J. A. McCRACKEN and B. V. CALDWELL
B. V. CALDWELL and R. M. MOOR
It has been well established that removal of the uterus in many mammalian species results in the prolongation of the function and life-span of corpora lutea (Bland & Donovan, 1966; Anderson, Bland & Melampy, 1969; Caldwell, Rowson, Moor & Hay, 1969; Schomberg, 1969; Caldwell, 1970). Furthermore, most evidence suggests that uterine transplantation to ectopic sites can at least partially reverse the extended life-span of the corpora lutea in hysterectomized animals (see Caldwell, 1970, for review). When these studies were extended to test various extracts of uterine tissue or flushings, however, the results were not conclusive. Both success and failure have been reported in the attempt to influence corpus luteum function in hysterectomized animals using extracts of uterine origin given by several routes of administration in various test animals and bioassay systems (Schomberg, 1969; Caldwell, 1970). Previous work has also
B. V. CALDWELL, R. M. MOOR and R. A. S. LAWSON
The normal length of pseudopregnancy in hamsters (9·2 days) is doubled (18 days) following hysterectomy. Transplanting either one hamster uterine horn, or pieces of endometrium to the cheek pouch of hysterectomized animals significantly reduces the length of induced pseudopregnancy from 18 to 13·5 days (Caldwell, Mazer & Wright, 1967). These authors also reported that transplanting rat uteri to the cheek pouch also reduced pseudopregnancy in hysterectomized hamsters (14·8 days), whereas the effects of transplanting rabbit uteri (15·5 days) were not as conclusive. Human endometrium had no apparent shortening influence on the pseudopregnancy cycle length (17·5 days).
These results suggested that the regulatory effect of the uterus on the life span of corpora lutea may not be species specific and the present study was initiated to investigate the influence of sheep endometrium and endometrial preparations on the
B. V. CALDWELL, R. M. MOOR, I. WILMUT, C. POLGE and L. E. A. ROWSON
Corpora lutea induced in pigs on Day 6 regressed with the naturally formed corpora lutea towards the end of the cycle. Hormonal induction of corpora lutea on Days 8, 10 or 16 significantly prolonged the cycle despite involution of the original corpora lutea about 16 days after ovulation. The interval between the exogenous administration of hcg and the appearance of the next oestrus varied with the day on which the accessory corpora lutea were formed. The estimated functional life span of the corpora lutea induced on Days 6, 8, 10 and 16 was 12·5 14·5, 15·0 and 19·3 days respectively. That these induced corpora lutea were fully functional was shown by the luteal progesterone levels estimated using the protein-binding and u.v. spectrophotometric techniques.
Hysterectomy resulted in both the spontaneous corpora lutea and those induced on Day 6 being maintained for at least 60 days.
It is concluded that Days 6 to 8 may represent a critical phase in the relationship between the uterus and the corpora lutea in non-pregnant pigs.
J. P. O'GRADY, E. I. KOHORN, R. H. GLASS, B. V. CALDWELL, W. A. BROCK and L. SPEROFF
Prostaglandins have been shown to be potent stimulants of cl steroid production in vitro (Pharriss & Wyngarden, 1969; Marsh, 1971; Speroff & Ramwell, 1970), yet prostaglandin F2α (PGF2α) given in vivo effectively inhibits progesterone secretion in rats, rabbits, guinea-pigs, sheep and the rhesus monkey (see Pharriss, Tillson & Erickson, 1972, for review). A better understanding of the possible rôle of prostaglandins has been confused by these paradoxical findings. In such studies, it would be of value to have as an experimental model, an in-vitro system in which it is possible to duplicate the inhibitory effects on luteal steroidogenesis seen with the use of PGF2α administered in vivo. This communication describes an in-vitro method in which sections of rabbit cl are maintained