Possible oncostatic action of cysteamine on the pituitary glands of oestrogen-primed hyperprolactinaemic rats

Abstract

ABSTRACT Cysteamine was investigated for its potential to reduce the size and secretion of oestrogen-primed hyperprolactinaemic rat pituitary glands. Subcutaneous administration of 80 and 120 mg cysteamine/kg significantly reduced plasma prolactin concentrations by 58 and 91% respectively, after 4 h. Administration of cysteamine (60 mg s.c./kg body weight per day) for 10 days, to rats which had received an injection of 2 mg oestradiol benzoate on day 1, resulted in a significant reduction in pituitary mass (19%) and GH concentration (21%). Oral administration of 60 mg cysteamine/kg body weight to hyperprolactinaemic rats also produced a significant reduction in plasma prolactin of 94% after 2 h. Oral administration of 60 mg cysteamine/kg body weight per day to rats for a 20-day period, during which they had received two injections of 2 mg oestradiol benzoate on day 1 and day 14 of treatment, resulted in a significant reduction in pituitary mass (29%) and the concentration of trunk blood prolactin concentration (35%). However, when oral cysteamine (60 mg cysteamine/kg body weight per day) was given for 20 days to rats which had been treated with 2 mg oestradiol benzoate once every 14 days over a 90-day period, it caused no change in pituitary weight, prolactin or GH concentration, or the concentration of prolactin in trunk blood. Encapsulating cysteamine in liposomes and subsequent oral administration at 60 mg/kg body weight per day for 10 days to rats which had received five injections of 2 mg oestradiol benzoate once every 14 days over a 80-day period, caused a significant reduction in pituitary weight (36%) and prolactin concentration (28%) as well as prolactin concentration in trunk blood (22%). Liposome-entrapped cysteamine was also able to reduce plasma prolactin concentrations in a time- and dose-dependent manner in hyperprolactinaemic rats. The profile of plasma prolactin depletion produced by liposome-encapsulated cysteamine was different from that of free cysteamine and may account for its ability to reduce the size and secretion of pituitaries from chronically hyperprolactinaemic rats. Journal of Endocrinology (1990) 127, 119–127