Nerve growth factor transiently increases tetrahydrobiopterin and total biopterin contents of pheochromocytoma PC12h cells

Nerve growth factor (NGF) is known to induce differentiation of pheochromocytoma into sympathetic neuron-like cells. Tetrahydrobiopterin (BPH4) and total biopterin (BP) levels in PC12h, a subclonal line of PC12, were transiently increased by NGF: the increase in BPH4 and BP reached the maximum (20-25 ng/mg protein = about 2-fold over the control level) at 24 h after the treatment was started. After 2-3 days, the BPH4 and BP levels decreased to the same level as in control cells. The NGF concentration which gave a half maximal BP increase by 24 h-treatment was around 1 ng/ml.     

Intestinal iron absorption

Intestinal iron absorption is a critical process for maintaining body iron levels within the optimal physiological range. Iron in the diet is found in a wide variety of forms, but the absorption of non-heme iron is best understood. Most of this iron is moved across the enterocyte brush border membrane by the iron transporter divalent metal-ion transporter 1, a process enhanced by the prior reduction of the iron by duodenal cytochrome B and possibly other reductases. Enterocyte iron is exported to the blood via ferroportin 1 on the basolateral membrane. This transporter acts in partnership with the ferroxidase hephaestin that oxidizes exported ferrous iron to facilitate its binding to plasma transferrin. Iron absorption is controlled by a complex network of systemic and local influences. The liver-derived peptide hepcidin binds to ferroportin, leading to its internalization and a reduction in absorption. Hepcidin expression in turn responds to body iron demands and the BMP-SMAD signaling pathway plays a key role in this process. The levels of iron and oxygen in the enterocyte also exert important influences on iron absorption. Disturbances in the regulation of iron absorption are responsible for both iron loading and iron deficiency disorders in humans.     

Intestinal absorption of fat

Summary It is generally accepted that between 50 and 70% of the fatty acids of ingested triglycerides are hydrolyzed prior to absorption and yet migration between the 2 and 1,3 positions is minimal. The occurrance of the monoglyceride pathway for triglyceride biosynthesis provides a logical explanation for these findings. In addition, this sequence provides a logical explanation of the particulate and lipolytic theories. Triglycerides are hydrolyzed at the 1 and 3 positions giving rise to fatty acids and 2-monoglycerides, which in combination with bile salts form micelles and penetrate the intestinal membrane. The fatty acids are activated to the respective CoA derivatives and acylate the 2-monoglyceride forming triglycerides. The triglyceride thus synthesized, has a similar chemical structure with regard to the 1,3 and 2 position as the original triglyceride. The triglyceride is coated with a-lipoprotein and is transformed into chylomicrons which enter the thoracic duct lymph.It is suggested that this mechanism be referred to as the PARLIP sequence since, particles in the form of micelles are involved in the absorption, and in addition a considerable amount of lipolysis occurs. This terminology would represent a scientific merger of the particulate and the lipolytic theories into a common sequence, while maintaining some identity in recognition of the numerous investigations that have occurred in the past 100 years to support these two basic postulates.     

Intestinal iron absorption in chickens

Intestinal iron absorption in chickens was studied in vivo, using an intestinal perfusion technique in closed circuit. The results obtained show that iron absorption, at 30 min intervals, is a linear function of test solution iron concentrations of up to 776 μg Fe/20 mL. At higher concentrations, iron saturation occurs. The mucosal epithelial cells seem to be less a limiting factor than in rats. However, in chickens, the binding capacity of plasma might play an important role in the regulation of iron absorption. Iron absorption versus time was analyzed in 15, 30, 60, and 120 min periods for the iron concentration of 14 μg Fe/20 mL. Intestinal iron absorption showed a linear relationship between these two parameters. A period of perfusion of either 30 or 60 min by a solution of 14 μg Fe/20 mL appears suitable since no interference by a saturation process can then occur.     

Intestinal cholesterol absorption.

The strong association between intestinal cholesterol absorption and total plasma cholesterol level has renewed interest in the absorptive process and stimulated the generation of new animal models. Increasingly, new studies suggest that cholesterol absorption is genetically controlled and supports a protein-mediated mechanism for cholesterol uptake into the intestinal mucosal cell. Insights into potential mechanisms are predicted to lead to novel pharmacological approaches to inhibit cholesterol absorption.