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Biomedical subjects

T Bennett

Publications and source records attributed to T Bennett.

At least 397 records · Page 22Linked to original sources
PubMed1969

A study of nexuses in visceral smooth muscle.

Nexuses are described between the smooth muscle cells of the gizzard of the chick and the pigeon, the vas deferens of the mouse and the guinea pig, and the taenia coli of the guinea pig. The nexuses in the gizzard were examined after osmium tetroxide and potassium permanganate had been used as fixatives. Although differences in the dimensions of the unit membranes and the nexuses were noted, the results with the two fixation techniques were complementary. The distribution of nexuses within the smooth muscle tissues examined was uneven. Nexuses were still present in both small and large pieces of tissue incubated in hypertonic solutions at varying temperatures. Other experiments showed that the degree of contraction at the time of fixation did not affect the presence of nexuses in the tissue. These results indicate that nexuses between smooth muscle cells are stable under a variety of conditions.

Animals↗
PubMed1969

The effects of hyoscine and anticholinesterases on cholinergic transmission to the smooth muscle cells of the avian gizzard.

1. Intracellular recordings were made from smooth muscle cells of the pigeon and chick gizzards. Hyoscine (10(-6) g/ml.) blocked, within 2 min, the excitatory junction potentials (E.J.P.s) evoked by transmural stimulation. As the amplitudes of E.J.P.s decreased, their durations also decreased. Hyoscine had no effect on the inhibitory junction potentials (I.J.P.s) evoked by transmural stimulation.2. Initially, physostigmine or neostigmine (10(-7) - 5 x 10(-6) g/ml.) caused a marked increase in the amplitudes of E.J.P.s, without affecting their time courses. Sometimes, anticholinesterases caused a single stimulus to evoke multiple E.J.P.s.3. After several minutes in the presence of high concentrations (10(-6) - 5 x 10(-6) g/ml.) of anticholinesterases the muscle cells were depolarized by about 15-20 mV, and thus the amplitudes of I.J.P.s evoked by transmural stimulation were larger than under control conditions. E.J.P.s summed at much lower stimulation frequencies than normal, an observation which indicated that high concentrations of anticholinesterases increased the durations of the E.J.P.s. Repetitive stimulation evoked a membrane depolarization which persisted for as long as 10 sec after stimulation was stopped.4. These results are discussed in terms of the action of the drugs at the nervesmooth muscle junction and on ganglion cells in the myenteric plexus.

Animals↗
PubMed1969

Nerve-mediated excitation and inhibition of the smooth muscle cells of the avian gizzard.

1. The electrical events evoked in smooth muscle cells of the chick and pigeon gizzards by vagal, perivascular sympathetic and transmural stimulation were recorded with intracellular micro-electrodes.2. Single stimulating pulses applied to the extrinsic nerves, or to intrinsic fibres, produced excitatory junction potentials (E.J.P.s) which were blocked by hyoscine. Repetitive stimulation caused facilitation of E.J.P.s and, at higher frequencies, summation. When the tissue was well oxygenated, maximal stimulation evoked action potentials and the tissue contracted. If the tissue was allowed to become anoxic, action potentials were blocked and thus junctional transmission could be observed uncomplicated by tissue contraction.3. Cholinergic E.J.P.s appeared to be due to stimulation of both post-ganglionic neurones and the pre-ganglionic input to post-ganglionic neurones, since ganglion-blocking drugs abolished the late phase of complex E.J.P.s while leaving unaffected their initial components.4. Repetitive perivascular sympathetic stimulation, after cholinergic E.J.P.s had been blocked by hyoscine, evoked a slow, long-lasting depolarization of the muscle cells. This depolarization was blocked by guanethidine (5 x 10(-6) g/ml.) and was mimicked by noradrenaline (10(-7) g/ml.).5. Under non-anoxic conditions, the tissue underwent rhythmical contractions which were associated with action potential firing. When the tissue was anoxic action potentials were not seen, but spontaneous membrane depolarizations resembling E.J.P.s were observed. Spontaneous miniature excitatory junction potentials (M.E.J.P.s) were observed only infrequently whether the tissue was well oxygenated or not.6. Single stimulating pulses applied to extrinsic or intrinsic nerves frequently evoked inhibitory junction potentials (I.J.P.s) in smooth muscle cells of the gizzards of both birds. I.J.P.s were blocked by tetrodotoxin (10(-7) g/ml.). Repetitive stimulation of inhibitory nerves gave rise to a membrane hyperpolarization; when stimulation was stopped the membrane potential showed rebound depolarization.7. These results are discussed in terms of the autonomic innervation of the avian gizzard, and possible explanations of the various types of activity observed are considered.

Action Potentials↗
PubMedDate not supplied

Lack of evidence for a temperature-mediated change of adrenoceptor type in the rat heart.

1. Responses to phenylephrine of left and right atria of the rat heart have been measured at 37 degrees C and 21 degrees C. 2. Differences in basal force of contraction at the two temperatures were attributable solely to differences in frequencies of contraction. 3. Reduction in temperature produced no change in EC50 for phenylephrine nor any greater susceptibility of the responses to blockade by phentolamine rather than propranolol. 4. It is concluded that beta-adrenoceptors of the rat heart are not converted to alpha-adrenoceptors by a reduction in temperature.

Animals↗
PubMedDate not supplied

The genetics of osteoporosis: vitamin D receptor gene polymorphisms and circulating osteocalcin in healthy Irish adults.

BACKGROUND: A relationship between bone turnover and the vitamin D receptor (VDR) genotype is reported in Australian subjects of UK-Irish descent. There is conflicting evidence of linkage between the VDR genotype and differences in bone mineral density. No such study has been carried out on a resident Irish population. AIMS: This study examined the relationship between serum osteocalcin (a marker of bone turnover) and VDR genotype in Irish adults. METHODS: One hundred and eighteen healthy Irish adults aged between 19 and 67 were recruited and had two fasting blood samples taken. One sample was analysed for osteocalcin by enzyme immunoassay. The other was used to isolate genomic DNA and determine VDR genotype. RESULTS: Tt was the most prevalent VDR genotype (53%) and tt (15%) the least prevalent in this group of healthy Irish adults. The tt VDR genotype was associated with significantly higher levels of serum osteocalcin (29% and 40%) than the Tt or TT VDR genotypes. CONCLUSIONS: These findings suggest that healthy Irish adults with the tt VDR genotype have higher rates of bone turnover than those with Tt or TTVDR genotypes. They may have a higher risk of low bone mineral density and osteoporosis in later life.

Adult↗
PubMedDate not supplied

Apolipoprotein E gene polymorphisms and serum cholesterol in healthy Irish adults: a proposed genetic marker for coronary artery disease risk.

BACKGROUND: The apolipoprotein (Apo) E gene, and thus its gene product, plays a central and pervasive role in lipid metabolism by serving as a ligand for lipoprotein receptors. Polymorphisms of this gene have been associated with variation in lipid phenotypes in some Caucasian and Asian populations, but not in others. No such study has been carried out in a resident Irish population. AIM: A study was designed to examine the relationship between serum cholesterols and Apo E genotype in a cohort of healthy Irish adults. METHODS: One hundred healthy Irish adults, aged 19-65 years, were recruited from the Cork City area. Two fasting blood samples were collected from each subject. One was assayed for serum cholesterols--total and low-density lipoprotein (LDL), and high-density lipoprotein (HDL)--while the other sample was used for isolation of genomic DNA and determination of Apo E genotype. RESULTS: While the E2 (12%) was the least prevalent, E3 was the most prevalent Apo E genotype (66%) in this group of healthy Irish adults. A significant Apo E gene-dosage effect was evident, whereby individuals with the Apo E2 genotype had a lower level of total cholesterol, E3 had intermediate levels, and E4 had a higher level. Moreover, those with the Apo E4 genotype had a significantly higher level of LDL cholesterol compared to E2 or E3 genotypes. There was no significant difference in mean serum adjusted HDL-cholesterol levels between the three Apo E genotypes. CONCLUSION: These findings suggest that healthy Irish adults with the Apo E4 genotype have higher serum total and LDL-cholesterol levels than those with E2 or E3 Apo E genotypes and therefore may have a higher risk of atherosclerotic coronary artery disease and coronary heart disease in later life.

Adult↗
PubMedDate not supplied

Brain neuropeptides: actions on central cardiovascular control mechanisms.

The many peptides we have not considered (e.g. gastrin, motilin, FMRFamide, carnosine, litorin, dermorphin, casomorphin, eledoisin, prolactin, growth hormone, neuromedin U, proctolin, etc.) were omitted due to lack of information as far as any putative central cardiovascular effects are concerned. However, even for some of these peptide pariahs intriguing snippets of information are available now (e.g. ref. 85), although as we write, the list of possible candidates for investigation grows longer. On an optimistic note, it is becoming clear that many brain neuropeptides may have important effects on cardiovascular regulation. It seems feasible that 'chemically coded' pathways in the brain might be the neuroanatomical correlate of a 'viscerotopic' organization of cardiovascular control mechanisms, whereby the activity of the heart and flows through vascular beds are individually controlled, but in an integrated fashion, utilizing particular combinations of neurotransmitters and neuropeptides within the brain. Such possibilities can only be investigated, properly, by measurement of changes in cardiac output and regional haemodynamics in response to appropriate interventions, in conscious, unrestrained animals.

Animals↗
PubMedDate not supplied

Training surgery residents in group practice management.

As health care delivery continues to grow in complexity and uncertainty, academic practitioners must integrate clinical disciplines with research, financial management, marketing, law and many other areas. Jill Ridky, Ph.D., and Tom Bennett, M.B.A., D.Div., M.S.W., write about survey results on the current use and need for practice management training in residency programs.

Academic Medical Centers↗
PubMedDate not supplied

Beyond marital status: relationship type and duration and the risk of low birth weight.

CONTEXT: Unmarried women have higher rates of low birth weight than married women. However, assumptions that unmarried women are uniformly at a disadvantage may be unfounded. A woman's relationship characteristics may be more relevant for infant health than her formal marital status. METHODOLOGY: Data from the 1995 National Survey of Family Growth were used to analyze associations between relationship characteristics and low birth weight among U.S. women aged 15-44 with a recent singleton live birth. Unadjusted odds ratios were generated to indicate the crude effects of independent variables, including relationship type and relationship duration at the time of conception. Multiple logistic regressions were performed to assess the impact of relationship variables on the likelihood of low birth weight, taking into account the effects of other covariates. RESULTS: In multivariate models of all women and non-Hispanic black women, relationship type and duration were not associated with low birth weight. However, low birth weight was almost six times as likely among Hispanic women in nonmarital, noncohabiting relationships as among those who were married. Surprisingly, among non-Hispanic white women, low birth weight was less likely among those in nonmarital, noncohabiting relationships than among those who were married. Unexpected associations also were found among low birth weight, race and ethnicity, and relationship duration: Low birth weight was more likely among non-Hispanic white women in relationships of from five to 10 years in length than among those in relationships of longer than 10 years and less likely among Hispanic women in relationships of one year or less than among those in a relationship for more than 10 years. CONCLUSION: Although unmarried women in the United States have higher rates of low birth weight than married women, many unmarried women are at no greater risk of low birth weight than their married counterparts. The findings confirm the need to consider the characteristics of relationships when examining the association of mother's "union status" and birth outcomes.

Adolescent↗
PubMedDate not supplied

Cost and reimbursement rates for investigational circulatory support.

The clinical evaluation of investigational circulatory support devices has, for the most part, been financed with private funds. St. Louis University initiated a system in 1986 to bill for investigational circulatory support devices and care related to their use. Charges for hospitalization and rates of reimbursement were reviewed in 32 patients who received Thoratec (Thoratec Laboratories Corp., Berkeley, CA [N = 26]), Novacor (Baxter Healthcare Corp., Oakland, CA [N = 4]), or Symbion (Symbion Inc., Tempe, AZ [N = 2]) total artificial heart devices. Duration of support ranged from 0.2 to 440 days (mean 32). Total charges ranged from $43,115 to $1,335,691 (mean $221,716). Charges for the devices and technical support relating directly to their use ranged from $10,305 to $96,030 (mean $28,246). The mean percentage of reimbursement (total charges/total paid) was 67%. Whereas it was uncertain in some patients whether or not the devices were paid for, commercial insurers are willing to reimburse at a high percentage for the total cost of care.

Costs and Cost Analysis↗