Warner M. Burch

Insulin-like growth factor I mediates selective anabolic effects of parathyroid hormone in bone cultures.

PTH was studied for its effects on bone formation in cultured rat calvariae. 0.01-10 nM PTH stimulated [3H]thymidine incorporation into DNA by up to 4.8-fold. Although continuous treatment with PTH for 24-72 h inhibited [3H]proline incorporation into collagen, transient (24 h) treatment enhanced [3H]proline incorporation into collagen 24-48 h after the hormone was removed. The collagen stimulated by PTH was type I and the effect was observed in the periosteum-free bone and was not blocked by hydroxyurea. Furthermore, treatment with 1-100 nM PTH for 24 h increased insulin-like growth factor (IGF) I concentrations by two to fourfold, and an IGF I antibody prevented the PTH stimulation of collagen synthesis, but not its mitogenic effect. In conclusion, continuous treatment with PTH inhibits calvarial collagen, whereas transient treatment stimulates collagen synthesis, and the stimulatory effect is mediated by local production of IGF I.

Triiodothyronine stimulates maturation of porcine growth-plate cartilage in vitro.

We studied the effect of triiodothyronine (T3) on mammalian growth-plate cartilage in vitro. Growth-plate cartilages from fetal pigs scapulae were incubated for 3 to 7 d in serum-free medium alone or medium containing T3. Alkaline phosphatase activity, a marker of hypertrophied chondrocytes, was increased in T3 (10 nM)-treated growth-plate cartilage 152 +/- 36% above that of cartilage incubated in medium alone after 3 d of incubation, and 324 +/- 47% after 7 d of incubation. There was a dose-response increase in alkaline phosphatase activity to T3 over the range of 0.01-10 nM. The rise in alkaline phosphatase activity was specific for T3 since growth-plate cartilage alkaline phosphatase activity was not increased by cortisol, insulin, parathyroid hormone, or 5% fetal calf serum. Histological studies of growth-plate cartilage showed that T3 in a concentration-dependent manner increased the width of the zone of maturation (hypertrophied chondrocytes). Histochemical staining for alkaline phosphatase activity demonstrated that T3 caused the recruitment of new cells into the zone of maturation. T3 also stimulated incorporation of L-[3H]leucine into protein and 35SO4 into proteoglycan in growth-plate cartilage. In contrast, T3 did not increase alkaline phosphatase activity or radiolabeled precursor incorporation into nongrowth-plate scapular cartilage. These studies demonstrate that T3 directly stimulates maturation and, to a lesser degree, growth-related processes in fetal mammalian growth-plate cartilage.

Parathyroid hormone stimulates growth of embryonic chick pelvic cartilagein vitro

SummaryAddition of N6-monobutyryl cyclic AMP (BtcAMP) or methylisobutylxanthine to embryonic chick pelvic cartilages incubated in a serum-free medium for 3 days stimulates the cartilages to grow predominately through increasing cellular hyperplasia [1]. The present study investigated whether parathyroid hormone (PTH) added to the serum-free organ culture system would mimic the growth-promoting effects of BtcAMP through increasing endogenous cartilage cyclic AMP content. Parathyroid hormone 10 nM stimulatesin vitro pelvic cartilage growth as compared with cartilage grown in medium alone, as estimated by increases in wet weight (64%), dry weight (91%), total soluble protein (19%), and deoxyribo-nucleic acid (DNA) content (51%). Parathyroid hormone (0.1–10nM) in a concentration-dependent manner produces increases in wet weight and radiolabeled precursor incorporation of [3H]thymidine and [14C]-L-leucine over cartilage incubated in medium alone. Both PTH-treated and BtcAMP-treated cartilage show histological changes of increased cellularity as well as raised DNA content and elevated DNA/protein ratios. PTH increases cartilage cyclic AMP content, with the maximum rise occurring after 30 min incubation, and a return to levels found in pelvic cartilages incubated in medium alone by 4 hours. Consequently, cartilages incubated in medium containing PTH for 4 hours and then incubated in medium alone for the remaining 3 days, grew as well as cartilages that had been incubated in medium containing PTH for the entire 72-hour period. Thus, PTH, by raising intracellular cyclic AMP, triggers cartilage growthin vitro.

Abnormalities of Vitamin D Metabolism and Action in the Vitamin D Resistant Rachitic and Osteomalacic Diseases

The burgeoning science of vitamin D metabolism and action has brought new perspective to disorders of calcium and bone metabolism in man. Rapid scientific advances have been paralleled by the development of new insights into the pathogenesis of, and new therapies for, human diseases. It is not surprising that the growing body of vitamin D knowledge has been applied to the vitamin D resistant rachitic diseases. Although “vitamin D resistance” may in many instances be a sobriquet imprecisely applied to these diseases, further definition of the disorders must be realized in order to affirm the validity of the newly born scientific assumptions concerning vitamin D.

Phosphotyrosine and phosphoprotein phosphatase activity of alkaline phosphatase in mineralizing cartilage.

We used embryonic skeletal cartilage known to have high levels of alkaline phosphatase activity to determine whether growing cartilage has phosphotyrosine phosphatase activity and phosphotyrosinyl histone phosphatase activity at physiologic pH. Embryonic chick pelvic cartilage and fetal pig scapular growth-plate cartilage were assayed using phosphotyrosine as substrate at pH 7.5 and the amount of tyrosine generated measured. Both cartilage models had Km for phosphotyrosine between 6 to 24 mus mol/L. Phosphotyrosine phosphatase activity correlated with alkaline phosphatase activity as assessed by (1) distribution of histologic staining for alkaline phosphatase within the cartilages, (2) hormonal stimulation of cartilage alkaline phosphatase activity in vitro, (3) comparison of alkaline phosphatase and phosphotyrosine phosphatase activities in the presence of known inhibitors (vanadate, levamisole, homoarginine, and zinc), and (4) assaying chick epiphyseal cartilage alkaline phosphatase purified to homogeneity for phosphotyrosine phosphatase activity. Areas of cartilage with elevated alkaline phosphatase activity also had raised phosphotyrosine phosphatase activity. Triiodothyronine, a known stimulator of cartilage alkaline phosphatase, increased chick cartilage alkaline phosphatase activity 88% and phosphotyrosine phosphatase activity 106%, and stimulated porcine growth-plate cartilage alkaline phosphatase activity 91% and phosphotyrosine phosphatase activity 145% after 3 days of in vitro incubation. Each of the inhibitors block alkaline phosphatase and phosphotyrosine phosphatase activities. The purified alkaline phosphatase had a Km for phosphotyrosine of 18 mus mol/L and Vmax of 5700 nmol tyrosine/mg protein/h, which is well over 1000-fold higher than the phosphotyrosine phosphatase activity found in the above preparations of pelvic and scapular cartilage.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine 3',5'-monophosphate: a modulator of embryonic chick cartilage growth.

We tested the hypothesis that cyclic AMP plays a significant role in modulating the growth of embryonic chick cartilage by determining whether cyclic AMP levels change in growing embryonic cartilage and whether cyclic AMP could stimulate embryonic cartilage growth in a long term in vitro organ culture. Cyclic AMP levels were low (0.1 pmol/mg wet wt) in 8-d chick embryo pelvic cartilage, and increased progressively through the 11th d of embryonic development at which time they reached a maximum (1.8 pmol/mg wet weight) and thereafter remained constant. We developed an in vitro organ culture system to determine whether cyclic AMP, a factor known to stimulate radiolabeled precursor incorporation into macromolecules in short-term studies does, in fact, stimulate growth of cartilage. Individual pelvic cartilages were isolated from 9-d chick embryos, placed in serum-free medium (BGJb-FJ modification) and incubated for 3 to 5 d during which time they increased in size (39 and 60% in length, respectively), wet weight (90 and 141%, respectively), and content of total soluble protein (30 and 48%, respectively). N6-monobutyryl cyclic AMP (BtcAMP) added to the medium caused a dose-dependent (0.05 to 1.0 mM) stimulation of growth. After 3 d of incubation, 1.0 mM BtcAMP increased wet weight (125%), [14C]leucine incorporation into protein (75%), and [3H]thymidine incorporation into DNA (48%) compared with control cartilages incubated in medium alone. 1-methyl-3-isobutyl xanthine, a phosphodiesterase inhibitor, also increased cartilage growth above control while sodium butyrate, AMP, and ATP had no effect. Histological examination of cartilage grown in medium was similar to that of cartilage developing in ovo, whereas, cartilage grown in medium containing BtcAMP showed marked hypercellularity with many immature chondrocytes. Our observations are compatible with the hypothesis that cyclic AMP can significantly modulate the growth of embryonic cartilage.

Enhancement of endocrine pancreatic secretions by essential fatty acids.

Recent studies have suggested the beneficial effects of essential fatty acids in postoperative patients receiving total parenteral nutrition. While there is abundant information on the role of glucose and amino acids on insulin release, the effect of essential fatty acids on endocrine pancreatic secretions is not clear. Since linoleic and linolenic acids are constituents of TPN solutions as well as dietary fat, our aim was to examine their effect on the endocrine pancreatic function, using isolated islets. In each experiment, six islets microdissected from three mice were preperifused at the rate of 1 ml/min with Krebs-Ringer bicarbonate (KRB) buffer pH 7.4 containing 2% bovine albumin and 5.5 mM glucose (basal) with continuous supply of 95%/5%, O2/CO2 for 1 hr, after which basal samples were collected on ice every minute. The perifusion was continued for 20 min after the addition of a mixture of 10 mM linoleic acid and 5 mM linolenic acid to the KRB. During each perifusion phase, effluent samples were also collected for insulin and glucagon assay. The mean integrated area under the curve/20 min showed an increase in both insulin and glucagon secretions with the addition of fatty acids. Hence insulin increased from a basal 3154.8 +/- 953.7 to 8393.0 +/- 2073.1 pg (P less than 0.025, n = 6) and glucagon increased from 193.7 +/- 46.9 to 1566.1 +/- 411.2 pg (P less than 0.0025, n = 5). The fatty-acid-induced insulin but not glucagon secretion was blocked by the addition of 2 mM palmoxirate an inhibitor of fatty acid oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Malignant teratoma of the thyroid in an adult: CT appearance

A case of malignant teratoma of the thyroid gland is presented. Computed tomography identified an inhomogeneous mass with dense calcifications involving the thyroid gland and compressing the upper airway. Enlarged, peripherally enhancing lymph nodes in the neck and mediastinum suggested its malignant etiology.

Chronic myopathy due to immunoglobulin light chain amyloidosis.

Amyloid myopathy associated with a plasma cell dyscrasia is a rare cause of muscle hypertrophy. It can be a challenging diagnosis, since pathological findings are often elusive. In addition, the mechanism by which immunoglobulin light-chain deposition stimulates muscle overgrowth remains poorly understood. We present a 53-year old female with a 10-year history of progressive generalized muscle overgrowth. Congo-red staining and immunohistochemistry revealed perivascular lambda light chain amyloid deposits, apparent only in a second muscle biopsy. The numbers of central nuclei and satellite cells were increased, suggesting enhanced muscle progenitor cell formation. Despite the chronicity of the light chain disease, the patient showed complete resolution of hematologic findings and significant improvement of her muscle symptoms following autologous bone marrow transplantation. This case highlights the importance of early diagnosis and therapy for this treatable cause of a chronic myopathy with muscle hypertrophy.

Homologous desensitization of pancreatic beta cells to glucose response by polyunsaturated fatty acids

Abstract We have shown recently that a mixture of 10 m M linoleic acid (18:2,ω6) and 5 m M linoleic acid (18:3,ω3) enhanced insulin secretion by microdissected islets. In the present study, our aim was to examine the effect of a prestimulus with this mixture of 10 m M linoleic acid and 5 m M linoleic acid on glucose and arginine-stimulated insulin response, by perifused isolated islets. Insulin secretion by untreated (control) islets estimated as integrated area under the curve (AUC/ 20 mins) above basal during three pulses of 27.7 m M glucose separated by 20 min periods of basal (washout) perifusions were 2950 ± 585 pg, 5185 ± 1258 pg, and 2410 ± 921 pg, a greater response (P M arginine. These data suggest that (1) a mixture of 10 m M linoleic acid and 5 m M linolenic acid can desensitize isolated perifused islets to glucose but not arginine; and (2) glucose intolerance associated with lipemia may result, at least in part, from a direct effect on the islets of Langerhans.