Hamsters versus rats: ventilatory responses in adults and newborns

Burrowing mammals often demonstrate structural and functional characteristics which could be interpreted as aspects of adaptation to the low PO2 and high PCO2 of their environment. Whether these characteristics are acquired by each individual as the result of life in the burrow or are genetic traits established through evolution is not clear. To examine the latter possibility aspects of ventilatory control were studied in newborns and adults of two rodents, the surface dwelling white rat (Rattus norvegicus, R) and the semifossorial syrian hamster (Mesocricetus auratus, H), both born and raised in normoxia. Adult H, but not R, manifested the burrowing preference whenever offered the opportunity. Adult H presented numerous differences from the adult R, including a higher normoxic oxygen consumption (VO2, +44%), higher hematocrit and heavier right heart. Ventilation (VE) was similar between the two species both in air and hyperoxia, although H had a deeper and slower pattern. Hence, resting VE/VO2 in H was low, probably contributing to the hypoxemia reported in this species. The acute ventilatory response to hypoxia (10 min 10% FIO2), was less in H, because of no increase in tidal volume. Most of the morphological and functional differences between adult hamsters and rats were not apparent between the newborns of the corresponding species. It is concluded that some of the physiological characteristics reported in burrowing species are also observed in adult hamsters which never lived in burrows, but not in the newborns; hence, they could represent genetic traits which are expressed postnatally with no needs of the special environmental conditions of the burrow.