Biomedical subjects

M Wilkinson

Publications and source records attributed to M Wilkinson.

At least 217 records · Page 12Linked to original sources

PubMed1988

Binding of 125I-labelled human chorionic gonadotropin to cell membrane receptors in rabbit ovarian slices.

The binding of 125I-labelled human chorionic gonadotropin (HCG) was studied using thick slices (300 micron) of rabbit ovarian tissue. Binding was saturable, reversible, stereospecific, and of high affinity. The amount of binding was proportional to the number of slices used and could be destroyed by boiling. Ovarian slices from eight individual rabbits were found to have two binding sites for 125I-labelled HCG with KD values of 272 +/- 64 and 1263 +/- 274 pM and Bmax values of 25.7 +/- 5.3 and 94.1 +/- 18.8 fmol/mg protein, respectively. In a comparative study the KD and Bmax values were 351 +/- 151 pM and 25.3 +/- 11.1 fmol/mg protein with slices from one ovary and 134 +/- 24 pM and 109 +/- 32 fmol/mg protein with membranes from the contralateral ovary. These data suggest that the binding of HCG can be determined in live tissue.

Animals↗

PubMed1988

Lack of effect of melatonin on sexual maturation in female rats.

Daily subcutaneous injections of 100 micrograms melatonin given to prepubertal female rats housed in 14L:10D or 12L:12D failed to delay puberty as evidenced by the age at which vaginal opening occurred; neither the Sprague-Dawley nor the Wistar strain rats were responsive to melatonin treatment. Reproductive organ weights (ovaries and uteri) at vaginal opening were unaffected by such treatment. Administration of melatonin through the drinking water in doses of 100, 500 or 1000 micrograms/day did not alter the timing of puberty or the reproductive organ weights in rats of the Sprague-Dawley or Long-Evans strains (housed in 12L:12D). Our experimental methods are identical to a previous report and we have no explanation for our failure to reproduce the earlier results.

Animals↗

PubMed1988

Influence of neonatal opioid blockade or injections of gonadotrophin-releasing hormone on the timing of puberty in female rats: correlation of opioid effects with occupation of hypothalamic mu-opioid receptors.

Hypothalamic opioid peptides have been implicated in the timing of sexual maturation in several species. We have examined the effects of neonatal opioid blockade on the timing of puberty in the female rat and have compared these with the effects of neonatal GnRH injection. Intermittent naloxone (2.5 mg/kg) or GnRH (200 ng/100 g body wt) injected s.c. at 6-h intervals for the first 10 days of life only slightly advanced the mean day of vaginal opening (VO). However, the degree of precocity was significantly more marked in a subgroup of drug-injected rats. In contrast, injections of the long-acting opioid antagonist naltrexone (50 mg/kg) had no effect on the timing of VO. The results suggested that the duration of opioid receptor blockade is critical in determining the degree of opioid antagonist effect. Therefore, additional studies were performed to compare receptor occupancy of naloxone and naltrexone in 9-day-old rat pups. An ex-vivo binding assay was utilized to determine the availability of hypothalamic opioid-binding sites at various intervals following a single s.c. injection of antagonist. The time-course of inhibition of tritium labelled [D-Ala2-N-Me-Phe4,Gly5-ol]-enkephalin [( 3H]DAGO) binding (mu-opioid sites) revealed that naloxone occupies the mu-receptor for a relatively short period of time. Naloxone (2.5 and 50 mg/kg) produced extensive inhibition of [3H]DAGO binding at 30 min following injection but binding was 100% of control at 1 h and 3.5 h respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

A pathophysiological study of 10 cases of hypoxic cor pulmonale.

A pathophysiological study of the pulmonary vasculature in 10 patients with hypoxic cor pulmonale and severe airways obstruction (five treated and five untreated with long-term oxygen) is presented. The media of muscular pulmonary arteries was normal or atrophic but, in the intima, there was active deposition of longitudinal muscle, fibrosis and elastosis. In the arterioles a medical coat of circular smooth muscle bounded by a new internal elastic lamina had developed, while there was deposition of longitudinal muscle and fibrosis in the intima. In five cases the lumen was subdivided into parallel tubes, found by serial section to lead into alveolar capillaries. These features are distinctive of hypoxaemia and obstructive airways disease. Changes continued until death. The conspicuous longitudinal muscle may be attributable to stretching of vessels round distorted terminal airways; further exploration into mechanisms is required. The hypothesis that vascular changes follow hypoxic vasoconstriction is no longer tenable. No correlations were found between quantitative pathological findings and arterial blood gas tensions, pulmonary artery pressure or haematocrit. There were no differences between patients treated or not treated with oxygen which might suggest that it arrests pathological changes. Thus, once a patient is given oxygen, survival probably depends as much on progressive mechanical changes in the lung as on continuing hypoxaemia.

Airway Obstruction↗

PubMed1987

Benzodiazepine ([3H]flunitrazepam) binding in cat visual cortex: ontogenesis of normal characteristics and the effects of dark rearing.

[3H]Flunitrazepam (FNZ) binding sites were characterized in homogenates of cat visual cortex during normal postnatal development and following dark rearing from birth. In parallel experiments, the distribution and density of [3H]FNZ binding sites were examined by in vitro autoradiographic or 'scrape' methods. In homogenates, Bmax measurements showed low early values, rising to a peak in receptor density at about 60 days postnatal, followed by a decline in adulthood. At all ages, gamma-aminobutyric acid (GABA) altered the Kd, but not the Bmax of [3H]FNZ binding sites. Kd values showed a general increase with age, parallelled by an increased sensitivity to GABA. Receptor autoradiography revealed that the highest density of [3H]FNZ binding sites was in layer IV of cats of all ages. Deafferentation of extrinsic inputs to the visual cortex by surgical undercutting did not alter this pattern of laminar distribution, indicating that the receptors were associated with intrinsic cortical elements rather than subcortical inputs. Dark rearing had no effect on [3H]FNZ laminar distribution in the visual cortex. The Bmax was higher at 30 days postnatal, but did not differ significantly thereafter. Modulation by GABA was concomitantly higher at 30 days, but lower than normal in dark-reared animals at ages greater than 30 days postnatal. The results are discussed in relation to the normal and abnormal development of GABA receptors in the cat visual cortex.

Animals↗

PubMed1987

Sequence analysis and expression of an X-linked, lymphocyte-regulated gene family (XLR).

The XLR gene family consists of approximately 10 X-linked genes, the expression of which is regulated in lymphocyte development. Certain members of the gene family are closely linked to the murine xid immune deficiency mutation. Sequence analysis of a cDNA clone pM1 derived from the plasmacytoma MOPC167 showed an open reading frame capable of coding for a protein of 208 amino acids and mol wt 24,000. The lack of a signal peptide or transmembrane region indicates a probable cytoplasmic or nuclear localization for the predicted pM1 protein. The predicted protein shares significant homology with lamins A and C and other members of the intermediate filament family of proteins, and shares features important for the coiled-coil structure proposed for these proteins. Analysis of cDNA clones derived from a presecretory lymphoma and from adult thymus indicates that B and T lymphocytes transcribe a common major mRNA identical to pM1, while other rare transcripts were also identified by these studies. A series of clonal T lymphoma lines representing distinct stages of thymic differentiation showed that, as with B lymphoid tumors, XLR expression is correlated with the maturation of the thymomas.

Amino Acid Sequence↗

PubMed1987

Beta-adrenergic ([3H] CGP-12177) receptors are elevated in slices of soleus muscle from CHE 147 dystrophic hamsters.

We have utilized a muscle slice technique to compare the ontogeny of cell surface beta-adrenergic receptor binding in soleus and extensor digitorum longus (EDL) muscles of male Golden Syrian (GS) and Canadian Hybrid Farms 147 (CHF 147) dystrophic hamsters. Binding of the beta-adrenergic antagonist, [3H] CGP-12177 (CGP), to GS muscle slices was reversible, saturable, stereospecific and of high affinity. Bmax was higher in the soleus (2.57 +/- .12 fmol/mg wet wt) than in the EDL (1.6 +/- .17 fmol/mg wet wt) of adult animals while affinities were similar (0.35 +/- .06 and 0.24 +/- .04 nM respectively). No differences in binding characteristics were seen in EDL of GS compared to CHF 147 animals. In soleus slices frm GS hamsters, Bmax was highest at 16 days of age (5.72 +/- 0.26 fmol/mg), decreased between 16 and 29 days and remained constant until 300 days (2.51 +/- 0.52 fmol/mg). In dystrophic soleus slices, Bmax was also higher at 16 days than at any other age but receptor number decreased gradually, remaining higher than in GS until 90 days of age (p less than 0.05). The failure of beta-adrenergic receptor number to decrease at a normal rate may be implicated in the pathogenesis of hamster polymyopathy.

Adrenergic beta-Antagonists↗

PubMed1987

A 6-hour human parathyroid hormone (1-34) infusion protocol: studies in normal and hypoparathyroid subjects.

Parathyroid hormone (PTH)-resistant states are usually diagnosed by the failure of an acute PTH injection to elicit a rise in urinary cAMP and phosphate or, less commonly, by the failure of repeated PTH injections to raise serum calcium. We have established a 6 hour infusion of human PTH (1-34) which identifies PTH-resistant hypoparathyroid subjects on the basis of serum 1,25-dihydroxyvitamin D (1,25(OH)2D) and calcium responses. 1,25-Dihydroxyvitamin D levels increased by at least 58 pmol/liter and serum calcium by at least 0.1 mmol/liter in PTH-responsive hypoparathyroid subjects (n = 6), whereas in pseudohypoparathyroid subjects (n = 5) these levels rose by less than 22 pmol/liter and 0.06 mmol/liter respectively. The responsiveness of urinary phosphate excretion, expressed as the renal threshold phosphate concentration (TmPO4/GFR), to PTH also clearly separated the pseudohypoparathyroid patients from the other subjects. Differences in urinary calcium responses were observed though this parameter was less reliable in the identification of individual PTH-resistant or PTH-sensitive hypoparathyroid patients. Nephrogenous cAMP did not discriminate between groups when this protocol was used. This test has the potential to facilitate and extend the classification of PTH-resistant states.

Adult↗

PubMed1987

Lithium and rhythms of beta-adrenergic ([3H]CGP-12177) binding in intact rat retina, pineal gland, and hypothalamus.

A new assay technique for the determination of neurotransmitter binding in retinal fragments has been used to characterize and quantify beta-adrenergic receptors with the ligand [3H]CGP-12177. This assay allowed us to quantify beta-adrenergic receptors in the retina, pineal gland, and hypothalamus obtained from individual rats during a 10-hr period around the switch from light to dark under a 12-hr light/12-hr dark lighting cycle. A significant rhythm of beta-adrenergic binding was observed in the retina and pineal gland. These rhythms were abolished by chronic lithium treatment. In contrast to previous observations in whole brain preparations, lithium did not affect beta-adrenergic binding in brain tissue (hypothalamus) using this assay. Our data suggest that lithium may attenuate beta-adrenergic receptor down-regulation in pineal and retinal tissue. To the extent that this mechanism is important for the coding of information about light and dark in the environment, these observations might assist in our understanding of the clinical chronopharmacological properties reported for lithium.

Animals↗

PubMed1987

The use of the accident and emergency department.

Many studies have shown that a high proportion of patients attending accident and emergency (A&E) departments have only trivial or non-urgent complaints. A&E staff treat these inappropriate attenders while recognizing that this detracts from the care given to more serious cases. Dwindling resources and higher attendances make it a matter of necessity that inappropriate attenders be treated by general practitioners or equivalent primary care services. In this study, the authors examined the feasibility of methods of reducing inappropriate attendance. The authors investigated patients' ability to accurately assess the urgency of their condition and, hence, their need for A&E services. The authors concluded that there is probably no practical way of reducing inappropriate attendance that does not involve risk to a proportion of patients. The possibility of extending the role of the A&E department to provide more general primary care is discussed.

Accidents↗

PubMed1987

Binding of the hydrophilic beta-adrenergic antagonist [3H]CGP-12177 to cardiac tissue slices: characterization and ontogenetic studies in dogs.

A new technique was developed to characterize the binding of a hydrophilic beta-adrenergic antagonist, [3H]CGP-12177, to 1-mm thick slices of canine cardiac tissue. This technique was used to quantify the density (Bmax) and the affinity (Kd) of these receptors in the right ventricular conus (RVC) and the left ventricle (LV) at day 1 to 6 weeks of age, and in the adult. Binding was found to be reversible, saturable, stereospecific, of high affinity, and thermolabile. There was an increase in the density of beta-adrenergic receptors between day 1 (Bmax = 2.2 +/- 0.3 fmol/mg tissue in RVC and 2.9 +/- 0.8 fmol/mg tissue in the LV) and 2 weeks of age postnatally, after which it remained constant until 6 weeks of age (Bmax = 7.5 +/- 0.4 and 6.8 +/- 0.9 fmol/mg tissue in RVC and LV, respectively); however, by 6 weeks of age it had not reached adult levels (10.3 +/- 1.0 fmol/mg tissue). The affinity of these receptors did not change between early neonatal life (Kd = 1.3 +/- 0.4 nM) and adulthood (Kd = 1.4 +/- 0.2 nM). The density of beta-adrenergic receptors in the RVC was similar to that in the LV. This new method of quantifying beta-adrenergic receptors in cardiac tissue is simple and fast, and requires minimal tissue handling. It proved to be useful in studying the development of cardiac beta-adrenergic receptors with age.

Adrenergic beta-Antagonists↗

PubMed1987

Endurance exercise potentiates the stimulatory influence of oestrogen-progesterone on LH and FSH release in the rat.

Ovariectomized rats were treated with oestradiol benzoate and progesterone or GnRH. Prolonged exercise (running 4 days per week for 6 weeks) markedly potentiated the oestrogen/progesterone-induced release of LH and FSH, but the pituitary response to an injection of GnRH was unaffected. In contrast, at 24 h after a single exercise bout there was no apparent effect on steroid and GnRH stimulated LH and FSH responses although an acute exercise session given on the day of the LH surge inhibited steroid-induced LH release in some rats. We conclude that strenuous, prolonged exercise-training in the ovariectomized rat seems to modify the ability of the hypothalamus to release GnRH. The results were not attributable to a single bout of exercise since the gonadotrophin responses immediately or 24 h after such exercise did not parallel the results observed in the trained rats.

Animals↗

PubMed1986

Tissue slices in radioligand binding assays: studies in brain, pineal and muscle.

The use of tissue homogenates in receptor binding assays raises serious questions as to the physiological value of a preparation which examines receptors (binding sites) in disrupted tissue. In order to usefully study the regulatory properties of neurotransmitter receptors under physiological conditions, the necessity for tissue preparations which retain some degree of cellular integrity is clear. We review here the experiments which have utilized intact tissue - largely in the form of thick slices - to perform radioligand binding assays. There are many reports which note marked differences between studies in intact versus broken cell preparations. For example, significant discrepancies in KD and Bmax values are apparent for [3H] quinuclidinyl benzilate (muscarinic) and [3H] ouabain (Na+/K+-ATP ase, sodium pump) sites in brain and muscle respectively. A further example is the well-described stimulatory effect of GABA on benzodiazepine binding sites which is not seen in tissue slices. Other examples are highlighted. For all ligands so far examined, binding to slices is reversible, stereospecific, saturable, displaceable by appropriate drugs and of high affinity (nM). The method developed in our own laboratory is inexpensive, rapid and involves a minimum of tissue preparation. The technique is so simple as to allow many workers to enter this field who would not otherwise have done so. We suggest that metabolically active tissue slices offer the simplest approach to the study of cell-surface receptor regulation in living tissue.

Animals↗

PubMed1986

The muscle slice--a new preparation for the characterization of beta-adrenergic binding in fast- and slow-twitch skeletal muscle.

A new procedure is presented that characterizes the specific binding of the beta-adrenergic antagonist, [3H]CGP-12177, to thick (1 mm) slices from fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) mouse skeletal muscle. Binding is reversible, saturable, stereospecific, of high affinity, and subject to agonist-induced desensitization, indicating that it is to beta-adrenoreceptors and not to other sites. In both muscles, the majority of specific binding is to the beta 2-receptor subtype. Bmax is approximately twice as high in the soleus (5.64 +/- 0.52 fmol/mg wet weight) as in the EDL (2.66 +/- 0.29 fmol/mg wet weight) (P less than 0.05), whereas affinity is higher in the fast-twitch (Kd = 0.30 +/- 0.08 nM) than the slow-twitch muscle (Kd = 0.45 +/- 0.08 nM). The minimal tissue disruption associated with this procedure, as well as its speed, simplicity and relatively low cost, suggest that the slice preparation may prove to be invaluable for the future study of beta-adrenergic receptor binding and associated responses in skeletal muscle.

Animals↗

PubMed1986

Brain opioid receptors in the hibernating bat, Myotis lucifugus: modification by low temperature and comparison with rat, mouse and hamster.

Several studies have provided evidence that brain opioid peptides may be involved in the control of the hibernation cycle. We have now examined the influence of hibernation on central opioid receptors. We have characterized the receptor binding properties of [3H]-naloxone in slices of the cerebral cortex and hypothalamus of the bat Myotis lucifugus. These receptors possess those characteristics expected of an opioid site namely high affinity, stereospecificity and saturability. Under normal incubation conditions (30 degrees C) we observed no effect of hibernation on [3H]-naloxone binding. However, when binding assays were performed at temperatures corresponding to the appropriate body temperature (e.g., 4 degrees C for hibernation) we detected a significant low temperature-induced increase in hypothalamic binding. Similar experiments in rat, mouse and hamster revealed that [3H]-naloxone binding was also increased at 4 degrees C when compared to 30 degrees C. This was true in hypothalamus and cortex. Additional studies in the rat demonstrated that the opioid receptor is of higher affinity at low temperatures. The behavioural and neurochemical consequences of this change in the opioid receptor, and whether this might be involved in the regulation of hibernation, remain to be studied.

Animals↗

PubMed1986

The laminar distributions and postnatal development of neurotransmitter and neuromodulator receptors in cat visual cortex.

We review efforts to further understand the development and nature of sensory processing mechanisms in the cat visual cortex. In vitro autoradiographic and homogenate assay techniques have been employed to determine the laminar distribution and characteristics of various neurotransmitter and neuromodulator receptor populations during postnatal development. Each receptor population shows a distinct laminar-specific pattern of binding, which, in most cases, is age-dependent. Changes in receptor number and affinity are also observed during postnatal development. These findings indicate that major alterations in the basic chemical circuitry of cat visual cortex are a normal feature of postnatal maturation and may play a role in plasticity mechanisms.

Aging↗

PubMed1986

Negative trans-regulation of T-cell antigen receptor/T3 complex mRNA expression in murine T-lymphoma somatic cell hybrids.

The antigen-specific T-cell receptor (TCR) is composed of variable antigen-recognition chains TCR-alpha and TCR-beta in noncovalent association with the invariant T3 multimer. The TCR-alpha and TCR-beta chains are encoded by gene segments that must be juxtaposed by rearrangement in order to be expressed. To examine whether mechanisms other than gene rearrangement might regulate TCR/T3 gene expression, somatic cell hybrids were formed among closely related murine SL12 T-lymphoma clones that differ in TCR/T3 mRNA levels. In hybrid cells formed between cell clones in which one parent is TCR-beta+ and the other is TCR-beta-, the resultant hybrid cells lack detectable TCR-beta transcripts. Since the protein synthesis inhibitor cycloheximide partially reverses TCR-beta repression in the hybrid cells, we postulate that a labile repressor protein is involved. The amount of mRNA encoding one of the T3 polypeptide chains, T3-delta, is also strongly negatively transregulated in the same hybrid cells in which TCR-beta mRNA expression is repressed. The negative trans-regulation of TCR-beta and T3-delta mRNA expression is relatively specific, since the levels of TCR-alpha mRNA and several thymocyte surface antigens are not repressed in somatic cell hybrids. Our results indicate that rearrangement of the TCR genes alone is not sufficient for TCR-beta expression and that trans-acting factors regulate the amounts of both TCR-beta and T3-delta mRNA in this system.

Animals↗

PubMed1986

Development of opiate ([3H] naloxone)-binding sites in female rabbit brain: correlation with prepubertal gonadotropin secretion.

In neurochemical terms, little is known concerning the control of puberty onset in the female rabbit. In view of the established involvement of brain opiates in the sexual maturation of the rat, we have investigated the prepubertal development of opiate-binding sites in the hypothalamus and cerebral cortex of the rabbit. Binding of the opiate antagonist, [3H] naloxone, to thick (350 micron) slices of rabbit brain was found to be reversible, stereospecific, saturable, and of high affinity. In all respects these sites possessed the characteristics of opiate receptors. Specific binding (Bmax and KD) values were determined at 1, 8, 29, 40, 51, 100, and 168 days after birth in the hypothalamus and cerebral cortex. All all ages binding in the hypothalamus was higher, per mg of tissue, than in the cortex. Major differences in the pattern of development were also evident. In the cortex the Bmax slowly increased from a minimum at Day 1 to a maximum at about 100 days when puberty normally occurs. In contrast, binding in the hypothalamus rose rapidly to a maximum at 40 days and then fell abruptly, by about 40% at Day 51, after which a slow increase through puberty took place. This peak in the hypothalamic Bmax value correlates closely with the major prepubertal surge of gonadotropin secretion. It remains to be determined whether the coincidence of spontaneous gonadotropin secretion with the rapid appearance of hypothalamic opiate receptors is developmentally meaningful for the reproductive system.

Age Factors↗