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Biomedical subjects

R E Stewart

Publications and source records attributed to R E Stewart.

At least 73 records · Page 4Linked to original sources
PubMed1990

Morphine-augmented hepatobiliary scintigraphy in the severely ill: caution is in order.

Morphine augmentation in hepatobiliary scintigraphy has been reported as a useful tool to shorten imaging time. The technique has not been extensively evaluated in patients who are severely ill and receiving total parenteral nutrition, although the study of these patients with non-morphine-augmented hepatobiliary scintigraphy is problematic. The authors retrospectively analyzed 51 morphine-augmented hepatobiliary studies performed in a tertiary referral center on a population with a high proportion of severe intercurrent illness (18 patients, 14 of whom were receiving total parenteral nutrition) and hepatocellular dysfunction (eight patients). The overall sensitivity was 94%, specificity was 69%, and the false-positive rate was 40% for the diagnosis of acute cholecystitis. The majority of the false-positive cases occurred in the severely ill subgroup (false-positive rate, 60%). Morphine-augmented hepatobiliary studies may be advantageous because of shortened imaging time. However, patients who have severe intercurrent illness, whether or not they are receiving total parenteral nutrition, have a higher frequency of false-positive morphine-augmented hepatobiliary studies, and positive findings at scintigraphy in this patient group should be interpreted with caution.

Acute Disease↗
PubMed1990

Myocardial clearance kinetics of technetium-99m-SQ30217: a marker of regional myocardial blood flow.

SQ30217 is a new, technetium-99m-(99mTc) labeled perfusion agent introduced for cardiac imaging. To evaluate the myocardial tracer kinetics, 99mTc-SQ30217, was injected intracoronarily in open-chested dogs under baseline conditions and after administration of intravenous (i.v.) dipyridamole. Myocardial first-pass retention fraction averaged 0.90 +/- 0.04. Clearance of the tracer occurred in a biexponential manner. Sixty-seven percent of retained activity cleared with a half-time of 2.3 +/- 0.6 min, while the residual activity demonstrated slow clearance. The clearance rate of the rapid phase correlated with myocardial blood flow (r = 0.72, p less than 0.001). Myocardial SQ30217 clearance rate following i.v. injection as determined by dynamic imaging with tomography (SPRINT) averaged 21 +/- 4 min and increased to 13 +/- 4 min following dipyridamole. Thus, 99mTc-SQ30217 is a promising flow tracer with high initial myocardial retention and rapid tissue clearance, which allow repeated flow determinations within short time intervals using advanced SPECT technology.

Animals↗
PubMed1989

Habituation of sympathetic-adrenal medullary responses following exposure to chronic intermittent stress.

Two experiments examined sympathetic-adrenal medullary responses of laboratory rats after exposure to a brief period of stressful stimulation daily for 26 consecutive days. In the first experiment, rats were exposed to restraint stress for 30 minutes per day and in the second experiment, rats were exposed to inescapable footshock for 10 minutes per day. For each experiment, handled controls were stressed acutely to provide a basis for comparison with chronically stressed animals. In both experiments, chronically stressed rats gained less weight than controls. Basal plasma levels of norepinephrine (NE) and epinephrine (EPI) were similar in control and chronically stressed rats. However, there was a substantial attenuation of the plasma catecholamine response to the 27th episode of restraint or footshock compared to acutely stressed controls. These findings indicate that sympathetic-adrenal medullary responses are dampened considerably in animals exposed to a highly predictable regimen of chronic intermittent stress.

Adrenal Medulla↗
PubMed1989

Sensitization of sympathetic-adrenal medullary responses to a novel stressor in chronically stressed laboratory rats.

Studies from this and other laboratories have demonstrated that sympathetic-adrenal medullary responses are reduced in laboratory rats exposed to chronic intermittent stress. To extend these findings, we have conducted three experiments in which laboratory rats were exposed daily for 26 consecutive days to the same (homotypic) stressor and then challenged with a novel (heterotypic) stressor. Each stress session lasted for 30 minutes and the following homotypic/heterotypic treatments were included: Experiment 1--restraint/footshock; Experiment 2--cold swim/restraint; and Experiment 3--footshock/cold swim. Controls were exposed to the heterotypic stressor only. Plasma levels of norepinephrine (NE) and epinephrine (EPI) were measured in blood samples taken from control and chronically stressed rats to provide an assessment of sympathetic-adrenal medullary activity. In each experiment, chronically stressed rats gained significantly less weight than handled controls. Basal plasma levels of NE and EPI were similar for chronically stressed and control rats. In contrast, plasma catecholamine responses to the heterotypic stressor were significantly greater in stressed rats compared to controls that were stressed for the first time. This pattern of exaggerated responses was especially evident for the cold swim/restraint and footshock/cold swim groups. These findings provide evidence for a sensitization of sympathetic-adrenal medullary responses to a novel stressor in animals previously exposed to chronic intermittent stress.

Adrenal Medulla↗
PubMed1989

Open-field behavior of spontaneously hypertensive and Wistar-Kyoto normotensive rats: effects of reciprocal cross-fostering.

The influence of the maternal environment on the development of open-field behavior in spontaneously hypertensive (SHR) rats was investigated using the technique of reciprocal cross-fostering. Entire litters of SHR and Wistar-Kyoto (WKY) normotensive rats were either reared by their natural mothers, in-fostered to dams of the same strain, or cross-fostered to dams of the opposite strain on the day after birth. Open-field behavior was assessed in male and female rats from the six groups (2 strains x 3 rearing conditions) at 30, 60, 90, and 120 days of age. Animals were observed in the open-field during a 5-min test period and the number of squares entered and hindlimb rears were recorded. At all ages tested, SHR rats were more active in the open field, entering more squares and rearing more frequently than WKYs. SHR females were more active than age-matched SHR males, while no sex differences were apparent in the WKY strain. At each age, open-field behavior was similar across WKY rearing groups. SHR control and in-fostered animals responded similarly in the open field; however, SHR cross-fostered rats (particularly females) tended to be more active than controls. Although cross-fostering has profound effects on cardiovascular development and functioning in the SHR, it appears that altering the early maternal environment experienced by SHR pups does not grossly affect the development of open-field behavior.

Animals↗
PubMed1989

Iodine-131 metaiodobenzylguanidine uptake in infantile myofibromatosis.

I-131 MIBG scintigraphy was performed on a neonate who presented with a left neck mass and brachial palsy. Increased uptake of the tracer was apparent in the mass, initially suspected as being a neuroblastoma, but later diagnosed as infantile myofibromatosis. Since MIBG is principally taken up by neuroendocrine tumors, this finding suggests caution be used when interpreting studies in this age group.

3-Iodobenzylguanidine↗
PubMed1989

Conception rates and calving intervals after prostaglandin F2 alpha or prebreeding progesterone in dairy cows.

Two experiments were performed in two different herds to determine if utilizing prostaglandin F 2 alpha to induce estrus for first services would be effective in reducing the duration and variability of calving intervals. In Experiment 1, cows were assigned randomly as controls (n = 217) to be inseminated as they were detected in estrus (beginning d 42 to 53 postpartum depending on replicate) or treated with prostaglandin F2 alpha (n = 185). In Experiment 2, the same treatments were utilized, except control cows (n = 124) were inseminated at their first detected estrus after d 40 postpartum, and treated cows received either one injection of prostaglandin F2 alpha between d 54 and 63 (n = 116) or were given progesterone (via a progesterone-releasing intravaginal device) for 7 d, with the device removed 24 h after prostaglandin F2 alpha (n = 116). More cows were inseminated and pregnancy rates were higher within 5 d after treatment with prostaglandin F2 alpha, and interval from prostaglandin F2 alpha to first service was reduced compared with that of control cows. Duration and variation of calving intervals were unaffected in either experiment, despite the fact the elective waiting period was 6 to 23 d longer for treated cows than for controls. Prebreeding treatment with progesterone failed to improve conception rates, but the efficiency of estrous expression increased from 54% in prostaglandin F2 alpha-treated cows to 71% in those cows also receiving prebreeding progesterone. We conclude that prostaglandin F2 alpha was ineffective in improving reproductive performance of these herds under good herd management. However, prostaglandin F2 alpha offers the convenience of inseminating small groups of cows, controlling when breedings occur during the work week, and prolonging the elective waiting period without extending the calving interval.

Animals↗
PubMed1988

Brain binding sites for atrial natriuretic factor (ANF): alterations in prehypertensive Dahl salt-sensitive (S/JR) rats.

The binding of radioiodinated atrial natriuretic factor (125I-ANF-28) to discrete areas of brain in 7 week old, inbred Dahl salt-sensitive (S/JR) and salt-resistant (R/JR) rats was studied utilizing quantitative film autoradiography. At this age, S/JR rats exhibit systolic blood pressures that are prehypertensive and tend to be slightly higher than systolic blood pressures of age-matched R/JR rats. Scatchard analysis of 125I-ANF-28 binding in forebrain revealed that S/JR rats have a significantly increased number of binding sites for 125I-ANF-28 in the subfornical organ as compared to R/JR controls. In contrast, values for 125I-ANF-28 binding capacity in the choroid plexus and area postrema were similar for both strains, and binding affinity constants for 125I-ANF-28 binding revealed no strain differences in any brain area examined. The elevation in the number of binding sites for atrial natriuretic factor may serve as a compensatory mechanism acting in part to lower fluid volume and sodium levels prior to the precipitous increase in blood pressure which occurs in S/JR rats by 10 weeks of age.

Animals↗
PubMed1988

ANF receptors: distribution and regulation in central and peripheral tissues.

Atrial natriuretic factor is a recently-discovered family of biologically active peptides produced in, stored and secreted by mammalian atria. ANF exerts a wide variety of actions in the periphery as well as within the central nervous system. In general, these actions are directed toward the maintenance of body fluid and electrolyte balance and regulation of arterial blood pressure. In a fashion similar to that of many other hormonal systems, the actions of ANF in various target tissues appear to be mediated by at least one class of specific receptors. However, while the biosynthesis and biological actions of ANF have been extensively investigated, little research has been focused on ANF receptor systems. In this article, we will provide an overview of current literature regarding the distribution and binding characteristics of receptor sites for ANF in peripheral and central target tissues. In addition, we will consider factors involved in the regulation and alteration of ANF receptor sites in various tissues. Finally, a brief discussion of the emerging concept of ANF and angiotensin II as mutual antagonists in body fluid homeostasis and cardiovascular regulation will be offered.

Animals↗
PubMed1987

Binding sites for atrial natriuretic factor (ANF) in kidneys and adrenal glands of spontaneously hypertensive (SHR) rats.

Binding sites for atrial natriuretic factor (ANF) were studied in kidneys and adrenal glands of 17 week old male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats by quantitative autoradiography using 125I-ANF-28. In kidney, 125I-ANF-28 binding sites were found in high concentrations in glomeruli and in much lower concentrations in the renal papilla. In adrenal gland, 125I-ANF-28 binding sites were highly localized to the zona glomerulosa and were of moderate density in the inner cortical regions. ANF binding sites did not occur in the adrenal medulla. The maximum binding capacity (Bmax) of 125I-ANF-28 was reduced by 50% in the kidney glomeruli of SHRs compared to WKY controls. In contrast, the affinity constant (Ka) for 125I-ANF-28 was elevated by 100% in kidney glomeruli of SHRs. There were no significant strain differences in values for Bmax or Ka for 125I-ANF-28 binding in the adrenal zona glomerulosa. These findings suggest that the natriuretic and diuretic actions of ANF within kidney glomeruli may be compromised in adult SHR rats and these alterations may contribute to the development and maintenance of hypertension in rats of this strain.

Adrenal Cortex↗
PubMed1987

Hormonal, estrual, ovulatory and milk traits in postpartum dairy cows following multiple daily injections of oxytocin.

Release of oxytocin at suckling or milking may delay onset of estrous cycles in postpartum cows. Twenty lactating Holsteins of mixed parity were given 100 mU oxytocin iv (n = 10) or 2 ml saline (control; n = 10) via jugular catheters at 0530, 0930, 1730 and 2130 daily from calving (d o) until 28 d postpartum. All cows were milked twice daily at 0130 and 1330. Blood was collected thrice weekly (Monday, Wednesday, Friday at 0530) for 12 wk and analyzed by radioimmunoassay for progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum. On d 12, blood was collected every 15 min for 6 h via jugular catheters and concentrations of luteinizing hormone (LH), cortisol and PGFM were determined. Rate of involution of the reproductive tract was estimated twice weekly by palpation per rectum. Overall mean, baseline concentrations, number of pulses/6 h, and pulse duration of LH on d 12 were similar among treatment groups. However, oxytocin seemed to reduce (P less than .10) pulse amplitude of LH in multiparous cows (.4 +/- .2 vs .8 +/- .1 ng/ml), but not in primiparous cows. Concentrations of cortisol and PGFM in serum on d 12 were unaffected by treatment. The average intervals from calving to first ovulation, based on changes of progesterone in serum and the intervals to first estrus, were similar between treatment groups. Rates of involution of the cervix and uterus also were similar between treatments. Milk yield, percent protein in milk and somatic cell counts did not differ between treatment groups. However, percent fat in milk tended to be higher (P less than .10) in cows given oxytocin than in controls (3.99 +/- .22 vs 3.68 +/- .21). These data indicate that multiple daily injections of oxytocin did not affect: 1) length of anestrus and anovulation in postpartum dairy cows, 2) LH release and 3) rates of cervical and uterine involution.

Animals↗
PubMed1987

Alterations in binding sites for atrial natriuretic factor in kidneys and adrenal glands of Dahl hypertension-sensitive rats.

Binding sites for atrial natriuretic factor (ANF) were studied in kidneys and adrenal glands of 7- and 10-week-old male Dahl hypertension-sensitive (S/JR) and hypertension-resistant (R/JR) rats by quantitative autoradiography. Binding sites for 125I-ANF-28 in kidney were highly localized and of high density in the glomeruli; binding sites were less concentrated in the renal papilla. In adrenal gland, binding sites for 125I-ANF-28 were highly concentrated in the zona glomerulosa, but were of a very low density in the inner adrenal cortex. At 7 weeks of age, the maximum binding capacity (Bmax) for 125I-ANF-28 in kidney glomeruli was increased by 21% in S/JR rats compared with R/JR rats. From 7 to 10 weeks of age, decreases in Bmax for 125I-ANF-28 in glomeruli occurred, with no apparent difference between strains. Strain or age differences in the affinity constant (Ka) for 125I-ANF did not occur in the kidney. In adrenal zona glomerulosa, the Bmax for 125I-ANF-28 binding was similar for S/JR and R/JR rats at 7 weeks of age. At 10 weeks of age, however, Bmax for 125I-ANF-28 in adrenal zona glomerulosa was increased by 19% in S/JR rats compared with age-matched R/JR controls. These findings suggest that alterations may occur in ANF binding sites in kidney and adrenal gland of S/JR rats in response to the sharp increase in blood pressure that is characteristic of rats of this strain.

Adrenal Cortex↗
PubMed1984

Craniofacial defects in the human skeletal dysplasias.

Many of the human skeletal dysplasias are accompanied by significant alterations in craniofacial growth. Several specific disorders have been discussed which show the effects of endochondral and membranous defects in the craniofacial complex. The craniofacial and other skeletal abnormalities observed in the skeletal dysplasias may indicate the sites and timing of the primary defects and provide direction to investigative efforts. In addition, a careful review of known pathogenetic and histomorphologic mechanisms in the skeletal dysplasias can provide valuable clues to the complex interactions necessary for normal craniofacial growth.

Achondroplasia↗
PubMed1983

Genetic linkage studies with cleft lip and palate: report of two family studies.

Genetic linkage studies are reported on two families with cleft lip +/- cleft palate. For the first family (LP01) the etiology of the clefting is unknown, and the linkage analyses were done assuming both autosomal dominant and autosomal recessive inheritance. Close linkage is rejected with the Duffy blood group under the dominant model and with four loci (Duffy, Kidd, and ABO blood groups and haptoglobin) under the recessive model. The second family (LP02) is a Mexican-American family segregating the van der Woude syndrome with lip pits. The linkage analyses for this autosomal dominant trait excluded close linkage with seven genetic markers, including three on chromosome one. The maximum lod scores were 0.6 with BF (chromosome 6) and 0.4 with the P blood group, which is not yet mapped.

Cleft Lip↗
PubMed1981

Indentikit Model II--a potential tool for judging cosmetic appearance.

The purpose of this paper is to introduce the Identi-kit Model II as a tool for investigation of social reactions to cosmetic variations associated with facial anomalies. In one study, a group of judges rated cosmetic appearance from photographs, while another group rated cosmetic appearance from Identi-Kit constructions. A high correlation was found between ratings obtained from the two sets of stimuli. In a second study, three groups of different judges rated cosmetic appearance of Identi-Kit constructions with three types of facial stigmata associated with facial clefting. Ratings of appearance were found to vary systematically as the number of stigmata were increased. Based on the findings of these studies, the authors suggest that Identi-Kit constructions may be useful for investigating the effects of changing specific facial characteristics while holding others constant.

Adolescent↗