Recombinant human thyrotropin administration enhances thyroid uptake of radioactive iodine in hyperthyroid cats.
BACKGROUND
Hyperthyroidism is the most diagnosed endocrine disorder in cats and radioiodine (131I) is the treatment of choice. The dose emission rate and radioactivity in urine, saliva, and on hair and paws are determined by the dose of administered 131I. A dose reduction of therapeutic 131I could possibly be achieved after recombinant human thyrotropin (rhTSH) administration as in humans with nodular goiter.


OBJECTIVE
rhTSH will increase radioiodine uptake in hyperthyroid cats.


METHODS
Five hyperthyroid cats.


METHODS
Twenty-five micrograms rhTSH (day 1) or 2 mL 0.9% sodium chloride (NaCl) (day 9) was injected IV. One hour later, 11.4 +/- 4.1 (mean +/- SD) MBq 123I was injected IV. Radioactive iodine uptake (RAIU) was measured 6, 12, and 24 hours after rhTSH (RAIU-rhTSH) or NaCl (RAIU-blanco) injection. Blood samples for measurement of TT4 were taken before injection of rhTSH or NaCl (TT4(0)) and at the time of imaging.


RESULTS
Percentages of RAIU-rhTSH (and RAIU-blanco) at 6, 12, and 24 hours after administration of rhTSH were 34 +/- 18 (31 +/- 21), 46 +/- 20 (38 +/- 18), and 47 +/- 15 (36 +/- 14). There was a statistically significant effect of rhTSH administration on RAIU (P = .043) but not on serum TT4 concentration. Baseline serum TT4(0) concentration influenced RAIU-rhTSH significantly at 6 hours (P = .037).


CONCLUSIONS
The increased RAIU observed after rhTSH administration in hyperthyroid cats could lead to a lower therapeutic dose of 131I after rhTSH administration in hyperthyroid cats and decreased risk of environmental and owner contamination during and after hospitalization.
van Hoek
I
I
Department of Medicine and Clinical Biology of Small Animals, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium. ingrid.vanhoek@ugent.be
Daminet
S
S
Vandermeulen
E
E
Dobbeleir
A
A
Duchateau
L
L
Peremans
K
K
D000818:Animals; D002371:Cat Diseases / Q000532:radiotherapy*; D002415:Cats; D006801:Humans; D006980:Hyperthyroidism / Q000532:radiotherapy / Q000662:veterinary*; D007455:Iodine / Q000627:therapeutic use*; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D013972:Thyrotropin / Q000494:pharmacology*
D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D013972:Thyrotropin; D007455:Iodine