ULTRASTRUCTURAL-STUDY OF ATRIAL SPECIFIC GRANULES IN EXPERIMENTAL RENOVASCULAR HYPERTENSION ELICITED BY THE CONSTRICTION OF BOTH RENAL-ARTERIES

The heart has an endocrine activity which depends on the secretion of a natriuretic, diuretic and hypotensive factor contained in osmophilic , secretory granules localized in the miocardiocytes and called ''atri al specific granules' (the atrial natriuretic factor, ANF). In this pa per, the relationship between these specific granules and renovascular hypertension elicited by the constriction of both renal arteries was investigated at the electron microscope level during the acute, subacu te and chronic phases of hypertension. Male Wistar CHbb THOM rats were divided in three groups: 1) clipped rats; 2) sham operated rats; 3) e ther anesthesia as unique manoeuver 48 h before decapitation. Blood pr essure increased progressively after the constriction of both renal ar teries. The atrial specific granules were not affected by ether anesth esia alone; 48-72 h after clipping the granules almost disappeared and this situation persisted up to the 6th week. In sham operated rats th e picture was very similar to the clip rats 48 and 72 h after surgery (severe granule disappearance); in contrast, at one, two and six weeks after surgery, the granularity of cardiomyocytes in sham rats was abs olutely restored. It is concluded that: 1) similarities in morphology of atrial specific granules in sham and clip rats 48 and 72 h after su rgery would suggest that stress plays a primary role in determining th e observed images; 2) thereafter, the contrast between sham and clip r ats 1, 2 and 6 weeks after surgery would indicate that the ANF is link ed to the subacute and chronic regulation of renovascular hypertension .