Decreased body-core temperature during acute hypoxemia in guinea pigs during postnatal maturation: a regulated thermoregulatory response.

In newborn mammals, hypoxemia produces a decrease in body-core temperature (Tbc), the mechanism of which is unknown. Experiments were therefore carried out to determine whether this decrease results from a regulated or a forced thermoregulatory response. Seven Hartley strain guinea pigs were studied on postnatal days 2, 5, 10, 15, and 26 following implantation of a biotelemetry transmitter into the peritoneal cavity on day 1 to measure Tbc. During each experiment, Tbc and selected ambient temperature were determined in a thermocline (15-40 degrees C gradient) during a control period of normoxemia, an experimental period of hypoxemia (produced by decreasing the fraction of inspired oxygen from 0.21 to 0.10), and a recovery period of normoxemia. We reasoned that no change or a decrease in selected ambient temperature while Tbc decreased during hypoxemia would indicate a regulated thermoregulatory response, whereas an increase in selected ambient temperature while Tbc decreased during hypoxemia would indicate a forced thermoregulatory response. Tbc decreased during hypoxemia at all ages; the response was accentuated on days 15 and 26 compared with day 2. Selected ambient temperature decreased during hypoxemia in the youngest animals but remained the same in the older animals. Our data provide evidence that postnatal maturation influences the thermoregulatory response to hypoxemia in guinea pigs and support the hypothesis that the decrease in Tbc during hypoxemia results from a regulated thermoregulatory response.