Changes in dietary fatty acids modify the decreased lipolytic beta3-adrenergic response to hyperinsulinemia in adipocytes from pregnant and nonpregnant rats

Adipose tissue development and lipid metabolism in the human fetus: The 2020 perspective focusing on maternal diabetes and obesity

During development, the human fetus accrues the highest proportion of fat of all mammals. Precursors of fat lobules can be found at week 14 of pregnancy. Thereafter, they expand, filling with triacylglycerols during pregnancy. The resultant mature lipid-filled adipocytes emerge from a developmental programme of embryonic stem cells, which is regulated differently than adult adipogenesis. Fetal triacylglycerol synthesis uses glycerol and fatty acids derived predominantly from glycolysis and lipogenesis in liver and adipocytes. The fatty acid composition of fetal adipose tissue at the end of pregnancy shows a preponderance of palmitic acid, and differs from the mother. Maternal diabetes mellitus does not influence this fatty acid profile. Glucose oxidation is the main source of energy for the fetus, but mitochondrial fatty acid oxidation also contributes. Indirect evidence suggests the presence of lipoprotein lipase in fetal adipose tissue. Its activity may be increased under hyperinsulinemic conditions as in maternal diabetes mellitus and obesity, thereby contributing to increased triacylglycerol deposition found in the newborns of such pregnancies. Fetal lipolysis is low. Changes in the expression of genes controlling metabolism in fetal adipose tissue appear to contribute actively to the increased neonatal fat mass found in diabetes and obesity. Many of these processes are under endocrine regulation, principally by insulin, and show sex-differences. Novel fatty acid derived signals such as oxylipins are present in cord blood with as yet undiscovered function. Despite many decades of research on fetal lipid deposition and metabolism, many key questions await answers.

The effect of maternal omega-3 long-chain polyunsaturated fatty acid (n-3 LCPUFA) supplementation during pregnancy and/or lactation on body fat mass in the offspring: a systematic review of animal studies

Dietary n-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) reduce adipogenesis and lipogenesis in adult rodents, but it is not clear whether an increased n-3 LCPUFA supply during the perinatal period influences body fat mass in the offspring. This systematic review aimed to evaluate the existing evidence from animal studies, which have addressed this question. Medline was searched for relevant articles. Studies were included if they involved maternal n-3 PUFA or LCPUFA supplementation and measured fat mass in the offspring. The design and quality of each study was assessed. Only four animal studies met our inclusion criteria. Three studies reported a lower fat mass in offspring of n-3 LCPUFA supplemented dams, however only one of these studies confined the intervention to the perinatal period. The dose of n-3 PUFA, the nature of the control treatment, the approaches used and outcomes assessed differed between studies. This review highlights the paucity of robust animal data as to the effect of increased n-3 LCPUFA exposure during the perinatal period alone, on body fat mass in the offspring and calls for further studies.

Enhanced utilization of glycerol for glyceride synthesis in isolated adipocytes from early pregnant rats

Adipose tissue normally has low glycerol kinase activity, but its expression is enhanced under conditions of augmented insulin sensitivity and/or obesity. Since these conditions occur during early pregnancy, the comparative utilization of glucose or glycerol by isolated adipocytes from rats at 0, 7, 14, or 20 days of pregnancy was studied. Incubations were carried out in the presence of [U(14)C]-glucose or -glycerol in medium supplemented or not with 5 mM glucose and 100 nM insulin. The conversion of glucose into esterified fatty acids and glyceride glycerol was greatest in adipocytes from 7-day pregnant rats, the effect being further enhanced by insulin. Both the amount of aquoporin 7 and the in vitro conversion of glycerol into glyceride glycerol were greatest in adipocytes of 7-day pregnant rats, the later being unaltered by insulin. In the presence of glucose, the overall glycerol utilization was lower than in its absence and glycerol conversion into glyceride glycerol was further decreased by insulin, the effect only being significant in adipocytes from 7-day pregnant rats. It is proposed that the enhanced utilization of glycerol for glyceride glycerol synthesis in adipose tissue contributes to the net accumulation of fat depots that normally takes place in early pregnancy.

Monounsaturatedn-9 fatty acids and adipocyte lipolysis in rats

To investigate the role of the monounsaturatedn-9 fatty acids (MUFA) in the lipolytic activity of adipocytes, a study was carried out in which an increase in MUFA was produced in the tissues by two different methods; by the dietary enrichment of oleic acid or by producing an essential fatty acid deficiency syndrome. For this, forty-five male Sprague–Dawley rats were fed with a normal-energy diet and were subdivided into three groups. The diets varied in the type of dietary fat; palmitic acid, olive oil, or soyabean oil+palmitic acid. At the end of the study measurements were taken of weight, plasma leptin, tissue concentration of fatty acids, fat-cell size in the epididymal and the omental adipose tissues, adipocyte lipolytic activity of both tissues after stimulation with adrenaline, and the capacity of insulin to inhibit lipolysis. The baseline and adrenaline-stimulated lipolytic activity were greater and the anti-lipolytic capacity of insulin lower in the animals undergoing an increase in MUFA in the tissues (palmitic-acid and olive-oil diets). The area under the curve of glycerol, used as an indicator of lipolytic activity, was positively correlated with the concentration of MUFA and negatively with polyunsaturated fatty acids in the adipose tissues. It is concluded that an increase in tissue MUFA, however obtained, induces an increase in lipolytic activity.

Injection of orexin A into the diagonal band of Broca induces symphatetic and hyperthermic reactions

This experiment tested the effect of an injection of orexin A into the diagonal band of Broca on the sympathetic activity and body temperature. Concentration of glycerol into white fat of lumbar region, firing rates of sympathetic nerves to interscapular brown adipose tissue (IBAT), IBAT and colonic temperatures, and heart rate were monitored in urethane-anesthetized male Sprague-Dawley rats for 30 min before and 150 min after injections of orexin A (0.4 and 0.7 nmol) into the diagonal band of Broca. The same variables were monitored in control rats with an injection of saline. The results show that orexin A increases glycerol concentration, sympathetic firing rate, IBAT and colonic temperatures, and heart rate. The saline injection did not induce any modification. These findings suggest that the diagonal band of Broca is a cerebral structure involved in the induction of the hyperthermia due to orexin A.

Fat accumulation in the rat during early pregnancy is modulated by enhanced insulin responsiveness

Insulin sensitivity has been implicated in the variation of fat accumulation in early gestation by as-yet-unknown mechanisms. In the present study, we analyzed the insulin sensitivity of lipolysis and lipogenesis in lumbar adipocytes from rats at 0, 7, 14, and 20 days of gestation. In adipocytes of 7-day pregnant rats, we found a twofold decrease in both beta-agonist (isoproterenol and BRL-37344)-stimulated lipolysis and beta3-adrenoceptor protein but not in lipolysis initiated by forskolin or isobutylmethylxanthine, suggesting a modification of the lipolytic pathway at the receptor level. Whereas adipocytes from 7-day pregnant rats showed a twofold increase in fatty acid synthesis from glucose, those from 20-day pregnant animals displayed a decreased lipogenic activity. Insulin responsiveness of the lipolytic and lipogenic pathways was analyzed by dose-response experiments, giving evidence for the involvement of improved insulin responsiveness in the enhanced lipogenic and reduced lipolytic activities of adipocytes in early pregnancy. In contrast, insulin resistance is responsible for lower antilipolytic and lipogenic actions of insulin in late pregnant animals. In conclusion, the present study shows that enhanced adipose tissue insulin responsiveness during early pregnancy contributes to maternal fat accumulation, whereas decreased insulin responsiveness during late gestation modulates fat breakdown.