Bone and serum calcium in normothermic, cold-acclimated and hibernating hamsters

Thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ) show microstructural bone loss during hibernation but preserve bone macrostructural geometry and strength

“…Osteocyte lacunar density is also increased in osteoporotic humans relative to age-matched controls, and may reflect decreased bone formation activity per osteoblast [resulting in earlier cell entrapment in the bone matrix (Shih et al, 1993;Mullender et al, 1996)]. Consistent with this hypothesis, osteoblasts are less active during hibernation (Steinberg et al, 1986) and bone formation decreases in hibernating compared with active rodents (Tempel et al, 1978). Thus, the increased osteocyte lacunar density that we observed in hibernating squirrels in this study could be indicative of a hibernation-induced reduction in osteoblast activity and bone formation, where instead of making bone, osteoblasts terminally differentiate into osteocytes sooner during hibernation.…”

“…Thus, small mammals have a mechanism by which calcium liberated from bone during hibernation could be excreted from the body, and therefore these animals may not have evolved the ability to maintain balanced bone remodeling activity and prevent bone loss as hibernating bears do . This is supported by the observation that bone formation is reduced in the metatarsals of hibernating hamsters, but resorption continues at a slow rate (Tempel et al, 1978). It has also been suggested that hibernating bats, hamsters and ground squirrels mobilize calcium from bone via osteocytic osteolysis to maintain homeostatic calcium levels by replacing calcium lost in the urine, and thus may also lose bone during inactivity because of increased osteocyte lacunar area (Haller and Zimny, 1977;Steinberg et al, 1981;Kwiecinski et al, 1987;Shackelford and Caire, 1993).…”

Thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ) show microstructural bone loss during hibernation but preserve bone macrostructural geometry and strength

“…Osteocyte lacunar density is also increased in osteoporotic humans relative to age-matched controls, and may reflect decreased bone formation activity per osteoblast [resulting in earlier cell entrapment in the bone matrix (Shih et al, 1993;Mullender et al, 1996)]. Consistent with this hypothesis, osteoblasts are less active during hibernation (Steinberg et al, 1986) and bone formation decreases in hibernating compared with active rodents (Tempel et al, 1978). Thus, the increased osteocyte lacunar density that we observed in hibernating squirrels in this study could be indicative of a hibernation-induced reduction in osteoblast activity and bone formation, where instead of making bone, osteoblasts terminally differentiate into osteocytes sooner during hibernation.…”

“…Thus, small mammals have a mechanism by which calcium liberated from bone during hibernation could be excreted from the body, and therefore these animals may not have evolved the ability to maintain balanced bone remodeling activity and prevent bone loss as hibernating bears do . This is supported by the observation that bone formation is reduced in the metatarsals of hibernating hamsters, but resorption continues at a slow rate (Tempel et al, 1978). It has also been suggested that hibernating bats, hamsters and ground squirrels mobilize calcium from bone via osteocytic osteolysis to maintain homeostatic calcium levels by replacing calcium lost in the urine, and thus may also lose bone during inactivity because of increased osteocyte lacunar area (Haller and Zimny, 1977;Steinberg et al, 1981;Kwiecinski et al, 1987;Shackelford and Caire, 1993).…”

The physiology of artificial hibernation

“…Black bars correspond to serum electrolyte levels, grey bars indicate electrolyte levels in muscle tissue. Animals included in this figure are: European hedgehog (Erinaceus europaeus, Linnaeus) [114][115][116], long-eared hedgehog (Hemiechinus auritus, Gmelin) [117], golden hamster (Mesocricetus auratus, Waterhouse) [118][119][120][121][122], common box turtle (Terrapene carolina, Linnaeus) [123], pond slider (Trachemys scripta, Thunberg) [123], painted turtle (Chrysemys picta, Schneider) [124][125][126][127], European ground squirrel (Spermophilus citellus, Linneaus) [128], thirteen-lined ground squirrel (Spermophilus tridecemlineatus, Mitchill) [121,122,129], groundhog (Marmota monax, Linneaus) [130,131], yellow-bellied marmot (Marmota flaviventris, Audubon & Backman) [132], Asian common toad (Duttaphrynus melanostictus, Schneider) [133], little brown bat (Myotis lucifugus, LeConte) [122,134,135], big brown bat (Eptesicus fuscus, Palisot de Beauvois) [122;134], American black bear (Ursus americanus, Pallas) [122], common musk turtle (Sternotherus odoratus, Latreille) [136], desert monitor (Varanus griseus, Daudin) [137] The third property of an Rx is its downward adjusting effect on the Ztn. In case of Mg 2+ there appears to be conflicting evidence; intracerebroventricular perfusion with a solution containing a supraphysiological concentration of Mg 2+ does not result in a hypothermic response in hamsters [144], rats [145], cats [146][147][148], and primates ...…”

Thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ) show microstructural bone loss during hibernation but preserve bone macrostructural geometry and strength

“…Osteocyte lacunar density is also increased in osteoporotic humans relative to age-matched controls, and may reflect decreased bone formation activity per osteoblast [resulting in earlier cell entrapment in the bone matrix (Shih et al, 1993;Mullender et al, 1996)]. Consistent with this hypothesis, osteoblasts are less active during hibernation (Steinberg et al, 1986) and bone formation decreases in hibernating compared with active rodents (Tempel et al, 1978). Thus, the increased osteocyte lacunar density that we observed in hibernating squirrels in this study could be indicative of a hibernation-induced reduction in osteoblast activity and bone formation, where instead of making bone, osteoblasts terminally differentiate into osteocytes sooner during hibernation.…”

“…Thus, small mammals have a mechanism by which calcium liberated from bone during hibernation could be excreted from the body, and therefore these animals may not have evolved the ability to maintain balanced bone remodeling activity and prevent bone loss as hibernating bears do . This is supported by the observation that bone formation is reduced in the metatarsals of hibernating hamsters, but resorption continues at a slow rate (Tempel et al, 1978). It has also been suggested that hibernating bats, hamsters and ground squirrels mobilize calcium from bone via osteocytic osteolysis to maintain homeostatic calcium levels by replacing calcium lost in the urine, and thus may also lose bone during inactivity because of increased osteocyte lacunar area (Haller and Zimny, 1977;Steinberg et al, 1981;Kwiecinski et al, 1987;Shackelford and Caire, 1993).…”

The physiology of artificial hibernation

“…Black bars correspond to serum electrolyte levels, grey bars indicate electrolyte levels in muscle tissue. Animals included in this figure are: European hedgehog (Erinaceus europaeus, Linnaeus) [114][115][116], long-eared hedgehog (Hemiechinus auritus, Gmelin) [117], golden hamster (Mesocricetus auratus, Waterhouse) [118][119][120][121][122], common box turtle (Terrapene carolina, Linnaeus) [123], pond slider (Trachemys scripta, Thunberg) [123], painted turtle (Chrysemys picta, Schneider) [124][125][126][127], European ground squirrel (Spermophilus citellus, Linneaus) [128], thirteen-lined ground squirrel (Spermophilus tridecemlineatus, Mitchill) [121,122,129], groundhog (Marmota monax, Linneaus) [130,131], yellow-bellied marmot (Marmota flaviventris, Audubon & Backman) [132], Asian common toad (Duttaphrynus melanostictus, Schneider) [133], little brown bat (Myotis lucifugus, LeConte) [122,134,135], big brown bat (Eptesicus fuscus, Palisot de Beauvois) [122;134], American black bear (Ursus americanus, Pallas) [122], common musk turtle (Sternotherus odoratus, Latreille) [136], desert monitor (Varanus griseus, Daudin) [137] The third property of an Rx is its downward adjusting effect on the Ztn. In case of Mg 2+ there appears to be conflicting evidence; intracerebroventricular perfusion with a solution containing a supraphysiological concentration of Mg 2+ does not result in a hypothermic response in hamsters [144], rats [145], cats [146][147][148], and primates ...…”

Thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ) show microstructural bone loss during hibernation but preserve bone macrostructural geometry and strength

“…Osteocyte lacunar density is also increased in osteoporotic humans relative to age-matched controls, and may reflect decreased bone formation activity per osteoblast [resulting in earlier cell entrapment in the bone matrix (Shih et al, 1993;Mullender et al, 1996)]. Consistent with this hypothesis, osteoblasts are less active during hibernation (Steinberg et al, 1986) and bone formation decreases in hibernating compared with active rodents (Tempel et al, 1978). Thus, the increased osteocyte lacunar density that we observed in hibernating squirrels in this study could be indicative of a hibernation-induced reduction in osteoblast activity and bone formation, where instead of making bone, osteoblasts terminally differentiate into osteocytes sooner during hibernation.…”

“…Thus, small mammals have a mechanism by which calcium liberated from bone during hibernation could be excreted from the body, and therefore these animals may not have evolved the ability to maintain balanced bone remodeling activity and prevent bone loss as hibernating bears do . This is supported by the observation that bone formation is reduced in the metatarsals of hibernating hamsters, but resorption continues at a slow rate (Tempel et al, 1978). It has also been suggested that hibernating bats, hamsters and ground squirrels mobilize calcium from bone via osteocytic osteolysis to maintain homeostatic calcium levels by replacing calcium lost in the urine, and thus may also lose bone during inactivity because of increased osteocyte lacunar area (Haller and Zimny, 1977;Steinberg et al, 1981;Kwiecinski et al, 1987;Shackelford and Caire, 1993).…”

The physiology of artificial hibernation

“…Black bars correspond to serum electrolyte levels, grey bars indicate electrolyte levels in muscle tissue. Animals included in this figure are: European hedgehog (Erinaceus europaeus, Linnaeus) [114][115][116], long-eared hedgehog (Hemiechinus auritus, Gmelin) [117], golden hamster (Mesocricetus auratus, Waterhouse) [118][119][120][121][122], common box turtle (Terrapene carolina, Linnaeus) [123], pond slider (Trachemys scripta, Thunberg) [123], painted turtle (Chrysemys picta, Schneider) [124][125][126][127], European ground squirrel (Spermophilus citellus, Linneaus) [128], thirteen-lined ground squirrel (Spermophilus tridecemlineatus, Mitchill) [121,122,129], groundhog (Marmota monax, Linneaus) [130,131], yellow-bellied marmot (Marmota flaviventris, Audubon & Backman) [132], Asian common toad (Duttaphrynus melanostictus, Schneider) [133], little brown bat (Myotis lucifugus, LeConte) [122,134,135], big brown bat (Eptesicus fuscus, Palisot de Beauvois) [122;134], American black bear (Ursus americanus, Pallas) [122], common musk turtle (Sternotherus odoratus, Latreille) [136], desert monitor (Varanus griseus, Daudin) [137] The third property of an Rx is its downward adjusting effect on the Ztn. In case of Mg 2+ there appears to be conflicting evidence; intracerebroventricular perfusion with a solution containing a supraphysiological concentration of Mg 2+ does not result in a hypothermic response in hamsters [144], rats [145], cats [146][147][148], and primates ...…”