Takao Okazawa

Change in digital blood flow with simultaneous reduction in plasma endothelin induced by hand-arm vibration

Involvement of endothelium-derived relaxing factor (EDRF) or endothelium-derived constricting factor (EDCF) has been proposed as the pathophysiologic mechanism of vibration-induced white finger (VWF). Recent evidence that endothelin is a potent vasoconstrictor peptide indicates that it may play a role in vasoregulation during vibration exposure through the local actions of EDRF or EDCF. Therefore, we examined the effects of grasping (50 N) and hand-arm vibration (50 m/s2 rms, 120 Hz, x-axis) on digital blood flow (DBF) and on the level of plasma endothelin in seven healthy male office workers. Grasping decreased DBF without affecting endothelin, and vibration increased DBF with a simultaneous reduction in endothelin. The grasping-induced decrease in DBF seemed to be due to mechanical compression of the vessels. The negative correlation between DBF and endothelin during vibration exposure suggests that a reduction in release of endothelin from smooth muscle into the vessel cavity during vibration leads to vasodilatation, possibly attributable to the local axon reflex.

Changes of cerebral vasoactive intestinal polypeptide- and somatostatin-like immunoreactivity induced by noise and whole-body vibration in the rat

To clarify the role of vasoactive intestinal polypeptide (VIP) and somatostatin, somatropin-release inhibiting factor, (SRIF) neurons in the response to organisms to noise or whole-body vibration stress, VIP and SRIF-like immunoreactivity were determined in various regions of the rat brain following exposure for 90 min to noise (broad band, 102 dB) or whole-body vibration (20 Hz, 4.0 g). Both noise and whole-body vibration significantly increased VIP-like immunoreactivity in the amygdala. A significant reduction of VIP like immunoreactivity in the hippocampus was induced only by whole-body vibration. On the other hand SRIF-like immunoreactivity was decreased significantly in the hypothalamus and increased significantly in the amygdala by noise and whole-body vibration, respectively. The present findings would seem to indicate that the amygdalofugal VIP neural system is involved in regulating hypothalamic and pituitary hormone secretions in non-specific reactions to stress. Responses of hippocampal VIP and the amygdalofugal SRIF to whole-body vibration stress are assumed to be activated as specific reactions to the stress.

Uterine circulatory dysfunction induced by whole-body vibration and its endocrine pathogenesis in the pregnant rat

Effects of whole-body vibration on normal pregnancy were studied in the rat. Uterine blood flow and five endocrine functions corticosterone (CS), estradiol (E2), progesterone (P), prostaglandin E2 (PGE2) and prostaglandin F2α (PGF2α) concentration were measured in rats exposed to whole-body vibration with an acceleration of 10 m·s−2 at a frequency of 8 Hz. While no change in uterine blood flow was observed in control rats, uterine blood flow was significantly decreased 75 and 90 min after exposure to vibration. The uterine blood flow at 15 and 30 min was increased by pretreatment with intraperitoneal injections of angiotensin 11 (AII). In contrast, in AII pretreated rats exposed to the vibration, uterine blood flow was significantly reduced 90 min after exposure. The CS concentration was increased by vibration independently of the pretreatment with All. Neither E2 nor PGF2α concentration were changed by the vibration with or without AII administration. The P and PGE2 concentrations were both decreased by vibration in the absence of AII, while the decrease in PGE2 induced by the vibration was also found in AII-treated rats. The present results indicated that the pregnant rats subjected to whole-body vibration responded with changes in uterine and ovarian function. The observed decrease in uterine blood flow may have been the result of reduced PGE2 concentration resulting from an indirect effect of vibration.

Pathophysiological significance of plasma endothelin in peripheral circulatory disturbances.

Endothelin (ET) is produced in blood vessels and is a novel potent vasoconstrictor. Although the presence of immunoreactive ET in the circulating blood suggests that ET plays an important role in the regulation of systemic and/or local hemodynamics, the role of circulating ET has not been ascertained using human populations. We examined the values of the ET level and peripheral blood flow, including other biochemical and physiological factors, in 108 healthy adults who participated in annual health examinations of Japanese adults living in a rural community in 1992 and 1993. A small change in ET after the passage of one year showed good reproducibility of the value. ET was positively correlated with diastolic blood pressure (BP) and negatively with finger skin blood flow in healthy adults. Multiple regression analysis demonstreted that the positive relationship between ET and diastolic BP was independent of other health indicators. A detailed examination using optical spectroscopy for elderly institutionalized subjects without any trouble in the activity of daily living revealed a negative correlation of ET with saturated oxygen in blood, tissue hemoglobin volume and local blood flow and a positive one with the local oxygen extraction fraction. The present study indicated that increased ET in the elderly subjects was associated with hypoxia not only in the local finger skin region, but also possibly in the arterial tissue, suggesting that ET is involved in atherosclerosis. The negative correlation between ET and finger skin blood flow seen in the healthy adults may be induced by hypoxia. Although we recognized a positive correlation between ET and BP, the increase in ET seemed to be an outcome of elevation in BP rather than a cause of hypertension.

Regional cerebral blood flow and vasoactive intestinal polypeptide (VIP) in rat exposed to whole-body vibration stress

To clarify the involvement of vasoactive intestinal polypeptide (VIP) in regional cerebral circulation during whole-body vibration (WBV), we determined regional cerebral blood flow and VIP-like immunoreactivity (VIP-LI) in rats following WBV for 90 min. at various accelerations (0, 2G and 4G rms), using the hydrogen gas electrolytic method. Interference electrodes were inserted into the frontal cortex and the hippocampus. Although we observed no change in hippocampal blood flow, the frontal cortical blood flow increased during the exposure in a manner that was dependent upon the acceleration. There was a significant reduction in hippocampal VIP-LI following WBV at an acceleration of 4G. The association between frontal cortical blood flow and hippocampal VIP-LI was significantly negative. Our results indicated that a local increase in blood flow in the frontal cortex of rats was induced by WBV. This increase seemed to be involved in the neural activation induced by WBV. Hippocampal VIP may have a role in the physiological regulation of frontal cortical circulation during WBV stress.