Involvement of beta-adrenoceptors in the regulation of luteal function in cattle

Onapristone (ZK299) and mifepristone (RU486) regulate the messenger RNA and protein expression levels of the progesterone receptor isoforms A and B in the bovine endometrium

The aim of this study was to examine whether progesterone (P(4)) and its antagonists, onapristone (ZK299) and mifepristone (RU486), affect the levels of PGRA and PGRB messenger RNA (mRNA) and protein in the cow uterus which may be important in understanding whether the final physiological effect evoked by an antagonist depends on PGR isoform bound to the antagonist. Endometrial slices on Days 6 to 10 and 17 to 20 of the estrous cycle were treated for 6 or 24 hours for mRNA and protein expression analysis, respectively, with P4, ZK299, or RU486 at a dose of 10(-4), 10(-5), or 10(-6) M. In the samples on Days 6 to 10 of the estrous cycle, PGRAB mRNA was stimulated by P(4) (10(-4) M; P < 0.01) and RU486 (10(-6); P < 0.001) and was decreased by ZK299 (10(-5); P < 0.05). In contrast, PGRB mRNA was decreased by the all P(4) (P < 0.01) and ZK299 (P < 0.001) doses and by two of the RU486 doses (10(-4) M; P < 0.01 and 10(-5) M; P < 0.01). In samples on Days 17 to 20 of the estrous cycle, PGRAB mRNA was stimulated by RU486 (10(-5) M; P < 0.001). PGRB mRNA was decreased by P(4) (10(-4) and 10(-5) M; P < 0.001), ZK299 (10(-4) and 10(-5) M; P < 0.001), and RU486 (10(-4) M; P < 0.01 and 10(-6) M; P < 0.001) and was increased by ZK299 (10(-6) M; P < 0.001) and RU486 (10(-5) M; P < 0.001). In samples on Days 6 to 10 of the estrous cycle, PGRB protein levels were decreased (P < 0.05) by all three ZK299 doses and by two of the RU486 doses (10(-4) M; P < 0.05 and 10(-5) M; P < 0.01). In contrast, in samples on Days 17 to 20, both PGRA and PGRB protein levels were decreased by ZK299 stimulation (10(-5) M; P < 0.05 and 10(-5) M; P < 0.01, respectively), whereas only PGRA protein levels were increased by RU486 (10(-5) M; P < 0.01). Both ZK299 and RU486 may exhibit both agonist and antagonist properties depending on which receptor isoform they affect. As a result, an increase or decrease in the expression of a particular PGR isoform will be observed.

Stimulatory effect of LH, PGE2 and progesterone on StAR protein, cytochrome P450 cholesterol side chain cleavage and 3beta hydroxysteroid dehydrogenase gene expression in bovine luteal cells

The aim of these studies was to investigate the effect of LH, progesterone (P4), PGE, noradrenaline (NA) and a nitric oxide donor, S-nitroso-N-acetylpenicillamine (S-NAP), on steroid acute regulatory protein (StAR), 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and cytochrome P450 side chain cleavage (P450scc) gene expression and on the synthesis of their protein products. Bovine luteal cells were collected and prepared on days 6-10 of the estrous cycle and preincubated in vitro for 24 h. Thereafter, medium was changed and supplemented with one of six treatments: control medium, LH (100 ng/ml), P4 (10(-5)M), PGE2 (10(-6)M), NA (10(-5)M) or S-NAP (10(-4)M). In Experiment 1, luteal cells (10(6)/well) were incubated for 3, 6, 18 and 24 h. After incubation, total RNA was isolated and P4 concentrations in medium was determined. Semiquantitative RT-PCR was used to measure gene expression. In Experiment 2, luteal cells were preincubated for 24h, then stimulated as in Experiment 1. Total protein was isolated from lysed cells and Western blot analysis was performed using specific antibodies against the StAR, 3beta-HSD and cytochrome P450scc proteins. Bands were analyzed by means of KODAK 1D Image Analysis Software. In Experiment 1, LH and PGE2 stimulated secretion of progesterone from luteal cells. Concentrations of mRNA for StAR, 3beta-HSD, cytochrome P450scc were increased after 6 h in cells stimulated with LH, PGE2 and P4 (P<0.05). Gene expression was not affected by NA. In Experiment 2, LH, P4 and PGE2 induced an increase in the concentration of these three proteins. S-NAP inhibited both concentrations of mRNA and protein for StAR, 3beta-HSD, cytochrome P450scc. Therefore, the increase in secretion of P4 induced by LH and PGE2 is associated with increases in StAR, 3beta-HSD and cytochrome P450scc gene expression. This genomic response may be mediated in part through a positive effect of P4 on the expression of these genes observed in this experiment.

Involvement of high-density lipoprotein in stimulatory effect of hormones supporting function of the bovine corpus luteum

The hypothesis that epinephrine (noradrenaline, NA) enhances utilisation of high-density lipoproteins (HDL) by bovine luteal cells and that this process involves phospholipase (PL) C and protein kinase (PK) C intracellular pathway was tested. Luteal cells from days 2-4, 5-10 or 11-17 of the oestrous cycle were preincubated for 20 h. Subsequently DMEM/Ham's F-12 medium was replaced by fresh medium and the cells were treated for 6 h as follows: In Experiment I with HDL (5-75 micrograms cholesterol per ml), NA, isoprenaline (ISO) or luteinising hormone (LH). In Experiment II cells were incubated for further 24 h in deficient medium (without FCS) and next treated as in Experiment I. In Experiment III cells were stimulated with NA, ISO or LH alone and together with HDL. In Experiment IV cells were treated with PLC inhibitor (U-73122) or with PKC inhibitor (staurosporine) or stimulator (phorbol 12-myristrate 13-acetate) and with either NA, insulin or LH. Only luteal cells from days 5-10 of the cycle responded on HDL and beta-mimetics (P < 0.05). LH stimulated progesterone secretion from the luteal cells during all stages of the cycle (P < 0.001). Cells incubated in deficient medium and supplemented with HDL secreted as much progesterone as those stimulated by LH in all stages of the cycle. Beta-mimetics were unable to enhance the stimulatory effect of HDL. Blockade of PLC had no influence on progesterone secretion from cells treated with either NA or LH, but this did impair the stimulatory effect of insulin (P < 0.05). Similarly, blockade of PKC by staurosporine impaired (P < 0.05) the effect of insulin only but not that observed after LH or NA treatment. We suggest that: (a) noradrenergic stimulation does not enhance utilisation of cholesterol from HDL for progesterone secretion; (b) the fasting of luteal cells seems to activate enzymes responsible for the progesterone synthesis; (c) effect of NA on progesterone secretion from luteal cells does not involve the PLC-PKC pathway.

Neural regulation of the bovine corpus luteum

The ovarian noradrenergic stimulation or noradrenaline (NA) administration directly to the ovary in cow increases ovarian oxytocin (OT) release and post-translational processing of OT synthesis within a few minutes has been established in both in vivo and in vitro studies. Furthermore, NA affects progesterone secretion and its synthesis by an increase of cytochrome P450scc and 3beta-hydroxysteroid dehydrogenase activity. This effect is mediated via luteal cell beta(1)- and beta(2)-receptors. Their total amount correlates with peripheral progesterone concentrations during the luteal phase and this reflects the ability of the ovary to react to beta-stimulation. On the other hand, ovarian denervation causes a decrease of steroidogenic activity in the CL, an increase of beta-receptors on luteal cells, a delay in follicular development and the disruption of cyclicity. Moreover, decrease of progesterone secretion by 20-30% was seen after brief pharmacological blockade of ovarian beta-receptors in the mid-cycle of cattle. We assume that tonic beta-stimulation of the CL ensures the basal secretion of progesterone, whereas acute noradrenergic activation supports the CL during stressful situations which could impair its function. Conversely, long-lasting increase in blood catecholamine concentrations markedly decreases the number of beta-receptors in CL, presumably due to their down-regulation. Concentrations of dopamine (DA) within the CL are highly correlated with those of NA during the estrous cycle, and are higher in the newly-formed than in the developed corpus luteum, the regressed corpus luteum or the corpus luteum of pregnant females. Bovine CL can synthesise de novo NA from DA as a precursor. Concluding, presented data indicate that noradrenergic stimulation can be an important part of mechanism supporting secretory function of CL.

Influence of noradrenaline on progesterone synthesis and post-translational processing of oxytocin synthesis in the bovine corpus luteum

Noradrenaline (NA) influences secretory function of the bovine corpus luteum (CL), stimulating secretion of progesterone and ovarian oxytocin (OT). To study whether NA is able to stimulate progesterone synthesis and to affect post-translational OT processing, different doses of NA alone or in combination with different doses of OT were added to bovine CL slices from 8 to 13 d of the estrous cycle. To determine which receptors NA affects, and if dopamine (DA) also affects CL function, we used NA or DA combined with a beta-antagonist (propranolol). The results indicated that NA stimulates both luteal progesterone and OT content; furthermore, it increased the activity of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and peptidyl glycine-alpha-amidating mono-oxygenase (PGA), terminal enzymes in synthesis of these 2 hormones. The stimulating effect of NA was inhibited by propranolol and by pre-treatment of CL slices with high OT doses. Post-translational processing of OT synthesis by PGA activation was also stimulated by DA, but this effect was inhibited by beta-receptor blocker. Thus DA acts in CL as a NA precursor. In conclusion, it can be assumed that the noradrenergic system affects CL secretory function on different levels of regulation. Furthermore, a high concentration of OT in CL prevents NA from activating PGA and thus decreases post-translational OT synthesis.

Involvement of adrenoceptors in the ovarian vascular pedicle in the regulation of counter current transfer of steroid hormones to the arterial blood supplying the oviduct and uterus of pigs

1. On Day 10 of the oestrous cycle in pigs, after laparotomy noradrenaline (NA), methoxamine (alpha 1-adrenomimetic, M), Prazosin (alpha 1-adrenolytic, Pr) in total doses of 4 mumol, and saline were infused (10 min) into the superficial layer of mesovarium on both sides of the ovarian pedicle vasculature, close to the ovary. 2. Blood flow in the ovarian artery, heart rate and progesterone (P4) and androstenedione (A4) secretion from the ovary and their concentrations in the ovarian venous effluent, as well as the concentrations of P4 and A4 in the blood supplying the oviduct and the uterus, were determined. 3. A significant increase of P4 and A4 secretion after NA and M infusion and increased concentrations of P4 and A4 in the ovarian venous effluent were found, but these changes did not influence the counter current transfer of hormones from the venous effluent into arterial blood supplying the oviduct and the uterus. 4. Infusion of Pr caused a significant decrease of P4 and A4 secretion and their concentrations in the ovarian venous effluent and significantly increased A4 concentration in the blood supplying the oviduct and uterus. 5. The results indicate that stimulation of alpha 1-adrenoceptors in the area of ovarian vasculature did not influence, whereas block of alpha 1-adrenoceptors affected, the local concentration of steroid hormones in the blood supplying the oviduct and the part of the uterus proximal to the ovary, despite the changes in the concentrations of steroid hormones in the ovarian effluent.

Influence of dopamine as noradrenaline precursor on the secretory function of the bovine corpus luteum in vitro

1. Dopamine is assumed to affect the ovary function after its conversion into noradrenaline (NA). 2. To study this bovine luteal slices from 11-14 days of the oestrous cycle were preincubated for 24 h to recover beta-receptors and next they were incubated for 1, 2 or 4 h with (a) different doses of dopamine; (b) dopamine together with a beta-antagonist (propranolol) or with a dopamine receptor blocker (droperidol); (c) dopamine with a dopamine-beta-hydroxylase inhibitor. 3. Dopamine stimulated the luteal content of oxytocin (OT) and progesterone. This effect was inhibited by propanolol but not by droperidol. 4. Dopamine added to the medium was followed by an increase of noradrenaline there. This rise was dose and time-dependent. 5. The dopamine-beta-hydroxylase inhibitor, inhibited the stimulating effect of dopamine on luteal progesterone and OT content. 6. Bovine corpus luteum can synthesize de novo NA from dopamine as a precursor.

Noradrenaline affects secretory function of corpus luteum independently on prostaglandins in conscious cattle

The aim of this study was to examine whether prostaglandins are involved in the effects of noradrenaline on corpus luteum (CL) function. To establish an effective dose of indomethacin (INDO) to prevent prostaglandin synthesis, different doses (120, 180, 240 and 300 mg) of drug were infused for 30 min on days 17-18 of the estrous cycle in four heifers and followed with 50 IU of OT. Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were measured, both to illustrate the concentrations of all prostaglandins and to establish the effective dose of INDO that can effectively block prostaglandins synthesis. In Experiment 2, on days 10-12 of the cycle, heifers (n = 6) were infused in a Latin square design with 4 mg of noradrenaline (NA) and pre-treated with 120 mg of INDO or with saline. In both cases, NA did stimulate progesterone and ovarian oxytocin secretion. We conclude that NA affects secretory function of the CL independently of prostaglandins.

Regulation of uterine estrogen receptors (ER) by beta-adrenergic stimulation in immature rats

The effects of a 3-day intramuscular (i.m.) administration of clenbuterol (25 micrograms/Kg), propranolol (12 mg/kg), clenbuterol (25 micrograms/kg) plus propranolol (12 mg/Kg) and estradiol (0.5 microgram) upon the female reproductive system were investigated in immature Sprague-Dawley rats. Clenbuterol and estradiol treatments induced a significant increase in uterus weight and in relative uterus weight, whereas in the groups treated with propranolol and clenbuterol plus propranolol no differences were detected versus controls. The uterine estrogen receptor levels were significantly increased by clenbuterol administration. In the rats dosed with propranolol and clenbuterol plus propranolol, no modifications occurred in estrogen receptor concentrations when compared with control values. Uterine progesterone receptors were never significantly affected by any of the considered treatments. Data obtained indicate that clenbuterol treatment induces an increase in uterus weight and in estrogen receptor levels and that these effects are regulated by acute beta-adrenergic stimulation, as the contemporaneous administration of high doses of a beta-blocker inhibit such effects.

The effects of adrenaline and atropine on oxytocin-induced estrus in the goat

Oxytocin-induced luteolysis in goats was associated with significant increases in peripheral plasma concentrations of 13,14-dihydro-15-keto-prostaglandin (PG) F(2alpha) (PGFM). This effect was not inhibited by concomitant administration of adrenaline (1 mg), although increases of PGFM were both delayed and diminished. Administration of atropine, a muscarinic cholinergic antagonist, inhibited the effect of oxytocin in three out of five goats. In these animals, increases in PGFM were inhibited.