Chris R. Thomas

Placental Transfer of Non-Esterified Fatty Acids in Normal and Diabetic Pregnancy

The placental transfer of non-esterified fatty acids, predominantly in the direction of mother to fetus, is regulated on a gross scale by the transplacental non-esterified fatty acid gradient. This is maintained by fetal liver lipid uptake and by enhanced lipolysis of circulating triacylglycerol in the pregnant mother. It is also dependent upon maternal placental blood flow, which is reduced in diabetes, upon the fetal umbilical blood flow, upon maternal and fetal albumin concentrations and upon intratrophoblastic fatty acid binding protein, which appears to be altered in diabetes. Circulating maternal triacylglycerols also directly contribute non-esterified fatty acids to the fetus by intraplacental hydrolysis and the hypertriglyceridaemia associated with maternal diabetes, in concert with changes in lipase levels will enhance maternal to fetal lipid flux.

Studies on the Placental Hydrolysis and Transfer of Lipids to the Fetal Guinea Pig

Early studies on the placental transfer of lipids using the sheep (James et al., 1971) and the rat (Koren and Shafrir, 1964) suggested that very little fat was transferred from mother to fetus. The majority of fetal lipids were assumed to be formed from transferred maternal glucose (Coltart, 1972). However, investigations in species such as rabbit (Elphick et al., 1975), guinea pig (Hershfield and Nemeth, 1968; Bohmer and Havel, 1975), primate (Portman et al., 1969) and more recently in the rat (Hummel et al., 1974) indicated that not only did free fatty acids (FFA) readily cross the placenta, but that they did so in amounts exceeding those required to fulfill lipid storage requirements (Jones, 1976).

Growth hormone increases IGF-I, collagen I and collagen III gene expression in dwarf rat skeletal muscle

The effect of short-term treatment with biosynthetic growth hormone (GH) of male dwarf rats was studied in EDL and soleus muscles. In situ hybridisation revealed that in the untreated dwarf rat collagen I, collagen III and insulin-like growth factor-I (IGF-I) mRNA is mainly expressed by fibroblasts between the muscle fibre areas. Quantitative image analysis showed that, 8 h after a single GH injection, the level of mRNA for all three genes increased compared to the untreated dwarf animal. IGF-I mRNA levels were similar in normals and untreated dwarf rats but significantly increased 8 h after a single GH injection in EDL (P < 0.01) and soleus (P < 0.001). In untreated dwarf rats, collagen I and III gene expression was significantly less than in normal animals (P < 0.001). Collagen III gene expression also increased significantly 8 h after a single GH injection, in both muscles (P < 0.01). Collagen I gene expression showed significant increases 8 and 24 h after GH treatment in EDL (P < 0.01), although the increases seen in soleus did not reach significance. The effects of multiple GH injections (one, two or four) did not appear to be additive. The results of the time course studies are consistent with an intermediary role for IGF-I in the production of collagen in muscle.

Upregulation of IGF-I and collagen I mRNA in human atherosclerotic tissue is not accompanied by changes in type 1 IGF receptor or collagen III mRNA: an in situ hybridization study.

BackgroundImmunoreactive insulin-like growth factor-I (IGF-I) has recently been localized to vascular smooth muscle cells in coronary atherectomy plaques, but it remains unclear whether these cells are the source of this growth factor. We therefore investigated the gene expression of this factor, and the expression of the genes for its receptor and two types of collagen known to be regulated by IGF-I, in vascular tissue samples from patients with atherosclerosis or restenosis. MethodsGene expression and localization were investigated by in situ hybridization, using 35S-labelled complementary RNA probes specific for IGF-I, its type 1 receptor, collagen I, and collagen III. The cellular composition of the tissue samples was determined by immunohistochemistry using antibodies specific for smooth muscle cells and macrophages. ResultsIGF-I and collagen I messenger RNAs were found in areas containing smooth muscle cells and macrophages, but collagen III and type 1 IGF receptor gene expression could not be detected in any tissue samples. ConclusionIGF-I appears to be involved in the progression of the atherosclerotic plaque, even at an advanced stage, but preliminary data from two restenotic plaques indicate that it may not be involved in the later stages of restenosis.

Placental transfer and uptake of 2-deoxyglucose in control and diabetic rats

Placental glucose transfer and sequestration were investigated in anesthetized control and streptozotocin-diabetic rats by perfusing the fetal side of one placenta in situ while infusing a mixture of [3H]D-glucose (to measure net transfer after metabolism) and [14C]2-deoxyglucose (to estimate tissue sequestration) into the maternal circulation. No difference was found between transfer ratios (perfusate/simultaneous maternal plasma ratio) of [3H]D-glucose (0.35 +/- 0.06, mean +/- SD) and [14C]2-deoxyglucose (0.36 +/- 0.06) in control rats. Ratios were reduced (P < .001) to the same extent in diabetic rats ([3H]D-glucose, 0.13 +/- 0.06; [14C]2-deoxyglucose, 0.15 +/- 0.07). Placental glucose utilization, estimated by the quantity of [14C]2-deoxyglucose-6-phosphate present, was increased from 66 nmol.min-1.g-1 in control to 595 nmol.min-1.g-1 (P < .001) in diabetic rats. Transfer to the perfusion fluid of unlabeled D-glucose was increased (P < .001) in diabetic rats (2.32 mumol/mL) compared with control rats (0.77 mumol/mL) due to elevated (P < .001) maternal plasma glucose levels. Upon phosphorylation, 2-deoxyglucose becomes trapped within the placenta, and therefore these results indicate that all the glucose destined for direct transfer to the fetus is protected from phosphorylation while traversing the placenta, and that diabetes appears to increase placental glucose utilization, but does not induce futile cycling of glucose in an attempt to protect the fetus from an excessive influx of glucose from the mother in the rat.

Effects of hypophysectomy and growth hormone administration on the mRNA levels of collagen I, III and insulin-like growth factor-I in rat skeletal muscle.

The effect of short-term treatment of normal or hypophysectomized rats with biosynthetic growth hormone (GH) was studied in extensor digitorum longus and soleus muscles. In situ hybridization revealed that in normal rats, mRNA for collagen I, collagen III and insulin-like growth factor-I (IGF-I) are expressed by fibroblasts between the muscle fibre areas and that the specificity of this location was not altered by GH administration. Hypophysectomy appeared to cause a decrease in IGF-I and decreased collagen I and III gene expression (P < 0.001, P < 0.001, respectively). GH administration seemed to increase IGF-I mRNA levels in all the animals studied. Quantitative image analysis that GH administration to hypophysectomized rats caused an increase in collagen I gene expression after 2 days (P < 0.05) and an increase in collagen III gene expression after 4 days (P < 0.05). The results indicate that the fibroblast cells are an important target for the action of GH on skeletal muscle and that the fibroblasts respond to GH by increases in the expression of mRNA for collagen I and collagen III.

Placental Transfer of Lactate, Glucose and 2-deoxyglucose in Control and Diabetic Wistar Rats

Placental transfer of lactate, glucose and 2-deoxyglucose was examined employing the in situ perfused placenta. Control and streptozotocin induced diabetic Wistar rats were infused with [U14C]-glucose and [3H]-2-deoxyglucose (2DG). The fetal side of the placenta was perfuseci with a cell free medium and glucose uptake was calculated in the adjacent fetuses. Despite the 5-fold higher maternal plasma glucose concentration in the diabetic dams the calculated fetal glucose metabolic index was not significantly different between the 2 groups. Placental blood flow was reduced in the diabetic animals compared with controls but reduction of transfer of [U14C]-glucose and [3H]-2-deoxyglucose and endogenously derived [14C]-Lactate to the fetal compartment, could not be accounted for by reduced placental blood flow alone. There was no significant net production or uptake of lactate into the perfusion medium that had perfused the fetal side of the placenta in either group. The plasma lactate levels in the fetuses adjacent to the perfused placenta were found to be higher than in the maternal plasma and significantly higher in the fetuses of the diabetic group compared with control group. In this model the in situ perfused placenta does not secrete significant quantities of lactate into the fetal compartment in either the control or diabetic group.