In order to explore the feasibility of using allogenic transplanted hepatocytes as an ectopic liver, an experiment was conducted in which hepatocytes were transplanted (2.5 times 10^7 cell/rat) into the spleens of rats that were rendered a hepatic (complete removal of the liver) (Markopoulos et. al., Hepatology, 28, 1998, 1365-1370). Recall that one of the liver\'s functions is to convert ammonia to urea for excretion in the urine. According to the paper, it was observed that, 12 hours after total hepatectomy, the Group 3 rats (those which had received the transplanted hepatocytes) had removed much more ammonia from their blood than the Group 4 rats (the controls that had only received saline injections). Use the results in the table, as well as the information that follows, to critically analyze the researchers\' findings. NH_3 present in Group 3 and Group 4 rats. 12 hours post-transplantation is given in following table Useful information: There are about 1 billion hepatocytes in a normal rat liver A healthy rat liver excretes 0.08g of nitrogen daily, with ~ 85% of it in the form of urea Chemical structure of urea is Rat intravascular plasma volume is 11 mL Extracellular volume in tissue (interstitial volume) is 43mL. Total fluid volume is equal to extracellular fluid volume (intravascular + interstitial volume) plus intracellular fluid volume What is the production rate of urea per hepatocyte (in a healthy liver)? Based on the results of Markopoulos s experiment, calculate the rate of NH_3 clearance in the Group 3 rats (with transplanted hepatocytes). Using results in part (b), calculate the rate of urea production in the rats with transplanted hepatocytes. What is the urea production rate for each transplanted hepatocyte? How does this compare with the function of hepatocyte in normal liver? What are some possible reasons for the discrepancy in hepatocyte function (between transplanted and normal cells) calculated in part (d)? Why wore rats given Cyclostome A? If we assume that some of the transplanted cells engraft and live and some of the cells die, then what implications does this have for gene therapy?
a)
A healthy rat liver excretes 0.08g of Nitrigen daily , with 85% in form of urea. From th The chemical formula of urea tells us that 28g N is present per 60g of urea. From this knowledge we can find that 0.146g of urea is excreted per day. Approx.. 10^9 hepatocytes are present per rat iver. From this info the urea production rate is 6x 10^-12g urea per hepatocyte per hour in a healthy rat liver
b)
Table 1 data (refer). The difference between the ammonia removal in transplanted and v/s control hepatocytes is 602µg/dl/12h. This is equivalent to 5.02 x 10^-4 g/L/h. Exttracellular fluid volume is 54 mL (Interstitial + Intravascular). Thus we have a Nh3 clearnce rate of (5.02 x 10^-4 g/L/h) x (54 x 10^-3 L) =
2.72 x 10^-5 g ammonia /h.
(c) Using results in part (b), calculate the rate of urea production in the rats with transplanted hepatocytes.
Rate of urea oroduciton in rats with transplanted hepatocytes is
= 2.72 x 10^-5 g ammonia /h x (14g N / 17g ammonia) x 60g urea / 28g N
= 4.78 x 10^-5 g urea/h
(d) What is the urea production rate for each transplanted hepatocyte? How does this compare with the function of hepatocyte in normal liver?
The no.of cells translplanted into each rat = 2.5 x 10^7 cells.
Therefore, urea production for each transplanted is =
(4.78 x 10^-5 g urea/h ) / (2.5 x 10^7 cells.) = 1.91 x 10^-12g urea /hepatocyte /h
We find that the normal hepatocytes ( part a ) is 3 times more functional than translplanted hepatocyte.
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