Effects of exogenous growth hormone on bone mineralization and remodeling and on plasma calcitriol in intact pigs

Influence of tool geometry on drilling performance of cortical and trabecular bone

Minimally invasive surgery poses high demands on tool design. The goal was to measure the influence of drill bit geometry on maximum thrust forces required for drilling, and compare this relative to the known influence of feed rate and bone composition. Blind holes were drilled perpendicular to the iliac crest up to 10 mm depth in cadaveric pelvic bones of 20 pigs (adolescent) and 11 goats (full grown) with eight substantially different drill bits of ∅ 3-3.2 mm. Subsequently, boreholes were drilled perpendicular to the ilium with the same drill bits at three different feed rates (0.58 mm/s, 0.83 mm/s, 1.08 mm/s). The mean maximum thrust force ranges from 10 to 110 N for cortical bone, and from 3 to 65 N for trabecular bone. The results show that both drill bit geometry and feed rate have a significant influence on the maximum thrust forces, with a dominant influence of drill bit geometry in terms of shape of the flutes, sharpness of cutting edges and value of point angle. The differences in thrust forces between cortical and trabecular bone are substantial for all measured conditions. The measured values can be used for drill design.

Different effects of physiologically and pharmacologically increased growth hormone levels on cholecalciferol metabolism at prepubertal age

The aim of the study was to investigate the influence of physiologically and pharmacologically increased plasma growth hormone (GH) levels on cholecalciferol metabolism at prepubertal age. Three groups of dogs raised on the same diet were studied from weaning till 21 weeks of age, i.e., small breed dogs (n = 7, control group); large breed dogs with 15-fold greater growth rates compared to the control group (n = 8, LB-group); and small breed dogs treated with pharmacological doses of growth hormone (n = 6, GH-group; 0.5IU GH per kg body per day) from 12 to 21 weeks of age. Excess of GH had the expected anabolic effect on growth rate and phosphate sparing. Increased plasma GH levels in the LB- and GH-groups versus the control group were accompanied by (1) greater plasma insulin-like growth factor I (IGF-I) levels, (2) greater plasma 1,25-dihydroxycholecalciferol (1,25(OH)(2)D(3)) levels, and (3) lower plasma 24,25(OH)(2)D(3) levels. In the LB-group, excess of GH favored plasma 1,25(OH)(2)D(3) levels by decreasing the clearance of 1,25(OH)(2)D(3), whereas in the GH-group by increasing the production of 1,25(OH)(2)D(3). The lowered plasma 24,25(OH)(2)D(3) levels in the LB- and GH-groups were likely attributed to a competitive inhibition of the production of 24,25(OH)(2)D(3) by GH and/or IGF-I.

Growth hormone modulates cholecalciferol metabolism with moderate effects on intestinal mineral absorption and specific effects on bone formation in growing dogs raised on balanced food

The aim of the study was to investigate the influence of growth hormone (GH) on Vitamin D3 metabolism and the subsequent effects on calcium (Ca) homeostasis and skeletal growth in growing dogs. A group of Miniature Poodles received supraphysiological doses of GH (GH group; n = 6; 0.5 IU GH per kg body per day) from 12 to 21 weeks of age and was compared with a control placebo-treated group (n = 8). Biologic activity of GH in the GH compared to the control group was indicated by (a) the 2.5- to 3.5-fold increase in the plasma concentrations of insulin-like growth factor I (IGF-I), (b) the increased production of 1,25-dihydroxycholecalciferol as indicated by the significantly increased plasma 1,25-dihydroxycholecalciferol concentrations and the 12.9-fold increase in renal 1alpha-hydroxylase gene expression, and (c) the inhibited production of 24,25-dihydroxycholecalciferol as indicated by the significantly lower plasma 24,25-dihydroxycholecalciferol concentrations and the similar levels of renal 24-hydroxylase gene expression. Despite the distinct effects on Vitamin D(3) metabolism in the GH group, there were only moderate effects on the intestine, i.e. at 20 weeks of age there was a significant increase of 14.4 and 5.6% in fractional absorption of Ca and phosphate (Pi), respectively, compared to the control group. GH administration resulted in significantly elevated glomerular filtration rate, with no differences in Pi urine excretion as a result of a concomitant increase in the tubular reabsorption of Pi. GH had only limited disturbing effects on endochondral ossification as indicated by the maintenance of the regularity of the growth plates. However, GH had specific anabolic effects on bone formation without concomitant effect on bone resorption that may result in disorders of skeletal remodeling and manifestation of enostosis.

Pathophysiological effects of low dietary phosphorus in pigs

SUMMARY

The homeostasis of inorganic phosphate (P(i)) is regulated by parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25(OH)(2)D), and P(i)itself in the intestine, kidney, and bone in all the mammalian species studied. Determinations of the serum concentrations of PTH, 1,25(OH)(2)D and osteocalcin were done in 82 southern Romanian Landrace pigs originating from three herds with dietary P(i)deficiency. Serum P(i)concentrations were negatively correlated with those of 1,25(OH)(2)D. In lactating animals and sucklings, the linear relationships between P(i)and 1,25(OH)(2)D were not present. Serum P(i)concentrations were positively correlated with those of PTH. In lactating animals and young pigs, the linear relationships between P(i)and PTH were not evident. PTH and 1,25(OH)(2)D concentrations were negatively correlated. The serum concentrations of 1,25(OH)(2)D and osteocalcin were positively correlated. Milk P(i)concentrations ranging from 3.10 to 7.49 mmol/L were correlated positively with urinary P(i)concentrations ranging from 0.26 to 11.37 mmol/L. In conclusion, similarly to other species, P(i)homeostasis is achieved in pigs by feedback mechanisms between P(i), PTH and 1,25(OH)(2)D and osteocalcin production is induced by 1,25(OH)(2)D. The effect of lactation on P(i)homeostasis remains to be explored.

In vivo bone metabolism and ex vivo bone marrow osteoprogenitors in vitamin D-deprived pigs

Vitamin D insufficiency is still a concern in countries where there is no routine food supplementation, such as France. A low vitamin D status is clearly associated with an increased risk of fracture in the elderly, but the long-term consequences of latent vitamin D insufficiency in young people and adults are not known. We fed 26 growing pigs a high calcium diet (1.1%) with a 1000 IU cholecalciferol/kg diet (controls), or without vitamin D (0D) for 4 months. We then analyzed the overall impact of low vitamin D status on osteotropic hormones (calcitriol and immunoreactive parathyroid hormone), plasma markers of bone remodeling (alkaline phosphatase [ALP] activity, carboxyterminal propeptide of type I procollagen [PICP], osteocalcin, hydroxyproline), whole bone parameters (ash content, bending moment), histomorphometry, and the populations of marrow osteoblastic and osteoclastic precursors by ex vivo cultures. The fall in plasma 25-dihydroxyvitamin [25(OH)D] in the 0D pigs indicated severe depletion of their vitamin D stores. However, they remained normocalcemic, were mildly hyperparathyroid after 2 months of vitamin D deprivation, and showed only a slight decrease in plasma calcitriol. The bone mineral content and bending moment of metatarsals decreased and they had increased osteoblastic (+59%, p < 0.05 0D vs. controls) and osteoclastic (+31%, p < 0.1 0D vs. controls) surfaces. This was not paralleled by increased bone turnover, because plasma hydroxyproline and ALP were unchanged and PICP and osteocalcin were decreased. The adherent fraction of bone marrow cells showed a great increase in the number of total stromal colony-forming units (CFU-F; +93%, p < 0.05 0D vs. controls) and in the percent of ALP(+) CFU-F (+58%, p < 0.01 0D vs. controls) in cultures from 0D pigs. More tartrate-resistant acid phosphatase-positive (TRAP(+)) multinucleated cells were generated in cultures of nonadherent marrow cells from 0D pigs, and the area of resorption was 345% greater than in controls. Thus, vitamin D deprivation caused only moderate hormonal changes in growing pigs fed a high-calcium diet, but affected their bone characteristics and greatly enhanced the pool of osteoblasts and osteoclasts by stimulating the commitment of their precursors in bone marrow.

Calcium-regulating hormones, bone mineral content, breaking load and trabecular remodeling are altered in growing pigs fed calcium-deficient diets

Studies on calcium nutrition in appropriate large animal models can be directly relevant to humans. We have examined the effect of dietary Ca deficiency on various bone and bone-related variables, including plasma markers, histomorphometry, mineral content and breaking strength in pigs. Three groups of eight 38-d-old female pigs were fed adequate (0.9%; control), low (0.4%; LCa) or very low (0.1%; VLCa) Ca diets for 32 d. Plasma Ca significantly decreased over time only in the VLCa-deficient pigs. The concentrations of the parathyroid hormones (PTH) and calcitriol increased as Ca deficiency developed, and the plasma PTH and calcitriol levels varied inversely with dietary Ca. The total bone ash contents, bending moments, trabecular bone volume and the mineral apposition rate all decreased as the calcium intake decreased. The osteoclast surface areas were greater than those of controls in both Ca-deficient groups, whereas the osteoblast surface areas were greater only in the VLCa group. The plasma osteoblast-related markers (alkaline phosphatase, carboxy-terminal propeptide of type I procollagen and osteocalcin) were either greater or unaffected in the Ca-deficient pigs. The results indicate that deficient bone mineralization combined with an increased bone resorption led to bone loss and fragility. The differences in the changes in bone cells (number and activity) between LCa and VLCa groups might be due to differences (time and extent) of circulating PTH and calcitriol. The defective mineralization in both Ca-depleted groups resulted mainly from the lack of Ca because their osteoblast activity was either maintained or stimulated. The results also underline the progressive sensitivity of pigs to Ca supply and the usefulness of this model.

Dexamethasone-induced abnormalities in growth and bone metabolism in piglets are partially attenuated by growth hormone with no synergistic effect of insulin-like growth factor-I

Dexamethasone (DEX) therapy improves pulmonary compliance in premature infants with chronic lung disease; however, normal growth and bone development are impaired. Because DEX may mediate its effects by altering the GH-IGF-I axis, we investigated whether adjunctive therapy with GH or GH + IGF-I during DEX therapy could attenuate these DEX-induced effects. Piglets were randomized to placebo, oral tapered DEX (0.5, 0.3, and 0.2 mg kg(-1) d(-1) over 14 d), DEX + GH (0.1 mg kg(-1) d(-1)) or DEX + GH + IGF-I (0.1 mg kg(-1) d(-1)). Final whole body weight and length were improved with GH or GH + IGF-I compared with the DEX alone group. Plasma GH and IGF-I were not influenced by DEX, but infusion of IGF-I resulted in higher (p < 0.05) plasma IGF-I compared with all other groups at d 15. DEX reduced (p < 0.05) circulating IGFBP-2 and IGFBP-3 and liver IGFBP-2 and IGFBP-4 mRNA expression compared with controls. Treatment with DEX alone resulted in lower (p < 0.05) plasma osteocalcin, urinary N-telopeptide, and whole body and femur bone mineral density compared with controls, whereas results with piglets receiving adjunctive GH or GH + IGF-I were similar to those of controls. Given adjunctively, GH alone appears to partially counter the abnormalities in growth and bone metabolism associated with DEX therapy; however, this improvement cannot be attributed to higher circulating IGF-I, because combined therapy did not further improve growth or bone homeostasis compared with DEX + GH treatment. Growth hormone therapy has the potential to stimulate growth in infants exposed to steroid treatment.

Duodenal Ca2+ absorption is not stimulated by calcitriol during early postnatal development of pigs

The role of calcitriol in stimulating intestinal active Ca2+ absorption during postnatal life was studied in newborn, suckling, and weaned control (Con) piglets and piglets suffering from inherited calcitriol deficiency (Def piglets). In addition, a group of Def piglets was treated with vitamin D3 (Def-D3 piglets), which normalized plasma calcitriol levels. Regardless of age, duodenal calbindin-D9k concentrations ranged between 1,839 and 2,846 microg/g mucosa in Con piglets, between 821 and 1,219 microg/g mucosa in Def piglets, and between 2,960 and 3,692 microg/g mucosa in Def-D3 animals. In weaned animals, active Ca2+ absorption as calculated from in vitro 45Ca2+ flux rate measurements in Ussing chambers could be related to calbindin-D9k levels. Thus active Ca2+ absorption was completely absent in Def animals but was reconstituted in Def-D3 animals. In contrast, in newborn Def piglets active Ca2+ absorption functioned normally despite the low plasma calcitriol and mucosal calbindin-D9k levels and could not be affected by treatment with vitamin D3. Similar results were obtained from suckling Def piglets. The microtubule-disrupting agent colchicine caused significant inhibition of transepithelial net Ca2+ absorption in duodenal epithelia from newborn piglets without exerting an effect in suckling and weaned animals. Colchicine had no effect on Ca2+ uptake across the brush border membrane of mucosal enterocytes or on glucose-dependent electrogenic net ion flux rates in duodenal preparations from newborn Con piglets. In conclusion, our findings reveal intestinal active Ca2+ absorption during early postnatal life of pigs that involves calcitriol-independent mechanisms and that may include intact microtubule actions.

Radiographic, densitometric, and biomechanical effects of recombinant canine somatotropin in an unstable ostectomy gap model of bone healing in dogs

OBJECTIVE

To determine the effect of recombinant canine somatotropin (STH) on radiographic, densitometric, and biomechanical aspects of bone healing using an unstable ostectomy gap model.

STUDY DESIGN

After an ostectomy of the midshaft radius, bone healing was evaluated over an 8-week period in control dogs (n = 4) and dogs receiving recombinant canine STH (n = 4).

ANIMALS OR SAMPLE POPULATION

Eight sexually intact female Beagle dogs, 4 to 5 years old.

METHODS

Bone healing was evaluated by qualitative and quantitative evaluation of serial radiographs every 2 weeks. Terminal dual-energy x-ray absorptiometry and three-point bending biomechanical testing were also performed.

RESULTS

Dogs receiving STH had more advanced radiographic healing of ostectomy sites. Bone area, bone mineral content, and bone density were two to five times greater at the ostectomy sites of treated dogs. Ultimate load at failure and stiffness were three and five times greater in dogs receiving STH.

CONCLUSIONS

Using the ostectomy gap model, recombinant canine STH enhanced the radiographic, densitometric, and biomechanical aspects of bone healing in dogs.

CLINICAL RELEVANCE

Dogs at risk for delayed healing of fractures may benefit from treatment with recombinant canine STH.

Histologic evidence: growth hormone completely prevents reduction in cortical bone gain and partially prevents cancellous osteopenia in the tibia of hypophysectomized rats

BACKGROUND

In previous studies we found that the cause of bone loss in young hypophysectomized (HX) animals was due primarily to an inhibition in growth-dependent bone gain and a decrease in bone turnover. The aim of this study was to determine whether growth hormone, which has stimulatory effects on bone growth and turnover, can prevent HX-induced skeletal alterations in rats.

METHODS

Female Sprague-Dawley rats were divided into baseline control (BASAL), age-matched control (CON), HX, HX plus low-dose GH (1.5 mg/kg/d, subcutaneously), and HX plus high-dose GH (4.5 mg/kg/d) groups. The BASAL group was sacrificed at 2 months of age and the remaining groups were sacrificed after 6 weeks of treatment. Cancellous and cortical bone histomorphometry was performed on double-fluorescent-labeled 40 microm-thick sections of the proximal tibia and tibial shaft.

RESULTS

Both low- and high-dose GH prevented the HX-induced decrease of IGF-I serum levels. High-dose GH also significantly increased the body weight and the wet weight of the gastrocnemius muscle when compared to the CON groups. In the tibial shaft, the periosteal labeled surface, mineral apposition rate and bone formation rate were higher in both of the GH-treated groups than in the HX group (P < 0.05). The tissue area and cortical bone area of the high-dose GH-treated rats were greater than those of the HX rats, but did not differ from those of the CON rats. In the proximal tibia, both low- and high-dose GH prevented an HX-induced decrease in the longitudinal growth rate and growth plate width, and increased surface-based bone formation compared to the HX and CON. Cancellous bone volume, tissue-based bone formation rate, and eroded surface in both of the GH-treated groups were higher than those of the HX group, but lower than those of the BASAL and CON groups (P < 0.05). Bone architecture of the HX rats was also improved after GH treatment.

CONCLUSIONS

This study clearly demonstrates that GH replacement at the dosage of 4.5 mg/kg/d can completely prevent the HX-induced reduction in cortical bone gain in the tibial shaft, but can only partially prevent cancellous osteopenia in the proximal tibia after six weeks.

Mineral bioavailability and bone mineral contents in pigs given calcium carbonate postprandially

We have further investigated the "meal effect" on mineral bioavailability in pigs by mineral balance studies and measurements of bone ash contents and bending moment. A group of seven pigs (CAA) was given all its dietary Ca as CaCO3 5 h after the first daily meal for 8 weeks. The control group of seven pigs received CaCO3 in the meal. Both groups were given normal P within the meals. Ca and P absorption and retention were evaluated by a 10-day balance trial. Several bones were collected at slaughter to determine bone ash, Ca, and P contents and bending moment (three-point bending test). Ingesting Ca after the meal did not affect Ca bioavailability or phosphorus absorption, but did reduce P retention, which in turn decreased the bone scores. Osteopenia, indicated by decreased total mineral contents of bones (and decreased ash:bone volume ratio), was associated with elevated plasma osteocalcin in the CAA group. Thus, CaCO3 need not be incorporated into a meal for high Ca absorption, provided that Ca is given after a meal, but simultaneous intakes of Ca and P are required for the best mineral retention.

Treatment with growth hormone and IGF-I in growing rats increases bone mineral content but not bone mineral density

Human growth hormone (hGH) and insulin-like growth factor I (IGF-I) both stimulate bone formation and have been proposed as therapeutic agents for osteoporosis. We examined the effect of hGH and IGF-I alone and in combination on bone size, bone mineral content (BMC), and bone mineral density (BMD) in 10- to 12-week old growing female Sprague-Dawley rats. Sixty rats were assigned to treatment with either placebo, hGH, IGF-I, or both for 4 weeks. After 4 weeks, the right femurs and tibias were excised, and ex vivo BMC and the area of the tibia and femur were measured by dual-energy X-ray absorptiometry (DXA); volume of these bones was measured by Archimedes' principle. In addition, proximal tibial bone density was measured directly by peripheral quantitative computerized tomography (pQCT). Bone length, area, and volume in all treated groups was greater than controls. Areal bone density by DXA (BMC/area) was higher in IGF-treated rats and lower in GH-treated rats than in controls. Volumetric bone density (BMC/volume) was lower in treated groups than in controls. Measurements by pQCT confirmed that true bone density was lower in all treated groups than in controls. We conclude that treatment with hGH or IGF-I increased bone size and mineral content but decreased bone density in growing rats. Because areal correction of BMC did not adequately correct for the increased bone volume in IGF-treated rats, results of areal bone density by DXA should be interpreted with caution when treatment causes a disparity in bone size between groups.

Prevention and treatment of osteoporosis

Because the lifetime risk of fragility fracture for a 50-year-old Caucasian woman is about 40 per cent, a whole-life strategy of osteoporosis prevention is necessary. In childhood, primary prevention of osteoporosis is based on exercise and adequate dietary calcium. In women undergoing menopause, hormone replacement therapy administered for at least ten years remains the preventive treatment of choice, and is associated with a substantial reduction in vertebral and non-vertebral fractures. Intranasal salmon calcitonin and bisphosphonates are effective alternatives, but their effects on fracture rate and their long-term safety require further evaluation. Regarding the prevention of the late bone loss leading to senile osteoporosis, there is now evidence that the reduction of the secondary hyperparathyroidism induced by calcium and vitamin D insufficiencies through the administration of calcium and vitamin D supplements significantly decreases the hip fracture incidence. There is no general consensus about the efficacy of treatment for established osteoporosis with fractures. Fluoride salts have proven their direct stimulating effects on bone formation; dosage must be moderate, and the duration of treatment should be limited to 2-3 years in order not to impair the quality of the new bone. Cyclical therapy with etidronate induces beneficial effects on bone mass in the spine, but its effect on the vertebral fracture rate is not yet established. The new bisphosphonates seem to be promising for the management of osteoporosis. Several other agents such as growth factors, silicon derivatives and strontium salts are in various stages of testing. The new definition of osteoporosis proposed by a WHO study group, no longer based on the fracture but on a low bone mass, is of major interest, because it should make possible to have a more effective therapeutic approach, before the occurrence of an irreversible degree of bone loss.