Effects of sulpiride and apomorphine on prolactin release in adrenalectomized animals. Role of sodium ions.

The present experiments were performed to demonstrate in vivo the existence of a modulatory role of Na+ in the inhibitory control of prolactin (PRL) secretion. Groups of adult male rats were either adrenalectomized (adrenex) or sham-operated (normals) and implanted in the right atrium with a chronic cannula for the infusion of solutions or the sequential withdrawal of blood samples. Four days later, adrenex rats were infused for 1 h with either saline 0.9% or dextrose 5.6% (310 mOsm/kg H2O) at the rate of 10 ml/kg/h from Time -60 min until Time 0 min. All animals were injected at Time -45 min with sulpiride 0.05 mg/kg. At Time 0 min, some animals received apomorphine 5 mg/kg while others received a 0.05 mg/kg dose of the drug. Blood samples were obtained at -45, -30, -15, 0, 5, 10, 20 and 30 min for PRL assay. Plasma Na+ concentration was measured at -45, 0 and 30 min and plasma osmolarity at 0 min in adrenex rats. In normal controls plasma Na+ values were measured at the end of the experiment. Binding values (KD and Bmax) of pituitary D2-receptors were measured in adrenex and sham-operated rats using [3H]spiroperidol as ligand and D-butaclamol to define non-specific binding. Plasma Na+ values remained constant in saline-infused adrenex rats and similar to those of normal controls, while in dextrose-infused adrenex rats they fell progressively during the experimental period and were always lower than in the two other groups.(ABSTRACT TRUNCATED AT 250 WORDS)