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Biomedical subjects

H Heath

Publications and source records attributed to H Heath.

At least 163 records · Page 9Linked to original sources
PubMed1980

Identification of fructose as the retinopathic agent associated with the ingestion of sucrose-rich diets in the rat.

In order to determine whether the fructose moiety of sucrose or the lack of some factor essential for the integrity of the microvascular system was responsible for the development of sucrose retinopathy in the rat, a series of diets containing possible sources of such a factor and/or fructose was tested over a 6-mo period. Examination of the isolated rat retinal vascular systems showed conclusively that fructose was the dietary microangiopathic agent associated with sucrose-induced retinopathy. The microvascular lesions produced were similar to those found in diabetic rats maintained over the same period. Cross-sectional studies of the retinas revealed that microvascular lesions preceded the associated degeneration of neural tissue rather than vice versa since the majority of rats with retinopathy showed no signs of neural damage. Sucrose feeding was found to produce a significant elevation (p < 0.001) in blood fructose concentration and a slight increase, albeit not significant (p < 0.01), in retinal fructose-1-phosphate (F1P) levels. The results are discussed in relation to the changes in retinal sorbitol, fructose, FIP, and lactate metabolism found in diabetes.

Animals↗
PubMed1980

A portal factor influences serum calcium homeostasis.

In order to evaluate the importance of a portal factor in serum calcium homeostasis, end-to-side portacaval shunts were performed in groups of adult, male Lewis rats either before or after parathyroidectomy. Subsequent changes in serum calcium values were followed. When parathyroidectomy was performed one day or 28 days after a portacaval shunt, hypocalcemic changes occurred soon after. However, in these shunted, parathyroidectomized animals which were maintained on a normal calcium diet the serum calcium concentrations soon began to rise and by three weeks after operationthe rats became normocalcemic. In animals which had a portacaval shunt performed three days after parathyroidectomy, the serum calcium levels again rose and became normal in approximately three weeks. In the shunted, parathyroidectomized animals, both the serum calcium and phosphorus concentrations remained normal as long as the rats were maintained ona normal calcium diet. When a low calcium diet was introduced, marked hypocalcemia occurred and serum parathyroid hormone values were barely detectable, both of which attest to the completeness of parathyroidectomy. These data support the hypothesis that following portacaval shunt, a calcium elevating factor, which is similar in action to parathyroid hormone but is not PTH itself, bypasses the liver and becomes effective in the systemic circulation. It acts to correct the hypocalcemia and hyperphosphatemia of parathyroidectomized rats. The possible role of various known gastrointestinal factors in this process is discussed.

Animals↗
PubMed1980

Production, degradation, and circulating levels of 1,25-dihydroxyvitamin D in health and in chronic glucocorticoid excess.

The decreased intestinal absorption of calcium and accelerated bone loss associated with chronic glucocorticoid excess may be mediated by changes in vitamin D metabolism, leading to decreased availability of circulating 1,25-dihydroxyvitamin D. This hypothesis was examined in 14 patients with either endogenous or exogenous glucocorticoid excess. Analysis of paired serum samples (mean +/- SE) in 13 patients during euglucocorticoidism and during hyperglucocorticoidism showed that glucocorticoid excess resulted in small decreases of plasma 25-hydroxy-vitamin D concentrations (22 +/- 2- 18 +/- 2 ng/ml; P < 0.05) but no significant changes in plasma 1,25-dihydroxyvitamin D (32 +/- 8- 23 +/- 6 pg/ml) or serum immunoreactive parathyroid hormone (21 +/- 2- 18 +/- 2 muleq/ml). Additionally, we studied plasma kinetics of [3H]1,25-dihydroxyvitamin D3 after intravenous bolus administration in 10 hyperglucocorticoid patients and in 14 normal controls. Assessment with a three-compartment model showed no significant abnormalities in production rates (hyperglucocorticoid patients 1.2 +/- 0.3 micrograms/d, controls 1.5 +/- 0.2 micrograms/d) or metabolic clearance rates (hyperglucocorticoid patients, 18 +/- 2%; controls, 14 +/- 2%) or feces (hyperglucocorticoid patients, 60 +/- 9%, controls, 54 +/- 6%). We conclude that glucocorticoid excess does not effect plasma levels, production, or degradation of 1,25(OH)2D in humans. Thus, other mechanisms must be postulated to explain satisfactorily the abnormalities of bone structure and intestinal calcium absorption that may occur after chronic glucocorticoid therapy.

Adult↗
PubMed1980

Metastatic canine medullary thyroid carcinoma: a case report.

A medullary carcinoma of the thyroid in a dog first became evident because of a distant metastasis. The histologic characteristics of the tumor differ from those previously reported in dogs in that this tumor was highly malignant; anaplasia and mitotic figures were common. The diagnosis was substantiated by radioimmunoassay for calcitonin. Serotonin and 5-hydroxytryptophan also were elevated in the neoplastic tissue. The relation of the biochemical alterations to the clinical course was not clear.

5-Hydroxytryptophan↗
PubMed1980

Provocative tests of parathyroid and C cell function in adrenalectomized and chemically sympathectomized rats.

Recent in vitro and in vivo evidence shows that secretion of parathyroid hormone (PTH) and calcitonin (CT) is stimulated by beta-adrenergic agonists and inhibited by beta-adrenergic antagonists. To assess the possible roles of adrenal medullary or adrenergic nerve terminal catecholamines in calcium homeostasis, we have examined serum calcium (Ca), immunoreactive PTH (iPTH), and immunoreactive CT (iCT) in control, adrenalectomized (ADRX), and chemically sympathectomized [6-hydroxydopamine (6-OHDA)] rats. Animals were studied in the fed and fasted states, after ip injection of CA and after ip injection of EDTA. In comparison with fasted rats, fed control rats tended to have increased serum Ca and iCT, but decreased or unchanged iPTH. Neither adrenalectomy nor 6-OHDA treatment notably altered this pattern. Serum iCT concentrations rose markedly after ip Ca, and peak iCT responses remained normal in ADRX and 6-OHDA-treated rats. Similarly, rises of iPTH levels after EDTA-induced hypocalcemia were normal in ADRX and 6-OHDA-treated rats. The only possible abnormality concerned basal serum iCT levels after 6-OHDA treatment, which were lower than control in five of six experiments, albeit not always significantly. We conclude that deprivation of either adrenal medullary or adrenergic nerve terminal catecholamines does not interfere with plasma Ca regulation or the homeostatic responses of PTH and CT in the rat.

Adrenal Medulla↗
PubMed1980

Parathyroid hormone does not increase nephrogenous cyclic AMP excretion by the dog.

The renal excretion of nephrogenous cyclic AMP (NcAMP) increases in response to parathyroid hormone (PTH) in man, and thereby serves as a test of parathyroid function. However, during studies of calcium-PTH (PTH) in man, and thereby serves as a test of parathyroid function. However, during studies of calcium-PTH interrelationships in dogs we observed no change in total urinary cAMP (UcAMP) excretion when endogenous plasma PTH levels were increased up to 10-fold. This study was designed to investigate the effects of physiologic and pharmacologic levels of PTH on NcAMP and UcAMP excretion in the dog. Maintaining plasma Ca 2 mg/dl below normal for 40 minutes caused an 8-fold increase in plasma PTH concentration, a 50% increase in the urinary fractional excretion of phosphate (FEP) but no changes in plasma cAMP levels or in UcAMP or NcAMP excretion. Infusion of a pharmacologic amount of parathyroid extract (15 U/min for 20 min) increased plasma cAMP 5-fold, UcAMP excretion 3-fold and FEP by 50% but was without effect on NcAMP excretion. We conclude that NcAMP excretion is not stimulated by PTH in the dog and thus cannot be used as an index of PTH action in vivo. The increase in UcAMP excretion by pharmacologic amounts of PTH results from glomerular filtration of increased plasma cAMP, which may be generated in bone.

Animals↗
PubMed1980

Failure of cimetidine to affect calcium homeostasis in familial primary hyperparathyroidism (multiple endocrine neoplasia, type 1).

Recent reports that cimetidine, a blocker of histamine H2 receptors, lowered serum calcium and/or immunoreactive parathyroid hormone (PTH) concentrations in primary or secondary hyperparathyroidism prompted us to administer the drug (300 mg, orally, every 6 h) to two patients with hyperparathyroidism accompanying familial multiple endocrine neoplasia type 1. The patients were hypercalcemic (10.9--11.2 mg/dl), hypophosphatemic (2.0--2.4 mg/dl), and hypercalciuric (greater than or equal to 410 mg/24 h), with elevated urinary cAMP and phosphate clearance and inappropriately high serum immunoreactive PTH levels. Multiple observations of these variables over 5 weeks of cimetidine treatment showed no systematic changes; in particular, serum and urinary calcium did not change, and there was no evidence of a decreased PTH effect on the kidneys. The data offer no support for the treatment of familial hyperparathyroidism with cimetidine.

Adolescent↗
PubMed1980

Orthophosphate therapy decreases urinary calcium excretion and serum 1,25-dihydroxyvitamin D concentrations in idiopathic hypercalciuria.

Orthophosphate treatment of patients with idiopathic hypercalciuria reduces the urinary excretion of calcium. To examine the role of altered vitamin D metabolism in reducing the renal excretion of calcium, we studied 11 patients with idiopathic hypercalciuria before and after 2 weeks of treatment with oral neutral orthophosphate (2 g phosphorus/day). Variables measured were urine calcium and phosphorus and seseserum calcium, phosphorus, immunoreactive parathyroid hormone, and 1,25-dihydroxyvitamin D [1,25-(OH)2D]. Oral phosphate treatment significantly decreased urine calcium excretion [mean change (delta), -123 mg/24 h], increased urine phosphorus (mean delta, serum levels of 1,25-(OH)2D (mean delta, -22 pg/ml). Pretreatment levels of 1,25-(OH)2D were high when compared with levels in age-matched controls, whether assessed as the arithmetic mean (57 vs. 33 pg/ml; P < 0.025), the logarithmically normalized (42 vs. 27 pg/ml). Phosphate treatment decreased serum levels of 1,25-(OH)2D to a mean of 35 pg/ml (logarithmically normalized mean, 22 pg/ml; median, 21 pg/ml), values not significantly different from those of normal controls. Serum calcium and phosphorus concentrations were not changed by treatment. Serum immunoreactive parathyroid hormone values increased minimally within the normal range (mean delta, +2 microleq/ml; P <0.025). We conclude that the effect of oral phosphate therapy in decreasing urinary calcium excretion may involve the reduced synthesis of 1,25-(OH)2D, independent of altered parathyroid function.

Calcitriol↗
PubMed1980

Urinary cyclic 3',5'-adenosine monophosphate responses to exogenous and endogenous parathyroid hormone in familial benign hypercalcemia and primary hyperparathyroidism.

FBH is characterized by symptomless hypercalcemia, low urinary calcium excretion, normal iPTH values, generally normal parathyroid histology, and failure of subtotal parathyroidectomy is normalize serum calcium. We studies six patients with FBH from three kindreds, six patients with sporadic 1 omicron HPT, and six healthy volunteers. To characterize the renal response to PTH, 14 of the subjects had infusions of bovine PTE (300 U intravenously over 15 min) and, separately, stimulation of endogenous PTH release by infusion of disodium EDTA (50 mg/kg over 2 hr). PTE induced striking increases of UcAMP (nM/100 ml of GF) that were indistinguishable between controls and subjects having FBH. However, the rise of UcAMP in 1 omicron HPT was significantly reduced (p < 0.001) compared to controls or the FBH group. EDTA-induced hypocalcemia raised serum iPTH and UcAMP in all three groups; the increases of iPTH (two assays of differing specificity) were greatest in 1 omicron HPT and least in FBH. In contrast, increases of UcAMP were greatest in FBH and 1 omicron HPT and indistinguishable from one another. The increase of UcAMP considered as a function of the increase in PTH showed significantly greater UcAMP responses in FBH than in the other groups. These results are consistent with primary or secondary alterations of renal responsiveness to PTH in both FBH and 1 omicron HPT, which may in part explain the different renal tubular calcium handling in the two conditions.

Adult↗
PubMed1980

The parathyroid glands in multiple endocrine neoplasia type 2b.

The histologic features of 21 parathyroid glands obtained from 16 Mayo Clinic patients aged 2 to 52 years who had multiple endocrine neoplasia type 2b (MEN 2b) were evaluated. The findings were correlated with the patients' ages and with the serum concentrations of calcium (15 patients), phosphorus (14 patients), and immunoreactive parathyroid hormone (iPTH) (11 patients), and with the response of serum iPTH to calcium infusion (6 patients). We also studied the histologic features of 13 parathyroid glands obtained from 8 patients not seen at the Mayo Clinic with MEN 2b. The microscopic appearance of the glands was normal in patients under the age of 17; with increased age, the glands did not exhibit normal involution, and an appearance consistent with mild chief-cell hyperplasia was evident. This abnormality was not associated with clinical or laboratory manifestations of hyperparathyroidism. We presently believe that parathyroidectomy for the disorder is not justified.

Adolescent↗
PubMed1980

Use of electrochemical sensors for on-line monitoring of ionized calcium, potassium, and glucose in whole blood of living dogs.

We report the development and evaluation of electrochemical sensors for continuous on-line measurement of whole-blood ionized calcium, potassium, and glucose in living animals. Ionized calcium and potassium are measured with ion-selective electrodes, by using a unique differential approach. A polarographic sensor coupled with a membrane with bound glucose oxidase is used in the glucose analyzer. The modular concept of instrument design permits one mainframe, computer, and pump system to house any analyzer module or a combination of modules. A small volume of venous blood (about 2 mL/h) is continuously withdrawn from the subject through a double-lumen catheter and pumped through the analyzer(s). Results of in vitro correlation studies and studies in normal dogs (including responses of ionized calcium, potassium, and glucose to various stresses) support the validity of the measurements.

Animals↗
PubMed1979

Pre- and postoperative studies of plasma calcitonin in primary hyperparathyroidism.

The importance of calcitonin in the homeostatic response to the chronic hypercalcemia of primary hyperparathyroidism is uncertain. To clarify this issue, we have used a new, sensitive radioimmunoassay for human calcitonin to measure basal plasma calcitonin concentrations in 50 patients with primary hyperparathyroidism (32 female, 18 male). We assayed calcium-stimulated calcitonin concentrations preoperatively in 22 of the patients (16 female, 6 male) and postoperatively in 6. Finally, we assayed pentagastrin-stimulated calcitonin concentrations preoperatively in eight of the patients (three female, five male). Plasma calcitonin values after an overnight fast were indistinguishable from those in normal subjects (mean+/-SE, males, 48+/-3 normal and 46+/-5 pg/ml hyperparathyroid, females, 31+/-2 normal and 37+/-3 pg/ml hyperparathyroid.) Among hyperparathyroid patients of both sexes, increases of calcitonin during Ca infusion (15 mg Ca/kg in 4 h) were within normal limits. However, the mean maximal increase of calcitonin was significantly lower in hyperparathyroid than in normal subjects (P < 0.05). In six patients normocalcemic 5-15 mo after parathyroid surgery, fasting plasma calcitonin values were not significantly different, but responses to Ca infusion were greater than preoperatively (Delta calcitonin +/-SE: 13+/-4 preoperatively and 53+/-35 pg/ml postoperatively). The mean maximal increase of calcitonin after pentagastrin (0.5 mug/kg i.v.) was slightly lower than normal in the patients (mean+/-SE, males, 45+/-8 normal and 38+/-10 pg/ml hyperparathyroid, females, 6+/-2 normal and 0 pg/ml hyperparathyroid). Thus, primary hyperparathyroidism is accompanied by normal steady-state concentrations of circulating calcitonin, and normal-to-blunted C-cell responses to pentagastrin or induced hypercalcemia, the response to calcium generally increasing after successful parathyroid surgery. These results clearly show that primary hyperparathyroidism is not characterized by hypercalcitoninemia. The seemingly paradoxical absence of elevated steady-state calcitonin concentrations may be accounted for partly by decreased secretory reserve. However, primary hyperparathyroidism may also be accompanied by an increase in the threshold of sensitivity for calcium stimulation of calcitonin secretion.

Adolescent↗
PubMed1979

Regulation of calcitonin secretion in normal man by changes of serum calcium within the physiologic range.

To examine the relative importance of calcium and gastrin in regulation of calcitonin secretion, we administered graded oral doses of calcium to 10 normal men, ages 23-29 yr. Each subject had previously shown an appropriate increase in calcitonin secretion in response to a pharmacologic (0.5 mug/kg) pentagastrin injection. On separate days and in random order, each man drank 250 ml of distilled water containing 0.0, 0.5, 1.5, and 3.0 g of elemental calcium as the gluconate salt. Blood samples were drawn before and at 30, 60, 90, 120, 180, and 240 min after the oral calcium dose. The samples were analyzed for calcium by atomic absorption spectroscopy, and for gastrin and calcitonin by radioimmunoassays of established sensitivity and specificity. Ingestion of water (control) caused no change in any of the three variables. Calcium ingestion resulted in dose-related increases, within the normal range, of all three variables. Immunoreactive gastrin rose promptly, peaking at 30 min, and returning to basal levels or below by 120 min. In contrast, calcium and immunoreactive calcitonin levels rose slowly and in parallel, peaking at 120-240 min. Changes in calcitonin and changes in calcium were strongly and positively correlated, r = 0.73, when all data were pooled. Furthermore, individual linear regressions for changes in calcitonin and calcium levels (calculated separately for the three oral calcium doses in each subject) had positive slopes in 28 out of 30 sets (P < 0.01). The changes in calcitonin concentrations were much more poorly correlated with the corresponding changes in serum gastrin levels; in fact, the regression coefficient was weakly negative, r = -0.20. These results show that, at least in young adult men, changes of ambient calcium concentration within the normal range may be of major importance in physiologic regulation of calcitonin secretion. The findings are consistent with the hypothesis that calcitonin functions to prevent excessive postprandial hypercalcemia.

Adult↗
PubMed1979

Calcium homeostasis in diabetes mellitus.

Experimentally diabetic rats have low serum 1,25-dihydroxyvitamin D, intestinal malabsorption of calcium, secondary hyperparathyroidism, and bone loss. To examine the hypothesis that abnormalities similar to those in the diabetic rat might explain human diabetic osteopenia, we studied calcium metabolism in 40 healthy control and 82 diabetic patients aged 18--75 yr [47 untreated: fasting plasma glucose (mean +/- SE), 267 +/- 8 mg/dl; 19 treated but hyperglycemic: glucose 305 +/- 24 mg/dl; 16 treated and in better control: glucose, 146 +/- 8 mg/dl]. Serum total calcium, ionic calcium, immunoreactive parathyroid hormone (Arnaud method, GP-1M and CH-12M antisera), 25-hydroxyvitamin D (Haddad method), and 1,25-dihydroxyvitamin D (Lambert method) concentrations were normal in all 3 groups of diabetics and were not significantly different from values in the control group. We determined absorption of calcium from the intestine by a double isotope method (100 mg Ca carrier; normal range, 40--80%) in 11 control and 13 untreated, uncontrolled diabetics (mean plasma glucose, 285 +/- 17 mg/dl). Absorption of calcium in controls was 60 +/- 3% and in diabetics was 56 +/- 3% (not significantly different). We have found no derangement of calcium metabolism in adults with insulin-requiring juvenile- and adult-onset diabetes regardless of treatment status. The experimental diabetic rat model does not appear to be useful for determining the pathogenesis of adult human diabetic osteopenia.

Adolescent↗