Dependence of multidrug resistance protein-mediated cyclic nucleotide efflux on the background sodium conductance.

Anterior pituitary cells fire action potentials and release cyclic nucleotides both spontaneously and in response to agonist stimulation, but the relationship between electrical activity and cyclic nucleotide efflux has not been studied. In these cells, a tetrodotoxin-resistant background N(+) conductance is critical for firing of action potentials, and multidrug resistance proteins (MRPs) MRP4 and MRP5 contribute to cyclic nucleotide efflux. Here, we show that abolition of the background Na(+) conductance in rat pituitary cells by complete or partial replacement of extracellular Na(+) with organic cations or sucrose induced a rapid and reversible hyperpolarization of cell membranes and inhibition of action potential firing, accompanied by a rapid inhibition of cyclic nucleotide efflux. Valinomycin-induced hyperpolarization of plasma membranes also inhibited cyclic nucleotide efflux, whereas depolarization of cell membranes induced by the inhibition of Ca(2+) influx or stimulation of Na(+) influx by gramicidin was accompanied by a facilitation of cyclic nucleotide efflux. In contrast, inhibition of cyclic nucleotide efflux by probenecid did not affect the background Na(+) conductance. In human embryonic kidney 293 cells stably transfected with human MRP4 or MRP5, replacement of bath Na(+) with organic cations also hyperpolarized the cell membranes and inhibited cyclic nucleotide efflux. In these cells, the Na(+)/H(+) antiporter monensin did not affect the membrane potential and was practically ineffective in altering cyclic nucleotide efflux. In both pituitary and MRP4- and MRP5-expressing cells, 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK571) inhibited cyclic nucleotide efflux. These results indicate that the MRP4/5-mediated cyclic nucleotide efflux can be rapidly modulated by membrane potential determined by the background Na(+) conductance.

Multiple roles of Gi/o protein-coupled receptors in control of action potential secretion coupling in pituitary lactotrophs.

G(i/o) protein-coupled receptors, signaling through G protein-dependent and protein-independent pathways, have prominent effects on secretion by modulating calcium signaling and regulating the size of the releasable secretory pool, the rates of exocytosis and endocytosis, and de novo synthesis. Pituitary cells fire action potentials spontaneously, and the associated calcium influx is sufficient to maintain prolactin (PRL) release but not gonadotropin release at high and steady levels for many hours. Such secretion, termed intrinsic, spontaneous, or basal, reflects fusion of secretory vesicles triggered by the cell type-specific pattern of action potentials. In lactotrophs, activation of endothelin ET(A) and dopamine D(2) receptors causes inhibition of spontaneous electrical activity and basal adenylyl cyclase activity accompanied with inhibition of basal PRL release. Agonist-induced inhibition of cAMP production and firing of action potentials is abolished in cells with blocked pertussis toxin (PTX)-sensitive G(i/o) signaling pathway. However, agonist-induced inhibition of PRL release is only partially relieved in such treated cells, indicating that both receptors also inhibit exocytosis downstream of cAMP/calcium signaling. The PTX-insensitive step in agonist-induced inhibition of PRL release is not affected by inhibition of phosphoinositide 3-kinase and glycogen synthase kinase-3 but is partially rescued by downregulation of the G(z)alpha expression. Thus, ET(A) and D(2) receptors inhibit basal PRL release not only by blocking electrical activity but also by desensitizing calcium-secretion coupling.

Beneficial aspect of oral estriol as hormone replacement therapy: consideration on bone and lipid metabolism.

To improve the quality of life of elderly people in Japanese society where women have the longest life expectancy in the world, osteoporosis, and hyperlipidemia are among the major targets of medical treatment. To differentiate two types of regimens for hormone replacement therapy (HRT), we tried to evaluate the efficacy on lipid and bone metabolism. With informed consent, 34 postmenopausal women of more than 2 years were assigned to receive 1 of 2 types of HRT (the HRT group) for 12 months observation: one with a combination of conjugated equine estrogen (CEE) 0.625 mg/day and medroxyprogesterone acetate (MPA) 2.5 mg/day (the CEE group), and the other with oral estriol (E3) 2 mg/day (the E3 group). Parameters of serum lipid were measured, as well as those of bone metabolism with bone mineral density (BMD) by dual-energy X-ray absorptiometry (DEXA) using QDR-2000. In HRT groups, lipid and bone metabolism were confirmed to be improved. Whereas, an increase of triglycerides (TG) observed in the CEE group was not observed in the E3 group. Thus, in the clinical management of postmenopausal women, oral E3 preparation as an alternative regimen for HRT for CEE might be efficacious.

Persistent ectopic pregnancy after laparoscopic salpingotomy: a manageable complication to preserve reproductive tubal function.

OBJECTIVE: We evaluated whether or not persistent ectopic pregnancy (PEP) is a preventable complication after conservative laparoscopic surgery (salpingotomy) for tubal pregnancy. METHODS: We reviewed the medical records of 139 patients who underwent salpingotomy between December 1992 and December 2008. RESULTS: Out of 139 patients, 23 (16.5%) were diagnosed with a PEP after salpingotomy. When compared with 114 (82.5%) successfully treated patients, there were no differences in preoperative features (gestational age, serum human chorionic gonadotropin [hCG] levels, and ultrasonography findings ) and postoperative reproductive potentials (ipsilateral tubal patency and pregnancy outcomes). CONCLUSIONS: PEP, when appropriately treated, does not adversely affect tubal functions and postoperative fertility. We should uniformly perform an exact surgery paying careful attention to preserving the tubal function regardless of preoperative features.

Dopamine inhibits basal prolactin release in pituitary lactotrophs through pertussis toxin-sensitive and -insensitive signaling pathways.

Dopamine D2 receptors signal through the pertussis toxin (PTX)-sensitive G(i/o) and PTX-insensitive G(z) proteins, as well as through a G protein-independent, beta-arrestin/glycogen synthase kinase-3-dependent pathway. Activation of these receptors in pituitary lactotrophs leads to inhibition of prolactin (PRL) release. It has been suggested that this inhibition occurs through the G(i/o)-alpha protein-mediated inhibition of cAMP production and/or G(i/o)-betagamma dimer-mediated activation of inward rectifier K(+) channels and inhibition of voltage-gated Ca(2+) channels. Here we show that the dopamine agonist-induced inhibition of spontaneous Ca(2+) influx and release of prestored PRL was preserved when cAMP levels were elevated by forskolin treatment. We further observed that dopamine agonists inhibited both spontaneous and depolarization-induced Ca(2+) influx in untreated but not in PTX-treated cells. This inhibition was also observed in cells with blocked inward rectifier K(+) channels, suggesting that the dopamine effect on voltage-gated Ca(2+) channel gating is sufficient to inhibit spontaneous Ca(2+) influx. However, agonist-induced inhibition of PRL release was only partially relieved in PTX-treated cells, indicating that dopamine receptors also inhibit exocytosis downstream of voltage-gated Ca(2+) influx. The PTX-insensitive step in agonist-induced inhibition of PRL release was not affected by the addition of wortmannin, an inhibitor of phosphatidylinositol 3-kinase, and lithium, an inhibitor of glycogen synthase kinase-3, but was attenuated in the presence of phorbol 12-myristate 13-acetate, which inhibits G(z) signaling pathway in a protein kinase C-dependent manner. Thus, dopamine inhibits basal PRL release by blocking voltage-gated Ca(2+) influx through the PTX-sensitive signaling pathway and by desensitizing Ca(2+) secretion coupling through the PTX-insensitive and protein kinase C-sensitive signaling pathway.

Platelet inhibition by single low-dose aspirin, using the newly developed aggregometry with the laser light scattering method.

Low-dose aspirin (acetylsalicylic acid 81 mg/day, LDA) is often used as an antiplatelet drug in the treatment of cardiovascular and cerebrovascular diseases as well as for patients with anti-phospholipid antibody syndrome. In this study, we explored the duration of the inhibitory effect of a single LDA on platelet aggregation, using the newly developed aggregometry with the laser light scattering method. Five healthy volunteers (females between 23 and 30 years old) ingested 81 mg of buffered aspirin. Platelet aggregation was measured with adenosine 5'-diphosphate before the ingestion and at the 1st, 2nd, 4th, 6th, and 8th day thereafter. The results showed that the effect of 81 mg of aspirin continues for at least 8 days, which suggested that the intermittent administration of 81 mg of aspirin (a few times a week) might be an alternative way to induce the anti-platelet effect.

Anesthesia and acoustic stress-induced intra-uterine growth retardation in mice.

Stress interferes with reproduction, adversely influencing implantation and fetal growth, and sometimes even leading to abortion. Here, we attempted to evaluate the early gestational effects of uncomfortable sound on pregnant mice and their offspring. Ten-week-old pregnant Jcl:ICR mice were exposed to sound (100 dB, random frequency between 9-34 kHz) for 8 hours on the 3(rd), 5(th) and 7(th) gestational days (GD). The effects of general anesthesia were also investigated, with or without acoustic stress. All groups were examined on the 18(th) GD for fetal growth. Fetal weight, number of ossified sacrococcygeal vertebrae and placental weight were all significantly reduced (P<0.0001) when stress was induced on the 7(th) GD, but not on the 3(rd) or 5(th) GD. This intra-uterine growth retardation (IUGR) was significantly inhibited by general anesthesia (P<0.0001), although general anesthesia alone induced significant IUGR (P<0.0001) when compared with control mice. This suggests that acoustic exposure indirectly exerts an effect on fetal growth, possibly via a psycho-maternal pathway. We also found that analysis of the number of ossified sacrococcygeal vertebrae is the most sensitive tool for the study of IUGR.

Preservation of tubal function following methotrexate treatment for ectopic pregnancy.

To evaluate methotrexate (MTX) administration as a conservative treatment for ectopic pregnancy, we reviewed the medical records of 248 cases (210 patients) of MTX treatment for tubal pregnancies at our department between December 1985 and December 2003, and compared its pregnancy prognosis with that of laparoscopic salpigotomy (59 patients). With the MTX treatment, 185 patients were successfully treated, and the subsequent pregnancy rate and ectopic pregnancy rate were 48.4 % and 18.4 %, respectively, while those rates were 49.2 % and 18.6 %, respectively, after the salpigotomy. These results suggest that MTX treatment is comparable to the more conservative operation. To clarify the (dys/) function of the ectopic implantation tubes and MTX-treated tube (s), we excluded patients who had a contra-lateral healthy tube, and extracted 40 patients as "the affected tube group", where the pregnancy-related parameters were not adversely affected. The findings suggest that MTX is not necessary to preserve tubal function.

Impact of menopause on lipid and bone metabolism and effect of hormone replacement therapy.

BACKGROUND: Hyperlipidemia and osteoporosis are the medical targets to improve the quality of life of increasing elderly women. OBJECTIVE: To elucidate the effect of menopause and hormone replacement therapy (HRT) on lipid and bone metabolism. SUBJECTS: With their written informed consent, studied were 89 postmenopausal with 30 premenopausal women, and postmenopausal 35 were assigned into HRT (n = 18) or control group (n = 17); the former received conjugated equine estrogen (0.625 mg/day) and medroxyprogesterone acetate (2.5 mg/day), the latter calcium aspartate (800 mg/day). OUTCOME MEASURED: Parameters were measured for lipids; total cholesterol (TC), high-density lipoprotein cholesterol (HDLC), low-density lipoprotein cholesterol (LDLC), triglycerides (TG), lipoproteins, and apolipoproteins as well as for bone metabolism; parathyroid hormone (PTH), 1,25(OH)2D3, bone type of alkaline phosphatase (b-ALP), intact bone gla protein (I-BGP), tartrate-resistant acid phosphatase (TRAP) in serum. Bone mineral density (BMD) of lumbar spine was measured by dual energy X-ray absorptiometry (DEXA). Two atherogenic indices (AIs) were calculated: AIc equals [TC - HDLC]/HDLC, and AIap equals (apolipoprotein B)/(apolipoprotein A1). RESULTS: TC increased in approximately 10% within 2 years after menopause with increased LDLC (approximately 20%) and decreased HDLC (approximately 10%), and atherogenic indices were both elevated. In HRT, HDLC increased, while TC and LDLC and TG showed no significant change; lumbar BMD increased by 3% after 12 month, while bone formation markers decreased; PTH increased and 1,25(OH)2D3 decreased. CONCLUSION: We provided the natural changes of lipid and bone metabolism after menopause and how extent an estrogen replacement can reset these changes.