KINETICS OF RAPID ⁴⁵Ca UPTAKE INTO CHICK SKELETON IN VIVO: EFFECTS OF MICROWAVE FIXATION

Abstract

SUMMARYWe have investigated uptake kinetics for 45Ca labels acutely administered as single intravenous injections into twelve-day-old chicks in vivo. Effects of microwave fixation on this process have aJlso been studied. Rapid uptake of 45Ca was demonstrated into the skeleton with approximately 40 % of injected label being found in the skeleton within the first 15 min. By 45 min tissue 45Ca levels had stabilized and showed little change during the following 90 min. Soft tissue isotope levels declined during the period from 3 to 135 min following injection. These data were obtained from animals in which tissue isotope levels were stabilized by fixation with microwaves at the point of killing by cervical dislocation. In animals where the microwave fixation step was omitted and tissues were dissected for counting at least 1 h after killing, 45Ca levels in both skeletal and soft tissues were 15-20 % higher than in those from microwaved groups during the period 3-15 min after injection. In a separate experiment, groups of chicks killed by cervical dislocation 3 min after isotope injection were fixed with microwaves at time intervals ranging from 0 to 45 min post-mortem. Isotope levels in femur increased with time and were significantly higher in groups in which fixation was carried out 12 and 45 min after death when compared with those fixed at the point of death. Data in calvarium reflected those in femur but were not statistically significant at the time intervals tested. Estimates of unidirectional plasma-bone Ca2+ influx (JPb40Ca) into chick bone indicate high values for femur, > 1 64,tmol min-' (g wet weight)-' and calvarium, > 1 26 /umol min-1 (g wet weight)-', respectively. This suggests that Ca2+ is cleared very rapidly between blood plasma and exchangeable pools in the skeleton of the chick. Estimated JPb40Ca values decline appreciably over short (15 min) time intervals, suggesting that significant backflux of the 45Ca marker occurs. These data collectively indicate that uptake of 45Ca into skeletal tissues occurs rapidly following its injection into chicks. 45Ca uptake continues for several minutes in the immediately post-mortem animal and this process is reduced by microwave fixation. It is important to bear these factors in mind, when considering the effects of hormones and drugs on the uptake of bone-seeking radionuclides.

Calcitonin gene‐related peptide promotes transient radiocalcium uptake into chick bone in vivo

“…However, this latter response is only apparent in 22-h-fasted chicks and not in those which are continuously fed. We have here investigated the possibility that this increased 45Ca clearance reflects its enhanced deposition into skeleton, since in chicks, 40 % of an injected bolus dose of 45Ca enters the skeleton within 45 min (Shaw, Whitaker & Dacke, 1989). A preliminary report of our findings in a pilot experiment has been presented elsewhere .…”

“…K. ANCILL AND OTHERS dissected from carcasses, ashed in a muffle furnace and dissolved in 2-3 ml 1 M-perchloric acid (Shaw et al 1989). Radioactivity was measured in 100 gl aliquots by liquid scintillation spectrometry; 45Ca uptake was standardized to bone Ca content (measured using Sigma Kit No.…”