Serotonin level and turnover rate in brown adipose tissue of developing rats.

The level and turnover rate (TR) of serotonin (5-HT) were determined in the brown adipose tissue (BAT) of rats born and reared at 28 degrees C and 16 degrees C. The serotonin/norepinephrine ratio was high in BAT of both groups for the first 2 days. Thereafter it fell. During the first 3 days, the TR was three times higher in 16 degrees C rats than in 28 degrees C rats. A similar difference was observed for the 5-HIAA/5-HT ratio during that period. It is concluded that 5-HT may act on BAT thermogenesis in cold-exposed pups but its mechanism of action is still hypothetical.

Postnatal development of nonshivering thermogenesis in rats: effects of rearing temperature.

A comparative chronological study (from 1 to 33 days post partum) was performed to establish the capacity for nonshivering thermogenesis (NST) in rats born and reared at 28 degrees C and at 16 degrees C. The resting metabolism measured at 33 degrees C was higher in the 16 degrees C rats than in the 28 degrees C rats from the 3rd day. When expressed per weight or per surface area units it was higher in 16 degrees C pups than in 28 degrees C pups until the end of the 3rd week. In fact the resting metabolism was significantly proportional to different powers of weight (W0.67 at 16 degrees C and W0.75 at 28 degrees C) during the suckling period. At birth, respiratory quotient (RQ) was the same in both groups (0.70); it increased slowly to the end of the 3rd week (about 0.80). During the 3rd week RQ was lower in 16 degrees C rats than in 28 degrees C animals. This indicates that 16 degrees C rats are more dependent on the milk supplied by their mother. After weaning there were no differences in RQ values (0.90). Rectal temperature was low in both groups on day 1 (about 32 degrees C). It increased until weaning when it stabilized at 37 degrees C. From day 1 to day 18, it was significantly lower in cold reared rats. The capacity for NST was measured by investigating the effect of an injection of norepinephrine (NE) on the metabolic rate at 33 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin content of the interscapular brown adipose tissue of growing rats.

In brown fat of newborn rats the serotonin (5HT) content is high during the first five days of life. This may play a part in the lipid repletion of the tissue, lipids being the main fuel for nonshivering thermogenesis. Subsequently 5HT increases more in young rats reared at 16 degrees C than in those reared at 28 degrees C but to a lesser extent than norepinephrine (NE) content. A possible role of 5HT in thermoregulation of the rat during the early postnatal period is discussed.

Catecholamine turnover in heart and adrenals of young rats: effects of rearing temperature.

1. A comparative chronological study (from birth to one month of age) was performed to establish the levels and turnover rates of catecholamines in the heart and adrenals of rats born and reared at 28 and 16 degrees C. 2. In the heart, cold induced marked increases of the norepinephrine level and turnover rate only from the second week of age. 3. In the adrenals there was considerable early stimulation of epinephrine production, but only in 28 degrees C rats. 4. The differences observed in the stimulation of the sympathetic nervous system according to the rearing temperature are possibly due to the behavior of the mother in warming the pups.

Thermogenic capacity of the brown adipose tissue of developing rats; effects of rearing temperature.

A chronological study was performed to investigate the postnatal development of the thermogenic capacity of the brown adipose tissue (BAT) comparing rats born and reared at 16 degrees C (cold) or 28 degrees C (control). Mitochondrial mass, cytochrome-c-oxidase activity (index of oxidative capacity) and GDP binding to mitochondria (uncoupling test) were investigated in rats from 1 to 33 days of age. Specific cytochrome-c-oxidase activity was the same in both groups during the first week, then increased in the cold group and decreased in controls; from the 9th day it was always twice as high in the former as in the latter. Specific binding of GDP to mitochondrial proteins remained almost constant in control rats during the first week contrasting with a rapid increase in that for cold rats. Afterwards it decreased in both groups until weaning but remained five times as high in cold rats as in control rats. As growth of BAT is faster and mitochondrial content greater in cold reared rats, the capacity of the tissue for thermogenesis appeared to be greatly temperature dependent soon after birth and during the entire suckling period. However the mechanisms of this stimulation remain to be elucidated.

Norepinephrine turnover in brown adipose tissue of young rats: effects of rearing temperature.

Brown adipose tissue (BAT) has an important role in the thermogenesis of newborn mammals and cold-acclimated rodents. Heat production within the tissue is regulated by the sympathetic nervous system (SNS) via norepinephrine (NE) release. As only little is known of the progressive role of SNS during the developmental period, NE content and turnover were determined in BAT of infant rats 1-33 days of age. The dams and the pups were kept at either 28 or 16 degrees C. It was observed that the NE level in the tissue and the mediator turnover had an almost parallel evolution during the experimental period. In the first week of life, level and turnover of NE were higher in the 28 degrees C group than in the 16 degrees C group. During the second week, the level remained constant in rats kept at 28 degrees C, but the NE turnover slightly decreased. In contrast, a large increase of both parameters was observed in rats kept at 16 degrees C. Then a decrease occurred in both groups until weaning. Subsequently the values remained almost constant. It must be noted that, from the end of the first week, NE content and turnover were always significantly higher in the 16 degrees C group than in the 28 degrees C group. At the end of the first month, the level was 50% higher in cold-acclimated rats and turnover was four times as high as in controls.(ABSTRACT TRUNCATED AT 250 WORDS)