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Biomedical subjects

G Ponsin

Publications and source records attributed to G Ponsin.

50 records · Page 3Linked to original sources
PubMed1980

Highly specific solid phase immunoextraction of TSH using anti-TSH antibodies purified by affinity chromatography.

Highly specific anti-TSH antibodies were purified from a crude antiserum preparation by affinity chromatography using TSH-sepharose column as the adsorbant. This procedure completely eliminated the original LH binding activities. The purified anti-TSH antibodies were then coupled to CNBr activated sepharose 4 B and used in separating TSH from rat pituitaries by batch procedure. This method is demonstrated to be highly specific for purifying labelled TSH from pituitaries previously incubated in the presence of [14C]tyrosine. The effect of TRH on TSH biosynthesis is presented as a biological application of this procedure.

Animals↗
PubMed1978

Regulation of TSH secretion in rats chronically exposed to heat (34 degrees C).

Previous studies have shown that in heat exposed rats, a decreased plasma T4 concentration was associated with a normal biologically active TSH concentration. This study was designed to clarify this apparent discrepancy in the regulation of TSH secretion. In experimental rats (34 degrees C for 25 days) and controls (25 degrees C), plasma total T4 was 3.2 vs. 5.7 x 10(-8) mol/l. (P less than 0.01), plasma total T3: 2.4 vs. 5.7 x 10(-10)mol/l. (P less 0.01) and plasma TSH: bioassay 0.34 vs 0.29 mU/ml (ns), radioimmunoassay: 1.04 vs. 0.87 microgram RP1/ml (ns). After TRH, plasma TSH increased identically in the two groups. In heat-exposed rats, the dialysable fraction of T4 and T3 were were increased: 0.032 vs. 0.020% (P less than 0.05) and 0.102 vs. 0.086% (P less than 0.05), respectively; accordingly, free T4 concentration was normal and that of free T3 was low; total plasma proteins were slightly increased. It is concluded that in heat-exposed rats: (1) plasma thyroid hormone binding activity was decreased as shown by the association: decreased plasma total T4--elevated free T4 fraction. The normality of the free T4 concentration accounted for the normal plasma TSH. (2) the combination of normal plasma TSH, normal plasma free T4, low plasma free T3 concentrations would suggest that T4 is predominantly involved in the regulation of TSH secretion.

Animals↗
PubMed1978

Participation of serotonin in thyrotropin release. I. Evidence for the action of serotonin on thyrotropin releasing hormone release.

Injection of serotonin (5-HT) into the third ventricle of the rat resulted in a rapid increase of serum TSH; a significant effect was observed 5 min after injection, whereas the maximal effect appeared 10 min after the injection of 1 microgram 5-HT. This stimulating effect of 5-HT was completely prevented by pretreatment with cyproheptadine, a blocker of 5-HT receptors, whereas fluphenazine, a dopamine receptor blocker, was unable to block it. Third venticle injection of 5-HT in rats bearing anterior hypothalamic lesions (which did not affect the suprachiasmatic nucleus or the medio-basal hypothalamus) also induced an increase of serum TSH similar to that observed in normal rats despite the fact that these animals show a lower basal TSH. In vitro, the addition of 5-HT to an incubation medium containing one hemi-anterior pituitary did not modify medium TSH, whereas 5-HT addition induced an increase of medium TSH in the system containing one hemi-anterior pituitary and two hypothalami. We conclude that 5-HT acts on TSH function probably through a stimulation of TRH release.

Animals↗
PubMed1977

Comparison of adiphenine and TRH effects on TSH release by rat pituitary in vitro.

The mechanism of action of adiphenine on in vitro rat anterior pituitary TSH release was compared to that of the physiological stimulator TRH. The comparative study showed that adiphenine and TRH were able to increase TSH release in a dose-dependent manner, had similar time courses of action for equipotent stimulating concentrations and produced similar aspects of stimulated TSH cells. However, there were several differences between the effects of adiphenine and TRH. Adiphenine action was inhibited by 20 mM K+; was not calcium dependent; was inhibited by neither thyroid hormones nor somatostatin; was little affected by energy depression. It is concluded that adiphenine probably acts near the ultimate steps of the TSH release pathway and could be a useful pharmacological tool for studying the mechanism of TSH release.

Animals↗
PubMed1975

[Prolactin adenoma. Study of gonadotrophic function by the sassoles G LHRH test].

An intravenous injection of synthetic LHRH (50mug) was given in 10 patients with prolactin secreting pituitary adenomas. Variations in circulating levels of gonadotrophic hormones were measured by radioimmunological estimation. The increase in blood level of luteinizing hormone was constant, low in three cases, normal in 3 and high in 4. An increase in follicle stimulating hormone (FSH) was absent in only two cases. The data obtained indicates the absence of any characteristic value of the LHRH test in the aetiological diagnosis of amenorrhoea/galactorrhoea syndromes. They represent an argument in favour of the relative character and of the functional nature of the gonadotrophic insufficiency of prolactin adenomas.

Adenoma↗
PubMedDate not supplied

[Metabolic consequences of the nonenzymatic glucosylation of apolipoproteins].

The non enzymatic glucosylation (NEG) of proteins is a complex chemical reaction resulting in the formation of a stable bond between a glucose molecule and a protein aminogroup. In diabetics, hyperglycaemia may induce a large increase of NEG. Although the NEG of apolipoproteins remains moderate because of their short half-life, it may alter some of their properties. The NEG of LDL apo B induces a decrease of their catabolism due to a lowering of their binding to the LDL receptor. Glucosylated LDL can accumulate in macrophages, thereby facilitating the development of foam cells. The LDL NEG may also cause other processes including apo B oxidation and production of anti-LDL antibodies. The HDL NEG which essentially corresponds to that of apo A-I, induces a shortening of their half-life. In vitro, the NEG of apo A-I results in a decrease of its interaction with HDL surface. Finally, the binding of glucosylated HDL3 to HDL receptors is decreased in cultured fibroblasts. Since the level of lipoprotein NEG in vivo is moderate, the question as to whether this process may affect quantitatively the metabolic behaviour of lipoproteins and participate to the development of atheroma in diabetic patients, has not been clearly answered.

Apolipoproteins↗
PubMedDate not supplied

[Role of high density lipoproteins (HDL) in reverse cholesterol transport].

The atheromatous risk is negatively correlated with the plasma concentration of HDL cholesterol. This might be due to the role of HDL in the reverse cholesterol transport. In the first stage, free cholesterol molecules from peripheral cells are taken up by HDL through a receptor-dependent mechanism. In HDL, the esterification of cholesterol is catalysed by the lecithin: cholesterol acyl transferase. The progressive accumulation of cholesterol esters leads to the formation of HDL2. Through the action of cholesterol ester transfer protein, HDL2 become enriched in triglycerides and transfer cholesterol esters to LDL. Finally, cholesterol may be taken up by the liver through two routes which are: the receptor-mediated LDL endocytosis and the direct uptake of cholesterol esters which occurs during the degradation of HDL2 by hepatic lipase.

Animals↗
PubMedDate not supplied

Characterization of the non enzymatic glycation of high density lipoprotein in diabetic patients.

In diabetic patients, hyperglycaemia results in the non enzymatic glycation of many proteins. We studied the glycation of HDL of patients with either type 1 or type 2 diabetes compared with that of control subjects. Although a basal glycation was detectable in HDL of normal individuals, this increased by about 400% in HDL of both groups of diabetic patients. The degree of HDL glycation was positively correlated with blood glucose concentration. All the HDL apoproteins were glycated but the glycation of apo A-I represented about 80% of the total HDL. These data were compared to those obtained in vitro after incubation of normal apo A-I either as free molecular species or as phospholipid/apo A-I complex, in the presence of glucose (0 to 80 mmol/l) at 37 degrees C. The resulting apo A-I glycation was dependent upon both time of incubation and glucose concentration and was largely increased in the presence of phospholipids. These data suggest that the in vivo glycation of HDL apoproteins might depend upon glucose concentration but might also be partly influenced by their lipid environment.

Adult↗
PubMedDate not supplied

[Multiple effects of resorcinol on thyroid function (author's transl)].

In rats, I.V. injected resorcinol led to a decrease in thyroid radioiodine uptake and labelled iodothyronine/iodotyrosine ratio with no changes in the percent of thyroidal labelled iodide or radioiodine release. When thyroid lobes were incubated in vitro with radioiodine, resorcinol concentrations from 10(-3)M to 10(-6)M gave an increase in the percent of thyroidal labelled iodide and iodotyrosine/iodothyronine ratio. In animals fed 5% resorcinol for 2 weeks we observed an increase in thyroid weight, a decrease in plasma T4, no change in the percent of free T4, a decrease in T4 half life and no significant changes in T3 half life. Thyroidal labelled MIT/DIT and T3/T4 atios increased. Resorcinol, given in diet during 5 days to rats which had a low thyroidal thyroglobulin content after PTU administration for 2 weeks, gave, in comparison with rats fed PTU only, an increase in thyroidal thyroglobulin/DNA ratio and a decrease in thyroidal radioiodine release contrasting with an increase in plasma TSH. These differences did not exist when resorcinol was given for one month.

Administration, Oral↗