Induction of Secretagogue Independent Gastric Acid Secretion via a Novel Aspirin-Activated Pathway.

Aspirin has been widely recommended for acute and chronic conditions for over 2,000 years. Either single or repetitive doses are commonly used for analgesic and antipyretic reasons and to prevent heart attacks, stroke, and blood clot formation. Recent studies show that it can also be used chronically to dramatically reduce the risk of a variety of cancers. However, prolonged usage of aspirin can cause severe damage to the mucosal barrier, increasing the risk of ulcer formation and GI-bleeding events. In the present study, we show the effects of acute low-dose aspirin exposure as an active secretagogue-inducing gastric acid secretion. Studies were carried out with isolated gastric glands using the pH-sensitive dye BCECF-AM to assess acid secretion. The non-selective NOS inhibitor L-NAME (30 µM), or the specific inhibitor ODQ (1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one) was applied while monitoring intracellular pH. The effects of basolateral exposure to aspirin (acetylsalicylic acid, ASA) caused activation of gastric acid secretion via the H+, K+-ATPase. Our data suggest that aspirin increases nitric oxide (NO) production, which in turn activates acid secretion. Exposure of gastric glands to either the non-selective NOS inhibitor L-NAME, and the highly selective, soluble guanylyl cyclase inhibitor 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) effectively inhibited aspirin-dependent gastric acid secretion. Aspirin can be considered as a novel secretagogue, in the way that it activates the H+, K+-ATPase. With increased daily aspirin consumption, our findings have important implications for all individuals consuming aspirin even in low doses and the potential risks for increased acid secretion.

Secretagogue-dependent and -independent transport of zinc hydration forms in rat parietal cells.

Prolonged exposure to gastric acid is a leading cause of gastroesophageal reflux disease (GERD) and esophagitis. With the ever increasing number of patients showing insensitivity to proton-pump-inhibitor (PPI) therapy with recurrence of symptoms over time, alternative treatment options remain an important issue. Previous studies from our laboratory have shown that a zinc sulfate salt can inhibit HCl generation at the cellular level of the parietal cell. In this paper, we examine the difference between two hydration forms of ZnSO4 (monohydrate H2O and heptahydrate 7H2O) in their entry characteristics into the parietal cell under several physiological conditions associated with acid secretion. Using the Zn sensitive fluorochrome Newport Green, we examined the rate of Zn entry in Δfluorescent units/second (ΔFU/second), at two different concentrations for both hydration states on both fasted and non-fasted animals. In a separate series of studies, we examined the effects of secretagogues on the entry rates and transport mechanisms. Exposure of the secretagogue carbachol transformed the resting parietal cell to an activated state and represents a stimulated condition through the neuronal pathway. The hormonal activation of the parietal cell was achieved by using histamine. Non-fasted conditions were considered to be a state between hormonal and neuronal activation. To demonstrate that ZnSO4 enters the parietal cell through the NKCC1 co-transporter, the inhibitor bumetanide was applied during secretagogue-stimulated acid secretion. Both salts, monohydrate and heptahydrate ZnSO4, show a concentration-dependent cell entry under all conditions studied. During stimulated acid secretion, induced through either the neuronal or the hormonal pathway, heptahydrate ZnSO4 enters the parietal cell significantly faster than monohydrate ZnSO4, whereas monohydrate ZnSO4 exhibits faster entry during resting conditions in fasted animals. At 30 µM following stimulation with histamine, heptahydrate ZnSO4 enters the cell faster than monohydrate ZnSO4 (ΔFU/second 30 µM ZnSO4*7H2O + histamine = 1.782, ΔFU/second 30 µM ZnSO4*H2O+histamine = 1.038, respectively). Three hundred micromolar, heptahydrate ZnSO4 shows a faster entry into the cells (ΔFU/second ZnSO4*7H2O300µM + carbachol = 4.02407) compared to monohydrate ZnSO4 (ΔFU/second ZnSO4*H2O300µM + carbachol = 3.225) following exposure to carbachol. The mechanism of entry of both salts was found to be predominantly via the basolateral NKCC1 transporter with the rate of zinc entry decreasing to minimal values (ΔFU/second = 0.275) after application of bumetanide during stimulated conditions.