Dopamine levels in the anterior pituitary gland monitored by in vivo electrochemistry.

The present study was designed to assess the contributions of the long portal vessel and neurointermediate lobe routes of dopamine delivery to the anterior pituitary gland. Dopamine levels were monitored in the anterior pituitary of anesthetized diestrus 1 rats using in vivo differential pulse voltammetry at a carbon paste electrode. Measurements were taken during control periods, following neurointermediate lobectomy and hypophysial stalk section or after inhibition of catecholamine synthesis and dopamine infusion. Neurointermediate lobectomy resulted in a slight rise in plasma prolactin and a significant fall in voltammetric current. Subsequent stalk section elevated prolactin significantly and further reduced the voltammetric output. Inhibiting catecholamine synthesis significantly elevated plasma prolactin and reduced the voltammetric current. Stepped infusions of dopamine then suppressed plasma prolactin and elevated the voltammetric output in a dose related manner. The final values of both parameters were not significantly different from pre-inhibition levels. These data provide direct estimates of the relative contributions of various vascular routes to dopamine in the anterior pituitary and support the sufficiency of dopamine as the physiological inhibitor of prolactin secretion.