Prolactin has long been known to have both luteotrophic and luteolytic effects in the rat. While the trophic actions of prolactin have been investigated extensively, the luteolytic effect of the hormone has received less attention and is not well understood. The luteolytic effect of prolactin can be readily demonstrated in hypophysectomized rats: injections of prolactin stimulate rapid regression of the corpora lutea, with concomitant decline in total steroidogenic capacity. We recently reported that this action of prolactin in hypophysectomized rats is associated with inflammatory/immune events in the corpora lutea, namely expression of monocyte chemoattractant protein-1 (MCP-1) and infiltration of monocytes/macrophages, accompanied by a decline in plasma progestins. buy cheap antibiotics
In the cycling rat, Gaytan et al. showed that blockade of the proestrous prolactin surge with a dopamine agonist decreased the number of monocytes/macrophages found in regressing corpora lutea on the following metestrus. Using a similar approach, Matsuyama et al. reported that blockade of the proestrous prolactin surge reduced the incidence of apoptotic cells in rat corpora lutea. In this investigation, the action of the dopamine agonist could be reversed by administration of prolactin. In the current study, we investigated whether inflammatory/immune events occur in the corpora lutea of normally cycling rats, as we have reported in hy-pophysectomized prolactin-treated rats, and whether the temporal expression of these immune and regressive events is consistent with the proposed luteolytic role of the pro-estrous prolactin surge.