Effect of diosgenin, a steroidal sapogenin, on the rat skeletal system.

Diosgenin is a steroidal sapogenin present in fenugreek and Dioscorea spp. as glycosides (saponins). Diosgenin has already been reported to inhibit osteoclastogenesis and to stimulate osteogenic activity of osteoblastic cells in vitro, and to exert some antiosteoporotic effects in rats in vivo. The aim of the present study was to investigate the effects of diosgenin administration on the skeletal system of rats with normal estrogen level and with estrogen deficiency induced by bilateral ovariectomy. The experiments were carried out on 3-month-old non-ovariectomized and ovariectomized Wistar rats, divided into control rats and rats receiving diosgenin (50 mg/kg p.o. daily) for 4 weeks. Serum bone turnover markers, bone mass and mineralization, histomorphometric parameters and mechanical properties were studied. Diosgenin improved some investigated parameters in both non-ovariectomized and ovariectomized rats, in which estrogen deficiency induced osteoporotic changes. Diosgenin increased compact bone formation and probably inhibited cancellous bone resorption, which led to improvement of mechanical properties of compact and cancellous bone. In conclusion, this in vivo study demonstrated that diosgenin may be one of sparse compounds increasing bone formation.

Unfavorable effect of trigonelline, an alkaloid present in coffee and fenugreek, on bone mechanical properties in estrogen-deficient rats.

SCOPE: Trigonelline (1-methylpyridinium-3-carboxylate), an alkaloid present in coffee and fenugreek seed, has been reported to exhibit phytoestrogenic activity. The aim of the present study was to investigate the effects of trigonelline on bone mechanical properties of rats with normal estrogen level and estrogen deficiency (developing osteoporosis). METHODS AND RESULTS: The experiments were performed on 3-month-old nonovariectomized and ovariectomized (estrogen-deficient) Wistar rats, divided into control rats and rats receiving trigonelline (50 mg/kg p.o. daily) for 4 weeks. The ovariectomy was performed 7-8 days before the start of trigonelline administration. Serum bone turnover markers and bone mineralization, as well as mechanical properties of the tibial metaphysis, femoral diaphysis, and femoral neck were examined. Estrogen deficiency caused worsening of bone mineralization and mechanical properties of the tibial metaphysis, as well as increases in bone turnover markers. Administration of trigonelline did not affect the investigated parameters in nonovariectomized rats, but it worsened the mineralization and mechanical properties of cancellous bone in ovariectomized rats. CONCLUSION: Unfavorable effects of trigonelline on the skeletal system depended on the estrogen status. They were observed only in cancellous bone of estrogen-deficient rats.

Favorable effect of moderate dose caffeine on the skeletal system in ovariectomized rats.

SCOPE: Caffeine, a methylxanthine present in coffee, has been postulated to be responsible for an increased risk of osteoporosis in coffee drinkers; however, the data are inconsistent. The aim of the present study was to investigate the effects of a moderate dose of caffeine on the skeletal system of rats with normal and decreased estrogen level (developing osteoporosis due to estrogen deficiency). METHODS AND RESULTS: The experiments were carried out on mature nonovariectomized and ovariectomized Wistar rats, divided into control rats and rats receiving caffeine once daily, 20 mg/kg p.o., for 4 wk. Serum bone turnover markers, bone mass, mass of bone mineral, calcium and phosphorus content, histomorphometric parameters, and bone mechanical properties were examined. Caffeine favorably affected the skeletal system of ovariectomized rats, slightly inhibiting the development of bone changes induced by estrogen deficiency (increasing bone mineralization, and improving the strength and structure of cancellous bone). Moreover, it favorably affected mechanical properties of compact bone. There were no significant effects of caffeine in rats with normal estrogen levels. CONCLUSION: In conclusion, results of the present study indicate that low-to-moderate caffeine intake may exert some beneficial effects on the skeletal system of mature organisms.

Alendronate prevents development of the skeletal changes induced by azathioprine in rats.

Immunosuppressive drugs are known to disturb bone remodeling. Azathioprine (AZA) is a potent immunosuppressive drug, but its effect on the skeletal system has not been reported so far. The aim of the present study was to investigate the effect of AZA on the rat bone remodeling, and the effect of alendronate on development of skeletal changes induced by AZA. The experiments were carried out on 3-month-old male Wistar rats, divided into the following groups: C - control rats (distilled water), AZA - azathioprine, ALN - alendronate, AZA + ALN - azathioprine and alendronate. Azathioprine (4 mg/kg po), alendronate (3 mg/kg po) and distilled water (2 ml/kg po) were administered once daily for 28 days. Bone remodeling was estimated based on quantitative and histomorphometric evaluation of the tibia and femur, and the mechanical properties of the femur and femoral neck. AZA at a dose of 4 mg/kg for 28 days induced bone remodeling disorders, inhibiting bone formation and mineralization. Alendronate prevented the development of skeletal changes caused by AZA administration, inhibiting bone resorption and increasing bone mineralization.

Do effects of propranolol on the skeletal system depend on the estrogen status?

BACKGROUND: Propranolol, a nonselective ß-adrenergic receptor antagonist, was reported to favorably affect the skeletal system in different animal models. The aim of the study was to investigate whether the effects of propranolol on the skeletal system depend on the estrogen status. METHODS: The in vivo experiments were carried out on the following groups of mature female Wistar rats: sham-operated control rats, sham-operated rats receiving propranolol, ovariectomized (OVX) control rats, OVX rats receiving propranolol, OVX rats receiving estradiol, OVX rats receiving estradiol and propranolol. Propranolol hydrochloride (10 mg/kg po) and/or estradiol (0.1 mg/kg po) were administered daily for 4 weeks. Bone mass, mineral and calcium content, macrometric and histomorphometric parameters, and mechanical properties were examined. In vitro, effects of estradiol and propranolol on the formation of mouse osteoclasts and on the mRNA expression of genes related to osteoclastogenesis, bone formation and mineralization, as well as adrenergic and estrogen signalling in mouse osteoblasts were investigated. RESULTS AND CONCLUSION: Propranolol exerted some favorable effects on the rat skeletal system in vivo, independently of the estrogen status. However, in vitro studies indicated a possibility of some antagonistic relations between the estradiol and propranolol effects.

Proton pump (H+/K+-ATPase) inhibitors weaken the protective effect of alendronate on bone mechanical properties in estrogen-deficient rats.

BACKGROUND: Alendronate can induce esophagitis and stomach ulceration requiring the concurrent use of drugs which decrease HCl production. The aim of the present study was to investigate the effect of concurrent administration of proton pump inhibitors, omeprazole or pantoprazole, and alendronate on the mechanical properties of long bones in bilaterally ovariectomized (OVX) rats. METHODS: The experiments were carried out on 3-month-old Wistar rats, divided into following groups: non-ovariectomized control rats, OVX control rats, OVX rats administered omeprazole or pantoprazole, OVX rats administered alendronate, OVX rats administered alendronate and omeprazole or pantoprazole. The drugs were administered to the rats for 28 days: alendronate at a dose of 3mg/kg po, omeprazole or pantoprazole at a dose of 3mg/kg ip. Mechanical properties of tibialmetaphysis, femoral diaphysis and femoral neck were assessed. Bone macrometric parameters, mass and mass of bone mineral were also examined in the tibia and femur. RESULTS: Estrogen deficiency caused development of osteopenia with significant worsening of bone mechanical properties. Alendronate counteracted the deleterious changes in bone mechanical properties of the tibial metaphysis and femoral neck induced by estrogen deficiency. Pantoprazole worsened mechanical properties of the tibia in estrogen-deficient rats. Omeprazole or pantoprazole administered concurrently with alendronate attenuated the effect of alendronate on mechanical properties of the tibial metaphysis and femoral neck in ovariectomized rats. The unfavorable effect of pantoprazole was stronger than that of omeprazole. CONCLUSION: Proton pump inhibitors weakened the protective effect of alendronate on bone mechanical properties in estrogen-deficient rats.

Bone remodeling after administration of proton pump (H+/K+-ATPase) inhibitors and alendronate in ovariectomized rats.

During osteoporosis therapy with alendronate, esophagitis and stomach ulceration may occur, requiring the concurrent use of drugs which decrease gastric juice production. The aim of the present study was to investigate the effect of concurrent administration of proton pump (H+/K+ATP-ase) inhibitors: omeprazole or pantoprazole and alendronate on bone remodeling in ovariectomized rats. The experiments were carried out on 3-month-old Wistar rats, divided into following groups (n = 8-10): NOVX - non-ovariectomized control rats; OVX - ovariectomized control rats; OVX + alendronate; OVX + omeprazole; OVX + omeprazole + alendronate; OVX + pantoprazole; OVX + pantoprazole + alendronate. The drugs were administered for 28 days: alendronate (3 mg/kg p.o.), omeprazole or pantoprazole (3 mg/kg i.p.). Bone remodeling was estimated based on histomorphometric evaluation of the tibia (endosteal and periosteal transverse growth and the osteoid width, transverse cross-section surface of the diaphysis and of the marrow cavity) and the femur (width of trabeculae in the distal epiphysis and metaphysis). Bone mass/100 g body mass and mass of bone mineral/100 mg bone mass in the tibia and femur were also determined. Pantoprazole stronger than omeprazole intensified bone remodeling disorders caused by estrogen deficiency in ovariectomized rats. Bone remodeling disorders were the result of intensification of bone resorption with concurrent inhibition of bone formation and mineralization. Pantoprazole, and to lesser extent omeprazole, weakened the preventive effect of alendronate on bone remodeling in ovariectomized rats.

Effects of vigabatrin on the skeletal system of young rats.

Long-term administration of antiepileptic drugs may be connected with the risk of impairment of bone remodeling. Contrary to the reported unfavorable effect of classic antiepileptic drugs on bone metabolism, little is known about the effect of the next generation antiepileptics on bone remodeling. The aim of the present study was to investigate the effect of vigabatrin, as a representative of new antiepileptics, on the skeletal system of young rats, in comparison with conventional drugs--phenytoin and valproic acid. The experiments were carried out on 4-week-old male Wistar rats, divided into the control rats, and rats receiving vigabatrin (250 mg/kg p.o. daily), phenytoin (20 mg/kg p.o. daily) or valproic acid (250 mg/kg p.o. daily). The drugs were administered for 28 days. Histomorphometric parameters of the tibia and femur, mechanical properties of the femur, and bone length, diameter, mass, content of mineral substances and calcium were examined. After administration of phenytoin or valproic acid, the investigated bone parameters did not significantly differ from those observed in the control rats. Administration of vigabatrin caused profound impairment of bone accrual with impairment of bone histomorphometric parameters, along with the significant decrease in the body mass gain.

Effects of propranolol on the development of glucocorticoid-induced osteoporosis in male rats.

Glucocorticoid-induced osteoporosis is the most frequently occurring type of secondary osteoporosis. Antagonists of ß-adrenergic receptors are now considered to be potential drugs under investigation for osteoporosis. The aim of the present study was to investigate the effects of propranolol, a nonselective ß-receptor antagonist, on the skeletal system of mature male rats and on the development of bone changes induced by glucocorticoid (prednisolone) administration. The experiments were performed on 24-week-old male Wistar rats. The effects of prednisolone 21-hemisuccinate sodium salt (7 mg/kg, sc daily) or/and propranolol hydrochloride (10 mg/kg, ip daily) administered for 4 weeks on the skeletal system were studied. Bone and bone mineral mass in the tibia, femur and L-4 vertebra, length and diameter of the long bones, mechanical properties of tibial metaphysis, femoral diaphysis and femoral neck, bone histomorphometric parameters and turnover markers in serum were determined. Prednisolone-induced unfavorable skeletal changes led to disorders in bone mechanical properties. Propranolol not only did not improve bone parameters, but even caused deleterious effects on the skeletal system. Concurrent administration of propranolol with prednisolone did not counteract the changes induced by prednisolone. The results of this study may help to understand the equivocal results of human studies on the effects of ß-blockers on the skeletal system. It is possible that the drugs exert biphasic effects on the skeletal system, both favorable and deleterious, depending on the dose or individual susceptibility.

Fenoterol did not enhance glucocorticoid-induced skeletal changes in male rats.

Glucocorticoids and ß(2)-adrenergic receptor agonists are the most commonly used drugs in the treatment of asthma. Both therapies are potentially dangerous to the skeletal system. The aim of the present study was to investigate the effects of fenoterol, a ß(2)-receptor agonist, on the development of bone changes induced by glucocorticoid (prednisolone) administration in mature male rats. The experiments were carried out on 24-week-old male Wistar rats. The effects of prednisolone 21-hemisuccinate sodium salt (7 mg/kg s.c. daily) or/and fenoterol hydrobromide (1.4 mg/kg i.p. daily), administered for 4 weeks, on the skeletal system were studied. Bone turnover markers, geometric parameters, mass, mass of bone mineral in the tibia, femur and L-4 vertebra, bone histomorphometric parameters and mechanical properties of tibial metaphysis, femoral diaphysis and femoral neck were determined. Both prednisolone and fenoterol had damaging effects on the skeletal system of mature male rats. However, concurrent administration of fenoterol and prednisolone did not result in the intensification of the deleterious skeletal effect of either drug administered separately.

Does maternal treatment with zidovudine affect changes in mandibles of newborns? Laser induced fluorescence study.

The influence of antiretroviral drug zidovudine treatment during pregnancy on mandible development in newborn rats was studied. The fluorescence of mandibles from 7-, 14- and 28-days old individuals was measured by means of fiber-optical fluorescence analyzer with 407 nm laser excitation. Obtained results revealed disturbing effect of maternal zidovudine administration on mandible fluorescence intensity which should decrease with bone development. Small changes in fluorescence of porphyrin forms are maintaining in the first month of newborns life while the changes observed in 440-585 nm range disappear.

Optical and X-ray fluorescence spectroscopy studies of bone and teeth in newborn rats after maternal treatment with indinavir.

An experiment estimating influence of antiviral drug indinavir treatment during pregnancy on bones and teeth development in newborn rats was performed. Two different fluorescence noninvasive spectroscopy techniques, i.e. laser (407 nm)-induced fluorescence method to characterize the organic fluorescent molecules and X-ray fluorescence analysis to determine mineral components were used to study the surface response of femur, mandible and incisor during their formation in the first month of a rat's life. Differences in autofluorescence depending on the form of the bone were observed on the basis of the emission from enamel in 7-, 14- and 28-day-old newborn rats. The dependence between decrease in intensity of fluorescence and increase in mineralization with age in newborn rats was observed. An enhancement of the autofluorescence and a decrease in the concentration of Ca as a main element, as well as disturbances in the concentration of Zn as trace element were observed for bone as well as teeth in newborns during the first month of their life after maternal administration of indinavir (500 mg kg(-1) p.o.) in comparison with the control group. The results indicate that indinavir causes a delay in development of the skeleton and teeth in newborn rats.

Effect of low-dose tacrolimus coadministered with raloxifene on the skeletal system in male rats.

Tacrolimus is an immunosuppressive drug, used to prevent organ transplant rejection. Immunosuppresants are known to unfavorably affect the osseous system. However, in our previous study on bone histomorphometric parameters we observed that low-dose tacrolimus intensified bone formation. The aim of the present study was to investigate the effects of low-dose tacrolimus on bone mechanical properties and mineralization in male rats. The effects of concurrent administration of tacrolimus and raloxifene were also studied. Raloxifene is a selective estrogen receptor modulator, used in the prevention and treatment of postmenopausal osteoporosis. In male rats raloxifene induces moderate intensification of bone mineralization. The experiments were carried out on mature male Wistar rats. The animals were divided into four groups (n = 7): control rats, rats treated with tacrolimus (0.3 mg/kg po), rats treated with raloxifene hydrochloride (5 mg/kg po) and rats treated with tacrolimus and raloxifene hydrochloride concurrently at abovementioned doses. The drugs were administered daily for 4 weeks. Body mass, bone mass and bone mineral content in the tibia, femur and L-4 vertebra, as well as mechanical properties of the whole femur (extrinsic stiffness, ultimate and breaking load, deformation caused by the applied load) and the femoral neck (load at fracture) were examined. Administration of tacrolimus at a dose of 0.3 mg/kg po for 4 weeks did not affect bone mechanical properties and mineralization. Concurrent administration of tacrolimus and raloxifene resulted in changes similar to those caused by raloxifene alone (statistically significant increases in the bone mass/body mass ratio, bone mineral content/body mass ratio and bone mineral content/bone mass ratio in comparison with the control rats, and no effect on bone mechanical properties). Results of the present study do not support the hypothesis that tacrolimus may be useful as a drug stimulating bone formation in skeletal diseases.

A comparative study of the effects of genistein, estradiol and raloxifene on the murine skeletal system.

Genistein, a major phytoestrogen of soy, is considered a potential drug for prevention and treatment of postmenopausal osteoporosis. The aim of the present study was to compare the effects of genistein, estradiol and raloxifene on the skeletal system in vivo and in vitro. Genistein (5 mg/kg), estradiol (0.1 mg/kg) or raloxifene hydrochloride (5 mg/kg) were administered daily by a stomach tube to mature ovariectomized Wistar rats for 4 weeks. Bone mass, mineral and calcium content, macrometric parameters and mechanical properties were examined. Also the effects of genistein, estradiol and raloxifene (10(-9)-10(-7) M) on the formation of osteoclasts from neonatal mouse bone marrow cells and the activity of osteoblasts isolated from neonatal mouse calvariae were compared. In vivo, estrogen deficiency resulted in the impairment of bone mineralization and bone mechanical properties. Raloxifene but not estradiol or genistein improved bone mineralization. Estradiol fully normalized the bone mechanical properties, whereas genistein augmented the deleterious effect of estrogen-deficiency on bone strength. In vitro, genistein, estradiol and raloxifene inhibited osteoclast formation from mouse bone marrow cells, decreasing the ratio of RANKL mRNA to osteoprotegerin mRNA expression in osteoblasts. Genistein, but not estradiol or raloxifene, decreased the ratio of alkaline phosphatase mRNA to ectonucleotide pyrophosphatase phosphodiesterase 1 mRNA expression in osteoblasts. This difference may explain the lack of genistein effect on bone mineralization observed in ovariectomized rats in the in vivo study. Concluding, our experiments demonstrated profound differences between the activities of genistein, estradiol and raloxifene towards the osseous tissue in experimental conditions.

Effects of raloxifene on development of the methotrexate-induced changes in bone mechanical properties of male rats.

Methotrexate, a cytostatic and immunosuppressive drug, has been reported to deteriorate the osseous system. Raloxifene, a selective estrogen receptor modulator, is used in the prevention and treatment of postmenopausal osteoporosis. There is a lack of data on possible ways of preventing the unwanted skeletal effects of prolonged immunosuppressive therapy. The aim of the present study was to investigate the effects of raloxifene on mechanical properties of the femur in male rats administered methotrexate. The experiments were carried out on mature male Wistar rats, which were divided into 6 groups: controls, rats administered raloxifene hydrochloride (5 mg/kg p.o.), rats administered methotrexate (0.5 mg/kg p.o. or i.m.), and rats administered raloxifene hydrochloride (5 mg/kg p.o.) plus methotrexate (0.5 mg/kg p.o. or i.m.). Raloxifene was administered for 28 days and methothrexate was administered for the first 10 days of the experiment. After 28 days of drug administration, mechanical parameters of the whole femur were determined: the extrinsic stiffness, the ultimate load and the breaking load, deformation caused by the ultimate and breaking loads, and the load causing fracture of the femoral neck. Additionally, the mass of isolated femurs and their mineral and calcium content were determined. Intragastrically or intramuscularly administered methotrexate impaired the endurance of the tested bones. Administration of raloxifene alone had no significant effects on the mechanical parameters of the femur. Administration of raloxifene resulted in a reduction of the adverse changes in the osseous system induced by methotrexate. Concluding, the experiments demonstrated a protective action of raloxifene against the effects of methotrexate on the osseous system in male rats.

Raloxifene similarly affects the skeletal system of male and ovariectomized female rats.

Raloxifene, a selective estrogen receptor modulator, is used for prevention and treatment of osteoporosis in postmenopausal women. Raloxifene use in male subjects is increasingly considered and a few clinical studies of its effect on bone turnover have already been performed. The aim of the present study was to investigate the effects of raloxifene on the skeletal system of healthy mature male rats. The experiments were performed on mature male Wistar rats, treated daily with raloxifene hydrochloride at a dose of 5 mg/kg po for 4 weeks. Bone mass, mineral content, macrometric and histomorphometric parameters, as well as mechanical properties were examined. For comparison, we also studied the effects of raloxifene on the skeletal system of mature ovariectomized female rats. Raloxifene administration to male rats caused statistically significant increases in the bone mass/body mass ratio, bone mineral content/body mass ratio and bone mineral content/bone mass ratio in comparison with those of the control rats. Bone mechanical properties and most of histomorphometric parameters remained unchanged. Also in ovariectomized female rats, raloxifene administration caused statistically significant increases in the bone mass/body mass ratio, bone mineral content/body mass ratio and bone mineral content/bone mass ratio in comparison with the results obtained in the ovariectomized control rats, to the level of sham-operated control rats. Moreover, raloxifene counteracted the development of changes in histomorphometric parameters caused by ovariectomy in female rats, but did not significantly affect bone mechanical properties. In conclusion, the changes induced by raloxifene in the skeletal system of male rats were similar to those induced by the drug in ovariectomized female rats.

Effect of pamidronate on the action of catecholamines on blood pressure in the marrow cavity of long bones in rats with prednisolone-induced osteoporosis.

Pamidronate is a representative of bisphosphonates, which are effectively used in the treatment of bone diseases. Although a number of properties of pamidronate have been recognized which influence the metabolic process in bones, the issue of the effect of bisphosphonates on the function of blood circulation and autonomic nervous system in osteoporotic bones remains open. In order to clarify this problem, the present study concentrated on the effects of pamidronate on catecholamine action on blood pressure in the marrow cavity in rats with prednisolone-induced osteoporosis. The animals were divided into 3 groups: I - control rats; II - rats which were given prednisolone at the dose of 5 mg/kg, im, for 3 weeks; III - rats which were given prednisolone at the dose of 5 mg/kg, im and pamidronate at the dose of 3 mg/kg, sc together, for 3 weeks. The experiments demonstrated that rats with prednisolone-induced osteoporosis displayed a decreased blood pressure in the marrow cavity. In addition, a disordered action of catecholamines (norepinephrine and epinephrine) on blood pressure in the marrow cavity of osteoporotic bone was observed. Pamidronate administration in osteoporotic rats resulted in smaller increases in the blood pressure caused by norepinephrine and epinephrine in the marrow cavity of long bones.

Effects of catecholamines on the intramedullary pressure in the femur in rats with prednisolone-induced osteoporosis.

Osteoporosis is a metabolic bone disease characterized by low bone mass, impaired micro-architecture and susceptibility to fracture. Osteoporosis may be, inter alia, a result of a long-term glucocorticosteroid therapy, e.g. with prednisolone. Although a number of properties of prednisolone in influencing bone metabolism have been recognized, the effect of prednisolone-induced osteoporosis on the function of blood circulation and autonomic nervous system in bones remains open. In order to clarify this problem, the present study concentrated on the effects of catecholamines on intramedullary pressure in rats with prednisolone-induced osteoporosis. Prednisolone was administered to male Wistar rats at the doses of 5 mg/kg im, for 3 weeks. Norepinephrine, epinephrine, isoprenaline as well as adrenoceptor antagonists (phentolamine and propranolol) were administered to the controls and to the rats with prednisolone-induced osteoporosis. The examinations demonstrated that rats with prednisolone-induced osteoporosis displayed a decreased intramedullary pressure. In addition, a disordered effect of catecholamines on intramedullary pressure of osteoporotic bone was observed.

Effects of catecholamines on blood pressure in the femoral bone marrow cavity in ovariectomized rats.

Menopausal women display changes in the osseous tissue (osteoporosis, pathologic fractures) and disorders in the function of cardiovascular system (hypertension, cardiovascular disease, arteriosclerosis, calcification). Additionally, interdependence was observed between the loss of osseous tissue and disordered circulation, but the mechanism of the interdependence has never been fully recognized. In order to clarify this problem, the present study concentrated on the effects of catecholamines on blood pressure in the femoral bone marrow cavity in ovariectomized rats. The Ficat-Arlet method was used to examine blood pressure in marrow cavity. Norepinephrine, epinephrine, isoprenaline as well as adrenoceptor antagonists (phentolamine and propranolol) were administered to the controls and the ovariectomized rats. The examinations demonstrated that ovariectomized rats displayed decreased blood pressure in the marrow cavity. In addition, an intensified effect of catecholamines on blood pressure in the marrow cavity of osteoporotic bone in ovariectomized rats was observed.

Raloxifene does not affect the changes in bone histomorphometric parameters induced by low dose tacrolimus in male rats.

Raloxifene is a selective estrogen receptor modulator. The drug reduces bone loss and prevents fractures in postmenopausal women. Tacrolimus, an immunosuppressant, is used to prevent organ transplant rejection. The effect of raloxifene and tacrolimus on the osseous bone in men has not been exhaustively determined. To study the effects of raloxifene, tacrolimus as well as concurrent administration of raloxifene and tacrolimus on the osseous tissue in male rats, a preliminary assessment of the drug action on histomorphometric parameters of rat bones was made. The experiments were carried out on mature male Wistar rats. The animals were divided into six groups, 7 animals each: I--control rats; II--rats which were administered raloxifene (5 mg/kg po daily); III-- rats which were administered tacrolimus (0.3 mk/kg po daily); IV - rats which were administered tacrolimus (0.6 mg/kg po daily; V-- rats which were administered raloxifene (5 mg/kg po daily) and tacrolimus (0.3 mg/kg po daily); VI - rats which were administered raloxifene (5 mg/kg po daily) and tacrolimus (0.6 mg/kg po daily). The drugs were administered for 4 weeks. Body mass, macrometric parameters of the tibia, femur and L-4 vertebra, histomorphometric parameters of tibia (transverse growth, width of osteoid, area of the transverse cross section of bone marrow cavity and cortical bone), and the femur (width of trabeculae, width of epiphyseal cartilage) were examined. The action of raloxifene in male rats was demonstrated through increased width of osteoid. An increased traverse growth of bone and osteoid width as well as transverse cross section of the cortical bone and the marrow cavity and increased thickness of trabeculae were observed in male rats receiving tacrolimus at 0.3 mg/kg. The administration of tacrolimus at 0.6 mg/kg resulted in increased traverse growth of bone and increased thickness of osteoid, whereas the thickness of trabeculae remained unaffected. The results obtained in the rats administered concurrently raloxifene and tacrolimus (at 0.3 mg/kg or at 0.6 mg/kg) were similar to those obtained in the group of rats receiving tacrolimus at 0.3 mg/kg. It seems that the most valuable in entire experimental system of the study are the results obtained in the group receiving tacrolimus at 0.3 mg/kg po, which are indicative of intensified bone remodeling processes with dominant the bone formation process.