Effects of Oestrogen, Administered Early or Late in the Oestrous Cycle, Upon the Survival and Regression of the Corpus Luteum of the Guinea-Pig

Abstract

The lytic effect of oestrogen administered within the first 5 days of ovulation in the guinea-pig can be abolished by hysterectomy and is greatly reduced by hypophysectomy. After Day 9 of the cycle, large doses of oestrogen resulted in the maintenance of the CL for at least 3 weeks after ovulation, and in many instances for more than 4 weeks, and their further growth to sizes seen after hysterectomy or during pregnancy (3\ m=. \ 2 \ m=+-\ 0\m=.\3 mm3). These large CL contained and secreted more progesterone than those of the normal cycle. Hypophysectomy did not abolish the antiluteolytic effect of oestrogen. A luteotrophic, not solely an antiluteolytic, effect of the hormone could be demonstrated. The luteolytic or luteotrophic action of oestrogen did not depend upon the age of the CL but upon pituitary and/or uterine factors. The study used mainly stilboestrol, but similar results were obtained with oestradiol compounds.

Luteal expression of factors involved in the metabolism and sensitivity to oestrogens in the dog during pregnancy and in non‐pregnant cycle

“…Thus, for example, in the rat and rabbit, oestrogens have luteotropic potential, whereas exogenous administration of oestrogens in rhesus monkeys shortens luteal life span (Hassani et al., 1978 ; Karsc & Sutton, 1976 ; Miller & Keyes, 1978 ; Townson et al., 1996 ; Tripathy et al., 2016 ). In the guinea pig, E2 effects appear to be time‐dependent, as administration of oestrogens in early dioestrus induces uterus‐mediated luteolysis, while application after day 9 of dioestrus prolongs luteal function (Illingworth & Perry, 1973 ). Interestingly, none of this is known for the dog, a species fully dependent on luteal steroids for the maintenance of pregnancy.…”

Follicular Growth and Estradiol Influence on Luteal Function in Mares

“…Increases in estrogen concentration during the luteal phase of the estrous cycle promote luteolysis in the cow (Brunner et al, 1969), hamster (Choudary and Greenwald, 1968), guinea pig (Illingworth and Perry, 1973) and ewe (Hawk and Bolt, 1970). The additional hormone is believed to originate within the growing follicles (Bjersing et al, 1972;Hixon et al, 1975).…”