Indication for Different Mechanisms of Kidney Uptake of Radiolabeled Peptides

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FIGURE 1.
(A) Renal accumulation of OCT in %IA/g 24 h after injection. Lys and GF significantly inhibit renal accumulation of OCT. Combination of both is more efficient in comparison with the single substances. (B) PGA does not show significant reduction of OCT uptake, whereas Lys (serving as control) does.
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FIGURE 2.
(A) Renal accumulation of MG in %IA/g 24 h after injection. GF and PGA significantly inhibit tubular accumulation of MG, whereas Lys does not. (B) Combination of GF and PGA does not exceed efficacy of PGA alone.
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FIGURE 3.
Renal accumulation of BOM in %IA/g 24 h after injection. BOM shows pattern comparable to that of MG as renal uptake can be reduced by PGA and GF, whereas Lys is not effective.
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FIGURE 4.
Renal accumulation of EX in %IA/g 24 h after injection. EX shows same pattern of uptake inhibition as MG and BOM, indicating that uptake mechanism may be the same. Combination of PGA and GF shows additive effect (significant in comparison with single substances).
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FIGURE 5.
Results of kidney autoradiography: (A) OCT, (B) MG, (C) EX, (D) BOM (from left to right). All compounds are colocalized in renal cortex; image quality reflects renal uptake of respective compounds.

TABLE 1

Overview of Influence of Different Substances on Renal Uptake of Radiopeptides

Radiopeptide	Lys	GF	PGA	GF + Lys	GF + PGA
OCT
0.97 ± 0.18	0.63 ± 0.07	0.57 ± 0.05	1.11 ± 0.1	0.49 ± 0.05	Not done
1.33 ± 0.28	P < 0.01	P < 0.01	P = 0.14	P < 0.01 (Lys)
				P = 0.01 (GF)
MG
12.16 ± 1.78	12.11 ± 1.04	6.69 ± 0.78	1.77 ± 0.25	Not done	1.95 ± 0.18
9.8 ± 0.77	P = 0.57	P < 0.01	P < 0.01		P < 0.05 (GF)
		6.89 ± 0.18	1.89 ± 0.14		P = 0.51 (PGA)
BOM
0.35 ± 0.06	0.34 ± 0.06	0.3 ± 0.02	0.27 ± 0.03	Not done	Not done
	P = 0.51	P = 0.005	P = 0.038
EX
20.52 ± 1.86	21.86 ± 2.57	16.68 ± 1.01	14.48 ± 1.43	Not done	12.08 ± 1.01
	P = 0.8	P < 0.01	P < 0.01		P < 0.01 (PGA, GF)

Kidney uptake values are given as mean ± SD in %IA/g. If results have not been obtained in 1 set of experiments, alternative results belonging together are given in italic. In the last 2 columns on the right, P values indicate significance in comparison with respective single substances.