Search PubMed⌕ Search

Biomedical subjects

C C Chan

Publications and source records attributed to C C Chan.

At least 487 records · Page 27Linked to original sources
PubMed1983

Effects of desmethylimipramine and normetanephrine on calorigenic response and plasma noradrenaline concentration in warm- and in cold-acclimated rats exposed to cold.

Oxygen consumption and plasma noradrenaline concentration were increased significantly above resting levels in warm-acclimated and in cold-acclimated rats exposed to an ambient temperature of 4 degrees C. Administration of normetanephrine (1 microgram X min-1 X g body weight-0.74), but not of desmethylimipramine (1 mg X kg-1), resulted in higher resting plasma noradrenaline levels at 24 degrees C and increased the length of time required for the oxygen consumption to return to resting levels after cold exposure in both acclimation groups. These observations support a significant role of extraneuronal uptake in noradrenaline inactivation under normal physiological conditions. Calorigenic responses to cold exposure were not affected at all by treatment of animals with desmethylimipramine and (or) normetanephrine in either warm-acclimated or cold-acclimated rats, although an enhancing effect of these uptake inhibitors on plasma noradrenaline was evident in cold-acclimated rats. It is suggested that a peripheral-central thermoregulatory mechanism adjusts activation of thermogenic effectors so as to maintain a steady calorigenic response, appropriate to the thermal demand of the environment, to compensate for changes in perineuronal concentration of noradrenaline in sympathetic thermoeffectors owing to blockade of extraneuronal uptake.

Acclimatization↗
PubMed1982

Ocular findings in osteogenesis imperfecta congenita.

Osteogenesis imperfecta is a rare, inherited, connective-tissue disorder. The three main signs of this disease are multiple bone fractures, blue scleras, and deafness (osteosclerotic type). In our research, only a few reports of the morphologic studies of the eyes of patients with osteogenesis imperfecta were found. This report describes the ocular histopathologic condition of four cases of osteogenesis imperfecta congenita, with emphasis on the ultrastructural characteristics of the collagen in the cornea and sclera.

Cornea↗
PubMed1982

Termination of responses to sympathetic nerve stimulation and to noradrenaline in a perfused arterial preparation: the role of neuronal and extraneuronal uptake.

Perfused branch vessels of bovine radial artery in vitro responded to sympathetic nerve stimulation and to noradrenaline added extralumenally and intralumenally with constrictions monitored as flow reductions. Cocaine and 17 beta-estradiol, inhibitors of neuronal and extraneuronal uptake, respectively, enhanced responses to exogenous noradrenaline given by either route. An analysis of response recovery rates, namely termination of action, revealed that the extraneuronal and neuronal uptake process each accounted for between 35 to 50% of the total inactivation capacity of the perfused neuroeffector system for noradrenaline. Responses to periarterial nerve stimulation over a 0.5 to 10 Hz frequency range, involving minimal to moderate flow reductions, were substantially magnified by cocaine and by 17 beta-estradiol. An analysis of response duration and recovery rates showed that extraneuronal processes were more significant than neuronal uptake in terminating noradrenergic transmitter action over the frequency band of 0.5 to 10 Hz.

Animals↗
PubMed1981

Central retinal vein occlusion: a prospective histopathologic study of 29 eyes in 28 cases.

The clinical and histopathologic features of 29 eyes from 28 patients with central retinal vein occlusion (CRVO) are reported. A fresh or a recanalized thrombus was observed in each eye. This study considers the temporal aspects of the cases, and it notes the different morphologic features of the occlusion. These observations explain most of the variability of the changes observed in previous reports. We believe these different features representthe various stages in the natural evolution of such a thrombus. The interval between CRVO and histopathologic study in our series ranged from six hours to more than ten years. Local and systemic factors were reviewed and were found to be important in the pathogenesis of thrombus formation. Local diseases with a predisposing effect on CRVO included: glaucoma, papilledema, subdural hemorrhage, optic nerve hemorrhage, and drusen of the optic nerve head. Associated systemic diseases included: hypertension, cardiovascular and cerebrovascular disease, diabetes mellitus, and leukemia with thrombocytopenia. A fresh thrombus in the CRVO was observed in three (10.3%), and a recanalized thrombus in 26 eyes (89.7%). Endothelial-cell proliferation was a conspicuous feature in 14 (48.3%) of the eyes. Chronic inflammation in the area of the thrombus and/or vein wall or perivenular area was observed in 14 (48.3%) of the eyes. Arterial occlusive disease was observed in seven eyes (24.6%). Cystoid macular edema was found in 26 (89.7%) of the eyes.

Aged↗
PubMed1981

Central retinal vein occlusion: a prospective histopathologic study of 29 eyes in 28 cases.

The clinical and histopathologic features of 29 eyes from 29 patients with central retinal vein occlusion (CRVO) are reported. A fresh or a recanalized thrombus was observed in each eye. This study considers the temporal aspects of the cases, and it notes the different morphologic features of the occlusion. These observations explain most of the variability of the changes observed in previous reports. We believe that these different features represent the various stages in the natural evolution of such a thrombus. The interval between CRVO and histopathologic study in our series ranged from six hours to more than 10 years. Local and systemic factors were reviewed and were found to be important in the pathogenesis of thrombus formation. Local diseases with a predisposing effect on CRVO included: glaucoma, papilledema, subdural hemorrhage, optic nerve hemorrhage, and drusen of the optic nerve head. Associated systemic diseases included: hypertension, cardiovascular and cerebrovascular disease, diabetes mellitus, and leukemia with thrombocytopenia. A fresh thrombus in the CRVO was observed in three (10.3%), and a recanalized thrombus in 26 eyes (89.7%). Endothelial-cell proliferation was a conspicuous feature in 14 (48.3%) of the eyes. Chronic inflammation in the area of the thrombus, and/or vein wall or perivenular area was observed in 14 (48.3%) of the eyes. Arterial occlusive disease was observed in seven eyes (24.6%). Cystoid macular edema was found in 26 (89.7%) of the eyes.

Adolescent↗
PubMed1980

Oculocerebral malformations. A reappraisal of Walker's 'lissencephaly'.

We describe an infant with multiple ocular and cerebral malformations. The eye lesions included microphthalmia, detachment and dysplasia of the retina, hypoplasia of the optic nerve, persistence of the primary vitreous, cataracts, obliteration of the anterior chamber, and vascularization of the cornea. In the brain, the salient features were microencephaly, agyria of an unusual type, cerebellar hypoplasia and dysplasia, persistent corpus pontobulbare, obliteration of the subarachnoid space, and a midline arachnoid cyst in the posterior fossa. We suggest that these lesions were the end result of a fetal infection that operated during a protracted period starting not later than the fourth month of intrauterine life.

Abnormalities, Multiple↗
PubMed1980

Isolated oculomotor palsy after measles immunization.

A 17-month-old healthy boy had a rapid onset of right oculomotor nerve palsy, and spontaneous recovery after measles immunization. Results of computed tomography scan, skull x-ray, chest x-ray, intravenous pyelogram, and bone marrow examination were all normal. Serum antibody titers showed effective measles immunization.

Blepharoptosis↗
PubMed1980

Inhibition by dopamine of the stimulation-induced efflux of [3H]noradrenaline in renal arteries: limitations of the unitary hypothesis of presynaptic regulation of transmitter release.

The supposition was tested that a pattern of agonist inhibition of 3H-labelled transmitter efflux which shows a decline in intensity as the frequency of stimulation rises provides major evidence for the existence of a functional autoinhibitory feedback loop mediated by released transmitter and located on adrenergic nerve terminals. For these experiments dopamine was used, as it is not released in significant quantities in the ordinary course of sympathetic nerve activation and it appears to act presynaptically in several tested tissues at a locus discrete from that acted on by noradrenaline. Dopamine (3 X 10(-7) and 3 X 10(-6) M) inhibited the stimulation-induced efflux of [3H]noradrenaline from cattle renal arteries and did so to a declining extent with increasing frequency (1-15 Hz). Known antagonists of dopamine action, pimozide and metoclopromide, antagonized this effect of dopamine but did not by themselves enhance stimulation-induced transmitter efflux or block the inhibiting effects of exogenous noradrenaline on efflux, establishing the specificity of dopamine action in renal artery and indicating the absence of an operative negative feedback loop mediated by dopamine. This interpretation was substantiated by the finding that although dopamine reduced the magnitude of contractile responses to nerve stimulation neither pimozide nor metoclopromide enhanced the amplitude of nerve-induced contractions. It thus appears that a pattern of agonist effect on transmitter efflux which manifests a diminution in intensity as the frequency of stimulation climbs is not derived from the operation of an ongoing autoinhibitory feedback system regulating transmitter release but by a yet to be established factor.

Animals↗
PubMed1980

Radiolysis of CoIII-EDTA solution by charged particles through 6Li(n,a)3H reaction.

This experiment was to study the radiolysis of CoIII-EDTA solution in 0.8N H2SO4 saturated with air by charged particles produced through 6Li(n,a)3H reaction. The experimental results show that the G(-CoIII-EDTA) decreases as the absorbed dose rate increases. For the same absorbed dose rate, the values of G(-CoIII-EDTA) are practically independent of absorbed dose. The effects of concentration and temperature are also studied.

Cobalt↗
PubMed1979

Infrequency of retinal neovascularization following central retinal vein occlusion.

Forty-eight patients with the clinical diagnosis of central retinal vein occlusion and ten surgically enulceated eyes with central retinal vein occlusion documented by histopathologic examination were studied and reviewed. Retinal neovascularization developed in only one of the ten eyes. Rubeosis iridis occurred in 14% (7) of the clinical cases and in all of the histopathologic cases. Ten eyes with neovascular glaucoma, enucleated following central retinal vein occlusion, showed absence of retinal endothelial cells. The absence of retinal capillary endothelial cells is significant in explaining the rare occurrence of retinal neovascularization following central retinal vein occlusion. However, the small number of cases may reflect a biased result. Further studies of more cases over a longer period are required to reach the final conclusion.

Humans↗
PubMed1979

An examination of the negative feedback function of presynaptic adrenoceptors in a vascular tissue.

1 The hypothesis was examined that presynaptic alpha-adrenoceptors exert a negative feedback function regulating noradrenergic transmission.2 Renal artery strips from cattle, pre-incubated with [(3)H]-noradrenaline, were stimulated with 300 pulses at 5 different frequencies, spanning the physiological range, and the efflux of tritium assessed both in the absence and presence of functional presynaptic receptors.3 Considerable variation in the synaptic level of free and active noradrenaline with increasing frequency was apparent from the rates of development and the magnitudes of the mechanical responses but the overflow of tritium was constant at 1, 2, 10 and 15 Hz and slightly elevated at 5 Hz, providing no evidence for presynaptic modulation of release.4 Phenoxybenzamine (3.3 x 10(-5) M) enhanced the overflow of tritium most at the lowest frequency tested and to a similar extent at the other test frequencies, except 10 Hz where its effect was slightly reduced.5 The conditions of the present experiments appeared optimal for the operation of the negative feedback system and the failure to observe an increased effectiveness of the antagonist with increasing frequency indicates that the physiological relevance of such a system is highly questionable and suggests that it may not function at all.

Animals↗
PubMed1979

Noradrenaline inhibition of transmitter efflux in a renal artery preparation and the presynaptic receptor theory.

The effect of noradrenaline on the stimulation-induced efflux of tritium in cattle renal arteries preincubated with [3H]noradrenaline was determined. Preparations were stimulated transmurally, with 300 shocks over a range of frequencies (1--15 Hz) in the presence and absence of noradrenaline (3 X 10(-6) M). The agonist inhibited the efflux most at 1 Hz but the extent of the inhibition did not vary with frequency between 2, 5, and 15 Hz. It is concluded that a negative feedback system, modulating neurotransmitter release, and increasingly activated by endogenously released noradrenaline as the frequency of stimulation rises, cannot account for the pattern of efflux inhibition induced by exogenous noradrenaline.

Animals↗
PubMed1979

Infrequency of retinal neovascularization following central retinal vein occlusion attributed to endothelial death.

48 patients with central retinal vein occlusion by clinical diagnosis and 10 eyes by histopathological documentation were studied and reviewed. Only 1 eye developed retinal neovascularization. Rubeosis iridis occurs in 14% of clinical cases and all of histopathologic cases. 10 long-standing neovascular glaucoma enucleated eyes following central retinal vein occlusion show absence of retinal endothelial cells. The absence of retinal capillary endothelial cells seems to be significant in explaining the rare occurrence of retinal neovascularization following central retinal vein occlusion. However, the small number sampling may reflect a biased result. Further prospective studies with more cases and time observation are required to draw the final conclusion.

Capillaries↗
PubMed1978

Multiple ocular anomalies associated with maternal LSD ingestion.

Severe ocular malformations, including microphthalmos, intraocular cartilage, cataract, persistent hyperplastic primary vitreous, and retinal dysplasia, occurred in a premature baby girl. The mother had ingested LSD during the first trimester of pregnancy. To our knowledge, this is the third case reported of ocular teratogenesis associated with maternal LSD ingestion. Further cases must be documented to establish an actual cause and effect relationship between the drug and the induced malformations.

Abnormalities, Drug-Induced↗
PubMed1975

Impairment of active avoidance in rats with unilateral hypothalamic lesion.

Male albino rats with unilateral hypothalamic (ULH) lesion on either the right or left side were trained to acquire active shock avoidance in a two-way shuttle box. With 20 trials in a session per day, either group scored responses below 50% by the 8th day, while intact rats attained the criterion of 80% correct responses by the 5th day. It is concluded that intact lateral hypothalamic areas are essential for successful learning of active shock avoidance.

Aged↗