Ovarian Steroids But Not the Locus Coeruleus Regulate Stress‐Induced Prolactin Secretion in Female Rats

Abstract

Stress has been proposed to stimulate prolactin release if its prestress levels are low, or to inhibit it if they are elevated, but the role of ovarian-steroid fluctuations in the prolactin stress response is not yet clearly understood. Because the noradrenergic nucleus locus coeruleus has been implicated in stress responses and generation of prolactin surges in female rats, the present study aimed to evaluate stress-induced prolactin secretion under different hormonal conditions, determining the effect of locus coeruleus lesion on each response. Blood samples were withdrawn from a jugular vein catheter 5 and 2 min before and 2, 5, 10, 15 and 30 min after ether stress in male rats, female rats during the oestrous cycle and ovariectomised rats treated with oil (OVX), oestradiol (OVE) or oestradiol plus progesterone (OVEP). Increased Fos immunoreactivity demonstrated locus coeruleus activation following ether stress. Ether stress increased both low (at 16.00 h in males, in OVX and on dioestrous and at 11.00 h on pro-oestrous and oestrous) and high plasma prolactin (at 16.00 h on oestrous and in OVE), but it decreased elevated prolactin levels during the afternoon on pro-oestrous and in OVEP. Locus coeruleus lesion prevented prolactin surges during the afternoon on pro-oestrous, oestrous, OVE and OVEP but did not modify either pattern (i.e. increase or decrease) or degree of prolactin stress response under any condition studied. The present data therefore suggest that oestradiol and progesterone modulate stress-induced prolactin secretion, regardless of its prestress levels. Moreover, the locus coeruleus is probably not involved in prolactin response to stress and most likely has a specific role in prolactin surges induced by ovarian steroids.

Effects of sulpiride on mRNA levels of steroid 5α‐reductase isozymes in prostate of adult rats

“…The prostate gland expresses both 5a-R isozymes (5a-R1 and 5a-R2), as previously demonstrated by our group and other researchers (8,9). In stress situations, PRL is hypersecreted (26,27), and there is an increase in both 5a-R isozymes in rat brain (unpublished observations). Hence the effects of PRL on prostate growth may be exerted by an increase in both 5a-R isozymes in this gland, among other factors.…”

“…We also recently observed (unpublished data) that stress situations increase transcription of 5a-R genes in brain. PRL is another hormone secreted in stress situations (26,27). Therefore, it is reasonable to speculate that the 5a-R enzyme may also mediate the action of PRL in the prostate gland.…”

GABAergic mediation of stress-induced secretion of corticosterone and oxytocin, but not prolactin, by the hypothalamic paraventricular nucleus

“…PRL has been shown to be increased by stress in several studies (Aizawa et al, 2006;Mastorakos et al, 2005;Tomei et al, 2006) and specifically after ether inhalation (Caldeira and Franci, 2000). On the other hand, stress induces a fall of prolactin secretion under certain conditions, such as during the proestrous afternoon surge in rats (Poletini et al, 2006) or hostile behavior during conflict in newly married humans couples (Webster and Glaser, 2008). The physiological importance to the organism of the PRL-secretory response to stress is unclear (Freeman et al, 2000).…”

Modulatory role of locus coeruleus and estradiol on the stress response of female rats

“…Thus, the expected stimulatory role of LC on corticosterone secretion was not observed. In fact, although LC neurons have been related to stress responses [4], we recently demonstrated that LC lesion does not affect the prolactin response to ether stress in female rats under different hormonal conditions [31]. Therefore, the role of norepinephrinergic neurons of LC on the stress response does not seem to be consistently excitatory.…”