Plasma Prolactin and Progesterone Responses to Mating Are Altered in Aged Rats

Abstract

The effects of varying amounts of copulatory stimulation on patterns of plasma concentrations of prolactin and progesterone were evaluated in 3- and 12-month-old female rats. The 12-month-old group included rats which still exhibited oestrous cycles and rats in persistent vaginal oestrus (PVO). The extent of copulatory stimulation was defined by the number of intromissions received during mating: less than or equal to 5, 15 or greater than 50. Blood samples were drawn over the 8 days after mating through a cannula inserted into the right external jugular vein. Plasma from the samples was assayed for prolactin and progesterone. In aged but still cyclic rats, pregnancy rates were positively correlated with the number of intromissions received during mating. Only one rat in PVO became pregnant. All animals which became pregnant and rats in PVO which, after mating, exhibited a disruption of the pattern of PVO, showed the nocturnal surge of plasma prolactin characteristic of pregnant and pseudopregnant rats. While these surges persisted until day 8 after mating in pregnant animals, they were absent by this time in the rats in PVO. Prolactin surges were present in some but not all of the aged rats which did not become pregnant. Progesterone concentrations were raised in all pregnant animals except the one pregnant rat in PVO and, while not related to the number of intromissions, concentrations were higher 8 days after mating in young compared with those in aged pregnant rats. Plasma progesterone was low in rats in PVO regardless of disruption of the pattern of PVO. We have concluded that the failure of limited copulatory stimulation to induce pregnancy in older rats results, at least in part, from its failure to initiate nocturnal prolactin surges. Nevertheless, our data suggest that matings which are not experimentally limited should provide ample stimulation to establish such surges. Although reduced plasma concentrations of prolactin and progesterone at pro-oestrus and reduced plasma progesterone through part of gestation may contribute to decreasing fertility in aged rats, other unidentified factors appear to be involved in mediating the capacity of extensive copulatory stimulation to induce pregnancy in these animals.

Central Administration of Antiserum to Vasoactive Intestinal Peptide Delays and Reduces Luteinizing Hormone and Prolactin Surges in Ovariectomized, Estrogen-Treated Rats

“…In regularly cycling and in steroid-treated OVX middle-aged females, the LH surge, but not the PRL surge, is attenuated compared to that observed in young animals [50], although some studies suggest that PRL release may also be affected [51]. It has been suggested that the effects of aging on reproduction in the female rodent may, at least in part, involve changes in the rhythmic output of the SCN [52].…”

Light and scanning electron microscopic study of testosterone‐restored penile papillae in castrated rats

“…An initial explanation (Beach and Levinson, 1950) was that they provide necessary sensory stimulation for the male, an idea that is not su orted by subsequent research (Hart, 1978 Spaulding andPeck, 1974). More likely, the spines provide mechanical stimulation necessary for the surges of progesterone and prolactin in the female that ensures impregnation (Hendricks and Blake, 1981). The implication is that simply copulating to ejaculation is not suflkientthat the type of copulatory behavior provided by the male is important for successful reproduction.…”

Infertility in a Line of Mice with the high growth Mutation Is Due to Luteal Insufficiency Resulting from Disruption at the Hypothalamic-Pituitary Axis1

“…Alternatively, the basal PRL levels could be suppressed in the HG females, such that additional stimulation is required to reach the necessary PRL threshold for the establishment and maintenance of pregnancy. One such condition is seen in old cyclic female rats, in which the PRL secretory system experiences a decreased sensitivity to the mating stimulus [29]. The HG females used in the present study were not old, but they could have experienced decreased sensitivity to the mating stimulus.…”