.

Educators are placing a greater emphasis on the development of cooperative laboratory experiences that supplement the traditional lecture format. The new laboratory materials should encourage active learning, problem-solving, and inquiry-based approaches. To address these goals, we developed a laboratory exercise designed to introduce students to the hemodynamic variables (heart rate, stroke volume, total peripheral resistance, and compliance) that alter arterial pressure. For this experience, students are presented with "unknown" chart recordings illustrating pulsatile arterial pressure before and in response to several interventions. Students must analyze and interpret these unknown recordings and match each recording with the appropriate intervention. These active learning procedures help students understand and apply basic science concepts in a challenging and interactive format. Furthermore, laboratory experiences may enhance the students' level of understanding and ability to synthesize and apply information. In conducting this exercise, students are introduced to the joys and excitement of inquiry-based learning through experimentation.

Blood Pressure↗
PubMed1999

Construction of a model demonstrating cardiovascular principles.

We developed a laboratory exercise that involves the construction and subsequent manipulation of a model of the cardiovascular system. The laboratory was designed to engage students in interactive, inquiry-based learning and to stimulate interest for future science study. The model presents a concrete means by which cardiovascular mechanics can be understood as well as a focal point for student interaction and discussion of cardiovascular principles. The laboratory contains directions for the construction of an inexpensive, easy-to-build model as well as an experimental protocol. From this experience students may gain an appreciation fo science that cannot be obtained by reading a book or interacting with a computer. Students not only learn the significant physiological concepts but also appreciate the importance of laboratory experimentation for understanding complex concepts. Model construction provides a hands-on experience that may substantially improve performance in science processes. We believe that model construction is an appropriate method for teaching advanced concepts.

Cardiovascular Physiological Phenomena↗
PubMed1999

Postexercise hypotension is mediated by reductions in sympathetic nerve activity.

Mean arterial pressure (MAP), the product of cardiac output (CO) and total peripheral resistance (TPR), is reduced below preexercise levels after a single bout of mild to moderate dynamic exercise. Thus acute, dynamic exercise may be used as a safe, therapeutic approach to reduce MAP. However, the mechanisms responsible for the postexercise hypotension (PEH) are unknown. We tested the hypothesis that PEH is associated with reductions in TPR and sympathetic nerve activity (SNA). Two experimental protocols were designed to test this hypothesis in male spontaneously hypertensive rats (SHR). In protocol 1 (n = 9), CO and TPR were determined before, during, and after exercise. In protocol 2 (n = 7), lumbar SNA (LSNA) was recorded before and after exercise. Rats in protocol 1 were chronically instrumented with left carotid arterial catheters and ascending aortic Doppler ultrasonic flow probes. Rats in protocol 2 were chronically instrumented with left carotid arterial catheters and electrodes around the lumbar sympathetic trunk. Dynamic treadmill exercise (9-12 m/min, 10% grade for 40 min) resulted in a postexercise reduction in MAP (from 143 +/- 5 to 128 +/- 4 mmHg, P < 0.05). Associated with the PEH was a reduction in TPR (from 28 +/- 3 to 19 +/- 2 mmHg/kHz; P < 0.05) and an elevation in CO (from 5.7 +/- 0.4 to 7.2 +/- 0.5 kHz; P < 0.05). The reductions in arterial pressure and TPR were associated with a decrease in LSNA (from 98 +/- 3 to 49 +/- 6%; P < 0.05). These results suggest that PEH is mediated by reductions in TPR and SNA.

Animals↗
PubMed1999

Muscle metaboreflex improves O2 delivery to ischemic active skeletal muscle.

Ischemia of active skeletal muscle elicits a powerful pressor response, termed the muscle metaboreflex. We recently reported that the muscle metaboreflex pressor response acts to partially restore blood flow to the ischemic active skeletal muscle. However, because this reflex is activated by reductions in O2 delivery rather than blood flow per se, gain of the muscle metaboreflex as analyzed on the basis of blood flow alone may underestimate its true strength if this reflex also acts to increase arterial O2 content. In conscious dogs chronically instrumented to measure systemic arterial pressure, cardiac output, and hindlimb blood flow, we activated the muscle metaboreflex via graded, partial reductions in hindlimb blood flow during mild (3.2 km/h) and moderate (6.4 km/h, 10% grade) workloads. At rest, during free-flow exercise, and with metaboreflex activation, we analyzed arterial blood samples for Hb concentration and O2 content and compared muscle metaboreflex gain calculations based on the ability to partially restore flow with those based on the ability to partially restore O2 delivery (blood flow x arterial O2 content). During both mild and moderate exercise, metaboreflex activation caused significant increases in arterial Hb concentration and O2 content. Metaboreflex gain quantified on the ability to partially restore O2 delivery was significantly greater than that based on restoration of blood flow during both mild and moderate workloads (0.52 +/- 0.10 vs. 0.39 +/- 0.08, P < 0.05, and 0.61 +/- 0. 05 vs. 0.46 +/- 0.04, P < 0.05, respectively). We conclude that the muscle metaboreflex acts to increase both arterial O2 content and blood flow to ischemic muscle such that when combined, O2 delivery is substantially increased and metaboreflex gain is greater when analyzed with a more integrative approach.

Animals↗
PubMed1999

Daily exercise enhances acetylcholine-induced dilation in mesenteric and hindlimb vasculature of hypertensive rats.

The effect of daily spontaneous running (DSR) on endothelial function was examined in spontaneously hypertensive rats (SHR). Following 8-11 weeks of DSR (n=15) or sedentary control (SED, n=15), rats were instrumented with arterial and venous catheters and mesenteric and iliac Doppler ultrasonic flow probes. Hemodynamic responses to vasodilator-mediated substances were determined under two experimental conditions; 1) bolus injection of indomethacin (10 mg/kg) and 4 bolus doses of acetylcholine (0.5-2.0 microg/kg); 2) bolus injection of N(omega)-nitro-L-arginine (5 mg/kg) and 4 bolus doses of nitroglycerin (3-12 microg/kg). Hindlimb vascular conductance decreased more in response to indomethacin in DSR vs. SED rats (-18.3+/-2.8% vs. -10.4+/-2.5%). However, the mesenteric or hindlimb vascular conductance responses to N(omega)-nitro-L-arginine were not different between DSR and SED rats. DSR also enhanced mesenteric and hindlimb vascular conductance responses to acetylcholine. Results suggest that DSR enhances acetylcholine-induced vasodilation in SHR.

Acetylcholine↗
PubMed1998

Early IL-4 induction in bone marrow lymphoid precursor cells by mycobacterial lipoarabinomannan.

IL-4 is produced promptly in response to certain infections and plays a key role in the Th1/Th2 T cell dichotomy; however, the cellular source remains a matter of debate. Here we describe the induction of IL-4 in bone marrow cells of normal and RAG-/- mice by both Mycobacterium tuberculosis and its major cell wall glycolipid, lipoarabinomannan. Characterization of the cell type responsible indicated that it was distinct from the NK1+ or CD4+ T cell previously ascribed the function of rapid IL-4 secretion. Cell-sorting experiments identified CD19+/B220+ precursor cells, presumably pre-B cells that produced IL-4 constitutively and whose frequency was rapidly and markedly up-regulated by lipoarabinomannan. Thus, pathogenic mycobacteria and their glycolipids may influence hemopoiesis by rapidly inducing IL-4 secretion in the bone marrow.

Animals↗
PubMed1998

Chemo-radiotherapy for localized pancreatic cancer: increased dose intensity and reduced acute toxicity with concomitant radiotherapy and protracted venous infusion 5-fluorouracil.

PURPOSE: Although concomitant radiation therapy (RT) and bolus 5-Fluorouracil (5-FU) have been shown to improve survival in locally confined pancreatic cancer, most patients will eventually succumb to their disease. Since 1994, we have attempted to improve efficacy by administering 5-FU as a protracted venous infusion (PVI). This study compares treatment intensity and acute toxicity of consecutive protocols of concurrent RT and 5-FU by bolus injection or PVI. METHODS AND MATERIALS: Since 1986, 74 patients with resected or locally advanced pancreatic cancer were treated with continuous course RT and concurrent 5-FU by bolus injection (n = 44) or PVI throughout the course of RT (n = 30). Dose intensity was assessed for both 5-FU and radiotherapy. Toxicity endpoints which could be reliably and objectively quantified (e.g., neutropenia, weight loss, treatment interruption) were evaluated. RESULTS: Cumulative 5-FU dose (mean = 7.2 vs. 2.5 gm/m2, p < 0.001) and weekly 5-FU dose (mean = 1.3 vs. 0.5 gm/m2/wk, p < 0.001) were significantly higher for patients receiving PVI 5-FU. Following pancreaticoduodenectomy, 95% of PVI patients maintained a RT dose intensity of > or = 900 cGy/wk, compared with 63% of those receiving bolus 5-FU (p = 0.02). No difference was seen for patients with locally advanced disease (72% vs. 76%, p = n.s.). Grade II-III neutropenia was less common for patients treated with PVI (13% vs. 34%, p = 0.05). Grade II-III thrombocytopenia was uncommon (< or = 3%) in both treatment groups. Mean percent weight loss (3.8% vs. 4.1%, p = n.s.) and weight loss > or = 5% of pre-treatment weight (21% vs. 31%, p = n.s.) were similar for PVI and bolus treatment groups, respectively. Treatment interruptions for hematologic, gastrointestinal or other acute toxicities were less common for patients receiving PVI 5-FU (10% vs. 25%, p = 0.11). CONCLUSION: Concurrent RT and 5-FU by PVI was well tolerated and permitted greater chemotherapy and radiotherapy dose intensity with reduced hematologic toxicity and fewer treatment interruptions compared with RT and bolus 5-FU. Longer follow-up will be needed to assess late effects and the impact on overall survival.

Adult↗
PubMed1997

Effects of fatty acids on apolipoprotein B secretion by McArdle RH-7777 rat hepatoma cells.

The effect of oleic acid (OA), stearic acid (SA) and elaidic acid (EA) on cellular and secreted apolipoprotein (apo) B was examined in McArdle RH-7777 (McArdle) hepatoma cells and in primary rat hepatocytes. ApoB secretion by McArdle cells was significantly inhibited by 20% in 8 h incubations in medium containing EA and SA and by 50% in medium containing OA. In contrast, apo B secretion and cellular apo B of primary rat hepatocytes was relatively unaffected by incubations in medium containing fatty acids. Both B100 and B48 secretion in McArdle wild type and B48 in apo B mRNA editing enzyme catalytic polypeptide transfectants expressing B48 were inhibited to a similar extent indicating an effect of OA on both apo B species. The effect of OA occurred without changes in cellular apo B or in apo B mRNA abundance suggesting a post-transcriptional mechanism. Time course studies indicate that the suppressive effect of OA requires 4 h of incubation suggesting the depletion of a limiting factor important in apoB secretion. By increasing the proportion of palmitic acid to OA in the medium, apoB secretion by McArdle cells was progressively restored to control levels implicating an unique role for newly synthesized saturated fatty acid.

Animals↗
PubMed1997

IL-6 produced by macrophages infected with Mycobacterium species suppresses T cell responses.

The ability of Mycobacterium bovis Calmette-Guérin bacillus-infected bone marrow-derived macrophages to process and present exogenously added Ags to T cells and stimulate their growth and production of IL-2 was examined. The infected macrophages were inhibited in their ability to activate T cells, and this inhibition could be transferred to uninfected macrophages with filtered supernatants from mycobacteria-infected macrophages. The inhibition was not due to decreases in macrophage viability, Ag uptake, or cell surface expression of MHC class II or other accessory molecules necessary for Ag presentation. Other intracellular pathogens such as Listeria monocytogenes and Leishmania mexicana did not induce the soluble inhibitory factor, while Mycobacterium avium strain 101 did, suggesting the factor is specific to infection with mycobacteria. The inhibitory effect was reversed completely by preincubation with neutralizing Abs against IL-6, and rIL-6 partially restored the effect. Approximately 10,000-fold more IL-6 was produced by mycobacteria-infected macrophages compared with uninfected controls. Such sustained levels of IL-6 may account for the immune unresponsiveness apparent in both human and murine mycobacterial disease.

Animals↗