Malpighian bodies

The functional unit of the kidney is the nephron. It is made up of the Malpighian bodies or renal corpuscles (consisting of Bowman s capsules and the glomerulus), the proximal tubule, Henle s loop, and the distal tubule, which passes into a collecting duct. The human kidney contains around one million nephrons. The nephrons form urine in the following three phases. 

Malpighian body (Malpighian corpus-cie) The part of a nephron in the kidney that consists of its cup-shaped end together with the giomeruius that it encioses. it is named after its discoverer, the itaiian anatomist Marceiio Maipighi (1628-94). 

Bowman W. On the structure and use of the Malpighian bodies of the kidney with observations on the circulation through them. Philos Trans R Soc Land 132 57-80, 1842. 

Far less is known about excretion by terrestrial insects than by terrestrial mammals. Metabolism can take place in the midgut and fat body. Excretion can occur via the malpighian tubules. 

Most of these studies have established that the enzyme is located in the mitochondrial fraction of tissue homogenates, although the enzyme in the fat body and Malpighian tubules of Locusta is reportedly associated with the microsomal fraction (30). All studies concur that the enzyme is a cytochrome P-450-mediated mixed-function oxidase and its requirements for NADPH and 02 and sensitivity to inhibitors such as carbon monoxide, metyrapone, etc., support this conclusion. As yet, there are no reports as to whether the enzyme is associated with an iron sulfur protein similar to the adrenodoxin of the mammalian mitochondrial steroid... 

Nitrobenzene reductase activity has been detected in the fat body, gut, and Malpighian tubules of the Madagascar cockroach, G. portentosa (Rose and Young, 1973). Anaerobic conditions are essential for activity. The enzymes in the microsomes are strongly NADH dependent, whereas those in the soluble fraction are strongly NADPH dependent. Activity is enhanced by the addition of flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN) or riboflavin. It appears that the true substrate for the nitroreductase is FMN and that the reduction of the nitro compounds occurs nonenzymatically (Figure 8.15). Similar results are obtained using azofuchsin as substrate. 

In insects, ecdysone is secreted from the prothoracic glands (PG) at every moulting and pupal stage. Conversion of ecdysone to 20-hydroxyecdysone occurred in fat body, Malpighian tubules, gut and body wall tissues [189]. Although ecdysone may have direct hormonal effects, it is generally held that ecdysone serves as a prehormone that is converted to 20-hydroxyecdysone which functions as the active hormone. This is because in many bioassay systems, 20-hydroxyecdysone appears to be much more active than ecdysone. 

Once OPs enter the body, they are mainly metabolized in the liver, gastrointestinal tract, malpighian tubulc.s, and body fat by mixed function oxida.ses, which further increase their toxicity. Oxidative desulfuration of OPs leads to maximum anticholincstera,se activity. To consider the possible toxic effect of OPs, it is necessary to take into account the type of chemical and the species in question because there are wide differences. For example, in vertebrates, after one. single exposure to OP pesticides the recovery time from the amicholincsicrase effecl-s ranges from I to 3 weeks, whereas only approximately 1 day is necessary to recover from exposure to a CM pesticide. Birds and mammals have similar metabolic responses to anticholinesterase pesticides. However, birds tend to be more sensitive to their toxic action, probably due to lower levels of metabolizing enzymes. 

The enzymatic activation of xenobiotics is known to take place in those organs in which the endoplasmic reticulum is developed. In insects, these functions are believed to be executed in fat bodies, Malpighian tubules, and various parts of the digestive tract. The age-activity profile of the relevant enzyme(s) in the silkworm shows that the most potent activity is seen in the late larval stage hence, the detection can be most effectively carried out by administering a test compound at this stage. 

---