Stress-induced release of prolactin: blockade by dexamethasone and naloxone may indicate beta-endorphin mediation.

Abstract

Basal levels of immunoreactive (ir) 4-endorphin, corticotropin (ACTH), and prolactin (PRL) in plasma of male rats decrease after dexamethasone pretreatment (400 ,sg/kg at 24 hr and 200 sg/kg at 2 hr before). Inescapable electric footshocks increase ir-p-endorphin, ACTH, and PRL plasma levels, and this effect is blocked by dexamethasone pretreatment. Morphine (20 mg/kg) also increases ir-O-endo in, ACTH, and PRL levels. Dexamethasone pretreatment blocks the morphine-induced release of ir-p-endorphin but does not prevent the morphine-induced release of PRL. Naloxone, the opiate antagonist, decreases basal plasma levels of PRL and partially blocks the stress-induced increase of PRL, but it has no effect on the basal or stress-induced release of ir--endorphin.These results are consistent with the proposal that P-endorphin may interact with an opiate receptor involved in the regulation of PRL secretion.Since the early studies by Selye (1), corticotropin (ACTH) has been recognized as the primary pituitary hormone secreted in response to acute stress in all species studied. Nicoll et al. (2) recognized that prolactin (PRL) was also released by stress.Recently, we reported that immunoreactive (ir) f3-endorphin was secreted in response to stress (3,4). Moreover, we showed that ir-f3-endorphin and ACTH were secreted concomitantly in nearly equimolar amounts.3-Lipotropin, the pituitary hormone of which f,-endorphin is amino acid sequence 61-91, was reported earlier to be released by stress (5). Although one recent report claimed that apparent f3-endorphin immunoreactivity in human blood was due only to the crossreactivity of the antiserum with f3-lipotropin (6), more recent reports from different laboratories have shown that, in fact, a 3-endorphin-like substance does exist in human and rat blood and that its levels are higher after stress (7-11). Nevertheless, the role of f3-endorphin in peripheral blood is still under scrutiny.In this study, we examined the possibility that f3-endorphin released by stress into the blood could promote the secretion of another pituitary hormone, PRL In order to test the possibility that f3-endorphin released by stress promotes PRL secretion through an opiate receptor, we compared the secretion of PRL and of fl-endorphin. Secretion was provoked by stress or morphine after animals were pretreated with naloxone or dexamethasone. The latter, a potent synthetic glucocorticoid, is known to suppress the morphine and stress-induced release of ACTH (14, 15). MATERIALS AND METHODSDesign of Experiments and Statistical Evaluation. The effects of dexamethasone pretreatment on footshock-induced release of ,3-endorphin were studied by using a two-way repeated measures design. In nine rats, a catheter (Corning Silastic) was implanted in the right jugular vein, passed under the skin, and mounted to a Luer needle hub on the skull by stainless steel screws and dental cement. This method allowed blood sampling during experimental manipulations without undue stress to the rats. Patency of catheters was...

From Galactorrhea to Osteopenia: Rethinking Serotonin–Prolactin Interactions

“…Various forms of stress are associated with increased PRL release, including ether stress (Johnston and Negro-Vilar, 1986), restraint stress (Torner et al, 2001;Gala, 1990;Neill, 1970;Rossier et al, 1980;Seggie and Brown, 1975) thermal stress (Vaha-Eskeli et al, 1991), social conflict in mice (Huhman et al, 1995), and academic stress in humans (Malarkey et al, 1991). PRL circadian rhythm disturbances occur in patients with premenstrual dysphoric disorder, which may be linked to chronobiologic abnormalities in this condition (Parry et al, 1996).…”

“…Opioids: Endogenous opioid peptides such as enkephalins and dynorphins are involved in the regulation of PRL secretion during pregnancy, lactation, and stress (Ferland et al, 1978;Rossier et al, 1980;Sagrillo and Voogt, 1991). The suckling-induced PRL surge is blocked by treatment with naloxone, a nonselective opioid antagonist (Selmanoff and Gregerson, 1986).…”

Regulation by endogenous opioids of suckling-induced prolactin secretion in pregnant and lactating rats: role of ovarian steroids

“…Endogenous opioid peptides play a role in the regulation of prolactin secretion in rats during proestrus (Ieri et al 1980), stress (Rossier et al 1979) and pregnancy (Sagrillo & Voogt 1991, Soaje & Deis 1994, 1997. Additionally, the participation of endogenous opioid peptides in the regulation of prolactin release in lactating rats has been reported by several authors (Ferland et al 1978, Selmanoff & Gregerson 1986, Baumann & Rabii 1991, Arbogast & Voogt 1998.…”

Bir grup laparoskopik kolesistektomi hastasında intraoperatif esmolol infüzyonunun postoperatif stres yanıt üzerine etkisi

“…Opioid receptors are thought to play role in secretion of prolactin. Endogen opioids like morphine, Met-enkephalin and β endophine all cause an increase in prolactin secretion, on the other hand naloxane was reported to decrease secretion 33 .…”