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Biomedical subjects

H Heath

Publications and source records attributed to H Heath.

At least 109 records · Page 6Linked to original sources
PubMed1986

Secretion and metabolism of monomeric human calcitonin: effects of age, sex, and thyroid damage.

Some data suggest that human calcitonin (CT) secretion is lower in women than in men, decreases with age and the menopause, and is absent in thyroidectomized persons. To further explore CT secretory physiology, we have studied basal and calcium-stimulated plasma immunoreactive CT (iCT) and silica-extractable monomeric CT concentrations in 148 healthy volunteers and 33 patients with a history of thyroid damage (total or subtotal thyroidectomy, radioiodine treatment for thyrotoxicosis). Both whole-plasma iCT and extractable CT levels were lower basally and after calcium infusion in women than in men, basal levels being reduced about 50% and calcium-stimulated values about 75% from those of male subjects. There were no significant changes in basal iCT or extractable CT concentrations with age, and CT secretory capacity (CT response to calcium infusion) likewise did not change with age. Infusion of monomeric CT to constant concentration in 27 persons permitted estimates of CT metabolic clearance rates (MCRs) and secretion rates (SRs). Calculated MCRs of about 9 ml/min.kg-1 (persons aged 21-30 yr) and 6 ml/min.kg-1 (persons aged 54-70 yr) were in good agreement with published data, and did not differ between the sexes. SRs were dependent upon the assay method used to estimate basal plasma CT concentrations, being highest when whole-plasma iCT values were used. Based on estimates of plasma monomeric CT from the silica extraction procedure, the SR of CT was 59 +/- 6 (SE) ng/d.kg-1 in men, and 22 +/- 3 ng/d.kg-1 in women. Thyroid damage reduced, but did not abolish, apparent CT immunoreactivity, even in silica extracts of plasma. However, all subsets of thyroid-damaged patients had absent-to-markedly-impaired CT secretion in response to calcium infusion. We conclude that CT secretion is substantially lower both basally and after stimulation in women than in men, and that this difference in CT immunoreactivity probably reflects differences in circulating CT bioactivity. The sex difference in plasma CT concentrations probably results from lower rates of CT secretion in women, not increased MCR. There is no age-related decrease of plasma CT concentrations (or CT secretory reserve), calling into question the concept that a progressive deficiency of CT is partly responsible for age-related ("senile") osteoporosis. Surgical or radiation damage to the thyroid gland commonly abolishes C-cell response to calcium; such CT-deficient patients form a population suitable for determining whether or not reduced CT secretion can impair skeletal homeostasis.

Adolescent↗
PubMed1986

Accumulation of cyclic 3',5'-adenosine monophosphate in cultured neonatal human dermal fibroblasts exposed to parathyroid hormone and prostaglandin E2.

We sought to determine whether cultured human dermal fibroblasts respond to parathyroid hormone (PTH) with accumulation of cyclic 3',5'-adenosine monophosphate (cAMP) reproducibly enough for such cells to be useful in characterizing states of altered end-organ response to PTH. Thus, we cultured fibroblasts from 15 human neonatal foreskins and tested fibroblast cAMP responses to addition of synthetic human PTH-(1-34), bovine PTH-(1-34), and native bovine PTH-(1-84) at concentrations of 10(-6) to 10(-10) M. Accumulation of cAMP (cells plus medium) was significantly enhanced by PTH in only 10 of 37 experiments. In cells that had a significant cAMP response to PTH, the ratio of treated to control cAMP values ranged only from 1.27 to 2.18. No study showed a clear-cut dose-response relationship. In six of six experiments, the cells responded to prostaglandin E2 (1 microgram/ml) with markedly increased accumulation of cAMP (9.7 to 110.9-fold the basal value). We conclude that cultured human dermal fibroblast cAMP responses to PTH with use of the current methods are too small and inconsistent for that tissue to be useful in studies of reduced end-organ responsiveness to PTH such as pseudohypoparathyroidism. Nevertheless, states of hyperresponsiveness to PTH might still be detectable by this method.

1-Methyl-3-isobutylxanthine↗
PubMed1986

Plasma calcitonin in primary hyperparathyroidism: failure of C-cell response to sustained hypercalcemia.

An acute increase in serum calcium stimulates calcitonin (CT) secretion, but the effects of chronic hypercalcemia are controversial. Histopathological studies have shown C-cell hyperplasia in primary hyperparathyroidism (1 degree HPT), although circulating levels of CT have been variously reported to be normal, elevated, or depressed. We reexamined this relationship using CT RIA in conjunction with a silica extraction technique that conveys improved sensitivity and specificity for monomeric CT. Nine men and seven women with surgically documented 1 degree HPT were studied preoperatively before and after a short calcium infusion (2 mg Ca/kg, for 5 min), as were 72 normal men and 76 normal women. Basal whole plasma immunoreactive CT and silica-extractable CT concentrations in 1 degree HPT were indistinguishable from normal, regardless of sex. In addition, the whole plasma and silica-extractable CT responses to calcium stimulation were normal or blunted in patients with 1 degree HPT. We conclude that hypercalcemia resulting from 1 degree HPT is not associated with augmented CT secretion in response to an iv calcium infusion.

Adult↗
PubMed1985

Calcitonin secretion in postmenopausal osteoporosis.

Calcitonin deficiency has been implicated in the pathogenesis of accelerated bone loss, especially in postmenopausal osteoporosis. To investigate this issue, we studied 25 patients with untreated postmenopausal osteoporosis, 14 age-matched and sex-matched healthy controls (spinal bone mineral density greater than or equal to age-specific and sex-specific mean), and 5 women who had undergone total thyroidectomy. Each subject received an intravenous infusion of 2 mg of elemental calcium per kilogram of body weight over 5 minutes, to test the C-cell secretory reserve. We measured calcitonin by radioimmunoassay in whole plasma and in silica-cartridge extracts of plasma, the latter method providing greatly improved sensitivity and specificity for monomeric calcitonin. Basal immunoreactive calcitonin concentrations, whether measured in whole plasma or in extracts, were significantly higher in the subjects with osteoporosis (P less than 0.01) than in the healthy controls. The calcitonin secretory reserve, as assessed by calcium stimulation, was normal in the osteoporotic group but virtually absent in the thyroidectomy group. We conclude that postmenopausal osteoporosis is not associated with and does not result from calcitonin deficiency. On the contrary, excessive skeletal calcium release may stimulate calcitonin secretion in patients with the disorder.

Adult↗
PubMed1985

Structural requirements for parathyroid hormone action in mature bone. Effects on release of cyclic adenosine monophosphate and bone gamma-carboxyglutamic acid-containing protein from perfused rat hindquarters.

To determine the structural requirements for parathyroid hormone (PTH) activity in mature bone, we perfused the surgically isolated hindquarters of adult male rats with either native bovine PTH-(1-84) [bPTH-(1-84)] or the synthetic amino-terminal fragment, bovine PTH-(1-34) [bPTH-(1-34)]. Changes in the release of cyclic AMP (cAMP) and bone Gla protein (BGP) were monitored as evidence of bone-specific response to PTH; tissue specificity of the cAMP response was confirmed through in vitro examination on nonskeletal tissue response to PTH. Biologically active, monoiodinated 125I-bPTH-(1-84) was administered to determine if mature murine bone cleaves native hormone. We found that perfused rat bone continuously releases BGP, and that both bPTH-(1-84) and bPTH-(1-34) acutely suppress this release. In addition, both hormones stimulate cAMP release from perfused rat hindquarters. When examined on a molar basis, the magnitude of the cAMP response was dose-dependent and similar for both hormones, with doses yielding half-maximal cAMP responses. The response for bPTH-(1-34) was 0.5 nmol and for bPTH-(1-84) was 0.7 nmol. Moreover, biologically active 125I-bPTH-(1-84) was not metabolized in our hindquarter perfusion system. These findings indicate that PTH-(1-84) does not require extraskeletal or skeletal cleavage to an amino-terminal fragment in order to stimulate cAMP generation in, or suppress BGP release from, mature rat bone.

Animals↗
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

Familial benign hypercalcemia (hypocalciuric hypercalcemia). Clinical and pathogenetic studies in 21 families.

Familial benign hypercalcemia (hypocalciuric hypercalcemia) was diagnosed in 125 members of 21 families. The syndrome was generally characterized by autosomal dominant inheritance of symptomless, nonprogressive hypercalcemia with normal serum immunoreactive parathyroid hormone concentrations, parathyroid glands that had normal gross and histologic features, relatively low urinary excretion of calcium, and failure to achieve normocalcemia after subtotal parathyroidectomy. Affected persons had normal longevity and no discernible increase in other medical problems except gallstones. The parathyroid glands were not seen using high-resolution ultrasonography. Plasma calcitonin and calcitriol levels were normal or low. Skeletal mass was normal as assessed by photon absorptiometry of the radius and lumbar spine, and fractures were not more frequent. Familial benign hypercalcemia or hypocalciuric hypercalcemia is a distinctive heritable syndrome that should always be considered in the differential diagnosis of asymptomatic hypercalcemia.

Adolescent↗
PubMed1984

Parathyroid glands in familial benign hypercalcemia (familial hypocalciuric hypercalcemia).

The histologic characteristics of the parathyroid glands in familial benign hypercalcemia (familial hypocalciuric hypercalcemia) are disputed, some finding parathyroid hyperplasia and others finding no abnormalities. To further investigate this issue, the histologic appearance of 82 parathyroid glands from 47 control patients (surgical and autopsy) were compared with those of 28 glands from 23 patients with familial hypocalciuric hypercalcemia who had undergone surgery for suspected primary hyperparathyroidism. Median and mean weights of 23 parathyroid glands from 12 patients with familial hypocalciuric hypercalcemia were 50 mg and 60 mg, respectively, with a range from 5 to 181 mg. Eighty-three percent of individual glands were within extreme normal limits for weight (less than 75 mg). Percent parenchymal area in familial hypocalciuric hypercalcemia was slightly but significantly less than control values (62 +/- 2 versus 71 +/- 2 percent, respectively; (p = 0.009). Conversely, percent fat was higher in familial hypocalciuric hypercalcemia than control values (30 +/- 3 versus 21 +/- 2 percent, respectively; p = 0.015). Stromal area was 8 +/- 1 percent in each group. Although 15 to 20 percent of parathyroid glands in familial hypocalciuric hypercalcemia exceeded normal size, most were indistinguishable from normal by size, weight, and microscopic appearance. The significantly reduced percent parenchyma in glands from patients with familial hypocalciuric hypercalcemia further suggests that the condition is not uniformly accompanied by typical parathyroid hyperplasia and should not be thought of as merely a variant of the latter.

Adenoma↗
PubMed1984

High-resolution parathyroid ultrasonography in familial benign hypercalcemia (familial hypocalciuric hypercalcemia).

Familial benign hypercalcemia, or familial hypocalciuric hypercalcemia (FHH), is frequently confused with primary hyperparathyroidism, but the consistent failure of subtotal parathyroidectomy to normalize serum calcium levels in FHH makes accurate distinction from familial hyperparathyroidism imperative. Because ultrasonography frequently demonstrates enlargement of the parathyroid glands in hyperparathyroidism, we examined 14 hypercalcemic adults (who had not undergone operation) from seven kindreds with FHH by using a high-resolution real-time scanner. We compared our results with those from 156 patients (who had undergone scanning preoperatively) with surgically confirmed hyperparathyroidism. Enlargement of the parathyroid glands was detected ultrasonographically in 137 of 156 (88%) of the total group of patients with hyperparathyroidism and in 17 of 24 patients (71%) with hyperparathyroidism who had hypercalcemia (serum calcium, 10.6 to 11.0 mg/dl) comparable to that of the FHH group (mean value, 10.7 mg/dl). In contrast, the single possible parathyroid lesion seen in the FHH group was substantially smaller (4 mm) than the smallest (7 mm, 75 mg) abnormal gland reliably detected by ultrasonography in the group with hyperparathyroidism and was conceivably normal in size. Patients with FHH have a dramatic absence of ultrasonographic parathyroid enlargement. High-resolution parathyroid ultrasonography may be of ancillary diagnostic benefit in patients with familial hypercalcemia.

Adult↗
PubMed1984

Bone mineral density and skeletal fractures in familial benign hypercalcemia (hypocalciuric hypercalcemia).

To determine whether familial benign hypercalcemia, or familial hypocalciuric hypercalcemia (FHH), has adverse effects on the skeleton, we measured bone mineral density (BMD) in 31 affected persons from 14 families (16 women and 15 men), ranging in age from 19 to 68 years. Forearm BMD was measured by single-photon absorptiometry, and spinal BMD was measured by dual-photon absorptiometry. In addition, we systematically queried 82 hypercalcemic and 52 normocalcemic family members about skeletal fractures. Both men and women with FHH had normal BMD (expressed as grams per square centimeter) in the lumbar spine, distal radius, and midradius. Osteoporotic-type fractures (vertebrae, hip, and distal radius) were virtually absent in both affected and unaffected family members. Detailed evaluation of larger numbers of of older affected persons may be necessary to resolve this issue definitively, but we conclude provisionally that FHH has no important adverse effects on skeletal health.

Adult↗
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

Impaired vitamin D metabolism with aging in women. Possible role in pathogenesis of senile osteoporosis.

Calcium absorption decreases with aging, particularly after age 70 yr. We investigated the possibility that this was due to abnormal vitamin D metabolism by studying 10 normal premenopausal women (group A), 8 normal postmenopausal women within 20 yr of menopause (group B), 10 normal elderly women (group C), and 8 elderly women with hip fracture (group D) whose ages (mean +/- SD) were 37 +/- 4, 61 +/- 6, 78 +/- 4, and 78 +/- 4 yr, respectively. For all subjects, serum 25-hydroxyvitamin D [25(OH)D] did not decrease with age, but serum 1,25-dihydroxyvitamin D [1,25(OH)2D], the physiologically active vitamin D metabolite, was lower (P = 0.01) in the elderly (groups C and D; 20 +/- 3 pg/ml) than in the nonelderly (groups A and B; 35 +/- 4 pg/ml). The increase of serum 1,25(OH)D after a 24-h infusion of bovine parathyroid hormone fragment 1-34, a tropic agent for the enzyme 25(OH)D 1 alpha-hydroxylase, correlated inversely with age (r = -0.58; P less than 0.001) and directly with glomerular filtration rate (r = 0.64; P less than 0.001). The response was more blunted (P = 0.01) in elderly patients with hip fracture (13 +/- 3 pg/ml) than in elderly controls (25 +/- 3 pg/ml). We conclude that an impaired ability of the aging kidney to synthesize 1,25(OH)2D could contribute to the pathogenesis of senile osteoporosis.

Aged↗
PubMed1984

Time- and dose-related biphasic effects of synthetic bovine parathyroid hormone fragment 1-34 on urinary cation excretion.

The reported effects of PTH on urinary excretion of cations are highly variable. We investigated dose and time relationships for urinary clearance of calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K) after infusions of synthetic bovine PTH fragment 1-34 [bPTH-(1-34)] in seven normal subjects. The bPTH-(1-34) was given over 15 min on widely separated days at doses of 10, 30, 75, 150, and 300 U/70 kg. The 75, 150, and 300 U/70 kg doses produced a biphasic excretory pattern for all four ions, with increased clearance from 0-30 min and enhanced reabsorption at 60-120 min. Lower doses produced only retention of Ca, Mg, and Na, but even 10 U bPTH-(1-34)/70 kg caused a marked biphasic excretory pattern of K. These data explain why in previous studies PTH increased, decreased, or had no effect on the excretion of divalent and monovalent cations and emphasize the importance of short, clearly defined urine collection intervals for in vivo studies of PTH action of the kidney.

Adult↗