Dihydrotestosterone prevents glucocorticoid-negative effects on fetal rat metatarsal bone in vitro.

The effects of dihydrotestosterone (DHT) on glucocorticoid-pretreated fetal rat long bone were studied in an in vitro culture system. First, dose-response curves of corticosterone, hydrocortisone, and dexamethasone were studied at several concentrations. Then, hydrocortisone (H) at 10(-5) M was selected for the second part of the study, as it slackened rudiment mineralization (104 +/- 16% of the initial dark zone vs. 141 +/- 9% in control bones), as well as its lengthening (140 +/- 4% of the harvesting day length vs. 160 +/- 1% in control bones), by both inhibition of cell proliferation and stimulation of resorption. On the contrary, in H-pretreated metatarsal bones, DHT (10(-7) M) partly limited slackening of mineralization (124 +/- 5%) and lengthening (153 +/- 2%). Moreover, a control-like cell proliferation was re-established and resorption holes were filled in. Thus, in this study, DHT partly limited hydrocortisone-induced impairment of fetal rat metatarsal bone development.

Influence of age and hormonal treatment on intestinal absorption of magnesium in ovariectomised rats.

This study was designed to assess the effect of age, ovariectomy and estrogen treatment on the absorption and the balance of Mg in the rat. Three groups of fifteen 6- (mature), 12- (old), and 30-month-old female rats (senescent), fed a diet containing 1.5 g of Mg/kg were used in the present study. Within each group, 10 rats were surgically ovariectomized (OVX). From day 2 until day 60 after OVX, they were s.c. injected with either solvant or 17 beta-estradiol (E: 10 mg/kg bw/48 h, n = 5). Five other rats were sham operated (SH, n = 5) and received solvent alone. Animals were pair fed 6 g/100 g bw/day and distilled water was available ad libitum. Food intake, urine and feces from each individual rat were measured 1 day per week, during the last 5 weeks. The results clearly showed that apparent Mg absorption (per cent) was not significantly altered with aging. Moreover, whatever the age, neither OVX nor E treatment had any significant effect on Mg apparent absorption.

Peripheral injection of growth hormone stimulates protein intake in aged male and female Lou rats.

It is well established that growth hormone (GH) induces growth rate and food efficiency and stimulates protein accretion in young mammals. Senescence is characterized by metabolic and hormonal disorders, particularly a decrease in protein turnover, which could be correlated to a decrease in GH and insulin-like growth factor I (IGF-I) secretion. We have shown that body weight, protein intake, and IGF-I plasma levels are greatly decreased with aging in Lou/C rats, particularly in males. In order to specify the GH effect on protein intake during aging, males and females (6, 19, and 24 mo) placed on a self-selection regimen were injected daily with a physiological dose of human GH (0.023 mg/rat sc). No GH effect on caloric intake was observed. Nevertheless, GH treatment stimulated body weight in older rats. It also increased protein intake in females and older males (19-24 mo). This stimulating effect was positively correlated with the degree of weight loss in senescent rats, suggesting that the decrease in protein intake observed with aging could be a marker of senescence.

[Calcitonin and stanniocalcin. Particular aspects of the endocrine regulation of phospho-calcium metabolism in mammals and fish]. / Calcitonine et stanniocalcine. Particularités de la régulation endocrinienne du métabolisme phospho-calcique chez les mammifères et les poissons.

The hypocalcemic and hypophosphatemic peptide calcitonin (CT) is secreted by mammalain thyroid parafollicular cells and fish ultimobranchial body. Over a dozen species of CTs have been cloned and/or sequenced. They can be separated into three classes based on structural and biological similarities: teleost/avian, artiodactyl, and human/rat. In mammals, CT exerts its anti-hypercalcemic and hypophosphatemic effects by inhibiting osteoclastic bone resorption and renal tubular phosphate reabsorption, respectively. CT receptors (CTRs) are members of a subfamily of seven-transmembrane domain, G protein-coupled receptors that include those for several other peptide hormones. Basic amino acid substitutions within the CT molecule enhance potency, probably by conferring a helical structure to the peptide. This might explain the enhanced potency of fish CTs for mammalian CTRs. The presence and secretion of salmon CT-like immunoreactive material have been described in both the murine and human central nervous systems, which possess CTRs. These findings are consistent with a role for this peptide acting as a neurotransmitter in mammals. Stanniocalcin (STC) is another hypocalcemic hormone originally identified in fish. In fish STC exerts its anti-hypercalcemic effect by regulating calcium and phosphate transports by the gills, intestine and kidney. Although fish ultimobranchial cells are much less responsive to the secretagogic effects of Ca2+ than mammalian parafollicular cells, the secretion of both CT and STC are positively regulated by extracellular calcium. STC has also been recently identified in humans and rats. It is released by some renal tubular cells and might play a role in the regulation of phosphate metabolism. Nevertheless, the true physiologic roles for CT in fish and STC in mammals, respectively, remain unknown.

Influence of aging on cortical and trabecular bone response to estradiol treatment in ovariectomized rats.

Three groups (n = 15/group) of 6-, 12- and 30-month-old (mature, old and senescent animals, respectively) female Wistar rats on a diet (6 g/100 g BW/ day) containing 0.8% calcium and 0.8% inorganic phosphorus were studied. Within each group, 10 rats were ovariectomized surgically and 5 injected s.c. with 17 beta-estradiol (E rats, 10 micrograms/kg BW/48 h) and 5 with solvent alone (OVX rats) from day 2 until day 60 after ovariectomy. Five other rats were sham-operated (SH rats) and received solvent only. All rats were killed by exsanguination 60 days after ovariectomy. Neither ovariectomy nor estradiol treatment had a significant effect upon tibial mechanical properties in 6-, 12- and 30-month-old animals. Bone mineral density (BMD) and bone mineral content (BMC) of the distal femur and BMC of the whole femur were decreased by ovariectomy in 6- and 12-month-old rats, but were not different in the SH and E groups. In senescent animals, in which the lowest BMD and BMC were measured, estradiol treatment was more effective in increasing these parameters than in adult and old rats. Image analysis of the distal femoral diaphysis showed that estradiol treatment prevented trabecular bone loss induced by senescence and/or ovariectomy. In each group, urinary deoxypyridinoline excretion and plasma osteocalcin concentration were higher in the OVX animals than in the controls, consistent with increased bone turnover in the estrogen-deficient state. Both biochemical turnover markers were reduced in the estrogen-treated groups. These results indicate that 17 beta-estradiol is particularly effective at preventing high-turnover-induced osteopenia in 30-month-old animals.

Influence of treadmill running on femoral bone in young orchidectomized rats.

Forty 6-wk-old male Wistar rats weighing 308 +/- 24 g were divided into two groups. On day 0, the 20 animals in one group were surgically castrated and the other group was sham operated. Within each group, 10 rats were selected for treadmill running (60% maximal O2 consumption, 1 h/day, 6 days/wk for 15 wk). The 20 sedentary rats were used as controls. At the time the rats were killed (day 105), running had no significant effect on femoral mechanical properties either in castrated or in sham-operated rats. Femoral bone density was lower in orchidectomized than in sham-operated rats. Nevertheless, it was higher in exercised than in sedentary rats. Femoral Ca content paralleled changes in bone density. Treadmill running had no significant effect on plasma osteocalcin concentration but inhibited the increase in urinary deoxypyridinoline excretion observed in castrated rats. Image analysis (measured at the distal femoral diaphysis) revealed that these effects mainly resulted from decreased trabecular bone resorption in castrated exercised rats.

Influence of ovariectomy and estradiol treatment on calcium homeostasis during aging in rats.

Study was carried out an Wistar female rats to evaluate the consequences of ovariectomy and 17 beta-estradiol substitutive treatment during aging on bone. Ca metabolism and calciotropic hormones. Three groups of fifteen rats, mature, old and senescent (4-, 10-, and 28 month-old) female were fed a diet (6 g/100 g BW/day) containing 0.9% Ca and 0.8% Pi, Within each group, 10 rats were surgically ovariectomized (OVX). From day 1 until day 60 after OVX, they were subcutaneously injected with either 17 beta-estradiol (E: 10 micrograms/kg BW/48 h; n = 5) or with solvent alone (OVX; n = 5). Five other rats were sham operated (SH) and received solvent alone. Animals were put in balance 1 day per week to determine Ca and Pi intestinal apparent absorption and urinary pyridinium cross-links excretion was measured by HPLC. All rats were killed by exsanguination 60 days after OVX. Plasma was collected for measurement of intact parathyroid hormone (PTH), calcitonin (CT), insulin-like growth factor-1 (IGF-1), Ca and Pi. The success of OVX was confirmed at necropsy by observation of marked atrophy of the uterine horns. The right femur was collected, cleaned from adjacent tissue and used for mineral analysis. Despite correct matching for feeding, BW was significantly larger in 6 and 12 month-old OVX rats. OVX and 17 beta-estradiol had no significant effect upon plasma Ca, Pi and CT concentrations. Aging is associated with increased circulating PTH levels (pg/ml) (SH-6 months: 50.8 +/- 12.6; 12 months: 219.1 +/- 34.9; 30 months: 158.7 +/- 23.5; P < 0.05). Urinary and fecal Ca and Pi excretion in senescent animals were higher than in adult or old rats, thus resulting in a drastic fall in both intestinal apparent absorption and retention of Ca and Pi in 30 month-old animals. In each group, urinary pyridinium cross-links excretion and plasma osteocalcin concentration were higher in the OVX animals than in the controls, consistent with increased bone turnover in the estrogen deficient state. Both biochemical turnover markers were reduced in the estrogen-treated groups. In the same way, OVX increased and estrogen decreased the plasma IGF-1 levels. We conclude that 17 beta-estradiol prevents high turnover-induced osteopenia even in 30 month-old rats.

Influence of ovariectomy on bone metabolism in very old rats.

Twenty-five 30-month-old Lou rats fed a diet (6 g/100 g BW/day) containing 0.9% Ca and 0.8% Pi were divided into five groups. Four groups were surgically ovariectomized. From day 2 until day 29 after ovariectomy, they were S.C. injected either with 17 beta estradiol (E2; 10 micrograms/kg BW/48 hours) or progesterone (P; 140 micrograms/kg BW/48 hours), or 17 beta estradiol + progesterone (E2P) at the same doses, or solvent alone (OVX). The fifth group was sham operated (SH) and injected with solvent. Urine was collected in metabolic cages from day 24 to 29 after ovx, and urinary pyridinoline (PYD) and deoxypyridinoline (DPD) excretion (markers of bone resorption) was measured by HPLC. All animals were killed 30 days after ovariectomy. Serum was then collected for measurement of osteocalcin (OC), alkaline phosphatase (ALP), parathyroid hormone (PTH), and calcitonin (CT). At necropsy, the success of ovariectomy was checked by marked atrophy of the uterine horns. Left and right femur were harvested for densitometric and mineral analysis, respectively. Ovariectomy had no significant effect upon plasma calcium and PTH concentrations. E2 or E2P treatment significantly increased plasma PTH and calcitonin concentrations. Plasma OC concentrations and ALP were not different in any of the groups. In contrast, urinary excretion of PYD and DPD was higher in OVX than in SH rats. Bone mineral density (BMD) of the distal femur was decreased by OVX, but was not different in the E2P and SH groups. A similar pattern was observed for the mineral or Ca content of whole femur. Thus, OVX decreased BMD and bone mineral content (BMC) in very old female rats. Plasma OC concentration and ALP activity failed to demonstrate any significant effect of OVX, whereas PYD and DPD were elevated. These results suggest that bone resorption is increased in OVX rats, even when supplemented with E2 or P alone. However, no significant difference was observed between SH and OVX rats treated with supplementation of both E2 and P. Thus, in very old rats, a combination of E2 and P is much more effective than E2 or P alone to prevent bone loss following ovariectomy.

EB 1089, a calcitriol analogue, decreases fetal calcium content when injected into pregnant rats.

EB 1089 is a calcitriol analogue with low calcaemic activity, which inhibits parathyroid hormone-related peptide (PTHrP) secretion in rats implanted with the Leydig cell tumour H-500. We have studied its effect on maternal and fetal plasma PTHrP concentrations and on fetal calcium and phosphorus contents in rats. Three groups of six pregnant rats were injected I.P. daily with EB 1089 (0.10, 0.25 and 0.50 microgram kg-1 in groups 1, 2 and 3, respectively, from day 12 to day 20 of gestation). The control group received an equal volume of solvent alone. On day 21 of gestation the animals were anaesthetized with chloral hydrate and blood samples were taken. Fetuses were collected, weighed and ashed for Ca and P measurements. PTHrP concentrations were measured by radioimmunoassay (RIA) in maternal and fetal plasma. Calcium content (mg (g fetal wt)-1; mean +/- S.E.M.) in control fetuses was not different from that measured in fetuses from dams given the lowest dose of EB 1089, but was higher than that in fetuses from rats injected with EB 1089 at 0.25 microgram kg-1 (1.18 +/- 0.20; P < 0.05) or 0.50 microgram kg-1 (1.08 +/- 0.29; P < 0.05). There was no difference in fetal P content between any of the groups of rats. The PTHrP concentration (pg equivalents human PTHrP(1-34) fragment ml-1) in maternal plasma from control rats (1.70 +/- 0.50) was not different from that in maternal plasma of rats given the lowest dose of EB 1089 (1.44 +/- 0.63).(ABSTRACT TRUNCATED AT 250 WORDS)

[Animal models of post-menopausal osteoporosis]. / Modéles animaux d'ostéoporose post-ménopausique.

Osteoporosis is a disease characterized by low bone mass, microarchitectural deterioration of bone tissue leading to enhanced bone fragility, and a consequent increase in fracture risk. In humans estrogen deficiency following menopause is associated with a more or less intense osteopenia. In some subjects, such a decrease in bone mass induces osteoporosis. Several animal models (ovariectomized female dogs, pigs and monkeys) are used to study the etiology, prophylaxis and treatment for osteoporosis. Nevertheless, the changes in bone metabolism following estrogen deficiency are very similar in rats and humans. Thus, the ovariectomized rat is the most frequently used model for such studies.

Preserved bone mass in ovariectomized rats treated with parathyroid-hormone-related peptide (1-34) and (107-111) fragments.

The effect of synthetic human PTHrP (1-34) or (107-111) fragments on bone loss was studied in rats, one month after ovariectomy (OVX). Four groups of 7-8-month-old rats were treated sc daily for 13 d with PTHrP (1-34) or (107-111) at the dose of 1 or 3 nmol/100 g body weight. Sham-operated (SHO) and control OVX rats received solvent alone. In our conditions, at the lowest dose, neither (1-34) nor (107-111) fragments had any significant effect. However, at the dose of 3 nmol/100 g daily for 13 d both treatments significantly increased femoral dry weight, ash weight, Ca content and densitometry of the femur. The effect of PTHrP (1-34) mainly resulted from increased cortical and trabecular bone (% recovery: 98.25 and 105.23%, respectively). For the PTHrP (107-111) fragment, a positive effect was only demonstrated on the cortical bone (98.25% recovery). The results of this study demonstrate that both hPTHrP (1-34) and (107-111, osteostatin) fragments are positive for bone when administered at the dose of 3 nmol/100 g body weight/d for 13 d to adult OVX rats.