Occurrence of catecholamine-containing specific granules in the venous endothelia of carp

The formaldehyde-induced fluorescence technique and the argentaffin reaction with ultra-thin sections were applied to the vessels of carp to demonstrate the presence of a catecholamine. After formaldehyde gas treatment for 30 minutes at 50 degrees C, the venous endothelia emitted a greenish-yellow fluorescence suggesting the presence of a primary catecholamine. In the endothelial cells of veins, the specific granules, consisting predominantly of spherical granules with a diameter of about 0.3 micrometer, showed heavily to moderately positive argentaffin reaction. Granules also occurred in the endothelial cells of arteries. However, these granules stained weakly or not at all with ammoniacal silver solution. It is concluded that the specific endothelial granules in veins of carp contain a primary catecholamine.