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Biomedical subjects

J M Allen

Publications and source records attributed to J M Allen.

At least 163 records · Page 9Linked to original sources
PubMed1988

Intramural distribution of regulatory peptides in the sigmoid-recto-anal region of the human gut.

The distribution of regulatory peptides was studied in the separated mucosa, submucosa and muscularis externa taken at 10 sampling sites encompassing the whole human sigmoid colon (five sites), rectum (two sites), and anal canal (three sites). Consistently high concentrations of VIP were measured in the muscle layer at most sites (proximal sigmoid: 286 (16) pmol/g, upper rectum: 269 (17), a moderate decrease being found in the distal smooth sphincter (151 (30) pmol/g). Values are expressed as mean (SE). Conversely, substance P concentrations showed an obvious decline in the recto-anal muscle (mid sigmoid: 19 (2.0) pmol/g, distal rectum: 7.1 (1.3), upper anal canal: 1.6 (0.6)). Somatostatin was mainly present in the sigmoid mucosa and submucosa (37 (9.3) and 15 (3.5) pmol/g, respectively) and showed low, but consistent concentrations in the muscle (mid sigmoid: 2.2 (0.7) pmol/g, upper anal canal: 1.5 (0.8]. Starting in the distal sigmoid colon, a distinct peak of tissue NPY was revealed, which was most striking in the muscle (of mid sigmoid: 16 (3.9) pmol/g, upper rectum: 47 (7.8), anal sphincter: 58 (14)). Peptide YY was confined to the mucosa and showed an earlier peak (upper sigmoid: 709 (186) pmol/g, mid-distal sigmoid: 1965 (484)). A clear differential distribution of regulatory peptides was thus shown in the region studied. A possible role is suggested for NPY and VIP containing nerves in the effector control of the human internal anal sphincter.

Aged↗
PubMed1987

A single gene codes for aromatic L-amino acid decarboxylase in both neuronal and non-neuronal tissues.

We have sought to determine whether aromatic L-amino acid decarboxylase which functions as a neurotransmitter biosynthetic enzyme in neuronal cells can be distinguished from an enzyme with similar activity found in peripheral tissues where no neurotransmitters are synthesized. Aromatic L-amino acid decarboxylase was purified to electrophoretic homogeneity from bovine adrenal medulla, and highly specific antibodies were produced. In addition, a DNA clone complementary to aromatic L-amino acid decarboxylase mRNA was isolated by immunological screening of a lambda gt11 cDNA expression library. We have used these antibodies and cDNA probes for biochemical, immunochemical, and molecular analyses. A single form of aromatic L-amino acid decarboxylase is detected in rat and bovine tissue. Specifically, aromatic L-amino acid decarboxylase protein is biochemically and immunochemically indistinguishable in brain, liver, kidney, and adrenal medulla. Hybridization to aromatic L-amino acid decarboxylase cDNA identifies a single mRNA species of 2.3 kilobase pairs in rat tissue. Furthermore, Southern blot analysis reveals that a single gene codes for aromatic L-amino acid decarboxylase.

Adrenal Medulla↗
PubMed1987

Direct excitatory effects of neuropeptide Y (NPY) on rat hippocampal neurones in vitro.

Intracellular recordings from granule cells of the rat dentate gyrus show neuropeptide Y (NPY) applied by pressure ejection from pipettes containing 1.2-12 microM by pressures of less than 200 kPa for 1-5 s in duration to consistently evoke membrane depolarisations accompanied by a reduction in membrane resistance. The depolarisations were accompanied by an increase in excitability. Since the depolarisations evoked by NPY were not attenuated by either tetrodotoxin or kynurenic acid a direct excitatory action of NPY is postulated.

Action Potentials↗
PubMed1987

Presence, distribution, and pharmacological effects of neuropeptide Y in mammalian gastrointestinal tract.

The quantitative distribution of neuropeptide Y (NPY) immunoreactivity has been determined along the length of the gastrointestinal tract in three mammalian species; rat, pig, and guinea pig. The peptide was shown to be present in all regions studied and in all three species. Exceptionally high concentrations were found in the region of the lower esophageal sphincter. Pretreatment of rats with 6-hydroxydopamine depleted NPY concentrations by 30-40%, indicating that NPY is colocalized in part with adrenergic nerves. Characterization of the NPY immunoreactivity by high-pressure liquid chromatography revealed a single major peak. NPY immunoreactivity derived from rat extracts eluted consistently earlier from the column than synthetic porcine standard, indicating minor species differences. Pharmacological studies using longitudinal muscle from guinea pig terminal ileum demonstrated that NPY caused a dose-dependent inhibition of the electrically stimulated, neurally mediated contraction of longitudinal smooth muscle. This suggested that NPY may act presynaptically to inhibit cholinergic transmission. The effects of various NPY fragments were also tested on the same preparation. The C-terminal fragments were active but were considerably less potent than NPY, while the free acid form of NPY and N-terminal fragment (1-19) were completely inactive. Thus, this study has demonstrated the presence of NPY in the gastrointestinal tract of various species, particularly within the lower esophageal sphincter. The pharmacological actions of the peptide suggest a role in the control of nonvascular smooth muscle tone.

Animals↗
PubMed1987

Neuropeptide Y gene expression in PC12 cells and its regulation by nerve growth factor: a model for developmental regulation.

Neuropeptide Y (NPY) is a 36 amino acid neuronal peptide which has previously been described within a subset of sympathetic neurons. The presence of the messenger RNA that encodes NPY (NPY mRNA) has been studied in the PC12 cell line, as this is commonly used as a model of neuronal differentiation. Low levels of the NPY mRNA were identified in resting naive cells. Levels were induced five-fold by the addition of nerve growth factor to the medium at a dose of 30 ng/ml. Lower doses of nerve growth factor had no effect on NPY mRNA. The effect was rapid in onset being apparent within 12 h and near maximal at 24 h. A smaller two-fold increase in NPY mRNA was observed in cells treated with epidermal growth factor (3 ng/ml) over the same time course but no effect was observed with fibroblast growth factor (3 ng/ml), bradykinin (10(-6) M) or dexamethasone (10(-6) M). These results indicate that NPY gene expression is regulated in PC12 cells at the level of NPY mRNA.

Animals↗
PubMed1987

A DNA segment controlling metal-regulated expression of the Drosophila melanogaster metallothionein gene Mtn.

Cloned fragments of DNA including the Drosophila melanogaster metallothionein gene Mtn and different amounts of 5' flanking sequences were introduced into flies by P-element-mediated germ line transformation. Comparison of RNA levels in different transformants revealed that metal-regulated and tissue-specific expression of Mtn requires no more than 373 base pairs upstream of the initiation site of transcription. Transformants having an additional, transcribed copy of Mtn could tolerate increased concentrations of cadmium, indicating that Mtn expression is directly related to this phenotype. In separate experiments, these D. melanogaster promoter sequences were fused to the coding sequences of the herpes simplex virus thymidine kinase (TK) gene. After transfection of this fusion into baby hamster kidney cells, increases in TK activity and accumulation of TK RNA were inducible by metals. A series of 5' and 3' deletions showed that D. melanogaster sequences from -130 to -6 were sufficient to confer metal-regulated expression to the TK gene. The function of the D. melanogaster metallothionein promoter in mammalian cells indicates that the mechanism controlling metal regulation is evolutionarily conserved.

Animals↗
PubMed1987

Co-secretion of calcitonin gene-related peptide, gastrin-releasing peptide and ACTH by a carcinoid tumour metastasizing to the cerebellum.

A carcinoid tumour presenting as Cushing's syndrome is reported. Although no tumour mass could be initially identified the patient returned with first a liver and subsequently a cerebellar mass both of which were resected. Only at post-mortem was the lung primary discovered. ACTH, gastrin-releasing peptide (GRP) and calcitonin gene-related peptide were elevated in plasma before resection of the hepatic tumour. These peptides were demonstrated in both the hepatic and cerebellar tumours by immunocytochemistry and radioimmunoassay. This case illustrates the occasional tendency of primary lung carcinoids to remain small and clinically undetectable while generating secondary tumours which are symptomatic. It is suggested that immunological demonstration of GRP may be diagnostically helpful in directing attention to the lung as a primary site in neuroendocrine tumours which present in this fashion.

Adrenocorticotropic Hormone↗
PubMed1987

Mechanism of alpha-adrenergic excitation in bovine lymphatic smooth muscle.

Measurements were made, using the double sucrose-gap technique, of electrical and mechanical responses of bovine lymphatic smooth muscle to constant current pulses. After beta-blockade with 10(-6) M propranolol, stimulation of the alpha-receptors with norepinephrine (5 X 10(-6) M) depolarized the membrane and decreased membrane conductance. The depolarization and decrease in membrane conductance persisted in Li+- and choline-substituted low-Na+ solution, in methanesulfonate-substituted low-Cl- solution, and in Ca2+- free solution containing 1 mM ethyleneglycol-bis(beta-aminoethylether)-N, N'-tetraacetic acid. Tetraethylammonium (10 mM) did not itself affect membrane resistance nor did it block the increase in resistance due to norepinephrine. In contrast, cesium (10 mM) increased membrane resistance and prevented norepinephrine from increasing this further. As well as these effects on membrane resistance, norepinephrine (5 X 10(-6) M) increased the duration of the action potential, and this was accompanied by an increased force of contraction. Tetraethylammonium prolonged the action-potential plateau and potentiated norepinephrine's effect. These results suggest that norepinephrine is likely to increase the efficiency of lymphatic pumping due to both its positive inotropic effect and the improved safety margin for propagation resulting from the increase in membrane resistance. The latter effect may be due to the suppression of an outward K+ current.

Animals↗
PubMed1987

Neuropeptide Y and its flanking peptide in human endocrine tumors and plasma.

Neuropeptide Y (NPY) and its flanking peptide (CPON) were measured in extracts of pheochromocytomas (n = 26), ganglioneuroblastomas (n = 8), and other tumors (n = 95) and plasma (n = 38). NPY was present in high concentrations in the majority of the pheochromocytomas, but was absent in 3 tumors. Similar concentrations of NPY were measured using N- and C-terminal-directed antisera, and there was a good correlation between the concentrations of NPY immunoreactivity and CPON immunoreactivity in the same extracts. Gel permeation chromatography revealed that the separate peptides NPY and CPON were the major products. No significant amounts of a large mol wt precursor containing both immunoreactivities was found. Among the other tumors, 6 of 22 carcinoid tumors, 2 of 2 somatostatinomas, and 3 of 18 insulinomas contained detectable amounts of NPY. Plasma NPY concentrations were very low in normal subjects, and extraction and a 10-fold concentration step were necessary to establish the normal range (0.35-1.25 pmol/L). Plasma NPY concentrations were detectable in unextracted plasma (10 pmol/L) in 50% of patients with pheochromocytomas, but no correlation was found between plasma NPY concentrations and either plasma norepinephrine or epinephrine concentrations. These results indicate that 1) NPY and CPON are present in most, but not all, pheochromocytomas and ganglioneuroblastomas; 2) secretion of NPY immunoreactivity may be independent of that of catecholamines; 3) CPON immunoreactivity is present in plasma of patients with pheochromocytoma; 4) the majority of NPY and CPON immunoreactivities appears to be in the form of the separate free peptide, and there is very little precursor containing both immunoreactivities expressed in these tumors; and 5) NPY immunoreactivity is present in a variety of other endocrine tumors.

Chromatography, Gel↗
PubMed1986

Effect of inhibition of acid secretion on the regulatory peptides in the rat stomach.

The effect of inhibiting acid secretion by pharmacologic agents on the gastric content of regulatory peptides has been determined by radioimmunoassay and immunocytochemistry. Plasma, antral, and fundic concentrations of gastrin were elevated in rats rendered virtually achlorhydric by treatment with high-dose omeprazole (400 mumol/kg daily for 10 wk). This was associated with an increase in the number and staining intensity of gastrin immunoreactive cells. A clear reciprocal relationship was observed between antral gastrin and somatostatin as assessed by both quantitative and qualitative methods. These changes had disappeared 10 wk after treatment was stopped. No alteration was found in the concentrations of other regulatory peptides proposed as important in control of acid secretion. Plasma and antral gastrin concentrations were elevated in rats treated with high-dose ranitidine (700 mumol/kg daily), but to a lesser extent than during omeprazole therapy, and somatostatin concentrations were unchanged.

Animals↗
PubMed1986

Neuromuscular transmission in bovine mesenteric lymphatics.

Neuromuscular transmission in bovine mesenteric lymphatics was investigated using the double sucrose-gap technique. Single pulses of 0.3 msec duration (35----90 V) elicited excitatory junction potentials (EJP's) with a time to peak of about 1 sec. The EJPs showed facilitation and at stimulus frequencies greater than about 0.25 Hz could summate to reach threshold for action potential firing. The action potential so produced was followed by a phasic contraction of an "all or none" type. Increasing the frequency of stimulation did not increase the force of contraction but the resulting sustained depolarization increased the probability of a second or third action potential (and thus contraction) being elicited. EJPs and their electrical and mechanical consequences could be blocked by tetrodotoxin (10(-6) M) and by phentolamine (5 X 10(-7) M) confirming their neural mediation and dependence on postjunctional alpha-receptors.

Animals↗
PubMed1986

NPY stimulates nett absorption across rat intestinal mucosa in vivo.

NPY is a peptide recently isolated from porcine brain which has been seen to be widely distributed in the central and peripheral nervous system. The peptide is known to be present in substantial quantities in the extrinsic and intrinsic innervation of the gut but few studies have yet been done on the functional activity of the peptide in this site. In this study, intravenous infusion of porcine NPY was seen to cause nett absorption in the proximal duodenum. In addition, NPY was found to inhibit the nett secretory effect of simultaneously infused VIP in the proximal duodenum and jejunum. This evidence of functional activity of NPY in the gut further supports a role for this peptide in controlling or modulating intestinal function.

Animals↗
PubMed1986

The effect of 6-hydroxydopamine, reserpine and cold stress on the neuropeptide Y content of the rat central nervous system.

Neuropeptide Y has previously been detected in neurons throughout the rat brain and spinal cord. On histochemical grounds, the neuropeptide Y-containing cell bodies have been subdivided into two groups: those in the brain stem in which colocalization with noradrenaline and adrenaline has been demonstrated and those in other brain regions where no catecholamine coexistence is found. In this paper the regional distribution of neuropeptide Y has been investigated in the rat brain by a specific neuropeptide Y radioimmunoassay, before and after the destruction of catecholaminergic nerve terminals by the administration of intraventricular 6-hydroxydopamine. Despite massive reductions in brain catecholamines, the neuropeptide Y level was unchanged in the cerebral cortex, striatum, spinal cord and hippocampus. A minor reduction in neuropeptide Y was found in the hypothalamus. Reserpine treatment, which is known to deplete brain nerve terminal stores of catecholamines, likewise did not result in any loss of neuropeptide Y. Cold stress which increases noradrenergic turnover in the rat brain stem had no effect on neuropeptide Y levels. These results suggest that the bulk of neuropeptide Y in the rat brain and spinal cord may not be stored in catecholaminergic nerve terminals.

Animals↗
PubMed1986

Effect of reserpine, phenoxybenzamine and cold stress on the neuropeptide Y content of the rat peripheral nervous system.

The effect of reserpine treatment on the neuropeptide Y content of the rat adrenal gland, heart, kidney and vasculature was studied using a specific radioimmunoassay. One hour after reserpine administration (5 mg/kg) the neuropeptide Y concentration in the adrenal gland was significantly reduced and after 4 h a similar reduction was seen in the heart and kidney. After 48 h, neuropeptide Y concentrations were reduced in all tissues. The greatest reduction occurred in the cardiac septum (77%) and the least in the inferior vena cava (25%). Phenoxybenzamine (2 mg/kg) also caused a reduction in neuropeptide Y concentrations which was less marked than after reserpine, except in the adrenal gland where it was similar. Cold stress caused no change in neuropeptide Y concentrations. The neuropeptide Y depletion induced by reserpine was compared to that following 6-hydroxydopamine. In the heart and pial arteries both drugs caused a similar neuropeptide Y depletion whilst in the pineal gland and renal artery 6-hydroxydopamine had more effect than reserpine. The implications of these results on NPY storage sites are discussed.

Animals↗
PubMed1986

Structure and ultrastructure of muscle systems within Grillotia erinaceus metacestodes (Cestoda: Trypanorhyncha).

Three distinct muscle types have been identified within the metacestode of Grillotia erinaceus. These consist of peripheral somatic myofibres plus two muscle systems directly involved in parasite attachment to the host, i.e. the tentacular bulb and its antagonistic retractor muscle. In common with other cestodes the somatic muscle consists of smooth-type fibres running longitudinally and obliquely to the main body axis. The retractor muscle consists of myofibres with centrally displaced nuclei. Upon contraction these latter fibres become spirally orientated causing the muscle to coil and lateral membranes to become elevated as spikes. Definitive nerve processes have not been identified within somatic or retractor muscle. Individual tentacular bulbs form the proximal terminus for a closed hydraulic system. Each bulb consists of overlapping, contrarotating myofibres which display obvious striations; the striations appear in alternate fibres to be in transverse and oblique planes. Adjacent myofibres are separated by approximately 0.5 micron, possess abundant mitochondria and have shallow t-tubules plus associated vesicles of sarcoplasmic reticulum at each Z line. Thick myofilaments are surrounded by 13, shared, thin myofilaments. Close neuronal control for the bulb muscle is suggested by the presence of obvious motor end-plates which contain both lucent and dense neurovesicles.

Animals↗
PubMed1986

Neuropeptide Y in renovascular models of hypertension in the rat.

Neuropeptide Y content of the kidneys, heart, blood vessels, adrenals and brain stem was determined in both two-kidney, one-clip and one-kidney, one-clip Goldblatt hypertension in rats and compared with levels in age- and sex-matched controls. Renal neuropeptide Y content was significantly reduced in the clipped kidney of rats in both Goldblatt two-kidney, one-clip and Goldblatt one-kidney, one-clip models of hypertension. The content of neuropeptide Y was also reduced but to a lesser extent in the contralateral, non-ischaemic kidney in the two-kidney, one-clip model. In both models of hypertension, neuropeptide Y content in the heart was significantly reduced in the left ventricle and septum but unchanged in the atria and right ventricle wall. There was no significant change in the concentration of neuropeptide Y through the vasculature (major arteries and veins), including the renal artery distal to the clip, or in adrenals and brain stem.

Adrenal Glands↗
PubMed1986

Neuropeptides and dopamine in the marmoset. Effect of treatment with 1-methyl-4-phenyl-1, 2, 3, 6 tetrahydropyridine (MPTP): an animal model for Parkinson's disease?

Neurochemical studies of post-mortem human parkinsonian brains have demonstrated specific alterations in neuropeptide concentrations within the substantia nigra and striatal structures. The drug, 1-methyl-4-phenyl-1, 2, 3, 6 tetrahydropyridine (MPTP) has been reported to act as a selective toxin to nigrostriatal dopamine neurons, and induces a parkinsonian-like syndrome in primates. In this study, marmosets developed features typical of Parkinson's disease following treatment with MPTP for four days. The effects of MPTP treatment on the concentrations of dopamine and neuropeptides were determined and changes compared with those reported for Parkinson's disease. It was found that within the substantia nigra, substance P concentrations doubled following treatment with MPTP; in contrast, concentrations of vasoactive intestinal peptide and neuropeptide Y were significantly reduced. No changes were observed in the concentrations of six other neuropeptides measured in this region, notably cholecystokinin. Despite marked depletion of dopamine within the caudate nucleus and putamen, concentrations of all neuropeptides within these structures remained unchanged with the exception of an isolated reduction of neuropeptide Y within the putamen. Somatostatin concentrations within the frontal cortex and hippocampus were significantly elevated in the marmosets treated with MPTP. These neuropeptide changes in the CNS contrast with those reported for Parkinson's disease. In view of the autonomic dysfunction associated with Parkinson's disease, peripheral concentrations of neuropeptides were determined. Significant depletion of neuropeptide Y was identified in the ureter, adrenal and cardiovascular tissue. Thus the neurochemical changes induced by MPTP may not be as selective as previously reported.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗