Retention among full-time occupational physicians in Japan.

BACKGROUND: To secure human resources for occupational medicine, it is important to analyse occupational physician retention trends and the factors associated with retention. However, little is currently known about this topic. AIMS: To identify occupational physician retention trends, to identify factors associated with this retention and to discuss the policy implications of the findings. METHODS: We analysed data from the biannual national physician census surveys conducted by the government of Japan from 2002 to 2014. In this study, those who chose 'working as an occupational physician' as their workplace/type of work from a pre-determined list in the survey questionnaire were considered full-time occupational physicians. We presented retention trends by calculating the annual retention rate for each set of two consecutive surveys. We then used logistic regression to identify factors associated with retention among occupational physicians. RESULTS: The annual retention rate of full-time occupational physicians from 2012 to 2014 was estimated as 76%, which represents a 6% improvement in retention over the study period. The odds of continuing to practise as an occupational physician were higher for occupational physicians working in cities compared with those working in towns or villages. CONCLUSIONS: Improving and facilitating smooth transitions between clinical practice and occupational medicine would help to secure human resources in occupational medicine, even if the current trend of low retention continues.

Number of nitrate groups determines reactivity and potency of organic nitrates: a proof of concept study in ALDH-2-/- mice.

BACKGROUND AND PURPOSE: Mitochondrial aldehyde dehydrogenase (ALDH-2) has been shown to provide a pathway for bioactivation of organic nitrates and to be prone to desensitization in response to highly potent, but not to less potent, nitrates. We therefore sought to support the hypothesis that bioactivation by ALDH-2 critically depends on the number of nitrate groups within the nitrovasodilator. EXPERIMENTAL APPROACH: Nitrates with one (PEMN), two (PEDN; GDN), three (PETriN; glyceryl trinitrate, GTN) and four (pentaerithrityl tetranitrate, PETN) nitrate groups were investigated. Vasodilatory potency was measured in isometric tension studies using isolated aortic segments of wild type (WT) and ALDH-2-/- mice. Activity of the cGMP-dependent kinase-I (reflected by levels of phosphorylated VAsodilator Stimulated Phosphoprotein, P-VASP) was quantified by Western blot analysis, mitochondrial dehydrogenase activity by HPLC. Following incubation of isolated mitochondria with PETN, PETriN-chromophore and PEDN, metabolites were quantified using chemiluminescence nitrogen detection and mass spectrometry. KEY RESULTS: Compared to WT, vasorelaxation in response to PETN, PETriN and GTN was attenuated about 10fold in ALDH-2-/- mice, identical to WT vessels preincubated with inhibitors of ALDH-2. Reduced vasodilator potency correlated with reduced P-VASP formation and diminished biotransformation of the tetranitrate- and trinitrate-compounds. None of these findings were observed for PEDN, GDN and PEMN. CONCLUSIONS AND IMPLICATIONS: Our results support the crucial role of ALDH-2 in bioactivating highly reactive nitrates like GTN, PETN and PETriN. ALDH-2-mediated relaxation by organic nitrates therefore depends mainly on the number of nitrate groups. Less potent nitrates like PEDN, GDN and PEMN are apparently biotransformed by other pathways.

Cerebral endothelial cells are a major source of adrenomedullin.

Adrenomedullin is a peptide hormone with multifunctional biological properties. Its most characteristic effects are the regulation of circulation and the control of fluid and electrolyte homeostasis through peripheral and central nervous system actions. Although adrenomedullin is a vasodilator of cerebral vasculature, and it may be implicated in the pathomechanism of cerebrovascular diseases, the source of adrenomedullin in the cerebral circulation has not been investigated thus far. We measured the secretion of adrenomedullin by radioimmunoassay and detected adrenomedullin mRNA expression by Northern blot analysis in primary cultures of rat cerebral endothelial cells (RCECs), pericytes and astrocytes. We also investigated the expression of specific adrenomedullin receptor components by reverse transcriptase-polymerase chain reaction and intracellular cAMP concentrations in RCECs and pericytes. RCECs had approximately one magnitude higher adrenomedullin production (135 +/- 13 fmol/10(5) cells per 12 h; mean +/- SD, n = 10) compared to that previously reported for other cell types. RCECs secreted adrenomedullin mostly at their luminal cell membrane. Adrenomedullin production was not increased by thrombin, lipopolysaccharide or cytokines, which are known inducers of adrenomedullin release in peripheral endothelial cells, although it was stimulated by astrocyte-derived factors. Pericytes had moderate, while astrocytes had very low basal adrenomedullin secretion. In vivo experiments showed that adrenomedullin plasma concentration in the jugular vein of rats was approximately 50% higher than that in the carotid artery or in the vena cava. Both RCECs and pericytes, which are potential targets of adrenomedullin in cerebral microcirculation, expressed adrenomedullin receptor components, and exhibited a dose-dependent increase in intracellular cAMP concentrations after exogenous adrenomedullin administration. Antisense oligonucleotide treatment significantly reduced adrenomedullin production by RCECs and tended to decrease intraendothelial cAMP concentrations. These findings may suggest an important autocrine and paracrine role for adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions. Cerebral endothelial cells are a potential source of adrenomedullin in the central nervous system, where adrenomedullin can also be involved in the regulation of neuroendocrine functions.

Adrenomedullin regulates blood-brain barrier functions in vitro.

Adrenomedullin (AM) is an important vasodilator in cerebral circulation, and cerebral endothelial cells are a major source of AM. This in vitro study aimed to determine the AM-induced changes in blood-brain barrier (BBB) functions. AM administration increased, whereas AM antisense oligonucleotide treatment decreased transendothelial electrical resistance. AM incubation decreased BBB permeability for sodium fluorescein (mol. wt 376 Da) but not for Evan's blue albumin (mol. wt 67 kDa), and it also attenuated fluid-phase endocytosis. AM treatment resulted in functional activation of P-glycoprotein efflux pump in vitro. Our results indicate that AM as an autocrine mediator plays an important role in the regulation of BBB properties of the cerebral endothelial cells.

Preferential potentiation by nitric oxide of spontaneous inhibitory postsynaptic currents in rat supraoptic neurones.

Magnocellular neurones in the supraoptic nucleus and paraventricular nucleus express mRNA for nitric oxide synthase (NOS) and the expression becomes more prominent when the release of vasopressin or oxytocin is stimulated. It has also been reported that NO donors inhibit the electrical activity of supraoptic nucleus neurones, but the mechanism involved in the inhibition remains unclear. In the present study, to know whether modulation of synaptic inputs into supraoptic neurones is involved in the inhibitory effect of NO, we measured spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) from rat supraoptic nucleus neurones in slice preparations identified under a microscope using the whole-cell mode of the slice-patch-clamp technique. The NO donor, S-nitroso-N-acetylpenicillamine (SNAP), reversibly increased the frequency of spontaneous IPSCs mediated by GABAA receptors, without affecting the amplitude, indicating that NO potentiated IPSCs via a presynaptic mechanism. The NO scavenger, haemoglobin, suppressed the potentiation of IPSCs by SNAP. On the other hand, SNAP did not cause significant effects on EPSCs mediated by non-NMDA glutamate receptors. The membrane permeable analogue of cGMP, 8-bromo cGMP, caused a significant reduction in the frequency and amplitude of both IPSCs and EPSCs. The results suggest that NO preferentially potentiates the inhibitory synaptic inputs into supraoptic nucleus neurones by acting on GABA terminals in the supraoptic nucleus, possibly via a cGMP-independent mechanism. The potentiation may, at least in part, account for the inhibitory action of NO on the neural activity of supraoptic neurones.

Increase of urocortin-like immunoreactivity in the supraoptic nucleus of Dahl rats given a high salt diet.

Urocortin-like immunoreactivity (Ucn-LI) in the supraoptic nucleus (SON) of Dahl rats was examined. Dahl salt-sensitive (S) rats fed with a high salt diet developed hypertension. Numbers of Ucn-LI neurons in the SON in Dahl S on a high salt diet were markedly increased, compared with those in Dahl salt-resistant (R) rats on the same. Sporadic Ucn-LI neurons were found in the SON of both Dahl S and R on a normal diet. Numbers of Ucn-LI neurons in the SON of spontaneously hypertensive rat (SHR) and stroke-prone SHR, genetic models of hypertension, and control rats (Sprague-Dawley and Wistar-Kyoto) were similar. These results suggest that Ucn in the SON is associated with salt loading-induced hypertension rather than spontaneous hypertension.

Effects of leptin on fasting-induced inhibition of neuronal nitric oxide synthase mRNA in the paraventricular and supraoptic nuclei of rats.

Fasting induced a reduction in neuronal nitric oxide synthase (nNOS) mRNA in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of rats. The effect of intracerebroventricular (i.c.v.) administration of leptin on the nNOS mRNA level in the PVN and SON of fasting rats was studied by in situ hybridization histochemistry. Leptin (10 microg/kg b.wt) or vehicle was administered i.c.v. at 1700 h on two successive days fasting for 2 days. Fasting for 2 days with i.c.v. administration of vehicle induced a significant reduction of nNOS mRNA in the PVN and SON. Central administration of leptin prevented the fasting-induced reduction of nNOS mRNA in the PVN and SON. Administration of leptin also prevented the fasting-induced reductions of thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) mRNAs in the parvocellular division of the PVN. These results suggest that leptin is associated with fasting-induced reduction of nNOS mRNA in the PVN and SON as well as TRH and CRH mRNAs in the PVN.

Adrenomedullin-like immunoreactivity in the rat hypothalamo-neurohypophysial tract.

Adrenomedullin-like immunoreactivity in the hypothalamo-neurohypophysial tract in colchicine-treated and hypophysectomized rats was examined by immunohistochemistry. Adrenomedullin-like immunoreactive (AM-LI) neurons were localized in the hypothalamic areas, including the paraventricular nuclei and the supraoptic nuclei. Abundant AM-LI fibers and varicosities were found in the hypothalamoneurohypophysial tract and the internal zone of the median eminence in the colchicine-treated and hypophysectomized rats, whereas in control rats few AM-LI fibers were observed. These results suggest that the axons of the AM-LI neurons in the hypothalamus may terminate in the neurohypophysis.

Inhibition of spontaneous inhibitory postsynaptic currents (IPSC) by noradrenaline in rat supraoptic neurons through presynaptic alpha2-adrenoceptors.

It has been shown that noradrenergic activation has great influence on the activities of hypothalamic supraoptic neurons. No direct evidence has been reported on the presynaptic effects of adrenoceptors in the actions of noradrenaline on supraoptic neurons, although postsynaptic mechanisms have been studied extensively. In the present study, we explored presynaptic effects of noradrenaline on the supraoptic neurons by measuring spontaneous inhibitory postsynaptic currents (IPSC) with the whole-cell patch-clamp technique. Noradrenaline reduced the frequency of IPSCs in a dose-dependent (10(-9) to 10(-3) M) and reversible manner. Noradrenaline did not affect the amplitude of IPSCs at concentrations of 10(-9) to 10(-5) M, but reduced the amplitude of IPSCs at high concentrations (10(-4) and 10(-3) M). The inhibitory effects of noradrenaline were mimicked by the alpha2-agonist clonidine (10(-4) M), but not by the alpha1-agonist methoxamine (10(-4) M) nor by the beta-agonist isoproterenol (10(-4) M). Moreover, the inhibitory effects of noradrenaline on IPSCs were blocked by the non-selective alpha antagonist phentolamine (10(-4) M) or the selective alpha2-antagonist yohimbine (10(-4) M), but not by the alpha1-antagonist prazosin (10(-4) M). These results suggest that noradrena-line inhibits release of GABA from the presynaptic GABAergic terminals of the supraoptic neurons by activating presynaptic alpha2-adrenoceptors and such presynaptic mechanisms may play a role in the excitatory control of SON neurons by noradrenergic neurons.

Increase of urocortin-like immunoreactivity in the rat supraoptic nucleus after dehydration but not food deprivation.

The effects of dehydration and food deprivation on urocortin-like immunoreactivity (Ucn-IR) in the rat supraoptic nucleus (SON) and the paraventricular nucleus (PVN) were examined by immunohistochemistry. Water deprivation for 48 h caused a significant increase in the number of Ucn-IR neurons in the SON, compared with control. Ucn-IR fibers and varicosities in the SON and the internal zone of the median eminence (ME) were increased, but a few and faint Ucn-IR neurons and fibers were observed in the PVN. On the other hand, food deprivation for 48 h caused a significant decrease in the number of Ucn-IR neurons in the SON, compared with control. Ucn-IR fibers and varicosities in the SON and the ME were fewer than those in controls. Ucn-IR neurons and fibers in the PVN were not detected after food deprivation. These results suggest that Ucn in the SON may be involved in the central regulation of water balance and nutrient homeostasis.

Increase of urocortin-like immunoreactivity in the rat hypothalamo-neurohypophysial system after salt loading and hypophysectomy.

The effect of chronic salt loading on urocortin-like immunoreactivity (Ucn-IR) was investigated in the rat hypothalamo-neurohypophysial system. In control rats a few Ucn-IR neurons were observed scattered throughout the supraoptic nucleus (SON) and few in the paraventricular nucleus (PVN). A small number of Ucn-IR fibers were observed scattered in the median eminence (ME) and the posterior pituitary. However, after 5 days of chronic administration of 2% saline, a marked increase in the number of Ucn-IR perikarya and fibers was observed in the PVN and the SON. Additionally, Ucn-IR varicosities and fibers were found in the internal zone of the ME and in the posterior pituitary. To confirm the findings and examine the possible involvement of anterior pituitary function in synthesis of Ucn, surgical hypophysectomized rats were used. Five days after hypophysectomy, a marked increase in Ucn-IR was observed in the PVN, the SON, and both the internal and the external zone of the ME. These results suggest that Ucn in the hypothalamo-neurohypophysial system may be involved in the regulation of salt balance, and possibly in the stimulation of ACTH release from the anterior pituitary.

PTH-related peptide-like immunoreactivity in the median emminence, paraventricular and supraoptic nuclei in colchicine-treated rats.

The existence of PTH-related peptide (PTHrP) in the hypothalamus was examined by immunohistochemistry in colchicine-treated rats. Two days after intracerebroventricular administration of colchicine dense PTHrP-like immunoreactivity (LI) was observed in the external zone of the median emminence (ME). PTHrP-LI cells were found in the paraventricular nucleus, the supraoptic nucleus and the periventricular region of the third ventricule. The effects of PTHrP on intracellular Ca2+ concentrations ([Ca2+]i) were examined by a Ca2+ imaging method using fura-2 in perifused preparations of isolated rat anterior pituitary cells. The rise in [Ca2+]i induced by PTHrP was found in approximately 17% of the cells examined. These results suggest that PTHrP-LI cells in the hypothalamus may project to the ME and contribute to the anterior pituitary function.

Adrenomedullin-immunoreactive neurons in the paraventricular and supraoptic nuclei of the rat.

The existence of adrenomedullin (AM) in the rat hypothalamus was examined by immunohistochemistry. AM-immunoreactive neurons were found in the supraoptic nucleus (SON) and in the magnocellular parts of the paraventricular nucleus (PVN). The co-existence of AM-, oxytocin- and/or vasopressin-immunoreactivity was identified in the same neurons in the hypothalamus. The results suggest that the AM may play a role in neurotransmission or in cardiovascular control with neurohypophyseal hormones.