Arctic ground squirrel (Spermophilus parryii) and american black bear (Ursus americanus) as models for human cryogenics researches

Hibernacija je proces od životne važnosti za organizme koji tijekom ekstremnih zimskih temperatura nemaju mogućnost migracije. Karakteristike svih hibernirajućih organizama su smanjen metabolizam, sniženje tjelesne temperature, povećana upotreba masnoća te još niz prilagodbi koje se razlikuju od jedinke do jedinke. Hibernacija sisavaca jedan je od najkompleksnijih oblika prirodnog hipometabolizma jer organizmi ne samo da su u stadiju mirovanja već periodično inhibiraju vlastitu termogenezu što omogućava drastični pad tjelesne temperature. Takvi procesi primjenjeni na čovjeka koriste se u svrhu ispitivanja kriogeneze koja u budućnosti obećava mnogo, od biotehnološke primjene do medicinskih ideja o dugovječnosti organizma. Proces kriogeneze omogućio bi jedinki ulazak u stanje mirovanja gdje su fiziološke i biokemijske aktivnosti potisnute, a potrošnja energije minimalna te po želji, ponovni povratak u normalni život. Ipak, do ostvarenja takvih želja potrebno je proučiti još velik broj hibernirajućih modela i povezati njihove prilagodbe s mogućim primjenama na čovjeka. Dva vrlo različita modela korisna za pručavanje prilagodbi na hibernaciju su arktička podzemna vjeverica i američki crni medvjed. Iako svaki organizam ima razvijene vlastite prilagodbe, zajednička karakteristika oba modela je opstanak u uvjetima snižene koncentracije kisika. Navedena prilagodba je moguća jer oba modela smanjuju broj otkucaja srca što dovodi do smanjene stope metabolizma i potrebe za kisikom. Arktička podzemna vjeverica ima prilagodbu srčanoga ritma na smanjeni broj otkucaja srca, no američki crni medvjed nema zbog čega mu se javljaju snažne varijacije u srčanome ritmu. Navedene prilagodbe te niz regulatornih molekula koje sudjeluju u procesima hibernacije, uz dodatni angažman i istraživanja, mogu se primjeniti na procese humane kriogeneze i medicinska unaprijeđenja.Hibernation is a process of vital importance to organisms that during extreme winter temperatures do not have the ability to migrate. Characteristics of all hibernating organisms are reduced metabolism, lowering body temperature, increased fat usage and a lot of adjustments that differ between individuals. Mammalian hibernation is one of the most complex forms of natural hypometabolism because organisms are not only in period of torpor but also periodically they inhibit their own thermogenesis, which allows drastic drop in body temperature. Those processes are used for the purpose of human cryogenics researches, which promises a lot in the future especially from biotechnological applications to medical ideas regarding extending the human lifespan. Cryogeneses would allow entry into a torpor where physiological and biochemical activities are suppressed, energy consumption is minimal and as desired, and returning to normal life in the desired moment. However, to achieve such a desire, it is necessary to study large number of hibernation models and to associate their adaptations with possible applications to humans. Two very different models useful for the research regarding the adjustments to hibernation are the Arctic ground squirrel and the American black bear. Although each organism has developed its own adaptations, the common feature of both models is survival in conditions of reduced oxygen concentration. This adaptation is possible because both models lower heart beating rate, which results in reduced metabolism and decreased oxygen demand. The Arctic ground squirrel has adjusted heart rhythm to the lowered heart beating rate, but American black bear did not develop this adaptation so that is the reason why he experiences strong variations in heart rythm. The aforementioned adaptations and a set of regulatory molecules participating in hibernation processes, with additional engagement and research, can be applied to human cryogenic processes and the advancement of medical services