Somatostatin modulates both endocrine and exocrine functions in the gastric mucosa, where three of the five cloned somatostatin receptors are present. This study examines changes in somatostatin receptor (SSTR) mRNA abundance during fasting, feeding, and profound acid inhibition with omeprazole. Serum gastrin as well as somatostatin and SSTR mRNA abundances were measured in antrum and corpus. In Northern blots of corpus RNA, the SSTR2 probe hybridized with two previously reported species of mRNA (2.4 and 2.8 kb); in addition, a weak previously unreported 1.6-kb band was detected. In antrum, the 1.6-kb band dominated. Fasting increased antral somatostatin mRNA from 100 +/- 8 to 161 +/- 24% and SSTR mRNA from 100 +/- 10 to 179 +/- 14% (P < 0.05). Omeprazole reduced antral somatostatin mRNA to 34 +/- 4% of control (P < 0.05) and elevated SSTR mRNA to 135 +/- 5% of control (P < 0.01). Omeprazole treatment reduced corpus somatostatin mRNA to 59 +/- 5% (P < 0.05), and elevated SSTR mRNA to 140 +/- 3% of control (P < 0.01). The results therefore indicate that a novel SSTR mRNA subtype exists in the stomach and predominates in the antrum. The abundance of this SSTR mRNA is upregulated by both fasting and achlorhydria; conditions that increase or decrease endogenous antral somatostatin, respectively.