G. H. Zeilmaker

Hysterectomy, decidualization, LH concentrations and corpus luteum function in the rat*

Abstract In 1923 Loeb described that the uterus plays an important role in the control of corpus luteum function in the guinea pig: removal of the uterus resulted in a prolongation of the luteal phase. Similar findings have been reported for several other mammalian species (Anderson, 1972). In the rat, hysterectomy does not alter the duration of the estrous cycle (Perry and Rowlands, 1961), but the duration of pseudopregnancy (the equivalent of the luteal phase in the reproductive cycle of other mammalian species) is extended after hysterectomy. The fact that hysterectomy leads to a prolonged luteal phase in certain mammalian species, pointed to the existence of a uterine luteolytic factor (Schomberg, 1969). Some evidence for the existence of a uterine luteolytic substance is available for the rat. It was shown that after removal of the endometrium the duration of pseudopregnancy was extended to almost that observed in hysterectomized rats (Waynforth, 1965). Hechter, Fraenkel, Lev and Soskin (1940) could reduce in the rat the duration of pseudopregnancy with uterine transplants. Furthermore, the duration of pseudopregnancy was shortened after injections of endometrial suspensions (Bradbury, Brown and Gray, 1950) or aqueous endometrial extracts (Dobrowolski, Snochowski and Stupnicki (1974). These observations suggest that the endometrium is the source of the luteolytic factor, and recently evidence was provided that a prostaglandin could be the uterine luteolytic factor (Pharriss, Tillson and Brickson, 1972; Labhsetwar, 1974). Studies in sheep (McCracken, Carlson, Glew, Goding, Baird, Green and Samuelsson, 1972) and in the guinea pig (Blatchley, Donovan, Horton and Poyser, 1972) have provided some evidence for this concept. Also in the rat a prostaglandin may be the uterine luteolytic factor: treatment with prostaglandin F 2α terminates pseudopregnancy in the rat by reducing ovarian and peripheral progesterone concentrations (Pharriss and Wyngarden, 1969; Behrman, Yoshinaga and Greep, 1971). The fact, however, that only a slight increase in F prostaglandins around day 7 of pseudopregnancy and no increase in E prostaglandins was observed (Saksena, Watson, Lau and Shaikh, 1974) throws some doubt upon the idea that a prostaglandin is the luteolytic factor in the rat. On the other hand, the finding that in a bioassay the dose-response curve of endometrial extract from pseudopregnant rats runs parallel with that of prostaglandin F 2α ; (Dobrowolski et al., 1974) could be considered as evidence that a prostaglandin is the uterine luteolytic factor in the rat. In the present paper the effects of hysterectomy and decidualization on certain aspects of pseudopregnancy in the rat are discussed.