Sympathetic nervous system activity in adipose tissues during pregnancy and lactation of the rat

The concentration and turnover of norepinephrine in white adipose and liver tissues were determined in pregnant, lactating, and age-matched virgin rats to elucidate the adaptations in sympathetic nervous system activity. In study 1, at d 18 of pregnancy and d 7 and 21 of lactation, animals were killed, and liver and cardiac perimetrial and retroperitoneal adipose depots were quick-frozen and then assayed for norepinephrine as a gross estimate of sympathetic innervation. In study 2, the same design was used to measure the turnover of norepinephrine as a measure of sympathetic activity. Animals were treated with alpha-methylparatyrosine, an inhibitor of norepinephrine synthesis, and killed at 0, 1.5, and 3 h after injection. In pregnant animals, basal norepinephrine concentrations were decreased compared with unbred controls in perimetrial and retroperitoneal depots. By d 21 of lactation, all adipose depots from lactating animals had more norepinephrine than did controls. The turnover of norepinephrine decreased in noncardiac adipose depots of pregnant animals. By d 21 of lactation, norepinephrine concentration was greater in all of the adipose depots than in controls. The turnover rate was faster in all adipose tissue depots but only significantly different in the cardiac depot. Sympathetic nervous activity in adipose tissue is diminished in pregnant rats, presumably to save energy for fetal growth and maternal fat storage. In late lactation, activity is increased, presumably to direct fatty acids away from adipose tissue towards milk production. The data from this study are consistent with the hypothesis that the sympathetic nervous system plays a role in the regulation of adipose metabolism in lactation.