A sample of giant Sb-Sc spiral galaxies for which there are highly accurate and extended rotation curves was considered. Having divided the galaxies into three groups as a function of the overall spatial density of luminosity (mass) within 0.5 Mpc (ρ_L), we investigated the characteristics of the rotation curves as functions of ρ_L. It turned out that for such massive galaxies, the shape of the rotation curve (the logarithmic gradient) and the Tully-Fisher relation do not depend on the overall space environment. The only difference is that the rotation curves of galaxies in regions with high ρ_L can be traced out to smaller relative distances from the nucleus, on the average. This may be related to destruction of the outer regions of their gaseous disks in gravitational interaction with surrounding galaxies.