Metabolic and endocrine modulation of anabolic and catabolic pathways of glucose and fatty acids. I. Chemical anatomy of the major metabolic pathways of the energogenic general function.

This study is an attempt to integrate the intermediary metabolism of energogenic substrates--glucose and fatty acids--within the framework of the energogenic general function (EGF), which is active in two distinct phases: anabolic and catabolic. EGF is a component of the metabolic general function (MGF), which together with the reproductive general function and the adaptation general function may be taken to represent three main "general functions of organisms" common to all beings, whether animal or vegetal. This initial paper presents, descriptively and graphically, the main anabolic functions and pathways of glucose and fatty acids and, separately, the main catabolic ones, in other words, the "chemical anatomy" of EGF. The study begins with the anabolic "digestive" function of the digestive tract, concerning the digestion and absorption of carbohydrates and proteins. Conversion of the non-absorbable macromolecules of ingested carbohydrates into absorbable micromolecules of glucose, is shown to enable the latter, after absorption, to carry out the two characteristic anabolic processes: transmembrane "transport" and "condensation". Absorption and vehiculation of hydrophobic lipids is carried out by means of the major function of intestinal cells: synthesis of chylomicrons. Chylomicrons are hydrophilic special lipoprotein particles which are able to transport fats to the adipose tissue and cholesterol to the liver. In the liver the anabolic aspects of EGF are represented by two main functions: glycogeno-genesis, i.e. "non-reductive" condensation of glucose into glycogen stores, and lipoproteino-genesis, i.e. "reductive" condensation of glucose into lipoproteins or VLDL (very low density lipoproteins). VLDL are hydrophilic (vehiculable) spheric particles (containing triacylglycerols and cholesteryl esters in their core, and phospholipids, cholesterol and apolipoprotein-B at their surface), which are to be released into the general circulation. The anabolic phase in the muscles is characterized by the transmembrane "transport" of glucose and its "condensation" into intracellular glycogen stores; in the adipose tissue it is characterized by accumulation of triacylglycerols. The chemical anatomy of the "gluco-keto-productive" catabolic liver is clearly different from that of the "VLDL-productive" anabolic liver. Hepatic production of glucose (gluco-genesis) is achieved via glycogeno-lysis and via gluco-neo-genesis (GNG) from lactate, amino acids and glycerol. Hepatic production of ketone bodies (keto-genesis) is achieved through processing the fatty acids mobilized from the adipose tissue.(ABSTRACT TRUNCATED AT 400 WORDS)