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Biomedical subjects

D A Calhoun

Publications and source records attributed to D A Calhoun.

64 records · Page 4Linked to original sources
PubMed1992

Atrial natriuretic peptide modulates baroreceptor reflex in spontaneously hypertensive rat.

Our previous studies have suggested that atrial natriuretic peptide in the caudal nucleus tractus solitarii is involved in the centrally mediated regulation of blood pressure in the salt-sensitive spontaneously hypertensive rat (SHR). The current study tested the hypothesis that endogenous atrial natriuretic peptide in the caudal nucleus tractus solitarii participates in baroreceptor reflex control of heart rate in this hypertensive model. Salt-sensitive SHR and control Wistar-Kyoto (WKY) rats maintained on basal (1%) salt intake were studied. Arterial baroreceptor reflex-mediated changes in heart rate were recorded in conscious unrestrained rats during phenylephrine (5-40 micrograms.kg-1.min-1 infusion; 30 minutes later, atrial natriuretic peptide (50 ng), monoclonal antibody to atrial natriuretic peptide (0.55 micrograms), purified mouse immunoglobulin G (0.55 micrograms), or artificial cerebrospinal fluid vehicle (50 nl) was microinjected into the caudal nucleus tractus solitarii. Phenylephrine infusion was then repeated and mean arterial pressure and heart rate were monitored as before. The slope of the heart rate/mean arterial pressure relation was significantly less (p less than 0.05) in the salt-sensitive SHR than in the WKY control, indicating that baroreceptor reflex control of heart rate was blunted in this hypertensive model. Microinjection of atrial natriuretic peptide into the caudal nucleus tractus solitarii further blunted (p less than 0.05) baroreceptor reflex control of heart rate in salt-sensitive SHR but not in WKY rats. In contrast, microinjection of the monoclonal antibody enhanced the sensitivity of baroreceptor reflex control of heart rate in salt-sensitive SHR but not in WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Cigarette smoking and the adrenergic nervous system.

The acute increase in blood pressure and heart rate that accompanies cigarette smoking is associated with a rise in plasma catecholamines and it is thus believed to result from stimulation of the adrenergic nervous system. We have employed direct recording of efferent post-ganglionic sympathetic nerve activity by the microneurographic technique from the peroneal nerve to determine whether this stimulation occurs centrally or peripherally. It was shown that during cigarette smoking blood pressure, heart rate, plasma norepinephrine and epinephrine do increase markedly. Sympathetic nerve activity, however, shows a concomitant specular reduction. Thus peripheral (adrenal gland stimulation, reduction in norepinephrine reuptake, reduction in catecholamine clearance, etc.) rather than central mechanisms explain the adrenergic involvement in the acute hemodynamic effect of smoking, the central sympathetic drive being inhibited rather than excited probably as a result of arterial baroreceptor stimulation.

Blood Pressure↗
PubMed1991

The calcium antagonists in the 1990s. An overview.

The calcium antagonists are effective in the treatment of essential hypertension. This quality, in addition to their ability to inhibit atherosclerotic lesion formation, may make them superior to other classes of antihypertensive agents in preventing vascular complications of mild to moderate hypertension. Preliminary results of clinical trials suggest that the calcium antagonists retard the progression of early atherosclerotic lesions in native coronary arteries and saphenous vein grafts, but have less effect on established lesions. Further study is needed to determine whether these agents have a favorable effect on the overall clinical outcome of patients with coronary artery disease. Clinical trials also suggest that the calcium antagonists retard the progression of renal insufficiency in hypertensive patients by mechanism(s) that do not depend on blood pressure lowering per se. Prospective studies with larger numbers of patients are needed to determine whether these apparent renoprotective effects are sustained for the long term in both diabetic and nondiabetic hypertensive populations. The dihydropyridine calcium antagonists are effective in reducing brain damage and mortality secondary to acute ischemic stroke. It is still unknown whether they are also effective in the primary and secondary prevention of ischemic stroke, and whether other classes of calcium antagonists are useful in the prevention and/or treatment of ischemic stroke. The potential antiatherosclerotic and cardio-, neuro-, and renoprotective effects of the calcium antagonists, coupled with their lack of adverse metabolic effects, have defined an expanding therapeutic role for these agents in the 1990s.

Animals↗
PubMed1991

High NaCl diet enhances arterial baroreceptor reflex in NaCl-sensitive spontaneously hypertensive rats.

Previous studies from our laboratory have shown that arterial baroreceptor reflex control of lumbar sympathetic nerve activity is blunted in the NaCl-sensitive spontaneously hypertensive rat (SHR-S) compared with either the NaCl-resistant spontaneously hypertensive rat (SHR-R) or the normotensive Wistar-Kyoto (WKY) rat. In the current study, the effect of dietary NaCl supplementation on arterial baroreceptor reflex control of lumbar sympathetic nerve activity and heart rate was assessed in SHR-S and control SHR-R and WKY rats. Male SHR-S, SHR-R, and WKY rats were fed diets containing either 1% or 8% NaCl beginning at 7 weeks of age and were studied at age 9-10 weeks. Arterial baroreceptor reflex-mediated changes in lumbar sympathetic nerve activity and heart rate were recorded in conscious, unrestrained rats during phenylephrine-induced (15-40 micrograms/kg/min) and nitroprusside-induced (15-300 micrograms/kg/min) changes in mean arterial pressure. SHR-S maintained on a 1% NaCl diet had blunted baroreceptor reflex control of lumbar sympathetic nerve activity during acute increases in MAP compared with SHR-R and WKY rats (p less than 0.05). After ingestion of the 8% NaCl diet, this blunting was absent, indicating enhancement of baroreceptor reflex control of lumbar sympathetic nerve activity. SHR-S maintained on a 1% NaCl diet also had blunted arterial baroreceptor control of lumbar sympathetic nerve activity during nitroprusside-induced decreases in mean arterial pressure compared with WKY rats, but this was not significantly altered during ingestion of the 8% NaCl diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Hypertension.

An estimated 58 million Americans are at increased risk of morbidity and premature death due to high blood pressure (BP) and require some type of therapy or systematic monitoring. This article focuses on recent advances in our understanding of the pathogenesis of hypertension, new approaches to the diagnosis and treatment of secondary hypertension, and current views of the most appropriate nonpharmacologic and pharmacologic therapy for essential hypertension. In view of the extremely high prevalence of the disorder, emphasis is placed on efficient and cost-effective strategies for diagnosing and managing the hypertensive patient. Recent evidence indicates that nonpharmacologic therapy, including dietary potassium and calcium supplements, reduction of salt intake, weight loss for the obese patient, regular exercise, a diet high in fiber and low in cholesterol and saturated fats, smoking cessation, and moderation of alcohol consumption produces significant sustained reductions in BP while reducing overall cardiovascular risk. Accordingly, nonpharmacologic antihypertensive therapy should be included in the treatment of all hypertensive patients. In persons with mild hypertension, nonpharmacologic approaches may adequately reduce BP, thereby avoiding the expense and potential side effects of drug therapy. In patients with more severe hypertension, nonpharmacologic therapy, used in conjunction with pharmacologic therapy, can reduce the dosage of antihypertensive medications necessary for BP control. Patients treated with nonpharmacologic therapy only should be followed closely, and if BP control is not satisfactory, drug therapy should be added. The large number of drugs available for use in hypertension treatment, coupled with our rapidly expanding knowledge of the pathophysiology of hypertension and of the adverse effects of these drugs in individual patient groups, make it possible to individualize antihypertensive treatment. When used as monotherapy, most agents effectively lower BP in the majority of patients with mild or moderate essential hypertension. Thus, a single agent from one of four classes: diuretics, angiotensin-converting enzyme inhibitors, calcium channel blockers, and beta-adrenergic blockers, usually provides effective BP control with minimal side effects in most patients. Therapy should be initiated with the agent most likely to be effective in BP lowering and best tolerated. If the initial agent is ineffective at maximal recommended therapeutic doses or has undue side effects, an alternative agent from another class should be tried. When monotherapy is unsuccessful, a second agent, usually of a different mechanism of action, should be

Adrenergic alpha-Antagonists↗
PubMedDate not supplied

Congenital ischemic forearm necrosis associated with a compound presentation.

An infant born in a compound presentation had ischemic forearm necrosis requiring amputation. Bilateral renal vein thrombosis predating labor and delivery was also diagnosed. The possibility of congenital ischemic necrosis in an extremity should not affect the obstetrical management of compound presentation, but if this complication occurs a search for an underlying coagulopathy is important.

Adult↗
PubMedDate not supplied

Granulocyte-macrophage colony-stimulating factor and interleukin-5 concentrations in premature neonates with eosinophilia.

OBJECTIVE: Eosinophilia is common among premature neonates, but little is known about the cytokines responsible for influencing its onset in neonates. In adults and transgenic mice, granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-5 (IL-5) influence the development of eosinophilia. We sought to prospectively determine whether these cytokines correlated with the development of eosinophilia in premature infants. STUDY DESIGN: We measured the absolute eosinophil count (AEC) and serial serum concentrations of GM-CSF and IL-5 in premature neonates with eosinophilia. RESULTS: Among 201 premature neonates, 21 had an eosinophil count of > 700/microliter (occurrence, 10.5%). Of these 21 neonates, 4 had mild (700/microliter to 999/microliter), 13 had moderate (1000/microliter to 2999/microliter), and 4 had severe (> 3000/microliter) eosinophilia. No differences in gestational age or age at onset of eosinophilia were observed between the groups, but the duration of eosinophilia was less with mild than with moderate or severe eosinophilia. A total of 20 of the 21 patients had an infection or necrotizing enterocolitis diagnosed within 48 hours of the onset of eosinophilia. In patients with mild and moderate eosinophilia, serial GM-CSF and IL-5 concentrations were below the lowest enzyme-linked immunosorbent assay standard. There was no correlation between AEC and GM-CSF or IL-5 concentration in these infants. However, in one patient with severe eosinophilia, two distinct elevations in IL-5 were noted (34.6 and 46.0 pg/ml); each peak occurred 7 to 8 days before a peak in eosinophil count. CONCLUSION: Eosinophilia is relatively common, and in those neonates with the highest AECs, the duration of eosinophilia can last for > 6 weeks. The majority of cases of eosinophilia occurred in temporal proximity to an infectious illness or necrotizing enterocolitis. Serum concentrations of IL-5 were elevated in only one of our patients with severe eosinophilia.

Biomarkers↗
PubMedDate not supplied

High blood pressure in women.

There is a sexual dimorphism in blood pressure of humans and experimental animals: males tend to have higher blood pressure than females with functional ovaries, while ovariectomy or menopause tends to abolish the sexual dimorphism and cause females to develop a "male" pattern of blood pressure. Hypertensive male laboratory animals tend to have NaCl-sensitive blood pressure, while females are NaCl resistant unless their ovaries are removed, in which case NaCl sensitivity appears. The hormonal basis of NaCl sensitivity of blood pressure and of the sexual dimorphism of hypertension remains to be defined. Synthetic estrogens and progestins, as found in oral contraceptives, tend to elevate blood pressure, while naturally occurring estrogens lower it, or have no effect. Hypertension increases cardiovascular risk in women, as well as men, although the benefits of antihypertensive treatment have been more difficult to demonstrate in women. In the population of the United States, women are more aware of their hypertension, more likely to be treated medically, and more likely to have their blood pressure controlled.

Adult↗