Separate and combined effects of growth hormone and parathyroid hormone on cortical bone osteopenia in ovariectomized aged rats.

The focus of this study is on whether cortical osteopenia occurs in ovariectomized aged female rats, and if so, whether growth hormone (GH) and parathyroid hormone (PTH) independently or together (GH+PTH) can rebuild the lost cortical bone. Tibio-fibula junction was analyzed by histomorphometry and peripheral quantitative computerized tomography (pQCT) densitometry. Significant loss of cortical bone area (Ct. BAr), cortical bone mineral content (Ct. BMC), cortical thickness (Ct. Th) and increase of endocortical perimeter occurred 4 months after ovariectomy. The rats were given GH, PTH, GH+PTH or vehicle for 2 months and sacrificed. GH, PTH and GH+PTH increased Ct. BAr, Ct. BMC, Ct. Th, periosteal perimeter, periosteal double-labeled perimeter, mineral apposition rate, and bone formation rate, but decreased marrow area. PTH and GH+PTH decreased endocortical perimeter, and increased endocortical double labeled perimeter and bone formation rate. In conclusion, ovariectomy induced cortical bone loss in aged rats by increasing endocortical bone resorption. Growth hormone increased periosteal bone formation, while PTH stimulated endocortical bone formation and in combination GH+PTH produced complementary effects thereby reversing osteopenia.

Analysis of the effects of growth hormone, exercise and food restriction on cancellous bone in different bone sites in middle-aged female rats.

The aim of this study is to determine the effects of growth hormone (GH), exercise (EX), GH+EX and food restriction on cancellous bone in middle-aged female rats. Female F344 rats aged 13 months were divided into (1) age-matched controls; (2) GH treated (2.5 mg/kg. 5 day/week); (3) EX (voluntary wheel running); (4) GH+EX; and (5) food restricted (FR) (fed 60% of the ad libitum food intake). The animals were treated for 18 weeks, at the end of which they were sacrificed. Cancellous bone and cortical bone in the fourth lumbar vertebra, proximal tibial metaphysis (PTM), distal femoral metaphysis (DFM) and femoral neck (NF) were analyzed using peripheral quantitative computerized tomography (pQCT) densitometry. Growth hormone increased cancellous bone area, cancellous bone mineral content, cortical bone area and cortical bone mineral content in the vertebra, PTM, DFM and NF. The tibial muscle wet weight was increased significantly after GH treatment. Exercise increased the cancellous bone area in the vertebra, PTM and DFM. Cortical bone area and cortical bone mineral content increased after EX in the vertebra, PTM, DFM and NF. No significant change was seen in the tibial muscle wet weight after EX. Growth hormone+EX increased cancellous bone area in the vertebra PTM and DFM but had no effect in neck of the femur. Cancellous bone mineral content, cortical bone area and cortical bone mineral content increased with GH+EX in the vertebra, PTM, DFM and NF. The tibial muscle wet weight was increased significantly with GH+EX. Food restriction decreased cancellous bone area and cancellous bone mineral content in all the bones studied. The decrease was statistically significant only at the distal femoral metaphysis. The tibial muscle wet weight decreased when compared with the age-matched control, but this decrease was not statistically significant. We conclude that the effect of the dose of GH used and the levels of voluntary wheel running EX used increased cancellous bone in intact rats; the effect of GH is much greater and different bones respond with varying intensities. The effects of combined treatment of GH and EX on cancellous bone are not always significantly higher than those of GH alone. FR at the level studied has a mostly negative effect on cancellous bone.

Effects of separate and combined therapy with growth hormone and parathyroid hormone on lumbar vertebral bone in aged ovariectomized osteopenic rats.

Previous studies have demonstrated that growth hormone (GH) has a marked anabolic effect on cortical bone, and parathyroid hormone (PTH) has been shown to increase cancellous bone markedly and cortical bone to some extent in ovariectomized (ovx) rats. Combined therapies mostly focused on combining a bone anabolic agent with an antiresorptive agent. The following study was carried out to examine the efficacy of combined therapy with GH and PTH, two bone anabolic agents in rebuilding bone after loss due to ovariectomy in lumbar vertebrae, which contain both cortical and cancellous bones. Twelve-month-old female F344 rats were divided into five groups: sham + solvent vehicle, ovx + solvent vehicle, ovx + GH (2.5 mg/kg/day), ovx + PTH (80 microg/kg/day), and ovx + GH (2.5 mg/kg/day) + PTH (80 microg/kg/day). After surgery, animals were left for 4 months to become osteopenic before the beginning of therapy. Hormone administrations were given 5 days per week for 2 months and the animals were killed. The L3 vertebra was removed and examined by pQCT densitometry and by histomorphometry. Compared with age-matched, sham-operated controls, there was a 21% decrease in total bone mineral content (BMC) (p < 0.0001), 17.0% decrease in total bone mineral density (BMD) (p < 0.0001), 25.4% decrease in cortical BMC (p < 0.001), 3.1% decrease in cortical BMD (p < 0.05), 50.5% decrease in cancellous BMC (p < 0.01), 47.3% decrease in cancellous BMD (p < 0.01), and 14.5% decrease in cancellous bone volume (BV/TV) (p < 0.05) in the vehicle-treated ovx rats. Compared with age-matched, vehicle-treated ovx controls, GH, PTH, and GH + PTH increased total BMC by 22.8% (p < 0.001), 32.4% (p < 0.0001), and 72.7% (p < 0.0001), respectively; total BMD by 9.7% (p > 0.05), 22.6% (p < 0.001), and 38.8% (p < 0.0001), respectively; cortical BMC by 28.8% (p < 0.01), 50.8% (p < 0.0001), and 98.4% (p < 0.0001), respectively; and cortical BMD by 4.5% (p < 0.01), 2.9% (p < 0.05), and 6.3% (p < 0.0001), respectively. PTH and GH + PTH significantly increased cancellous BMC by 95.3% (p < 0.01) and 255.8% (p < 0.0001), respectively; cancellous BMD by 77.6% (p < 0.05) and 181% (p < 0.0001), respectively; cancellous BV/TV by 38.6% (p < 0.0001) and 55.9% (p < 0.0001), respectively; and trabecular thickness by 48% (p < 0.0001) and 68.3% (p < 0.0001), respectively. Note that GH by itself had no significant effect on vertebral cancellous BMC, cancellous BMD, and cancellous BV/TV. In conclusion, the effect of PTH was mostly more marked than that of GH. GH acted mainly by increasing cortical bone with less effect on cancellous bone, while PTH acted by increasing both cortical and cancellous bones. Combined therapy with GH and PTH was more effective in rebuilding bone after ovariectomy than either therapy alone. The effects of combined therapy with GH and PTH were additive in vertebral bone in the aged osteopenic rats.

Bone anabolic effects of separate and combined therapy with growth hormone and parathyroid hormone on femoral neck in aged ovariectomized osteopenic rats.

Previous studies have demonstrated that growth hormone (GH) has a marked anabolic effect on cortical bone and parathyroid hormone (PTH) has been shown to increase cancellous bone and cortical bone markedly in ovariectomized (OVX) rats. Most previous combination therapies used the bone anabolic agent (PTH) and the anti-resorptive agents. In this study, two bone anabolic hormones, GH and PTH, were used in rebuilding bone following loss due to ovariectomy in the femoral neck, which contains both cortical and cancellous bones. Twelve-month-old female F344 rats were divided into five groups: Sham+solvent vehicle, OVX+solvent vehicle, OVX+GH (2.5 mg/kg/day), OVX+PTH (80 microg/kg/day), and OVX+GH (2.5 mg/kg/day)+PTH (80 microg/kg/day). Following surgery, the animals were left for 4 months to become osteopenic before the beginning of hormone therapies. Hormone administrations were given 5 days per week for 2 months and the animals sacrificed. The right femurs were removed and the femoral necks were examined by pQCT densitometry and by histomorphometry. There was a 12.3% decrease in total bone mineral content (BMC) (P<0.01), a 6.2% decrease in total bone mineral density (BMD) (P<0.01), a 12.8% decrease in cortical BMC (P<0.05), a 25.9% decrease in cancellous BMC (P<0.0001), a 20.4% decrease in cancellous BMD (P<0.01), and a 34.2% decrease in cancellous bone volume (BV/TV) (P<0.0001) in vehicle-treated OVX rats. Growth hormone, PTH and GH+PTH treatment increased total BMC of the OVX rats by 14.4% (P<0.01), 23.5% (P<0.0001) and 30.6% (P<0.0001), respectively; increased total BMD by 7.0% (P<0.01), 9% (P<0.001) and 14.8% (P<0.0001), respectively; increased cortical BMC by 15.9% (P<0.05), 25.5% (P<0.001) and 29% (P<0.001), respectively; increased cancellous BMC by 40.9% (P<0.0001), 61.9% (P<0.0001) and 86.8% (P<0.0001), respectively; increased cancellous BMD by 31% (P<0.001), 41.8% (P<0.0001) and 61.8% (P<0.0001), respectively; increased cancellous BV/TV by 30.6% (P<0.05), 76.3% (P<0.0001) and 94.9% (P<0.0001), respectively; and increased trabecular thickness by 26.4% (P<0.05), 41.5% (P<0.001) and 43.2% (P<0.001), respectively, compared to the age-matched vehicle-treated OVX controls. In conclusion, both GH and PTH increased cortical and cancellous bone mass at the osteopenic femoral neck. Using two techniques, it was observed that the effects of PTH were mostly more marked than those of GH. Combined therapy with GH+PTH was more effective in rebuilding cortical bone and cancellous bone than either therapy alone in the aged ovariectomized osteopenic rats, which is in line with our hypothesis.

Parathyroid hormone and growth hormone have additive or synergetic effect when used as intervention treatment in ovariectomized rats with established osteopenia.

The severely osteoporotic human skeleton is characterized by thin cortices and a very fragile cancellous framework. To increase the biomechanical competence of such a skeleton, powerful anabolic agents are needed. The aim of the present study was to compare the effect of parathyroid hormone (PTH), growth hormone (GH) and combination treatment with PTH and GH in an aged, rat model with established osteopenia. Furthermore, envelope- and site-specific effects of the two agents are described. Twelve-month-old virgin F344 rats were divided into six groups with 11 animals per group: (1) baseline; (2) sham-operated + solvent vehicle (s.v.) (sham); (3) ovariectomized + s.v. (ovx); (4) ovx + GH 2.5 mg/kg body weight per day; (5) ovx + PTH 80 microg/kg body weight per day; and (6) ovx + GH and PTH treatment. Group 1 were killed to establish baseline values. Groups 2 (sham) and 3 (ovx) were killed after 24 weeks. Groups 4, 5, and 6 were allowed to develop osteopenia for 16 weeks before treatment was initiated. Treatment was given for a period of 8 weeks. The effects of GH, PTH, and GH + PTH cotherapy were measured by biomechanical testing at four different skeletal sites: lumbar vertebra; femoral diaphysis; femoral neck; and distal femoral metaphysis. In addition, static histomorphometry was performed at the middiaphyseal region. Ovx induced a loss of bone strength at all sites, but this was significant only at the femoral diaphysis and distal metaphysis. GH could reverse the loss of strength at the diaphysis, but not at the metaphysis. PTH, on the other hand, reversed the loss of strength to values significantly over ovx at all four sites. At the metaphysis, PTH monotherapy increased strength to above sham levels. However, GH + PTH cotherapy showed additive or synergistic effects at the four tested sites, leading to strength values significantly over sham at all these sites. Static histomorphometry showed that GH exerted its main effect on the periosteal envelope and PTH on the endocortical envelope; for this reason, the GH + PTH combination treatment had an additive or synergistic effect. We conclude that GH and PTH have a very pronounced anabolic effect when given in cotherapy. Therefore, this treatment regime seems promising in the clinical situation for management of patients with severe, established osteoporosis.

Analysis of the effects of growth hormone, voluntary exercise, and food restriction on diaphyseal bone in female F344 rats.

The aim of this study is to examine the effects of growth hormone, exercise, and weight loss due to food restriction on tibial diaphyseal bone and on tibial muscle mass. Thirteen-month-old female F344 rats were divided into six groups: group 1, baseline controls (B); group 2, age-matched controls (C); group 3, GH treated (GH); group 4, voluntary wheel running exercise (EX); group 5, GH + EX; and group 6, food restricted (FR). The dose of GH was 2.5 mg recombinant human (rh) GH/kg body weight/day, 5 days per week, given in two divided doses of 1.25 mg at 9-10 A.M. and 4-5 P.M. Food-restricted rats were fed 60% of the mean food intake of the age-matched controls. All animals except the baseline controls were killed after 4.5 months. The baseline controls were killed at the beginning of the study. Growth hormone increased the body weight and tibial muscle mass of the rats markedly, while EX caused only a slight decrease in body weight and partially inhibited the increase caused by GH in the GH + EX group. Food restriction greatly decreased body weight below that of age-matched controls, but neither FR nor EX had a significant effect on the mass of the muscles around the tibia. Growth hormone and EX independently increased tibial diaphyseal cortical bone area (p < 0.0001, p < 0.0001), cortical thickness (p < 0.0001, p < 0.0001), cortical bone mineral content (p < 0.0001, p < 0.0001), periosteal perimeter (p < 0.0001, p < 0.0001), and bone strength-strain index (SSI) (p < 0.0001, p < 0.0001). The effects of GH were more marked and resulted in a greater increase in the weight of the mid tibial diaphysis (p < 0.0001). The combination of GH and EX produced additive effects on many of the tibial diaphyseal parameters, including bone SSI. GH + EX, but not GH or EX alone, caused a significant increase in endocortical perimeter (p < 0.0001). In the FR rats, cortical bone area and cortical mineral content increased above the baseline level (p < 0.001, p < 0.0001) but were below the levels for age-matched controls (p < 0.0001, p < 0.0001). In addition, marrow area, endocortical perimeter, and endocortical bone formation rate increased significantly in the FR rats (p < 0.01, p < 0.0001, p < 0.0001). Three-point bending test of right tibial diaphysis resulted in maximum force (Fmax) values that reflected the group differences in indices of tibial diaphyseal bone mass, except that GH + EX did not produce additive effect on Fmax. The latter showed good correlation with left tibial diaphyseal SSI (r = 0.857, p < 0.0001), and both indices of bone strength correlated well with tibial muscle mass (r = 0.771, Fmax; r = 0.700, SSI; p < 0.0001). GH increased serum IGF-I (p < 0.0001), and the increase was partially reduced by EX. Serum osteocalcin was increased by GH with or without EX (p < 0.01, p < 0.01), and FR or EX alone did not alter serum IGF-I and osteocalcin levels. The bone anabolic effects of GH with or without EX may relate, in part, to increased load on bone from tibial muscles and body weight, which were increased by the hormone. The osteogenic effect of EX with or without GH may relate, in part, to increased frequency of muscle load on bone as EX decreased body weight (p < 0.05), but had no significant effect on tibial muscle mass. The enhanced loss of endocortical bone by FR may relate, in part, to decreased load on bone due to low body weight (p < 0.0001), as FR did not cause a significant decrease in tibial muscle mass (p = 0.357). The roles of humoral and local factors in the bone changes observed remain to be established.

Calcium absorption and bone loss in ovariectomized rats fed varying levels of dietary calcium.

The following studies were undertaken to examine whether estrogen deficiency impairs calcium absorption in aged rats, and to determine whether impaired calcium absorption and the level of dietary calcium are related to the degree of bone loss due to estrogen deficiency. Sixty rats were sham operated (Sham) or ovariectomized (Ovx) to make them estrogen deficient and divided into three dietary groups of 10 rats per group: Group 1 (Sham) and Group 2 (Ovx) were maintained on a diet containing 0.5% calcium; Group 3 (Sham) and Group 4 (Ovx) were maintained on a diet containing 0.1% calcium; Group 5 (Sham) and Group 6 (Ovx) were maintained on a diet containing 0.02% calcium. Calcium absorption was measured in all animals at the beginning of the study and 2 weeks, 1 month, 2 months, and 3 months following surgery, then the animals were sacrificed. In Ovx rats fed 0.5% Ca diet, calcium absorption decreased progressively and the decrease became statistically significant 8 and 12 weeks following ovariectomy (P < 0.05). A similar ovariectomy-related impairment of calcium absorption was not observed in animals fed diets with lower calcium content, making the Ovx rat a tenuous model of intestinal calcium malabsorption. Low dietary calcium decreased cancellous bone mineral content and density at the proximal tibial metaphysis and the decrease was augmented by ovariectomy. The degree of osteopenia due to ovariectomy was not related to the level of dietary calcium or the efficiency of calcium absorption.

Growth hormone and the expression of mRNAs for matrix proteins and oncogenes in bone.

To examine the effects of growth hormone (GH) on the expression of the mRNAs of bone matrix proteins, three experiments were carried out with 3-month-old female Sprague-Dawley rats. In the first experiment rats were given a single subcutaneous injection of recombinant human GH (8 mg rhGH/kg b. wt.), sacrificed 15 min, 1 h, 2 h, 4 h, 8 h, 16 h and 24 h later, and RNA isolated from cancellous bone from the distal femoral metaphysis. Growth hormone increased the level of type I collagen mRNA by 187, 417, and 509% over the control level at 15 min, 1 h and 2 h, respectively; the mRNA levels declined to 119 and 99% at 4 and 8 h, respectively, and then rose again to 351 and 423% over the control level at 16 and 24 h, respectively. Osteocalcin mRNA transcript increased by 89, 90, 325, 342, 361, and 407% over the control level at 15 min, 1 h, 2 h, 4 h, 8 h and 16 h, respectively, and fell to 66% at 24 h. The level of IGF-I mRNA increased by 45, 83, 120, 140, and 175% over the control level at 2, 4, 8, 16, and 24 h, respectively. In the second experiment, following the administration of rhGH (8 mg/kg b. wt.) bone osteocalcin mRNA increased by 127, 177, 361, and 413% over the control level at 30 min, 1 h, 2 h and 4 h, respectively; IGF-I mRNAs increased by 38, 33, 87, and 437 at 30 min, 1 h, 2 h and 4 h, respectively, but the levels did not become significant until 2 h; c-fos mRNA increased significantly at 30 min, and c-jun and c-myc mRNAs did not increase until 4 h. In the third experiment, animals were given a single injection of rhGH (8 mg/kg b. wt.) and the animals were bled at timed intervals and acid ethanol-extractable serum IGF-I determined. Serum IGF-I increased significantly only at 12 h following rhGH administration. Our data indicate that GH stimulates a rapid increase in the expression of mRNAs for the bone matrix proteins, type I collagen and osteocalcin, by a mechanism that appears to be independent of IGF-I, the early response oncogenes or an increase in osteoblast number.

Additive effect of voluntary exercise and growth hormone treatment on bone strength assessed at four different skeletal sites in an aged rat model.

The aim of the study was to assess the effect of growth hormone (GH), voluntary exercise (Ex), and the combination of GH and Ex on bone strength, mass, and dimensions in aged, intact female rats. In addition, the effect of food restriction (FR) was studied. Fourteen-month-old virgin F-344 rats were divided into 6 groups with 13 animals in each: (1) baseline (BSL); (2) control + solvent vehicle (CTRL); (3) GH 2.5 mg/kg/day (GH); (4) exercise, voluntary: 0.6-0.7 km/day (Ex); (5) GH treatment and voluntary exercise (GH + Ex); and (6) FR. Group 1 was killed at the beginning of the study and served as baseline. All the other groups were killed after 18 weeks' treatment. The effects of aging and treatment regimes were measured at four different skeletal sites: lumbar vertebrae, femoral cortical bone, femoral neck, and the distal femoral metaphysis. Aging in itself induced a decline in vertebral body strength and ash density. At the appendicular skeletal sites, bone mass and strength were unchanged or increased. Treatment with GH alone induced a significant increase in the biomechanical parameters at the vertebral body and the femoral diaphysis, but not at the femoral neck or the distal femoral metaphysis. Voluntary exercise on its own increased load values significantly over CTRL at the vertebral body site, but not at any of the appendicular skeletal sites. The combination of GH and voluntary exercise resulted in an additive effect at the vertebral site and at the femoral diaphysis, and a synergistic (potentiating) effect at the two femoral metaphyses. FR, on the other hand, had a negative effect on cortical bone area and strength at the femoral diaphysis, but no significant effect on the other sites tested. We conclude that GH treatment and voluntary exercise both have skeletal anabolic effects; however, these effects are exerted to differing degrees at different sites. Importantly, when dosed together, GH and Ex have either an additive or synergistic anabolic effect on all sites (axial and appendicular).

Aged-rodent models of long-term growth hormone therapy: lack of deleterious effect on longevity.

Studies were carried out to examine the effects of long-term recombinant human growth hormone (GH) therapy on longevity in rodents. In the first study, 150 18-month-old female F344 rats were divided into three groups of 50 rats per group: Group 1, solvent vehicle; Group 2, 10 microg GH/kg body weight three times per week; Group 3, 50 microg GH/kg body weight three times per week. GH and solvent vehicle therapies were started at 18 months of age and continued until all the animals died spontaneously. Serum insulin-like growth factor (IGF)-I was measured at 18 and 29 months of age and on 3-month-old rats. Serum IGF-I level decreased between 3 and 29 months of age. GH therapy reversed the decrease in a dose-dependent manner, with the 50 microg GH dose returning the serum IGF-I level to that of 3-month-old animals. However, statistical analysis revealed no significant effect of GH therapy on median life span, 10th percentile life span, or maximum life span. Similar observations on longevity were made on aged F344 male rats and on aged Balb/c mice, even when the dose of GH was increased to 1.0 mg/kg body weight two times per week. The main pathologic lesions in control animals were nephropathy, cardiomyopathy, leukemia, and testicular interstitial cell tumor; the prevalence of these lesions was not significantly altered by GH therapy. We conclude that long-term low-dose GH therapy that includes doses in the range that is given to humans in clinical trials in GH deficiency and to revert age-related physiologic declines has no overt deleterious effects on longevity and pathology in aged rodents.

Growth hormone increases vertebral and femoral bone strength in osteopenic, ovariectomized, aged rats in a dose-dependent and site-specific manner.

The aim of the study was to assess the effect of growth hormone (GH) as restorative therapy in an aged, ovariectomized rat model with established osteopenia. The study was planned as a dose-response study, and four different skeletal sites were investigated by mechanical testing and measurements of bone mass and dimensions. Twelve-month-old virgin F344 rats were divided into eight groups with ten animals per group: (1) sham operated (sham); (2) ovariectomized (ovx); (3) sham + solvent vehicle (sv); (4) ovx + sv; (5) ovx + GH 50 microg/kg body weight/day; (6) ovx + GH 1.25 mg/kg body weight/day; (7) ovx + GH 2.5 mg/kg body weight/day; and (8) ovx + GH 5.0 mg/kg body weight/day. Groups 1 and 2 were killed after 3 months to establish that bone loss had occurred due to ovx. One month later, the remaining groups began 3 months of treatment, at the end of which the animals were also killed. The effects of ovariectomy (ovx) and GH therapy were measured at four skeletal sites: lumbar vertebrae; femoral diaphysis; femoral neck; and distal femoral metaphysis. Ovariectomy induced a significant loss of bone strength at all sites apart from the femoral neck. The loss was most pronounced at the distal femoral metaphysis. GH was able to reverse the ovx-induced loss of strength at the vertebral site in a dose-dependent manner. At the femoral diaphyseal site, GH not only reversed the ovx-induced changes but increased load values significantly above sham level. However, at the distal femoral metaphysis, which is dominated by cancellous bone, only partial reversal was seen after GH treatment. The lowest GH dose had no significant effect at any site tested. We conclude that GH treatment can reestablish vertebral bone loss due to ovariectomy in a dose-dependent manner. The restorative effect is only partial at the distal femoral metaphysis even at a high dose. At skeletal sites with less pronounced ovx-induced bone loss (femoral neck and diaphysis), GH treatment increased bone strength to sham level or above sham level. Therefore, the effect of ovariectomy is dependent upon the skeletal site investigated, and the effect of GH treatment is dependent on both the skeletal site and the size of the ovx-induced bone loss at this site.

Inhibitory effect of melatonin on cataract formation in newborn rats: evidence for an antioxidative role for melatonin.

We evaluated the inhibitory effect of melatonin, a recently discovered scavenger of free radicals, on cataract formation in the newborn rat. The glutathione synthesis inhibitor, buthionine sulfoximine (BSO) (3 mmol/kg), was intraperitoneally injected into newborn rats for 3 consecutive days starting on day 2 after birth. These glutathione depleted rats develop cataracts. Melatonin (4 mg/kg) was injected intraperitoneally into half of the rats once a day beginning at day 2 after birth; the other half of the animals received solvent daily. The incidence of cataract was observed on day 16, after the eyes of the newborn animals had opened. Both reduced glutathione (GSH) and oxidized glutathione (GSSG) levels were measured. Cataracts were observed in all animals (18/18) treated with BSO plus solvent. The incidence of the cataract in the animals cotreated with melatonin was only 6.2% (1/15). Total lenticular glutathione (GSH + GSSG) levels in BSO only treated rats were reduced by 97%. The total glutathione in the lens of the BSO plus melatonin group was significantly higher (by 3%) than that of the BSO only group. The percentage of the total glutathione as GSSG for the BSO plus solvent group was higher than the control value. Cotreatment of BSO injected rats with melatonin (4 mg/kg/day) clearly reduced cataract formation proving that it is directly or indirectly protective against oxidative stress which accompanies glutathione deficiency. The inhibitory effects of melatonin on cataract formation in this study could be due to melatonin's free radical scavenging activity or due to its stimulatory effect on glutathione production.