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THE INFLUENCES OF IONIC CONCENTRATIONS AND THE INTERVALS BETWEEN CURVES ON VASCULAR TISSUE RESPONSES ANDREW C. UGWU AND JOHN C. McGRATH Abstract The effect of pre-exposure ("priming") of vascular smooth muscle to different levels of calcium concentrations before the construction of the normal concentration - response curves (CRCs) in different calcium concentrations, was investigated. The results showed that when the rat tail artery was primed with 3μM noradrenaline (NA) in 0.3mM Ca2+ or 2.5mM Ca2+ before constricting CRCs, desensitization was produced more quickly in the tissues primed in 2.5mM Ca2+ than the ones primed in 0.3mM. In either case, however, the sensitivity of the tissue later became reduced but more "stable." This stable level is determined by the calcium concentration during priming and the maximum calcium concentration of the tissues' CRC. The study apparently suggests that priming tissues at 0.3mM with CRC maximum at 0.3mM Ca2+ is more sitale for avoiding progressive desensitisation than when the tissue is primed in 2.5mM and its CRC maximum taken to 5mM Ca2+. It follows therefore that high calcium concentration or calcium overload reduces tissues' sensitivity. The effect of length of intervals between calcium concentration-response curves on the desenitisation of the rat tail artery was also examined. It was observed that desensitisation was not a functionof time elapsed before first testing, but interval between curves as well as some other factors. The progressive loss of sensitivity could attenuated by increasing the interval between curves. Also increasing the tissue stabilisation period beyond an optimal level does not confer on the tissue a greater or lesser sensitivity. Keywords Priming - Calcium Concentration - Respons - Noradrenaline - Interval Lenghts - Desensitisation - Stabilisation

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ANDREW C. UGWU AND JOHN C. McGRATH Résumé L' effect de l'exposition des muscles vascularies non. stries aux differentes concentrations du calcuim (ca) suivit de la construction des curbes de concentration normale - reaction ces differentes concentration du calcuim etact experimente Les resullats ont montres que lorsque liartese de la queue du nat etait expose avec 3 um de noradrenaline (NA) dans 0.3 Mca2+ ou 2.5 mM Ca2+. l'insensitivite' etait produit plus rapidement dans les tissues expose a 2.5 mMCa2+ que celles a 0.3 mMCa2+. Dans chaque eas, la sensitivite' du tissue devenait plutard reduite mais plus stable. ce niveau de stabilite est determine par la concentration du calcium pendant l'exposition et la concentration maximale du ca dans les tissues. L'etude aqqaremment suggere que l'exposition - reaction maximale a 0.3 mMCa2+ est plus stable pour eviter l'insensitevite' progressive que lorsque le tissue exposee a 25 mM et sa courbe de concentration - reaction a 5 mM Ca2+. il etait obsenve que la forte dose de concentration ducalcium reduit la sensitivite des tissues. L'effect de l'intervalle du temps entre la courbe de concentration-reaction du calcium sur l'insensitivite de L'artese dela queue du ret a ete examine' iL a ete dsere que l'ensensitivite' n' etait jas function du temps avant le premier test mais l' intervalle entre les courbes bienque d'autres fucteurs. La peite progressive de l'insensitivite' pourrait etre attenue en augmentant l'intervalle entre les courbes. Aussi augmentant la periode de stabilisation du tissue au dela d' un niveau optimal ne confere pas plus on moins sun le sensitivite du tissue.

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