Factors contributing to increases in circulating hypertensive peptides in genetic hypertension

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1) We investigated the effects of high salt intake on cardiopulmonary baroreflex control of renal sympathetic nerve activity (RSNA) in SHR and WKY. The stimulus ( <DELTA> LV end-diastolic pressure)-response ( <DELTA> RSNA) relationship in SHR with normal salt intake was shifted toward a higher pressure range compared with that in WKY with normal salt intake. High salt intake decereased the gain of the reflex both in SHR and WKY. However, changes in the gain caused by salt loading were comparable between SHR and WKY.2) We also examined release of atrial natriuretic peptide (ANP) in response to atrail stretch in vitro. We found, first, that ANP release decreased gradually with time despite that an increase in resting tension was maintained, Which suggests that adaptation occures in ANP release in response to atrial stretch. Second, we found that ANP release did not occure when the atria were stretched in the medium with diltiazem <10^(-5)> M or the calciums-free medium. However, repetitive stretch at a frequency of 300 beats/min increased ANP release despite the presence of diltiazem <10^(-5)> M. These results indicate that active muscle contraction or calcium entry into myocytes is not prerequisite for ANP release.