Search PubMed⌕ Search

Biomedical subjects

J C Stevenson

Publications and source records attributed to J C Stevenson.

At least 163 records · Page 9Linked to original sources
PubMed1986

Vertebral CT scanning.

Quantitative CT of vertebral trabecular bone is established as a useful technique for assessing bone mass. We have developed a modified method of spinal CT which can be used on any standard third or fourth generation whole body scanner without requiring extra software or hardware. Measurements have a high precision and accuracy, with acceptable cost and radiation exposure. We have shown that our results compare favourably with those from other centres. The sensitivity of the measurements encourages the widespread clinical application of this technique.

Adult↗
PubMed1985

Calcitonin gene-related peptide: potent vasodilator and major product of calcitonin gene.

In addition to calcitonin and katacalcin, the human calcitonin gene encodes a novel peptide--calcitonin gene-related peptide (CGRP)--a potent vasodilator. A sensitive and specific radioimmunoassay was developed to study plasma levels of CGRP in normal subjects. CGRP circulates at five times the concentration of calcitonin, suggesting that it may be an important physiological regulator of vascular tone and blood flow.

Adult↗
PubMed1985

Osteoporosis of pregnancy.

Eight women with pregnancy-associated osteoporosis were studied for up to ten years. Back pain and vertebral collapse usually occurred in the first pregnancy and did not recur in two subsequent pregnancies. Except in one patient, bone histology showed no increase in resorption. Plasma concentrations of 1,25-dihydroxyvitamin D tended to be low whereas those of calcitonin were, with one exception, normal. It is suggested that in these patients there may have been a transient failure of the usual changes in calciotropic hormones to prepare the maternal skeleton for the stress of childbirth. However, subsequent pregnancies in such patients are not necessarily contraindicated.

Adult↗
PubMed1985

Immunoglobulin allotypes in Jewish populations living in Israel and the United States.

The ongoing interest in the interrelationships of Jewish populations justifies inclusion of the immunoglobulin allotypes in an ethnohistorical analysis. A total of 2,184 serum specimens obtained from unrelated Israeli Jewish and self-identified Milwaukee, WI, Jewish blood donors were classified as Ashkenazi, Sephardi, Asiatic, or North African and tested for G1m (a, x, z, and f), G3m (b0, b1, b3, b5, g), A2m (1 and 2), and Km (1). Selected sera were also tested for G3m (s, t, c3, c5). The estimated maximum likelihood Gm-Am haplotype frequencies were used in a heterogeneity chi-square analysis. The results indicate that there is less heterogeneity within Jewish populations from Europe, Middle East, and North Africa than in corresponding non-Jewish populations representing the same geographical areas. In order to avoid the hazards of a univariate focus, previously published data were incorporated into two additional analyses: 15 populations with information on 16 genetic loci and 24 populations with information on five genetic loci. Both sets of data were analyzed using principal-components and cluster analysis. In both sets of analyses, with the exception of the Yemenite Jews, Jewish populations grouped together. These analyses support the belief that Jewish populations appear to be derived from a common gene pool, and there has been some genetic drift and minimal gene flow with surrounding populations.

Humans↗
PubMed1985

Effect of calcitonin on gastrointestinal regulatory peptides in man.

A major physiological role of calcitonin in humans appears to be regulation of skeletal turnover. It has been suggested that another function of calcitonin is to prevent post-prandial rises in calcium, particularly in animals, but the importance of such a function in man remains to be determined. Although it is known that calcitonin has an inhibitory effect on the secretion of gastrin and insulin, its actions on other gut and pancreatic hormones have not previously been studied. To investigate interrelations between calcitonin and gastrointestinal regulatory peptides, 0.5 mg synthetic human calcitonin was administered to 10 fasting patients. No changes in the plasma concentrations of glucose, somatostatin, neurotensin, enteroglucagon, vasoactive intestinal polypeptide or bombesin were observed. In contrast, profound falls in the circulating levels of gastrin, insulin and pancreatic glucagon were seen, reaching a maximum shortly after the peak of plasma calcitonin concentration. Marked changes were also observed in the levels of motilin, pancreatic polypeptide and, to a lesser extent, gastric inhibitory polypeptide, but the maximal falls occurred about 40 min later, coinciding with a significant fall in serum calcium. It is possible that the effect of calcitonin on these hormones was direct, perhaps receptor-mediated. The falls in levels of motilin and pancreatic polypeptide could have been further enhanced by changes in extracellular calcium ion concentrations. Whether any of these effects of calcitonin occur physiologically remains to be determined. However, these findings suggest new therapeutic possibilities for calcitonin.

Adult↗
PubMed1985

Calcium absorption in rheumatoid arthritis.

Calcium absorption, assessed by a double isotope method, was found to be impaired in postmenopausal women with rheumatoid arthritis of recent onset (mean 14.2 months) compared with controls. Circulating levels of 1,25-dihydroxyvitamin D (calcitriol) were higher than in controls, suggesting a primary malabsorption of calcium in these patients. The reduction in calcium absorption correlated with several measures of disease activity, suggesting that the disease process was responsible for the intestinal defect, but an effect from non-steroidal anti-inflammatory agents cannot be excluded. A primary reduction in calcium absorption may increase the risk of osteoporosis in women with rheumatoid arthritis.

Adult↗
PubMed1984

Racial differences in calcitonin and katacalcin.

Profound racial differences exist in the incidence of osteoporosis, particularly in women. To investigate possible underlying reasons for this, we have measured the circulating levels of calcitonin (iCT), a bone-protecting hormone, and its flanking peptide, katacalcin (iKC), in black Gambian and white British populations. Whilst sex differences in both peptides were observed, with males having higher levels than females, the most striking finding was that white women have the lowest iCT levels. This important observation may explain, at least in part, why osteoporosis is particularly a disease of white, postmenopausal women.

Adult↗
PubMed1984

Fluid and electrolyte disorders. Calcium.

Parathyroid hormone, 1,25-dihydroxyvitamin D, and calcitonin are the three primary calcium-regulating hormones. Physiological changes in these occur throughout normal life but it is when levels remain excessively high or low, or when their target organs are diseased, that hypocalcaemia or hypercalcaemia may develop.

Adult↗
PubMed1983

Regulation of calcium-regulating hormones by exogenous sex steroids in early postmenopause.

A major function of calcitonin in humans appears to be maintenance of the skeleton. There is a marked sex difference in circulating calcitonin levels: women have much lower levels. This has led to speculation that calcitonin lack may be one factor involved in the pathogenesis of postmenopausal bone loss. We have measured levels of calcitonin and the other major calcium-regulating hormones in healthy women during the early menopause, and studied the effects of reversing their oestrogen deficiency with natural and synthetic oestrogen. The major findings were that calcitonin levels were increased by oestrogen administration (P less than 0.02-less than 0.001) and that the levels of the bone-resorbing hormones, parathyroid hormone and 1,25 dihydroxyvitamin D, were not higher in postmenopausal than in premenopausal women. We suggest that loss of oestrogen at the menopause accelerates the natural age-related decline of calcitonin secretion, thus further decreasing the calcitonin levels. This leads to increased sensitivity of the skeleton to the actions of the bone-resorbing hormones. It seems likely that the well-known effect of oestrogen in preventing postmenopausal bone loss is achieved, at least in part, by enhancement of calcitonin secretion.

Adult↗
PubMed1982

Regulation of calcitonin and parathyroid hormone secretion by oestrogens.

Calcitonin is a peptide hormone secreted by C-cells which, in humans, are found mainly in the thyroid gland. It now seems that a major physiological function of this hormone in man is the long-term maintenance of the skeleton achieved by control of bone resorption. A marked sex difference in circulating calcitonin levels normally exists, with a relative deficiency in women as compared to men. It has now been found that oestrogens regulate calcitonin secretion and it appears likely that the loss of ovarian function at the menopause accelerates the natural decline in calcitonin secretion which occurs with age. Thus, post-menopausal women are more markedly calcitonin-deficient. Levels of the bone-resorbing hormones, parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D are not elevated post-menopausally and it seems likely that the increased bone resorption which leads to post-menopausal bone loss is due mainly to the loss of oestrogen and calcitonin secretion.

Aging↗