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Biomedical subjects

A Logan

Publications and source records attributed to A Logan.

At least 109 records · Page 6Linked to original sources
PubMed1985

Identification and partial purification of fibroblast growth factor from the brains of developing rats and leucodystrophic mutant mice.

High titres of fibroblast growth factor activity (assessed by mitogenicity for Balb/c 3T3 fibroblast cells in vitro) have been extracted from the brains of foetal and neonatal rats long before myelinogenesis commences, from the brains of hypomyelinated, leucodystrophic, murine mutants and from normal adult rats. Partial purification, by ion-exchange chromatography and gel filtration, indicates that the brain fibroblast growth factor activity from these sources is associated with very similar basic protein fractions. These results, together with the observation that none of the samples of partially purified basic fibroblast growth factor elicits the experimental allergic encephalomyelitis response attributed to myelin basic protein in the rat, suggest that basic fibroblast growth factor is not a degradation product of myelin basic protein.

Aging↗
PubMed1983

Deposition of scar tissue in the central nervous system.

Standard parasagittal lesions were placed stereotactically in the cerebral hemispheres of neonatal and adult rats in order to compare scarring in the immature and mature animal. Lesions were examined by light and electron-microscopy and immunofluorescence to study the astrocyte reaction, collagen deposition, and the formation of the basement membrane of the glia limitans. Normal mature scarring characterized by the deposition of collagen, astrocyte end-feet alignment over a glia limitans, and the permanent presence of mesodermal cells (fibroblasts and macrophages) in the core of the lesion, does not occur in wounds before 8-10 days post-partum (dpp). Instead there is no deposition of collagen, and only a transitory astrocyte response occurs with the formation of an interrupted glia limitans. These latter features disappear with time so that the wound is ultimately obliterated by the growth of axons and dendrites through the lesion. Mature scarring is attained over 8-12 dpp when increasing amounts of collagen are deposited and a continuous permanent glia limitans is formed. The acquisition of the mature response to injury from 8-12 dpp may be correlated with the presence of increasing titres of a fibroblast growth factor (FGF), derived from autolytic digestion of injured brain tissue. We have investigated FGF activity using a 3 T 3 fibroblast tissue culture assay to detect mitogenic activity in brain extracts from rats lesioned at different ages and from leukodystrophic mice which have no myelin. Our results show that high titres of FGF are present in the developing brain long before myelination commences, and that normal levels of FGF are found in the brains of leukodystrophic mice which have no myelin. Scarring in brain lesions in these mutants is quite normal.

Animals↗
PubMed1983

Experimental production of diffuse pulmonary fibrosis and alveolitis in cattle: the effects of repeated dosage with 3, methyl indole.

Eleven Friesian steers were given 3, methyl indole (3MI) orally at dose rates ranging from 0.1 to 0.3 g/kg. Three of these (group B) received a single oral dose of 0.2 g/kg and subsequently developed respiratory distress. Their plasma 3MI concentrations six hours after dosing were between 2.25 and 7.23 micrograms/ml. The steer with the highest six-hour plasma value died at this stage and the dominant pathological feature was severe pulmonary oedema. The other two steers survived until they were slaughtered 96 hours after dosing; the major pathological findings in them were interstitial emphysema, hyaline membranes and alveolar epithelial hyperplasia. The other eight steers (group C) each received weekly oral doses of 0.1 g 3MI/kg for 10 weeks. One animal died after developing severe respiratory distress following its third dose. Thereafter, the others developed two separate patterns of response. Three steers (subgroup C1) became progressively more tolerant to oral 3MI, even in the face of dose rates increased to 0.2 and 0.3 g/kg during the 11th to 14th weeks of the study and also in the presence of relatively high plasma 3MI concentrations after dosing. One animal was slaughtered after its 10th dose and two after their 14th dose of 3MI; post mortem examinations revealed that their lungs were macro- and microscopically normal. The other steers (subgroup C2) all continued to react after each weekly oral dose of 3MI and their post-dosing plasma 3MI concentrations consistently remained relatively low. Latterly, each of the three steers which survived to the 14th week also exhibited persistent tachypnoea and marked hyperpnoea between dosings. On post mortem examination, in addition to the signs generally associated with acute 3MI toxicity (see above), each of the subgroup C2 steers were found to have diffuse pulmonary fibrosis and an alveolitis. While certain cattle appear to become tolerant to the effects of repeated doses of 3MI, the results of this study clearly demonstrated that, in others, such treatment eventually gives rise to diffuse pulmonary fibrosis and alveolitis.

Animals↗
PubMed1981

Melanotrophin-potentiating factor (MPF) potentiates MSH-induced melanogenesis in hair follicle melanocytes.

Melanotrophin-potentiating factor (MPF) is a fragment of human beta-lipotrophin (LPH 88-91) which potentiates the action of alpha-MSH on Anolis skin. In the present study, we investigated the effect of MPF on MSH-induced melanogenesis. Pooled hair follicle scrapings from Siberian hamsters (Phodopus sungorus) were incubated for 48 hours with or without alpha-MSH and/or MPF. Melanogenesis was monitored by measuring tyrosinase activity and melanin accumulation. 10-8 M MPF potentiated the effect of no effect on melanogenesis, but 10-9 to 10-7 M alpha-MSH caused a dose-related increase. 10-8 M MPF potentiated the effect of each dose of alpha-MSH. Thus MPF potentiated MSH action on mammalian melanogenesis as well as on reptilian melanosome dispersion. Although each of these processes involve different intracellular responses the receptor mechanisms involved in each may therefore be the same.

Animals↗
PubMed1981

Interaction of alpha-melanocyte-stimulating hormone, melatonin, cyclic AMP and cyclic GMP in the control of melanogenesis in hair follicle melanocytes in vitro.

In short-term (48 h) cultures of hair follicles alpha-melanocyte-stimulating hormone (alpha-MSH) and cyclic AMP stimulated melanogenesis through an increase in tyrosinase activity. In contrast cyclic GMP mimicked the effects of melatonin by inhibiting melanin production without causing a concomitant decrease in tyrosinase activity. Both cyclic GMP and melatonin blocked the stimulatory effects of cyclic AMP and alpha-MSH on melanin production but they left the increased levels of tyrosinase activity unaffected. Phosphodiesterase inhibitors (3-isobutyl-1--methylxanthine and papaverine) simultaneously stimulated tyrosinase activity and inhibited melanin production, presumably by allowing endogenous cyclic AMP and cyclic GMP to accumulate intracellularly. It is suggested that whereas MSH stimulates melanogenesis through a cyclic AMP-dependent mechanism there must also be an inhibitory cyclic GMP-dependent mechanism, perhaps activated by melatonin, which operates at some post-tyrosinase step in the melanin biosynthetic pathway.

Animals↗
PubMed1981

Effects of alpha-melanocyte-stimulating hormone and [8-arginine]-vasotocin upon melanogenesis in hair follicle melanocytes in vitro.

alpha-Melanocyte-stimulating hormone (alpha-MSH) has been shown to act directly on the mammalian melanocyte in short-term cultures of hair follicles obtained from the Siberian hamster. Melanogenesis was stimulated through an increase in tyrosinase activity which resulted in an increase in melanin production. The response of hair follicle melanocytes to alpha-MSH occurred only in follicles taken from moulting animals, implying that they show a discontinuous expression of MSH receptors during the hair follicle growth cycle. Synthetic 1-24 ACTH had no effect on melanogenesis regardless of whether the follicles came from moulting or non-moulting animals. The pineal peptide, [8-arginine]-vasotocin (AVT), inhibited melanin production without a concomitant decrease in tyrosinase activity. In this respect AVT resembled melatonin, although AVT showed a potency ratio of less than half on a molar basis. The action of AVT, like that of melatonin, must ultimately be on some post-tyrosinase step in melanin biosynthesis. In these hair follicle melanocytes AVT seems to bind to specific receptors since neither of the closely related peptides, oxytocin and [8-arginine]-vasopressin, displayed any activity in our culture system.

Adrenocorticotropic Hormone↗
PubMed1980

Post-tyrosinase inhibition of melanogenesis by melatonin in hair follicles in vitro.

In short-term (48 hr) culture hair follicles of the Siberian hamster retain both tyrosinase activity and the capacity to produce melanin. The addition of melatonin to such cultures at concentrations between 10-6 M and 10-10 M brings about a dose-related inhibition of melanogenesis but tyrosinase activity is unaffected. The use of a series of melatonin analogues and blockers suggests that the hair follicle melanocytes possess melatonin receptors, although their location remains to be determined. Melatonin also inhibits the increase in melanogenesis brought about by alpha-melanocyte-stimulating hormone (MSH) but again it has no effect upon the increased levels of tyrosinase which accompany this MSH response. It is suggested that melatonin inhibits melanogenesis through a mechanism which operates at some post-tyrosinase step in the melanin biosynthetic pathway.

Animals↗
PubMed1980

Photoperiodic dependence of seasonal changes in pituitary content of melanocyte-stimulating hormone.

In the Siberian hamster the pituitary content of bioassayable MSH has been shown to be seasonally variable, being greater during the long days of spring and summer than during the short days of autumn and winter. Similar changes in the pituitary content of both bioassayable MSH and immunoreactive alpha MSH can be induced by transfer of animals between artificial light photoperiods of appropriate duration.

Animals↗
PubMed1978

Pelage color cycles and hair follicle tyrosinase activity in the Siberian hamster.

Hair follicle tyrosinase levels and melanin content, together with serum tyrosine levels have been studied in relation to annual pelage color changes in the Siberian hamster. Tyrosinase levels were found to peak not only at the spring moult when pigmented hair is produced but also at the autumn moult when the hair produced is unpigmented. The melanin content of hair follicles was high in summer and low in winter but serum tyrosine levels did not differ at the spring and autumn moults. These results suggest that some factor must exist to prevent the raised tyrosinase levels of the autumn moult being expressed as melanogenesis and that this factor must be photoperiodically modifiable, being controlled through a neuroendocrine mechanism.

Animals↗
PubMed1977

Pulsion intubation for palliation of carcinoma of the oesophagus.

One hundred and eighty-one patients with carcinoma of the upper thoracic oesophagus were intubated perorally using a Procter-Livingstone tube. The mortality was 16-6 per cent but, in the patients who survived, the palliation achieved, as judged by improved swallowing, was considered satisfactory. Factors influencing the success of intubation are also considered.

Adult↗
PubMed1977

Plasma insulin and glucose levels in maturity onset diabetics treated with chlorpropamide.

19 diabetic patients taking various doses of chlorpropamide were studied throughout a normal day. Plasma chlorpropamide levels were related to the daily dose of the drug and were relatively constant throughout the day. Blood glucose concentration was highest and the plasma insulin concentration lowest in patients taking the largest dose of chlorpropamide. Patients on a small daily dose of chlorpropamide were well controlled and had higher than normal insulin levels. --12 patients were restudied 10 days after stopping chlorpropamide. Although diabetic control deteriorated in all patients, plasma insulin concentration did not change significantly. This suggests that the long-term hypoglycaemic action of chlorpropamide is not dependent on an effect on the concentration of insulin in peripheral venous blood.

Aged↗
PubMed1977

Isolation of Campylobacter fetus from recent cases of human vibriosis.

Campylobacter fetus was isolated from five recent cases of human vibriosis, of which two were adults and three were children. One adult presented with pericarditis and the other with recurrent pyrexia. Campylobacter fetus subsp. intestinalis which resembled cattle strains serologically, was isolated under CO2 or anaerobic conditions from blood cultures of these patients. Two of the three children had kwashiorkor and the third was only 8 days old. Isolates identified as Campylobacter fetus subsp. jejuni were cultured from blood of these patients, two of whom had diarrhoea. Three patients succumbed, despite adequate antibiotic therapy. The epidemiology of the disease is discussed and it is suggested that infection may have been from the patients' own flora.

Adult↗