The effect of phenothiazine on plasma prolactin levels in non-pregnant mares

Sixteen non-pregnant pony mares were divided into four groups of similar age and bodyweight (bwt). Groups were randomly assigned to one of four treatments consisting of oral administration of perphenazine (0.5 and 1.0 mg/kg bwt, phenothiazine (10 mg/kg bwt) and a control group. Blood samples were taken by jugular venepuncture and plasma prolactin concentrations measured using an homologous assay for equine prolactin. Analysis of variance was conducted on data designed as a split plot over time. Perphenazine given orally (0.5 and 1.0 mg/kg bwt) increased plasma prolactin concentrations when measured 3 and 6 h following feeding (P less than 0.05). Prolactin concentrations returned to normal by 11 h post drug administration. There was no response in plasma prolactin concentrations following oral phenothiazine treatment (10 mg/kg bwt). Perphenazine at the 1.0 mg/kg bwt level was discontinued after two days due to two mares exhibiting signs of hyperesthesia.