Possible direct effect of prolactin on catecholamine synthesis and release in rat adrenal medulla: in vitro studies

Effects of Fatty Acid Amide Hydroxylase Inhibitor URB597 on the Catecholaminergic Activity of the Adrenal Medulla in Stressed Male and Female Rats

INTRODUCTION

The present study examined the effects of fatty acid amide hydrolase inhibitor URB597 on the level of plasma catecholamine and their content, synthesis, and degradation in the adrenal medulla of male and female rats subjected to chronic unpredictable stress (CUS).

MATERIAL AND METHODS

Male and female Wistar rats were exposed to the 6 weeks of CUS and treated intraperitoneally with either 0.3 mg/kg/day of URB597 or vehicle in the last 2 weeks of stress protocol. Catecholamines' plasma levels and catecholamines' levels in adrenal medulla were examined using Elabscience ELISA kits. Western blot analysis was used to detect the protein in the medulla.

RESULTS

The results of our experiment showed that adrenal weights and catecholamine of unstressed control were higher in females and that CUS induced further enlargement of adrenal glands and catecholamine content and its synthesis compared to male rats. CUS caused an increase of plasma norepinephrine and depletion of norepinephrine content as well as unchanged synthesis and degradation of catecholamine in the adrenal medulla of male rats. URB597 reduced enlarged adrenals and catecholamine content and its synthesis in stressed female rats. URB597 reduces increased plasma norepinephrine and restores its content in the adrenal medulla, unchanging the expression of enzyme synthesis, while reduced protein levels of monoamine oxidase A in male rats are exposed to CUS.

DISCUSSION

Our results support the role of endocannabinoids as an antistress mechanism that inhibits elevated adrenomedullary activation and promotes its recovery to baseline in both male and female stressed rats.

Effects of reproduction on spontaneous development of endometrial adenocarcinomas and mammary tumors in Donryu rats

Effects of reproduction on spontaneous development of uterine endometrial adenocarcinomas and mammary tumors in Donryu rats were investigated. While the incidence of endometrial adenocarcinomas in Donryu rats was not influenced by a single reproductive experience (SRE), it showed a tendency to decrease in animals having three reproductive experiences (TRE), compared to the nulliparous case (NRE). In addition, both SRE and TRE animals showed delayed occurrence and decreased incidences and mean numbers of mammary tumors, along with reduced incidences of proliferative lesions in the pituitary gland and mucinous epithelium in the vagina. The appearance-time and incidences of persistent estrus in TRE rats were delayed and low, respectively, compared to the SRE and NRE values. The hormonal environment was altered in both groups, the prolactin level in TRE especially being decreased. These results suggest that suppression of the occurrence of endometrial adenocarcinomas and mammary tumors in rats experiencing reproduction is associated with change in the hormonal milieu.

Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Is prolactin playing a role in the regulation of catecholamine synthesis and release from male rat adrenal medulla?

Previous evidence allows one to suspect that prolactin (PRL) may be a physiological regulator of catecholamine (CA) synthesis and release in the adrenal gland of rodents. To explore this possibility, we studied the in vivo and in vitro metabolism and release of noradrenaline (NA) and adrenaline (A) in the adrenal gland of male rats. The study was carried out with animals exhibiting a moderate increase in plasma PRL levels induced by grafting of additional pituitaries or a severe hyperprolactinemia produced by diethylstilbestrol (DES)-induced pituitary hyperplasia. The latter animals exhibited a significant increase in adrenal weight, associated with decrease in tyrosine hydroxylase (TH) activity and in NA content. Moreover, the adrenal activity of phenylethanolamine-N-methyl transferease (PNMT) was decreased in DES-treated animals. Pituitary-grafted rats also displayed an increased adrenal weight, together with decreases in the activities of PNMT, catechol-O-methyl transferase and monoamine oxidase. These in vivo observations were followed by in vitro studies, which showed a decrease in the basal release of both CAs from incubated adrenals of DES-treated rats, with no changes in pituitary-grafted rats. In addition, exposure to PRL of the incubated adrenals of animals exhibiting normal PRL levels produced decreases in A release and storage and in TH activity. These observations allow us to conclude that: i) PRL appears to exert an inhibitory influence on the catecholaminergic activity in the adrenal gland; and ii) its effect seems to be exerted by a direct action on this gland.

Prolactin inhibits the activity of tyrosine hydroxylase in cultured bovine adrenal chromaffin cells in a dose-dependent manner

Prolactin can modulate the adrenal medulla function, but it has not yet been established whether its action is directly exerted on the adrenal medulla cells. In this work, we have studied the effect of several concentrations of prolactin on the synthesis, storage and release of norepinephrine and epinephrine using cultured bovine adrenal chromaffin cells. In these cells, prolactin inhibited the activity of tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine synthesis, in a dose-dependent manner, from a concentration above 50 ng/ml of prolactin in the incubation medium. Surprisingly, this dose-dependent decrease was not accompanied by changes in the catecholamine release, since the secretion of both norepinephrine and epinephrine as well as the total catecholamine secretion were not significantly altered by the different prolactin concentrations. Moreover, the cellular content of both catecholamines was not altered by prolactin. In summary, these observations allow us to conclude that prolactin exerts a direct inhibitory effect on the tyrosine hydroxylase activity in cultured adrenal chromaffin cells without altering catecholamine release.

Role of ovarian steroids on the catecholamine synthesis and release in female rat adrenal: in vivo and in vitro studies

In a previous report, we describe the existence of an effect of ovarian steroids on the adrenal medulla activities of the enzymes involved in catecholamine (CA) catabolism. To complete that study, we have now examined the adrenal medulla activity of tyrosine hydroxylase (TH), the rate limiting enzyme of the CA synthesis, as well as the in vitro release of CAs from incubated adrenal medullas. The study has been performed with adrenal medullas from female rats with physiological (estrous cycle) or pharmacological (steroid treatment) alterations in their circulating levels of estrogens and progesterone. The in vitro release of CAs from incubated adrenal medullas of estradiol-treated rats was lower than that obtained in vehicle-treated animals. In consequence, the preovulatory increase of estradiol would be the responsible of the low in vitro release of CAs observed during the estrous phase of ovarian cycle. However, this steroid does not seem to affect the CA synthesis, since the adrenal medulla activity of TH was not altered after the estradiol treatment nor during the estrous cycle. On the contrary, progesterone treatment increased TH activity 24 h after the steroid injection. This effect was independent of estradiol. However, an estrogen-dependent increase in TH activity occurred short-time after the steroid administration. Although progesterone by itself failed to modify the in vitro release of both CAs, it was able to reverse the estradiol-induced decrease in epinephrine release. In summary, estradiol seems to decrease the ability of the adrenal medulla to release CAs to the peripheral blood, without affecting the CA synthesis, whereas progesterone mostly affects TH activity, being its effects temporary and partially depending on estrogens.