RETENTION OF PLASMA SOMATOMEDIN ACTIVITY IN THE FOETAL RABBIT FOLLOWING DECAPITATION IN UTERO

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Abstract
One rabbit foetus within each litter was decapitated in utero on day 24 of gestation. Plasma somatomedin activity and costal cartilage metabolism were studied 5 days later in the experimental foetuses and control litter-mates. Somatomedin was assayed by the uptake of [35S]sulphate in vitro into costal cartilage from intact foetuses. Uptake was proportional to logarithmic increases in the concentration of both foetal and maternal rabbit plasma. The mean (± 1 s.d.) somatomedin activity of four plasma pools, each pool being derived from the intact foetuses within each of four litters, was 1·3 ± 0·3 compared with a potency of unity for the reference pool of maternal plasma. The plasma somatomedin activity of decapitated foetuses did not differ significantly from that of control litter-mates when analysed by rank test, but the costal cartilage of decapitated foetuses took up less [35S]-sulphate in basal medium when compared with that of intact litter-mates. The headless body weight of the decapitated foetuses did not rank in a position significantly different from the one expected. The concentration of plasma growth hormone in the decapitated foetuses was less than 5 ng/ml and that of the intact foetuses was more than 157 ng/ml. It is concluded that plasma somatomedin activity in the rabbit foetus is not dependent on foetal growth hormone.