Inactivation of porcine corpus luteum lutropin receptors by a microsomal enzyme: Activation in ageing and regressing corpora lutea

The binding of ¹²⁵I-labelled human choriogonadotropin (hCG) to homogenates of porcine corpora lutea showed a marked departure from ideal behaviour, due to a time- and temperature-dependent inactivation of both free hormone and unoccupied receptors. Occupied receptors were not affected. Lutropin (LH)-receptor-inactivating activity was detected after preincubation of homogenates, particulate fractions and microsomes, but little activity could be demonstrated in cytosol fractions. Inactivation was dependent on the temperature and pH of preincubation, and on tissue concentration: LH-receptor inactivation was first-order with respect to preincubationtime. Lutropin-receptor-inactivating activity was low in early-luteal and mid-luteal phase in pig corpora lutea, but was increased significantly in late-luteal and regressing corpora lutea.     

Liver extract (chalone) antimitotic activity assayed with chick embryos

Extracts prepared from the 30 % distilled water homogenates of rat liver have been found to contain an anti-mitotic factor(s). In the 15-day-old chick embryo, the antimitotic effect was tissue specific in that only hepatocytes and not control tissues had depressed mitotic indices. The antimitotic effect was observable by 4 h after egg shell air sac injection but abolished by 8 h. These data are consistent with the presence of a G2—M blocking factor. These data also indicate that the 15-day-old chick embryo will be useful as a chalone assay system.