WIDESPREAD DISTRIBUTION OF SOMATOSTATIN RECEPTOR MESSENGER RIBONUCLEIC-ACIDS IN RAT PITUITARY

The expression of five somatostatin receptor subtypes, rsstr1-5, was e xamined 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 o bserved in the intermediate lobe of the pituitary. If all five rsstr p roteins are expressed in the pituitary, the effects of somatostatin an d somatostatin-28 on pituitary function may therefore represent the co mposite-activation of more than one sstr. Co-localization studies on t he same pituitary sections revealed a widespread distribution of rsstr mRNA in the major endocrine cell groups. Somatotrophs showed a relati vely high level of rsstr4 and -5 mRNA expression while thyrotrophs pre dominantly expressed rsstr2 mRNA. These data may point to the potentia l roles for sstr subtypes in mediating SRIF physiology in the pituitar y.