Radiopharmacological profiles of tracers under pathophysiological conditions. Bone uptake of 99mTc-phytate in vitamin D deficient rats.
The radiopharmaceutical 99mTc-phytate, formed by reacting the phosphatic ligand, myo-inositol hexakisphosphate with a reduced form of 99mTcO4-, is widely employed in diagnostic nuclear medicine for scinti-imaging the RE system. Despite it being a compound derived from a ligand containing phosphatic functional moieties it does not concentrate to a significant extent in the osseous tissue following i.v. injection into animals or humans. Neither has there been any clinical report citing its localization in the skeletal tissue consequent to its i.v. injection into patients with different types of pathophysiological conditions/metabolic bone disorders. In the course of our study of the homing characteristics of radiopharmaceuticals into specific organ systems or secondary target sites we found that 99mTc-phytate could be directed to some extent into the skeletal tissues of experimental rats by altering its physiological milieu--viz. by decreasing blood calcium levels and increasing bone resorption. Such an altered physiologic condition is obtained by experimentally inducing vitamin D deficiency in animals. Our results show that 8-10% of the administered dose could be redirected to the bone matrix but at the expense of the liver. The study also indicates that many so-called organ specific 99mTc-radiopharmaceuticals could have more than one target tissue/organ system for accumulation consequent to being introduced into the systemic circulation. In a number of instances the secondary target may be masked and may be elicited only under certain specific pathophysiologic conditions.
Noronha
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Bhabha Atomic Research Centre, c/o Tata Memorial Hospital Annexe, Parel, Bombay, India.
Pahuja
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D000818:Animals; D001842:Bone and Bones / Q000000981:diagnostic imaging* / Q000378:metabolism; D008297:Male; D009942:Organometallic Compounds / Q000493:pharmacokinetics*; D015609:Organotechnetium Compounds; D010833:Phytic Acid / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D051381:Rats; D011919:Rats, Inbred Strains; D013667:Technetium; D014808:Vitamin D Deficiency / Q000000981:diagnostic imaging* / Q000378:metabolism
D009942:Organometallic Compounds; D015609:Organotechnetium Compounds; C026177:technetium phytate; D013667:Technetium; D010833:Phytic Acid