Estimation of the in vivo concentration of salsolinol and tetrahydropapaveroline in rat brain after the administration of ethanol.

Tetrahydroisoquinolines (TIQs) are not only pharmacologically active, but their intraventricular infusion evokes alcohol drinking in rats. It is not known if salsolinol or tetrahydropapaveroline (THP), the two most commonly studied TIQs, spontaneously form in vivo in brain during chronic or acute consumption of ethanol. A theoretical calculation based on a steady-state assumption was made in order to estimate what could be the upper limit of these compounds in rat brain. The model used was that the rate of formation was equal to the rate of disappearance. The latter term is the rate constant for metabolism times the TIQ concentration. The former was estimated for salsolinol from data obtained from human urine while for THP it was simply the second order rate equation. The values obtained for both concentrations were ca 1 ng/g-brain tissue.