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Biomedical subjects

J S Sham

Publications and source records attributed to J S Sham.

142 records · Page 8Linked to original sources
PubMed1986

Comparative study on the cardiac actions of bovine parathyroid hormone (1-34).

The cardiac stimulatory effects of bovine parathyroid hormone (1-34) [bPTH-(1-34)] were studied on isolated atria and ventricular strips from cobra snakes (Naja naja), ducklings (Anas platyrhynchos), pigeons (Columba livia), Japanese quails (Coturnix coturnix japonica), laboratory rats (Rattus norvegicus), and dogs (Canis familiaris). In all atrial preparations, bPTH-(1-34) caused positive chronotropism. This suggests that the chronotropic effect of PTH is ubiquitous among the terrestrial vertebrates. Only the atria of cobra snakes and ducklings gave positive inotropic responses to PTH. No ventricular preparations showed significant response to bPTH-(1-34). This suggests the absence of cardiac stimulatory PTH receptors in the ventricles. Dog papillary muscle, however, showed slight but significant responses to bPTH-(1-34). The reason for this discrepancy between the responses of papillary muscles and the ventricular strips to PTH is unknown.

Animals↗
PubMed1986

Interaction between thermal environments and hormones affecting skin-shedding frequency in the tokay (Gekko gecko) (Gekkonidae, Lacertilia).

Effects of thyroidectomy and/or hypophysectomy on the skin-shedding frequency (SF) in the tokay Gekko gecko and of thyroid hormones on the oxygen consumption (OCR) at various temperature regimes have been determined. Surgery invariably protracted the cycle length, thus decreasing SF; the extent of these changes was temperature dependent, the higher the temperature, the less the difference. Effects of hypophysectomy on cycle length were expressed in two phases; an extended first post-operative cycle was followed by a further extended second post-operative cycle, with cycle length forming a plateau thereafter. With time, the operated tokays would die without shedding during a greatly protracted cycle. OCRs in the tokay were temperature dependent, but between 28 and 34 degrees C, no significant difference could be seen. Effects of thyroid hormones on OCR were also temperature dependent. Furthermore, tokays having higher OCR were shown to have shorter cycles and vice versa. Results showed that whatever effect hormone(s) have on SF is indirect through general metabolic changes. SF is merely a reflection of the general metabolic status of the animal. It is proposed that the role of hormone(s), those of the thyroid in particular, is to act as "fine-tuning" devices in the regulation of metabolism and, as such, of the viability of the animal.

Acclimatization↗
PubMed1985

Adrenergic receptors of isolated snake atria.

Cardiac adrenergic receptors in snakes were examined using an isolated atria preparation of Naja naja and Ptyas korros. Treatments included an examination of the atrial responses to selective alpha- and beta-adrenergic agonists and antagonists. In both species, both phenylephrine and isoproterenol produced dose-dependent increases in the atrial beating rate and tension. Phenylephrine-induced increases were characterized with a high affinity and low affinity components. These positive chronotropic and inotropic effects produced by phenylephrine and isoproterenol were abolished with propranolol and in the phenylephrine-induced response phentolamine also attenuated the low affinity response and blocked the high affinity response. With catecholamines depletion via 6-OH dopamine or reserpine, the high affinity component in the phenylephrine-induced response was no longer observed. It is concluded that beta-adrenoceptors are the predominant post-synaptic adrenoceptors in snake atria. Stimulatory presynaptic alpha-adrenoceptors for modulating noradrenaline release may also be present.

Animals↗
PubMed1984

Cardiac actions and structural--activity relationship of parathyroid hormone on isolated frog atrium.

The hypercalcemic and hypotensive actions of parathyroid hormones (PTH), parathyroid extract, and synthetic PTH-(1-34) have been reported in many different animals. However, their cardiac action was only recognized recently. In the present study, experiments were designed to examine (1) whether PTH possesses any cardiac action on the isolated frog atrium, and (2) the importance of methionine and arginine of bPTH-(1-34) in cardiac action. Six different bPTH analogs were tested in frog atria in vitro: bPTH-(1-34); H2O2-treated bPTH-(1-34); [Nle8, Nle18, Tyr34]-bPTH-(1-34); H2O2-treated [Nle8, Nle18, Tyr34]-bPTH-(1-34); arginine-modified bPTH-(1-34); and arginine-regenerated bPTH-(1-34) (Nle-norleucine). bPTH-(1-34) produced positive chronotropic and inotropic responses. Oxidation with hydrogen peroxide abolished both actions of bPTH-(1-34). [Nle8, Nle18, Tyr34]-bPTH-(1-34) also possesses this cardiac-stimulating property. The H2O2 treatment of this analog did not alter the chronotropic action, but a decrease in the inotropic action was observed. The arginine-modified bPTH-(1-34) was much less potent than its native hormone, while the reversal of the arginine modification partially restored the biopotency. From these data, it is concluded that (1) bPTH-(1-34) possesses both positive chronotropic and inotropic effects on the frog atrium, (2) the cardiac actions of bPTH-(1-34) may be closely related with its hypotensive property, (3) methionines are not necessary for the cardiac actions, and (4) arginines are important for the cardiac-stimulating effects of bPTH.

Animals↗
PubMed1984

Cardiac actions of bovine parathyroid hormone fragment (1-34) in some lower vertebrates.

Only recently have the cardiac actions of parathyroid hormone and its N-terminal (1-34) fragment (bPTH(1-34] been examined. Parathyroid hormone was found to exert a positive chronotropic effect on the heart tissue of several mammals and one amphibian in vivo and/or in vitro. The purpose of the present study was to examine in vitro the heart tissue of several lower vertebrates, particularly aquatic vertebrates, for responsiveness to bPTH(1-34) and, for comparative purposes, isoproterenol. Heart tissue (atrium or the entire heart) from all the animals studied (trout, mudpuppy, bullfrog tadpole, and adult bullfrog) responded to isoproterenol in a dose-dependent fashion with increased heart rate and contractile force. Only the atria from the adult bullfrog, however, responded in a similar manner to the administration of bPTH(1-34). In all cases propranalol (10(-6) M) was able to block both chronotropic and inotropic effects of isoproterenol but had no effect on the cardiac stimulation induced by bPTH(1-34) in the adult bullfrog atrium. The data suggests that cardiac responsiveness to bPTH(1-34) is associated with a terrestrial as opposed to an aquatic existence.

Animals↗
PubMed1984

The vasopressor action of the renin-angiotensin system in the rat snake, Ptyas korros.

The pressor actions of homologous kidney extract and human angiotensins I and II were studied in the conscious rat snake, Ptyas korros. A converting enzyme inhibitor (captopril), an angiotensin II analogue [( Sar1,Ala8]ANG II), an alpha-adrenergic receptor antagonist (phentolamine), and a catecholamine releaser (reserpine) were used to elucidate their actions. It was found that captopril attenuated the pressor effects of the kidney extract and angiotensin I but not that of angiotensin II. [Sar1,Ala8]ANG II and phentolamine both significantly attenuated, but did not completely inhibit the vasopressor actions of the kidney extract and angiotensins I and II. However, reserpine administration did not reduce the action of angiotensin II. These findings suggest that the renin-angiotensin system in snakes is similar to those present in mammals and other nonmammalian species, except for the mechanism of angiotensin II action. In the present study, angiotensin II was found to act partly through the alpha-adrenergic receptor which is not as specific as that in mammals and thus may respond to an agonist other than its usual ones, and partly through the vascular angiotensin II receptor.

Angiotensin I↗
PubMed1984

Blood pressure homeostasis in Rana catesbeiana under normal and hypovolemic conditions.

The effects of phentolamine, KBIV24 and captopril on the mean arterial blood pressure of normal and treated (dehydration, hemorrhage) frogs were determined. Hemorrhage but not dehydration led to a decrease in MAP. Only phentolamine attentuated MAP in both normal and treated frogs. KBIV24 and captopril were ineffective. It was concluded that the blood pressure of frogs is regulated by catecholamine. Neither arginine vasotocin nor the renin-angiotensin system play any role in blood pressure homeostasis in normal and hypovolemic conditions.

Animals↗
PubMed1983

Hypotensive actions of snake parathyroid glands.

Parathyroid gland extracts from four different snake species, Ptyas korros, Ptyas mucosa, Elaphe radiata, and Naja naja, were prepared and their hypotensive actions were assayed in anesthetized P. korros. All extracts were hypotensive and the responses, except that of N. naja, were dose related. Their potencies were, however, different in different species. These data suggest that the hypotensive property of the parathyroid hormone is probably widely distributed in submammalian vertebrates.

Animals↗
PubMedDate not supplied

New approach to the nasopharynx: the maxillary swing approach.

A new approach to expose the nasopharynx and the paranasopharyngeal space is described. The maxilla, severed from its bony connections, is swung laterally to provide exposure of the nasopharynx. Tumors in the nasopharynx and the paranasopharyngeal space can be adequately resected and tubings for afterloading brachytherapy can be positioned accurately during surgery. The blood supply of the maxilla is from the attached cheek flap and masseter muscle. Three illustrative cases are presented. The wounds in all of them healed primarily with minimal morbidity. The only disadvantage is the development of mild trismus, which responded to conservative treatment.

Adult↗
PubMedDate not supplied

Prognostic value of paranasopharyngeal extension of nasopharyngeal carcinoma on local control and short-term survival.

The local tumor control of 262 patients with nasopharyngeal carcinoma (NPC) at median follow-up of 27 months was studied with reference to the paranasopharyngeal and other aspects of extranasopharyngeal extension of tumor, as well as to other possible prognostic factors. Only cranial nerve palsy, oropharyngeal involvement, and paranasopharyngeal extension of tumor were found to be significant in a multivariate analysis using Cox model for factors influencing local tumor control. Other factors and other parameters of extranasopharyngeal extension of tumor, namely, erosion of the base of skull, intracranial extension, and involvement of nasal fossa, were found not be significant. The degree of paranasopharyngeal extension in each side was correlated with scales measuring extranasopharyngeal extension of tumor in other directions (p = 0.001). Although the T stage and the paranasopharyngeal extension were individually found to be well correlated with local tumor control, the prognostic value of paranasopharyngeal extension remained significant among subgroups of patients with T3 and T4 disease (p = 0.1044 and 0.0010, respectively).

Adult↗
PubMedDate not supplied

Serous otitis media and paranasopharyngeal extension of nasopharyngeal carcinoma.

Two hundred thirty-two patients with nasopharyngeal carcinoma were evaluated for serous otitis media (SOM) at diagnosis. The diagnosis of SOM required the detection of effusion behind the tympanic membrane in association of air-bone gap of 10 dB or more in pure tone audiogram. These patients were also evaluated by computed tomography for the degree of tumor extension. By stepwise logistic regression analysis, the degree of paranasopharyngeal extension of tumor, erosion of petrous temporal bone, and the obliteration of pharyngeal recess were significantly related to the development of SOM, but sex and age were not. The findings of computed tomography may influence the plan of management for SOM in patients with nasopharyngeal carcinoma at diagnosis.

Adolescent↗
PubMedDate not supplied

Value of clinical follow-up for local nasopharyngeal carcinoma relapse.

Three hundred seventy-nine new patients with nasopharyngeal carcinoma (NPC) were followed clinically and the physical examination, including that of the nasopharynx by indirect mirror for symptoms after treatment. At the time of analysis, with a median follow-up of 34.8 months, 47 patients had developed recurrent disease in the nasopharynx and in the immediately adjacent regions. In 31 patients the first clinical features to suggest local recurrence were progressive symptoms (group A). In another 13 patients recurrence of tumor in the nasopharynx was detected by indirect mirror examination (group B). In the remaining three patients, the diagnosis was made during investigation for neck node recurrence. The more common symptoms at diagnosis of local recurrence were headache; cranial nerve palsy involving the third, fourth, fifth, and sixth nerves; and ear and nasal symptoms. Group B patients tended to have less of these symptoms. The presence of tumor was confirmed by fiberscopic examination and biopsy in all group B patients and 14 of 31 group A patients, the tumor was submucosal in the remaining 17 group A patients. The recurrence in group B patients was diagnosed significantly earlier than the group A patients (p = 0.0294), and group A patients suffered from more invasive and extensive disease in comparison with group B patients (p = 0.0044). There were significantly less patients in group A who were amenable to curative brachytherapy (p = 0.0280). Clinical follow-up for local NPC recurrence was found to be useful. More frequent use of fiberscopic examination in the follow-up, especially for those not adequately examined by indirect mirror examination, will improve the detection rate. Cross-sectional imaging techniques and the monitoring of tumor markers may supplement clinical and fiberscopic examinations. An algorithm for diagnosing recurrent NPC and possible treatment are suggested.

Algorithms↗
PubMedDate not supplied

Nasopharyngeal carcinoma: review of how imaging affects staging.

Imaging plays an important role in the staging of carcinoma of the nasopharynx. Accurate staging is necessary as the treatment is directly dependent on stage. Clinical examination provides information on mucosal involvement but is unable to determine the deep extension or presence of skull base invasion or intracranial spread. The 1997 International Union Against Cancer (UICC) and American Joint Committee on Cancer (AJCC) staging manuals were a collaborative project that provided a unified classification for nasopharyngeal carcinoma (NPC). The majority of staging can be identified only on imaging and not by clinical examination. The intent of this article is to provide information on the specific imaging findings that will directly affect the stage and treatment of NPC.

Brain↗
PubMedDate not supplied

Regulation of telomerase activity by gamma-radiation in nasopharyngeal carcinoma cells.

Since telomerase has been suggested to play a role in radiation response, the effect of radiation on the regulation of telomerase activity was studied on two NPC cell lines, CNE1 and 915. In order to investigate the correlation between cell survival and telomerase activity, three low doses (0.25, 0.5 and 1 Gy) and three high doses (2, 4 and 8 Gy) of gamma-radiation were used. We found that low doses of radiation induced telomerase activity (up to 250% of untreated controls) followed by a cell cycle G1 arrest, suggesting that the up-regulation of telomerase may play a role in initiating radiation induced cell cycle arrest. High doses of radiation resulted in decreased telomerase activity (down to 30% of untreated controls) and this was followed by an increased cell death. Our results indicate that the up-regulation of telomerase activity is an important response to radiation induced sub-lethal DNA damage. Our results also suggest that inhibition of telomerase activity by high doses of radiation may play a role radiation-induced cell death.

Carcinoma↗
PubMedDate not supplied

Nasopharyngeal carcinoma: CT evaluation of patterns of tumor spread.

In a prospective study using CT as the initial means of radiologic evaluation in 262 patients with proved nasopharyngeal carcinoma, the paranasopharyngeal space was found to be the most commonly involved region (84.4%), both uni- and bilaterally. Unilateral involvement was found in 44.3% of patients (116/262) and bilateral involvement in 40.1% (105/262). The other structures or regions that were involved, in decreasing order of frequency, were the sphenoid sinus (26.7%), nasal fossa (21.8%), and ethmoid sinus (18.3%). Erosion of the base of the skull and intracranial intracranial extension into the middle cranial fossa were common (31.3% and 12.2%, respectively). The primary tumor in the nasopharynx was found to be contiguous with metastatic upper cervical nodes through paranasopharyngeal extension of tumor in 35 patients (13.4%). A qualitative method to assess the degree of paranasopharyngeal extension is proposed. The extent of paranasopharyngeal extension so evaluated was correlated with other attributes of tumor extent (p = .0001), namely, nasal or oropharyngeal extension, which constitutes a T3-level tumor, and erosion of the base of the skull or orbit, which constitutes a T4-level tumor. The extent of paranasopharyngeal extension was also correlated with local control of the tumors (p = .0001). At a median follow-up of 27 months, only three (7.9%) of the 38 patients with no paranasopharyngeal extension had nasopharyngeal relapse, while 12 (11.2%) of the 107 and 17 (34.7%) of the 49 patients with types 1 and 2 paranasopharyngeal extension, respectively, had nasopharyngeal relapse.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗