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Biomedical subjects

E Laurent

Publications and source records attributed to E Laurent.

At least 37 records · Page 2Linked to original sources
PubMed1989

Decreased basal and stimulated thyrotropin secretion in healthy elderly men.

To delineate the effects of aging on basal and stimulated TSH secretion, we studied the 24-h profile of plasma TSH levels and the TSH response to TRH stimulation (200 micrograms TRH, iv) in eight healthy elderly men, aged 67-84 yr, and eight normal young men, aged 20-27 yr. Subjects with thyroid antibodies against microsomal or thyroglobulin antigens were excluded. During the 24-h study, blood was sampled at 15-min intervals. TSH levels were measured by an ultrasensitive immunoradiometric assay. Sleep was polygraphically monitored, and circadian and pulsatile TSH variations were quantified using specifically designed computer algorithms. In older men, the 24-h mean TSH concentration was approximately 50% lower than that in young men (0.78 +/- 0.37 vs. 1.43 +/- 0.41 microU/mL; P less than 0.01), but basal T3 levels were only slightly lower (93 +/- 12 vs. 115 +/- 16 ng/dL; P less than 0.02), while basal T4 levels were normal. The normal diurnal variation of TSH levels, with a nocturnal acrophase and an afternoon nadir, as well as the pulsatile nature of TSH release were preserved in elderly men. When expressed in microunits per mL, the amplitude of these temporal variations was reduced in elderly men compared to that in younger subjects. However, when expressed in relation to the mean TSH levels, the amplitudes of diurnal and pulsatile variations were similar in both groups of subjects. TRH-induced TSH secretion was lower in old than in young men (area under the curve, 15.9 +/- 6.3 microU/mL.10 min in elderly men vs. 42.0 +/- 16.6 microU/mL.10 min in young men; P less than 0.002). However, the TRH-induced elevations of T3 and T4 were of similar magnitude in both groups. These results indicate that in healthy elderly men, the overall 24-h TSH secretion is decreased, and the pituitary is less responsive to stimulation by TRH. However, the chronobiological modulation is preserved. These alterations could reflect an adaptative mechanism to the reduced need for thyroid hormones in old age. The thyroid keeps an intact capacity to respond to acute increases in TSH concentrations.

Adult↗
PubMed1989

Effects of inactivity and exercise on bone.

Bone mass and muscular mass show a parallel evolution during growth, and parallel involution with age. However, the bone loss related to the withdrawal of oestrogens is independent of muscular waste. The extensive study of disuse osteoporosis shows that exercise without weightbearing cannot counteract the loss of bone mass provoked by bed rest or weightlessness. Physical training, even at low frequency (30 to 60 min/day, 2 or 3 days/week), can increase bone mass or reduce bone loss associated with age. This effect is even present when exercise is practised by very old people at a seemingly low level of muscular tension on bone. It is not known whether muscular exercise could be helpful in pathological osteopenia. Experiments in animals indicate a short-lived benefit of exercise practised during a definite growth period; the long term effect of physical training in humans, after cessation of such activity, has not been studied extensively. Equal distribution of tension on all parts of the skeleton is probably not mandatory to obtain a general effect of exercise on bone mass. It is assumed that muscular exercise acts through tension exerted on bone, but the exact mechanism is unknown, as are the specifications of effective exercise in terms of site of application, intensity, frequency and duration. Moreover, little is known about the expected synergy between exercise and occupational activity.

Aging↗
PubMed1987

Carbachol and sodium fluoride, but not TSH, stimulate the generation of inositol phosphates in the dog thyroid.

In dog thyroid slices prelabeled with myo-[2-3H]inositol, carbachol (10(-7)-10(-4) M) and NaF (10-20 mM) stimulated IP1, IP2 and IP3 generation. These effects did not require the presence of extracellular calcium. Atropine and PDBu inhibited the action of the cholinergic agonist. No effect of TSH (1-100 mU/ml) could be detected on PIP2 hydrolysis and IP production. These results suggest that IP3 could play a role in the metabolic actions of carbachol in the thyroid; a G-protein coupling the hormone-receptor binding to phospholipase C activation exists in the thyroid membrane; the well known TSH-induced increased PI turnover does not result in IP3 accumulation.

Animals↗
PubMed1987

Dual activation by thyrotropin of the phospholipase C and cyclic AMP cascades in human thyroid.

In human thyroid slices prelabeled with myo-[2-3H]inositol, thyrotropin (TSH, 3-30 mU/ml) stimulated IP3, IP2 and IP1 generation over a prolonged time course. The cAMP response was much more sensitive to TSH, peaking between 1 and 5 mU/ml. Forskolin (10(-5) M) and isoproterenol had no effect on basal IP levels, while carbamylcholine (10(-5) M, 10(-4) M) also increased IP accumulation. These data suggest that in the human thyroid, TSH activates a phospholipase C generating IP3 and diacylglycerol independently of the well-known adenylate cyclase stimulation. They validate in the human model a dual mode of action of the hormone previously proposed on the basis of indirect observations.

Cyclic AMP↗
PubMed1987

The usefulness of fructosamine determination in diabetic patients and its relation to metabolic control.

In 116 diabetics and 101 control subjects, we measured both HbA1 and fructosamine values, neither could definitely separate the 2 populations. We observed an excellent correlation between both variables and between each of them and various other parameters of metabolic control. It appeared that the correlation with recent (4 weeks) diabetes control was better with fructosamine than with HbA1 levels. The opposite was true when a 8 week period was considered. The presence of diabetic complications did not modify the fructosamine levels. These results confirm the value of fructosamine measurement in the evaluation of recent diabetes control, but clearly, HbA1 determination remains the best parameter of long-term glycemic control.

Blood Glucose↗
PubMed1980

A new cryopathic syndrome.

One case of a syndrome simulating a systemic disease is reported. An HLA-B, patient presented with apparent toxoplasmosis, retinal vein occlusion, autoantibodies against cephalin, contact factors and lipoproteins, immune complexes, rheumatoid factor, and cryoprecipitate. A representation of the immunological mechanisms involved is proposed.

Antigen-Antibody Complex↗