Suppression of cold‐induced thermogenesis in full‐term pregnant rats.

Abstract

SUMMARY1. Thermoregulation against cold exposure was studied in rats during pregnancy and early lactation, and compared with that of virgin rats.2. When exposed to 0 TC for 60 min, rats which were within 24-48 h of parturition (pre-1-day rats) and those within 24 h of parturition (pre-0-day rats) showed significantly larger falls of colonic temperature (To) than virgin rats. The temperature decrease was greatest in the pre-0-day rats, being 4' 1 + 0 4 0C (mean + S.E.M.) at the end of cold exposure, compared with a decrease of 1-7 + 0-3 0C in the virgin rats. The tail skin temperature fell to 0 0C during cooling in all virgin rats and in pregnant rats at each gestational stage.3. During cold exposure at 10 0C for 30 min, pre-0-day rats also showed significantly larger falls in Tco (1I8+006 'C) than virgin (0-4+0-2 'C), pre-1-week (0-8 + 0 3 0C), post-0-day (0 3 + 0 3 0C) or post-I -week rats (0 4 + 0 3 0C). Although body weights in pre-0-day rats were far larger than those in virgin rats, the increase in oxygen consumption per animal during cold exposure was 50 % lower in pre-0-day rats (2-2 + 0 5 ml/min) than in virgin rats (5 3 + 0-3 ml/min). There was no difference in basal oxygen consumption per animal between the late pregnant and virgin rats.4. Within 24 h after parturition, both the decrease of Tco and the increase of oxygen consumption during cold exposure returned to the values observed in virgin rats.5. The present results demonstrate clearly that cold-induced thermogenesis is significantly suppressed in rats at a late stage of pregnancy.

Vasopressin‐Induced Antipyresis: Sex‐ and Experience‐Dependent Febrile Responsesa

“…In keeping with this idea, thermogenic responses to cold are reduced in full‐term pregnant rats. 41 Similarly, pressor and tachycardic responses recorded in our laboratory following icv PGE 2 are reduced at the same time that febrile responses are reduced. As fever is brought about mainly by sympathetic activation, the reduction of fever at term may be a reflection of reduced sympathetic drive or response at this time.…”

Rat Brown Adipose Tissue Thermogenic Features are Altered During Mid-Pregnancy

“…Inhibition of cold-induced thermogenesis in late-pregnant rats has also been reported [6]. This diminished thermogenic activity is related to lowered levels of UCP1 expression and GDPbinding activity [7,8], as well as decreased lipoprotein 204 lipase and iodothyronine 5'-deiodinase activity levels [9].…”

Prostaglandin Fever in Rats Throughout the Estrous Cycle Late Pregnancy and Post Parturition

“…Whether the fever suppression seen at the lower dose is a specific deficit in fever mechanisms or represents a more generalized thermoregulatory deficit is not known. However, it has been reported that rats in late pregnancy are less able to maintain their body temperature during acute cold exposure than are middle term or post partum rats (48). Brown adipose tissue activity, which is important in fever thermo-genesis (49,50) also declines in late pregnancy, but its further decrease during lactation, (when we are able to obtain fever) make this an unlikely candidate (51).…”