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Biomedical subjects

J Fox

Publications and source records attributed to J Fox.

At least 235 records · Page 13Linked to original sources
PubMed1985

Electrical and chemical stimulation of cervical sympathetic nerves in the dog does not affect secretion of parathyroid hormone.

beta-Adrenergic agonists stimulate PTH release in vitro. The present studies were designed to test the hypothesis that norepinephrine released from sympathetic nerve terminals in the parathyroid glands might be a physiological regulator of PTH secretion. In 22 dogs, electrical stimulation (20 Hz, 1 msec, 50 V nominal) of the right cervical vagosympathetic trunk had no significant effect on release of PTH into the precava, whether the animals were normocalcemic or hypocalcemic, and whether or not they were pretreated with the alpha-adrenergic antagonist phenoxybenzamine. In 4 other dogs, stimulating release of endogenous nerve terminal norepinephrine by iv injection of tyramine (200 micrograms/kg) also failed to raise precaval plasma immunoreactive PTH concentrations. In all studies, induction of mild hypocalcemia raised immunoreactive PTH levels. From these and other studies, we conclude that beta-adrenergic agonists of neural origin are not important regulators of canine PTH release in vivo.

Adrenergic beta-Agonists↗
PubMed1985

Effects of low phosphorus and low calcium diets on the production and metabolic clearance rates of 1,25-dihydroxycholecalciferol in pigs.

Severe dietary calcium (Ca) or phosphorus (P) deficiency leads to a similar degree of stimulation of plasma and intestinal 1,25-dihydroxycholecalciferol (calcitriol) levels and intestinal Ca absorption. In contrast, P depletion causes a much smaller increase in the renal 25-hydroxycholecalciferol-1-hydroxylase enzyme activity than does Ca depletion. To test the hypothesis that a reduced metabolic clearance rate (MCR) during P depletion might, in part, account for the observed increase in calcitriol levels, we have developed a simple primed-infusion technique to determine the MCR and production rate (PR) of calcitriol, in vivo, in pigs fed low Ca and low P diets. The MCR of calcitriol was unchanged (0.92 ml/min per kg metabolic body size (MBS)) when low P diets were fed, but showed a significant 15% increase (1.06 ml/min per kg MBS) during the feeding of low Ca diets. The PR of calcitriol increased by 2.3-fold when low P diets were fed and by fourfold during Ca depletion. Thus the increase in plasma calcitriol levels during P depletion of pigs is caused by an increase in production rather than a decrease in clearance. In contrast, Ca depletion is associated with a slightly higher PR than indicated by measurement of plasma calcitriol levels because of the increased MCR.

Animals↗
PubMed1985

Mast cell heterogeneity: effects of neuroenteric peptides on histamine release.

Recent reports suggesting that the actions of certain neuroenteric peptides may be mediated in part by the secretion of histamine and other mast cell contents could have important implications for gastrointestinal motility and secretion. However, evidence for a mast cell-hormonal interaction is based on studies using peritoneal or cutaneous mast cells. Because intestinal mucosal mast cells (MMC) differ functionally from peritoneal mast cells (PMC), we compared the effects of several neurotransmitters and intestinal hormones on histamine secretion from two mast cell types in the rat. MMC hyperplasia was induced in rats by infection with the nematode Nippostrongylus brasiliensis, and MMC were isolated from the small intestine by collagenase digestion. Substance P, somatostatin, vasoactive intestinal polypeptide (VIP), neurotensin, and bradykinin had a potent secretagogue effect on (10(-7) to 10(-4)M) PMC which was temperature-, energy-, and calcium-dependent. In contrast to PMC, MMC released significant amounts of histamine only when challenged with substance P. Acetylcholine, bombesin, motilin, and pentagastrin had no secretory effect on either PMC or MMC. The differences between PMC and MMC in responsiveness to peptides could not be attributed to the MMC isolation procedure because PMC treated similarly or mixed with MMC suspensions retained their responsiveness to these stimuli. Our results extend the concept of neurocrine control of mast cell function, but indicate that mast cells from different sites have distinct profiles of responsiveness to regulatory peptides.

Animals↗
PubMed1984

Effect of plasma calcium concentration on the metabolic clearance rate of calcitonin in the dog.

Plasma immunoreactive calcitonin (iCT) levels generally are not elevated in chronic, nonmalignant, hypercalcemic states. Normocalcitoninemia might occur despite increased CT secretion if hypercalcemia itself accelerated the clearance of CT from the circulation. Therefore, we have measured the metabolic clearance rate (MCR) of human CT (hCT), infused to constant plasma levels in thyroparathyroidectomized dogs, under conditions of acute and chronic hypo- and hypercalcemia. Acute increases of plasma calcium were without significant effect on the MCR of hCT, but chronic hypercalcemia, induced by dihydrotachysterol treatment, reduced the MCR of hCT by 30% (P less than 0.05) and glomerular filtration rate (GFR) by 40% (P less than 0.02). There was a significant, positive correlation (r = 0.60, P less than 0.02) between GFR and the MCR of CT. The data suggest that failure to detect elevated iCT levels in chronic hypercalcemia is not the result of an increased MCR of CT. In fact, hypercalcemia should exaggerate the effect of increased CT secretion by decreasing the renal clearance of the hormone.

Animals↗
PubMed1984

An Indian community with a high suicide rate--5 years after.

This report deals with the five year follow-up after a suicide epidemic on a Manitoulin Island Indian Reserve in 1974 and 1975. In the succeeding years, the suicide rate has dropped to a tenth of the level of the epidemic and has reached the levels for the rest of Manitoulin Island including the White and Native population. There has been a corresponding drop in the rate of violent death and of the number of suicide attempts. It is suggested that the multi-dimensional prevention and intervention measures reported here have contributed to a significant improvement in present conditions.

Adolescent↗
PubMed1984

Plasma levels of immunoreactive beta-endorphin and adrenocorticotropic hormone during labor and delivery.

beta-endorphin and adrenocorticotropic hormone (ACTH) are derived from the same precursor protein, and the plasma levels of beta-endorphin and ACTH are thought to be representative of the pituitary secretion of these peptides. Simultaneous measurements of immunoreactive beta-endorphin and ACTH were done on plasma samples from pregnant women at term and found to be normal, but a significant increase was observed during the stress of labor. Simultaneous measurement of immunoreactive beta-endorphin and ACTH in the umbilical vein at time of vaginal delivery demonstrated elevated levels of both peptides. The newborn also demonstrated an increased ratio of beta-endorphin to ACTH, of which the role is uncertain at present.

Adrenocorticotropic Hormone↗
PubMed1984

Radioimmunoassay of calcitonin in normal human plasma: problems, perspectives and prospects.

Radioimmunoassay of calcitonin in normal human plasma is hindered by immunochemical heterogeneity in plasma, variable susceptibility of antisera to non-specific factors, limited assay sensitivity, and other problems. Many controversial points in the literature arise from these difficulties. Measurement of calcitonin after various extraction procedures yields greater consistency of results. Recent advances in calcitonin assay technology offer the promise of measuring calcitonin monomer with sufficient sensitivity to permit studies of normal calcitonin physiology and of the hormone's role in human disease.

Animals↗
PubMed1984

Public policy review. A ten-year progress report on a family practice residency network in northern California.

We are now beginning to be able to evaluate the results of the rapid growth of family practice residency training programs during the past decade. Because this growth has been supported by federal and state funds, it is particularly important to review these programs to measure their progress toward the public policy goals established by legislation. The University of California, Davis, School of Medicine has been an innovator and leader in training family physicians. Graduates of the UC Davis Network of Family Practice Residency Programs are locating in medically underserved areas and are helping to respond to the perceived problems of specialty and geographic maldistribution of physicians.

Area Health Education Centers↗
PubMed1983

The effects of betamethasone, low calcium and low phosphorus diets on growth in chicks.

The effects of oral betamethasone (25 micrograms/kg/d), low calcium (1 g/kg), and low phosphorus (2,5 g/kg) diets on weight gain were investigated in 513 growing chicks. The chicks were divided according to initial weight into a lower weight group (less than 100 g each) and a higher group (more than 100 g each). The increases in weight were recorded after periods of 7, 14 and 21 days. The increases in weight in the older chicks (high weight group) were less than in the younger chicks. There was a greater reduction in rate of growth in chicks fed the low phosphorus diet than in those fed the low calcium diet, particularly in the older birds. Betamethasone administration also reduced the rate of growth but this was not additive to the effect of a low calcium diet. In contrast, the greatest reduction in growth rate was observed in the chicks fed the low phosphorus diet and given betamethasone.

Aging↗
PubMed1983

Do tissues other than the kidney produce 1,25-dihydroxyvitamin D3 in vivo? A reexamination.

Recent experiments have shown that 1,25-dihydroxyvitamin D3-like material is produced in cultured nonrenal cells and may be present in the sera of anephric patients. We reexamined the question of whether 1,25-dihydroxyvitamin D3 can be synthesized extrarenally in the rat in vivo. To intact, sham-operated, ureter-ligated, or acutely nephrectomized vitamin D-deficient rats raised on a diet normal in calcium and phosphorus, we gave a physiologic dose of high-specific-activity 25-hydroxy-[3H]vitamin D3 (3.6-3.8 microCi; approximately equal to 25 pmol per rat). Twenty-four hours later we examined their tissues and plasma for the presence of radiolabeled 1,25-dihydroxyvitamin D3. Large amounts of radioactivity that behaved chromatographically as identical with authentic 1,25-dihydroxyvitamin D3 were present in the plasma, bone, and intestine of the intact, sham-operated, or ureter-ligated rats. However, no radioactivity eluting in a manner similar to 1,25-dihydroxyvitamin D3 was found in plasma, bone, or intestine of acutely nephrectomized rats. We conclude that, in the acutely nephrectomized living rat, 1,25-dihydroxyvitamin D3 is not present in plasma, bone, or intestine in quantities detectable by the sensitive techniques we have used. No conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 was observed during a 24-hr period after nephrectomy of vitamin D-deprived rats. This fact casts doubt upon the significance of the in vitro production of 1,25-dihydroxyvitamin D3 by nonrenal cells as an in vivo phenomenon.

Animals↗
PubMed1983

Changes in body heat during transvesical prostatectomy. A comparison of general and epidural anaesthesia.

The superficial and deep body temperatures of 15 patients were measured before, during and for 6 hours after transvesical prostatectomy. The patients were divided randomly into two groups who received either a standard general anaesthetic or epidural analgesia. Total body heat and mean body temperature fell more rapidly in the epidural group, reaching statistical significance in the early postoperative period. Both groups showed a net heat gain 6 hours postoperatively. One patient in each group became hypothermic (core temperature less than 35 degrees C). Warming of both intravenous and bladder irrigation fluids to body temperature is recommended for patients receiving epidural or general anaesthesia.

Aged↗
PubMed1983

A comparison of socioeconomic differences in mortality between Japan and England and Wales.

Japan and England and Wales have long traditions of publishing mortality rates by occupation. These data have been used in the present study to see how mortality from different causes of death is related to socioeconomic status in each country. In general, males in higher employment grades have been found to have lower mortality from most diseases. However, because mortality from certain diseases such as diabetes mellitus and ischaemic heart disease has been higher in the upper social classes (but is now lower in the upper classes) the relationship is not necessarily consistent. The aim of this study was, by comparing rates for Japan with those for England and Wales, to highlight differences in socioeconomic gradients which may indicate etiological differences between the 2 countries.

Actuarial Analysis↗
PubMed1983

Effect of plasma calcium concentration on the metabolic clearance rate of parathyroid hormone in the dog.

Low perfusate calcium concentrations reportedly enhance the degradation of intact bPTH in isolated rat liver and dog kidney. Depending on the magnitude of such effects, they might affect the metabolic clearance of intact PTH in vivo. Therefore we have investigated the effect of acute and chronic hypocalcemia and hypercalcemia on the MCR of intact PTH in vivo in dogs. The t 1/2 of endogenous PTH was unchanged after 5, 30, and 480 min of hypocalcemia and ranged from 1.2 to 2.8 min. The MCR of bPTH infused to constant plasma levels in TPTX dogs also did not change with short- or long-term changes in the plasma calcium concentration by approximately 7 mg/dl. The MCR averaged 13 ml/min per kilogram for fully biologically active bPTH and 6 ml/min per kilogram for oxidized bPTH. Thus neither acute nor chronic hypocalcemia or hypercalcemia at extremes observed in disease states significantly altered the MCR of PTH. We conclude that changes in plasma intact PTH concentrations during changes in plasma calcium accurately reflect PTH secretion rate.

Animals↗