Regulation of cyclic AMP level by progesterone in ovariectomized rat neocortex

The cyclic AMP-dependent protein kinase A pathway is involved in progesterone effects on calcitonin secretion from TT cells

It is well known that gonadal steroid hormones influence the level of plasma calcitonin (CT), but the mechanism by which progesterone affects CT secretion is not clear. Immortalized TT cells are a reliable model system for studying the endocrine function of human parafollicular cells. In the present study, the effects of progesterone on CT secretion were examined in TT cells. TT cells were incubated in medium containing vehicle (DMSO), progesterone or BSA-progesterone for 60 or 150 min, and then the levels of CT in the medium, progesterone receptors, cAMP accumulation and CT mRNA expression were measured. To study the correlation between progesterone effects and the cAMP-dependent protein kinase A (PKA) pathway, cell lysates or cells in 24-well plates were treated with either vehicle or progesterone plus RU486, SQ22536, KT5720, or 3-isobutyl-1-methylxanthine. Then, adenylyl cyclase and protein kinase A (PKA) activities were measured in the cell lysates, and the CT levels were measured in the medium from the 24-well plate. The activated cAMP response element binding protein (P-CREB) was also measured by immunofluorescence. Administration of 1 microM progesterone or 500 nM BSA-progesterone increased the secretion of CT by 381% and 100%, respectively. Progesterone receptors A and B were downregulated by progesterone treatment. The cAMP concentration, adenylyl cyclase and PKA activity, CT mRNA expression, and nuclear P-CREB concentrations all showed an increase after progesterone treatment. RU486, SQ22536 and KT5720 inhibited the progesterone-stimulated effects. These results suggest that a cAMP-dependent PKA pathway is involved in progesterone-stimulated effects on CT secretion from TT cells.

In the ventral tegmental area, cyclic AMP mediates the actions of progesterone at dopamine type 1 receptors for lordosis of rats and hamsters

Progesterone-facilitated lordosis is enhanced by activation of, and inhibited by antagonism of, dopamine type 1 receptors (D1) in the ventral tegmental area (VTA). Given that D1 activation leads to increases in cyclic AMP (cAMP), we hypothesised that, in the VTA, progesterone's actions on lordosis that involve D1 are mediated, in part, by cAMP. In Experiment 1, naturally receptive rats and hamsters were pretested for lordosis, infused with the cAMP analogue 8-bromo-cAMP (200 ng) or vehicle to the VTA, and tested again 30 min later. In Experiments 2 and 3, ovariectomised, oestradiol (10 microg) + progesterone (0 or 100 microg)-primed rats and oestradiol (10 microg) + progesterone (0 or 200 microg)-primed hamsters were pretested for lordosis and infused with 8-bromo-cAMP (200 ng), the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (12 microM) or vehicle to the VTA. Subjects were tested again 30 min later. In Experiment 4, oestradiol + progesterone-primed rats and hamsters were pretested and infused with the D1 agonist SKF38393 (0 or 100 ng) to the VTA. Thirty minutes later, subjects were tested again and infused with 2',5'-dideoxyadenosine (12 microM) or vehicle. Subjects were tested again 30 min later. VTA infusions of 8-bromo-cAMP enhanced lordosis of naturally receptive or hormone-primed rats and hamsters and 2',5'-dideoxyadenosine decreased lordosis of oestradiol + progesterone-primed rats and hamsters. D1-mediated increases in progesterone-facilitated lordosis were reduced by 2',5'-dideoxyadenosine. These data suggest that progesterone-facilitated lordosis of rats and hamsters may be modulated by D1 and cAMP activity in the VTA.

Progestin facilitation of lordosis in rodents involves adenylyl cyclase activity in the ventral tegmental area

Increasing cAMP, or activating dopamine type 1 (D(1)) or GABA(A)/benzodiazepine receptor complexes (GBRs), in the ventral tegmental area (VTA) enhances lordosis of rodents. Whether D(1)- and/or GBR-mediated increases in progestin-facilitated lordosis involve the cAMP-synthesizing enzyme, adenylyl cyclase, in the VTA, was investigated. In Experiment 1, ovariectomized estradiol (E(2); 10 microg at h 0)+progesterone (P; 250 microg at h 45)-primed hamsters first received bilateral infusions of the adenylyl cyclase inhibitor, 2',5'-dideoxyadenosine (DDA; 12 microM/side), or vehicle, and then were infused with the D(1) agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or vehicle, to the VTA. Lordosis was evaluated before and 30 min after each infusion. In Experiment 2, ovariectomized, E(2)-primed (10 microg at h 0) rats received VTA infusions of DDA (12 microM/side) or vehicle; SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle; and the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 100 or 200 ng/side), or beta-cyclodextrin vehicle. Lordosis was assessed before the series of infusions, immediately after drug infusions and 10 or 60 min after 3alpha,5alpha-THP infusions. Progestin- or progestin plus SKF38393-or muscimol-mediated increases in lordosis were blocked by DDA pretreatment. Thus, in the VTA, progestins' membrane action may involve adenylyl cyclase.

Progestins' effects on sexual behaviour of female rats and hamsters involving D1 and GABA(A) receptors in the ventral tegmental area may be G-protein-dependent

In the ventral tegmental area (VTA), progestins have actions involving dopamine type 1-like receptors (D(1)) and gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) for lordosis. Evidence suggests that D(1) and GBRs can have G-protein-mediated effects. We investigated if, in the VTA, inhibiting G-proteins prevents D(1)- and/or GBR-mediated increases in progestin-facilitated lordosis. Hamsters, with bilateral guide cannulae to the VTA, received systemic E(2) (10 microg) at hour 0 and progesterone (P, 250 microg) at hour 45. At hour 48, hamsters were pre-tested for lordosis and infused with the G-protein inhibitor, guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S, 50 microM/side), or 10% DMSO saline vehicle. Thirty minutes after initial infusions, hamsters were re-tested and then immediately infused with the D(1) agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or saline vehicle. Hamsters were post-tested for lordosis 30 min later. For rats, E(2) (10 microg) priming at hour 0 was followed by lordosis pre-testing at hour 44. After pre-testing, rats received infusions of GDP-beta-S or vehicle, followed by infusions of SKF38393, muscimol, or vehicle and then infusions of the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP, 100 or 200 ng/side), or beta-cyclodextrin vehicle. Rats were tested immediately after each infusion of SKF38393, muscimol or vehicle, as well as 10 and 60 min after 3alpha,5alpha-THP or vehicle infusions. Inhibiting G-proteins, in the VTA, reduced the ability of systemic P or intra-VTA SKF38393 or muscimol to facilitate lordosis of E(2)-primed hamsters. Blocking G-proteins, in the VTA, prevented SKF38393-, muscimol- and/or 3alpha,5alpha-THP-mediated increases in lordosis of E(2)-primed rats. Thus, progestins' actions in the VTA for lordosis that involve D(1) and/or GBRs may also include recruitment of G-proteins.

In the ventral tegmental area, progestins' membrane-mediated actions for lordosis of hamsters and rats involve protein kinase A

Progestin-facilitated lordosis of hamsters and rats is enhanced by activation of dopamine type 1 (D1) or GABAA/benzodiazepine receptor complexes (GBRs) in the ventral tegmental area (VTA) and these effects involve G-proteins and second messengers, such as adenosine 3',5'-monophosphate (cAMP). We examined whether D1- and/or GBR-mediated increases in progestin-facilitated lordosis of female hamsters and rats involve the cAMP-dependent protein kinase, protein kinase A (PKA), in the VTA. In experiment 1, ovariectomized hamsters, primed with estradiol (E2; 10 microg at h 0) + progesterone (P; 100 microg at h 45), were first pre-tested for lordosis and motor behavior (h 48) and then infused with the PKA inhibitor, Rp-cAMP (100 ng/side), or vehicle. Thirty minutes later, hamsters were retested and then received infusions of the D1 agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or vehicle to the VTA. Hamsters were post-tested for lordosis and motor behavior 30 min later. In Experiment 2, ovariectomized rats, primed with E2 (10 microg at h 0), were first pre-tested for lordosis and then infused with Rp-cAMP (100 ng/side) or vehicle to the VTA at h 44. Immediately after testing, rats received infusions of SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle and were retested for lordosis. Rats were then infused with the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 100 or 200 ng/side), or beta-cyclodextrin vehicle and were post-tested for lordosis and motor behavior 10 and 60 min later. The enhancing effects of progestins or progestins plus D1 or GBR activation on lordosis of E2-primed hamsters and rats were blocked by the PKA inhibitor, Rp-cAMP. Thus, in the VTA, progestins' membrane actions involving D1 or GBRs are mediated, in part, by PKA.

Proteins of multiple classes may participate in nongenomic steroid actions

Responses to steroids initiated from non-nuclear receptors impinge on a wide variety of cellular responses and utilize nearly all known signal transduction webs. While the mechanisms by which steroid receptors localize in the membrane are still unclear, it is apparent that this alternative localization allows steroid receptors to participate in a wide range of complex functions influencing cell proliferation, death, and differentiation. The central debate still remains the identity of the protein class or classes that mediate membrane-initiated (nongenomic) responses. The data thus far have supported several possibilities, including: nuclear steroid receptor-like forms in non-nuclear locations; other known (nonsteroid) membrane receptors or channels with additional steroid-binding sites; enzymes; transporters; receptors for serum steroid-binding proteins; unique and previously undescribed proteins; or chimeras of typical steroid receptor domains with other unique or known protein domains. Categorizing membrane steroid receptor proteins based exclusively on the actions of antagonists and agonists, without considering cell context and protein partnering issues, may mislead us into predicting more receptor subtypes than really exist. However, the plethora of signaling and functional outcomes may indicate the participation of more than one kind of steroid-binding protein. Resolving such unanswered questions will require future investigative focus on this alternative arm of steroid action, which is likely to yield as many therapeutic opportunities as have nuclear steroid mechanisms.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.