H+ back diffusion stimulating gastric mucosal blood flow in the rabbit fundus

The effect of barrier breakers on gastric mucosal blood flow (MBF) has been disputed, but the influence of acid back diffusion alone has never been studied. In anesthetized New Zealand white rabbits, intramural pH (pHi) and gastric MBF were measured with an antimony microelectrode and with radioactive microspheres (51Cr, 85Cr, 141Ce), respectively. Innervated fundic pouches were perfused with solutions of varying [H+] at 37 degrees C. In the rabbit, back flux of H+ is linearly dependent on luminal [H+] and in the present studies a direct positive linear correlation was found between luminal [H+] and MBF (r = 0.97 P < 0.001) while pHi remained unchanged up to luminal [H+] of 80 mM. The usual 80% increase in MBF induced by 80 mM HCl was prevented by pretreatment with vasopressin, which decreased pHi and caused gross ulceration. Without vasopressin, [H+] of 120 mM HCl produced gross mucosal ulceration and a decrease in MBF and pHi. Our data suggest that back diffusion of H+ influences MBF in the rabbit. There is an increasing MBF caused by increasing luminal [H+] up to 80 mM, beyond which MBF decreases. When the balance between back diffusion and MBF is disturbed by a vasoconstrictor or a high luminal [H+], pHi decreases and gross ulceration occurs.