Functional and morphological characteristics of the first corpus luteum formed after parturition in ewes

Abstract

The ability of sheep luteal cells from the first corpus luteum formed after parturition (Group F) to secrete progesterone in the presence or absence of LH was compared with that of luteal cells obtained from normal cyclic ewes (Group C). Luteal concentrations of receptors for LH and prostaglandins (PG) F-2α (PGF-2α) and the cellular composition of corpora lutea from Groups F and C were also compared. Luteal cells from Group F secreted less progesterone in either the presence or absence of LH (P < 0.01). There was no difference in the number of receptors for LH or PGF-2α per luteal cell between Groups F and C (P > 0.1), nor was there a difference in the number of large or small steroidogenic luteal cells (P > 0.1). It was concluded that, if short-lived corpora lutea are insensitive to gonadotrophins, this response is not mediated by decreased numbers of receptors for LH. In addition, if the first corpus luteum formed post partum in ewes is more sensitive to the luteolytic effects of PGF-2α, this effect is not mediated by an increased number of receptors for PGF-2α or an increased proportion of PGF-2α-sensitive large luteal cells.