Assessment of sheep blastocyst effects on neutral lipids in the uterine caruncular epithelium

Neutral lipids in the maternal uterine caruncular epithelium were studied by histochemical localization with Oil Red O. Results using a scoring system of 1 (negligible lipid) to 5 (maximal lipid) showed that intraepithelial lipid stores were minimal until Days 7-8 of the oestrous cycle and then increased to have a mean score of 4.4 on Day 14-15. In early pregnancy, although relatively high with a mean score of 3.2 at Day 15-16, such neutral lipids were significantly lower than those present at a comparable stage in the oestrous cycle. Thereafter, levels declined to a mean score of 1 on Days 21-23 of pregnancy. Such neutral lipid loss appears to be one of the first signs of the maternal response to the implanting embryo and precedes morphological evidence of transformation of either maternal or fetal tissues.     

Jugular levels of 13,14-dihydro-15-keto-prostaglandin F and progesterone around luteolysis and early pregnancy in the ewe

Six non-pregnant ewes at day 12 of the estrous cycle each had a day-12 embryo transferred into the uterine horn ipsilateral to the corpus luteum, and 4 non-pregnant ewes at day 13 each had a day-13 embryo similarly transferred. Four control ewes, 2 at day 12 and 2 at day 13 received sheep serum into the uterine horn ipsilateral to the corpus luteum. Jugular blood samples were taken at 2-hourly intervals for 3 days post-surgery, then twice-daily for a further 4 days, and the plasma radioimmunoassayed for progesterone and 13,14-dihydro-15-keto-prostaglandin F. All control ewes exhibited estrus within the expected time range and pulsatile peaks of 13,14-dihydro-15-keto-prostaglandin F occurred coincident with declining progesterone levels. With one exception, the recipient ewes had prolonged cycles and those ewes found pregnant at necropsy, 30 days after transfer, showed no progesterone decline and no pulsatile peaks of prostaglandin during days 12 to 16 after estrus. These observations suggest that the presence of the embryo at a critical stage after mating suppresses the release of uterine prostaglandin F_2α.     

Fluorescence studies of the binding of a yeast tRNAPhe derivative to Escherichia coli ribosomes.

The equilibrium binding of a highly fluorescent derivative of yeast tRNA^Phe to Escherichia coli 70 S ribosomes was studied fluorimetrically at 7 °C in 25 mm-magnesium. Under these conditions 70 S ribosomes bind two deacylated tRNAs stoichiometrically. An analysis of the binding data using a model in which occupancy of the weaker site requires prior occupancy of the stronger site leads to apparent association constants of (1.00 ± 0.05) × 10⁹m^?1 and (3.4 ± 0.2) × 10⁷m^?1. The use of an independent site model does not change these values appreciably. The observed binding constants do not depend upon the presence or absence of the messenger RNA, poly(U). However, spectroscopic evidence strongly suggests that the anticodons of both bound tRNAs are in contact with the message. This evidence further suggests that in the presence of poly(U) the environment of the hypermodified base adjacent to the anticodon is substantially different in the two sites. This may reflect a difference in the conformation of the anticodon loops or an interaction between the hypermodified base of the weak site tRNA and the anticodon loop of the strong site tRNA.