Stability of dopamine in an in vitro incubation system using Medium 199

This study investigated the stability of exogenous dopamine (DA) in vitro in a commercially available medium (Medium 199), with and without additional ascorbic acid, during incubation with pituitary halves in prolactin secretion experiments. After a 3-h incubation period, 26 and 15% of the starting concentrations of DA were degraded in the absence and presence of 1 mM ascorbic acid, respectively; in the absence of pituitary tissue, these reductions in DA concentration were 19% and 0%, respectively. In contrast, 98% of DA was degraded after 3 h of incubation in Krebs-Henseleit bicarbonate buffer which contained no tissue or no antioxidants. A number of antioxidants (including a low concentration of ascorbic acid) which are already present in Medium 199 are most likely responsible for the relative stability of DA in this medium. The loss of DA during incubation in Medium 199 is considered small for this type of study, and additional ascorbic acid only marginally improves DA stability in this medium. We have concluded that there is no need to be overly concerned about the degradation of exogenous DA in vitro for some incubation experiments using Medium 199, and the addition of extra ascorbic acid (which may be deleterious) is not necessary.