Widespread distribution of somatostatin receptor messenger ribonucleic acids in rat pituitary.

The expression of five somatostatin receptor subtypes, rsstr1-5, was examined in rat pituitary by in situ hybridization histochemistry. The anterior lobe of the pituitary expressed mRNA encoding all five rsstr subtypes. Relatively high levels of rsstr3 mRNA expression were also observed in the intermediate lobe of the pituitary. If all five rsstr proteins are expressed in the pituitary, the effects of somatostatin and somatostatin-28 on pituitary function may therefore represent the composite activation of more than one sstr. Co-localization studies on the same pituitary sections revealed a widespread distribution of rsstr mRNA in the major endocrine cell groups. Somatotrophs showed a relatively high level of rsstr4 and -5 mRNA expression while thyrotrophs predominantly expressed rsstr2 mRNA. These data may point to the potential roles for sstr subtypes in mediating SRIF physiology in the pituitary.