Effects of expansion of blood volume and bilateral vagotomy on specific heart granules and release of atrial natriuretic peptide in the rat.

There was no statistically significant difference in basal concentrations of immunoreactive atrial natriuretic peptide (ANP), as assessed by radioimmunoassay, between right and left atrial muscle of control rats; similarly, stereological analysis showed no statistically significant difference in the fractional volume of myocytes occupied by specific heart granules, or in numerical density of granules, between right and left atria. Nevertheless, correlated radioimmunoassay and ultrastructural investigations showed that the major source of elevated plasma levels of ANP after expansion of blood volume was the right atrium. Substantial expansion of blood volume caused an increase in the proportion of peripherally located granules in myocytes of both atria, but reduction in the number of granules and in the concentration and total content of ANP occurred in the right atrium only. Bilateral cervical vagotomy also caused a statistically significant elevation of plasma ANP concentration, accompanied by a statistically significant reciprocal reduction in right atrial ANP content; no statistically significant change occurred in left atrial ANP. When blood volume was expanded after bilateral vagotomy, there was a further statistically significant increase in plasma ANP concentration; this was accompanied by further reduction in right atrial ANP and, moreover, the combined manoeuvre also elicited a statistically significant reduction of ANP in the left atrium. Ultrastructural studies confirmed that, under these conditions, myocytes in both atria showed a marked depletion of specific heart granules.