Effect of hyperosmolality on the sensitivity of right and left atria of the rat to noradrenaline

ABSTRACT

This study analyzes the effects of hyperosmotic solutions on the sensitivity of the rat isolated right and left atria to the chronotropic and inotropic effects of noradrenaline (NA), respectively. Hyperosmotic NaCl solution caused subsensitivity to both effects of NA (pD2 values for NA, right atria control 7.42 ñ 0.06, NaCl 6.83 ñ 0.18, P < 0.05; left atria control 7.67 ñ 0.22, NaCl 6.61 ñ 0.18, P < 0.05). Hyperosmotic sucrose solution produced a similar effect in right atria (pD2NA 6.96 ñ0.17, P < 0.05), whereas in left atria it depressed the maximum inotropic response to NA by about 80%. All chagnes, except that of maximun inotropic response, were abolished following combined pretreatment with 6-hydroxydopamine, phenoxybenzamine, atropine and imipramine. These data suggest that the noradrenergic subsensitivity induced in atrial tissue bu hyperosmolality is probablu not due to changes of beta-adrenoceptor function and/or coupling of these receptors to the effectors mechanisms