  The upper critical field $H_{c2}$ is one of the many non conventional
properties of high-$T_c$ cuprates. It is possible that the $H_{c2}(T)$
anomalies are due to the presence of inhomogeneities in the local charge
carrier density $\rho$ of the $CuO_2$ planes. In order to study this point, we
have prepared good quality samples of polycrystalline $La_{2-x}Sr_xCuO_{4}$
using the wet-chemical method, which has demonstrated to produce samples with a
better cation distribution. In particular, we have studied the temperature
dependence of the second critical field, $H_{c2}(T)$, through the magnetization
measurements on two samples with opposite average carrier concentration
($\rho_m=x$) and nearly the same critical temperature, namely $\rho_m = 0.08$
(underdoped) and $\rho_m = 0.25$ (overdoped). The results close to $T_c$ do not
follow the usual Ginzburg-Landau theory and are interpreted by a theory which
takes into account the influence of the inhomogeneities.
