Biological potency and radioimmunoassay of canine calcitonin.
Calcitonin (CT) is a major calcitropic hormone. Because of low cross reactivity of canine CT (cCT) in radioimmunoassays (RIA) developed for other species, a homologous RIA is needed. Synthesis of cCT allowed study of its biologic potency using a rat bioassay and its plasma half-life in dogs. The availability of cCT also made possible the development of a homologous RIA for measurement of basal and stimulated plasma CT concentrations in dogs. The biologic potency of the synthesized cCT in rats is 24 IU/mg of peptide, which is low in comparison with the 4,000 IU/mg of the salmon CT standard. In the dog, an even lower potency of 4.4 IU/mg of cCT was found. Measurement of the disappearance of iv-injected radioiodinated or nonradioiodinated cCT revealed a short biologic half-life of less than 3 min, followed by a long half-life of 20 min. A polyclonal antiserum against synthetic cCT was raised in a goat. Using a final antiserum dilution of 1:12,000 and 125I-labeled synthetic cCT, the RIA had a detection limit of 6.5 ng/l. The antibody did not crossreact with standard human CT and had <0.1% cross reactivity with porcine CT. For measurement of plasma cCT concentrations, an extraction procedure was developed using ethanol. Dilutions of synthetic cCT and canine plasma extracts revealed parallelism over a wide range of concentrations. Size exclusion chromatography of canine plasma extracts on Biogel P-10 revealed a single cCT peak at the same position as [125I]-cCT, showing that there was little interference by other proteins or cCT prohormone. Basal plasma CT concentrations were 12-80 ng/l, and there was an 8- and 20-fold increase after calcium (1 and 2.5 mg/kg body weight) bolus infusion.
Hazewinkel
H A
HA
Department of Clinical Science, Companion Animals, Utrecht, The Netherlands. H.A.W.Hazewinkel@vet.uu.nl
Schoenmakers
I
I
Pelling
D
D
Snijdelaar
M
M
Wolfswinkel
J
J
Mol
J A
JA
D000818:Animals; D002116:Calcitonin / Q000493:pharmacokinetics / Q000502:physiology*; D003429:Cross Reactions; D004285:Dogs; D006207:Half-Life; D006801:Humans; D008297:Male; D011863:Radioimmunoassay / Q000662:veterinary*; D051381:Rats
D002116:Calcitonin