Before we  proceed, lets just make sure we appreciate what this experiment reveals. The dogs were infused with 14,000,000 nmoles/l of H+ but the plasma [H+] only changed by a bit over 0.002%. By any analysis, this is a system which powerfully resists change in [H+]. (My personal analogy on appreciating the magnitude of this is to use the analogy of depositing $14,000,000 in the bank, but then finding that after 'bank charges' my account only went up by $36.)