High, vasopressin-reversible, immunoreactive somatostatin in specific hypothalamic nuclei of rats with diabetes insipidus (Brattleboro rats).

Somatostatin content was studied in brain nuclei and pituitary lobes of homozygous Brattleboro rats lacking vasopressin (DI rats) with and without vasopressin replacement, and their corresponding controls, heterozygous Brattleboro (HZ) rats and Long-Evans (LE) rats. High, vasopressin-reversible, somatostatin levels occurred in DI rats. The changes in somatostatin were localized to the nucleus periventricularis and to brain areas receiving somatostatin projections from this nucleus, including the eminentia mediana. In contrast, vasopressin administration failed to alter somatostatin levels in HZ rats. In brain areas not belonging to the somatostatin periventricular system, the peptide concentration in DI rats was not higher than that of LE controls. High somatostatin levels were present in the intermediate lobe of the pituitary gland. Somatostatin was higher in DI and HZ rats when compared to LE rats. In the posterior pituitary lobe, HZ rats had higher, and DI rats lower, somatostatin than control LE rats. These results suggest that rat brain and pituitary vasopressin and somatostatin systems are interrelated.