Vasoactive intestinal polypeptide and dopamine in the hypothalamus and pituitary of ageing rats with prolactinomas

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Abstract
Vasoactive intestinal peptide (VIP), and dopamine have been measured in the hypothalamus and anterior pituitaries of female rats at three different ages. Rats aged 19 months had a high incidence (35%) of prolactin-secreting tumours of the pituitary and these animals had increased hypothalamic and pituitary VIP compared with three-month-old rats or rats without tumours. VIP in old animals without tumours was similar to that in young animals. The third group, with an even more advanced age of 22-28 months, had a lower incidence of PRL-secreting tumours, and pituitary and hypothalamic VIP concentrations similar to those in young animals. Dopamine was significantly increased in the pituitaries of 22-28-month-old nontumours rats and slightly raised in 19-month-old rats. We conclude that the increased pituitary and hypothalamic VIP content of 18-month-old rats could be a factor in the development of tumours seen at this age, and the differences seen in the two groups of old rats may be related to changes in the steroid environment.