We propose a theory of gravity based on the interaction of the gauge f
ield representing gravitation with a suitable vector ''substratum'' (p
hysical vacuum). To build up the new theory, we exploit the formalism
of the Symbolic Gauge Theory, an application to gauge theories of the
General System Logic Theory, which results from the Fusion of three ma
thematical structures, the logical theory of systems, the categorial a
lgebra and the Lie algebra. The coupling of gravity to the substratum
implies the nonconservation of the energy-momentum tenser. The derivat
ive coupling term is approximated to the first order, and a Schwarzsch
ild-like solution of the corresponding nonconservative gravitational e
quations is obtained. It is shown that, in this approximation, the mai
n effect of the new theory is to introduce an extra-mass term in the s
tandard Schwarzschild metric. The application of such a result to peri
helion shifts and light deflection yields results comparable to those
obtained in General Relativity. Gravitational-wave solutions of the ne
w equations are derived in the weak field approximation. It is shown t
hat our nonconservative theory of gravity implies a cosmological model
with a locally varying, non-zero cosmological ''constant''.