Changes in Myogenic Tone in Spontaneously Hypertensive Rat: Role of RhoA and Protein Kinase C

BACKGROUND AND OBJECTIVES: The myogenic response was originally described as a contraction of a blood vessel that occurred following an increase in intravascular distending pressure. Conversely, a reduction in intravascular pressure produces myogenic vascular relaxation. Recent attention has focused on the potential role of this myogenic mechanism in the control of tone in the resistance vasculature, and in particular on how this mechanism may contribute to the increased vascular resistance seen in hypertension. Therefore, in the present study, we investigated the role of myogenic tone in the generation and/or maintenance of hypertension. MATERICAL AND METHODS: Myogenic tone was developed by stretching of the basilar arteries of WKY (istar Kyoto rat) and SHR (spontaneously hypertensive rats). Contractile responses, PKC (protein kinase C) immunoblots and translocation of PKC and RhoA were measured. In the presence of extracellular Ca2+ the stretching of the resting vessel evoked a myogenic contraction in the basilar arteries of SHR and WKY. Myogenic tone was significantly greater in SHR than in WKY. However, in the absence of extracellular Ca2+, stretching evoked a myogenic contraction in SHR, but not in WKY. The stretch-induced myogenic tone was inhibited by nifedipine. The effect of nifedipine was similar in both SHR and WKY rats. H-7, calphostin C and Y-27632, also inhibited stretch-induced myogenic tone in both SHR and WKY. The inhibitory effects of these drugs were greater in SHR than in WKY. Immunoblotting showed rho A and PKC alpha were translocated from the cytosol to the cell membrane with stretching in both SHR and WKY. PKC beta, however, was translocated to the cell membrane with stretching in SHR, but not in WKY. CONCLUSION: These results suggest that stretch-induced myogenic tone is significantly greater in SHR than in WKY. Furthermore, the increase in amount and/or activity of PKC beta and ROK (rhoA-associated kinase) may be a key mechanism accounting for the enhanced myogenic tone in SHR.

Predictive Factors of Unexpected Death in Emergency Department

BACKGROUND: Unexpected deaths of the patients at ED are surprising to the medical staffs as well as the families. It may also increase the possibilities of medico-legal problems. This study was conducted to review the unexpected death in ED and find the predictive factors leading patients to unexpected death. METHODS: A retrospective study with reviewing available medical records of 183 patients who were expired at ED of Shinchon Severance Hospital from Mar. 1997 to Feb. 1998 and 103 patients of Youngdong Severance Hospital from Mar. 1996 to Feb. 1998 was done. Analyses were 4one on 30 variables of physical findings, laboratory results, procedures and therapies. We used univariate analysis, such as t-test and x2-test and multiple logistic regression analysis. RESULTS: Of the total 286 deaths in ED, 153 cases were enrolled in this analysis. The number of unexpected deaths were 76. Age, mental status, fraction of neutrophil count, BUN level, whether endotracheal incubation was done, use of inotropics were the factors with statistical ,significance on the univariate analysis, but only comatose mentality, endotracheal incubated case, and use of the inotropics were significant on logistic regression analysis. The longer the ED length of stay, the higher the rate of mortality and unexpected death. CONCLUSION: This result suggest that medical attention is needed on the patients with comatose decreased mental stylus, endotracheally intubated case and needing inotropic agents to prevent unexpected deaths. Shortening the ED length of stay may also be a factor for decrease the unexpected death rate.