Dependence of NQR frequency, nu-Q(Cu) on pressure up to 1.3GPa is reported for La1.85Sr0.15CuO4 and YBa2Cu4O8. Correlations are found between some physical quantities and the ratio of the hole density in Cu2 to that in O2(3), n(Cu2)/n(O2, 3) which is extracted from nu-Q's. It is proposed tha there exists an optimum of n(Cu2)/n(O2, 3) for T(c) and that the increase of T(c) under pressure is due to the approach of n(Cu2)/n(O2, 3) to the optimum through the local hole transfer.