Effect of Adrenalectomy on Mating-Induced Prolactin Surges and Pseudopregnancy in the Female Rat

Abstract

In the estrous female rat, mating stimulation induces an acute surge of prolactin (PRL) within 20 min after mating followed by the onset of twice-daily PRL surges which persist for an 8- to 13-day period of acyclicity called pseudopregnancy. In Experiment 1, we examined whether the release of adrenal hormones after mating modulates mating-induced PRL secretion during the first 38 h after mating. Ovariectomized females were adrenalectomized (Adx) or sham-operated (Sham) and were implanted with jugular vein catheters 2 days later. They were given estrogen and progesterone and mated 6 days after the last surgery until they received 15 intromissions or 15 mounts-without-intromission from a male. Blood samples were collected beginning 20 min before mating at 23:00 h and continuing for 38 h. Plasma PRL concentrations were measured using radioimmunoassay. Mating that included intromissions induced an acute (20-min) PRL response which was higher in Adx than in Sham animals, and advanced in the Adx animals in the onset of the first daily PRL surge to 10:00 h, some 18 h before the surge was observed at 04:00 h in the Sham-mated animals. A small but measurable nocturnal surge was observed in Adx and Sham groups 18–24 h later at 04:00–10:00 h. In Experiment 2, Adx- and Sham-cycling animals received 5 (5I) or 7 (7I) intromissions from a male 12–16 days after surgery. Adx animals receiving 5I showed a significantly higher incidence of pregnancy or pseudopregnancy (%P/PSP) than did Sham 5I animals, while there was no difference in %P/PSP in the 7I groups. We conclude that adrenal gland secretions normally suppress plasma PRL concentrations immediately post-mating and before the onset of the nocturnal mating-induced PRL surge and also inhibit pseudopregnancy when females receive a subthreshold number of intromissions normally required for its induction.

Fos Expression after Mating in Noradrenergic Cells of the A1 and A2 Areas of the Medulla is Altered by Adrenalectomy

“…This was unexpected because activity of tyrosine hydroxylase has been shown to increase in A1 and A2 by 8 days after adrenalectomy in males (22), and the numbers of DBH‐IR cells colabelled with Fos in response to lipopolysaccharide challenge in A2 was increased by adrenalectomy (27). The absence of increases in cellular activation after intromissions in ADX rats in A2 suggests that activation within 1.5 h after mating is not necessary for mating‐induced pseudopregnancy because fewer than 15 intromissions are required for pseudopregnancy in adrenalectomized females (21). We must assume either that adrenalectomy interfered with intromission‐induced noradrenaline release in forebrain target areas involved in induction of pseudopregnancy and/or that an increase in noradrenergic tone did not occur in A2 as a result of adrenalectomy.…”

“…We have demonstrated that the activity of forebrain nuclei involved in mating‐induced pseudopregnancy can be suppressed or enhanced by hormones from the adrenal gland (20), and that adrenalectomy increases the likelihood of a female rat becoming pregnant or pseudopregnant in response to low numbers of intromissions (21). In the paraventricular nucleus of the hypothalamus, baseline release rates of noradrenaline remain unchanged after adrenalectomy, but stress has been shown to increase noradrenaline release in this nucleus to a greater degree in adrenalectomized (ADX) compared to intact control rats (22).…”

A Case of Pseudo-Pregnancy in Captive Brown Howler Monkeys (Alouatta guariba)

“…Hormonally, it is caused by the superproduction of progesterone and the abnormal persistence of the corpus luteum [Gobello et al, 2001]. Spontaneous cases of pseudo-pregnancy are widely reported in a number of mammalian species, including dogs, cats, bears, rodents and humans [Drife, 1985;Gobello et al, 2001;Cameron et al, 2003;Schulz et al, 2003]. Spontaneous pseudocyesis is most common in species with copulation-induced ovulation (e.g.…”