RT-PCR analysis with guanylin-specific primers shows amplification products of correct size in rat whole hypophysis, PT of the hypophysis, and duodenum; 15 μl of RT-PCR products were loaded on a 1.8% 89 mM Tris/89 mM boric acid/2 mM EDTA (pH 8.3) agarose gel containing ethidium bromide. (Lane 1) PT, GAPDH; (lane 2) hypophysis, GAPDH; (lane 3) PT, guanylin; (lane 4) hypophysis, guanylin; (lane 5) duodenum, guanylin; (lane 6) 100-bp marker.