tetrodotoxin and Cryptosporidiosis

Piglet cryptosporidiosis is characterized by intestinal villous damage and malabsorption, and by reduced NaCl absorption in response to prostaglandins (PGs), which act directly on the epithelium and indirectly through enteric nerves. We hypothesized that phagocyte-derived reactive oxygen metabolite (ROM) production contributed to PG synthesis and altered transport in inflamed ileum. Ileal mucosa from control and infected piglets was analyzed for villous height, PGE2, catalase (an endogenous antioxidant), and malondialdehyde (MDA, a by-product of lipid peroxidation) from d 2-8 after infection. The response of control ileal mucosa to exogenous ROM and infected mucosa to antioxidant treatment was also studied in tissues mounted in Ussing chambers. Increased levels of MDA on d 2 preceded increased PGE2 on d 3-4, which correlated with the acute diarrheal phase; however the most severe villous atrophy (d 8) correlated with the highest levels of catalase and MDA but low levels of PGE2. Control mucosa responded to H2O2 with indomethacin- and tetrodotoxin-sensitive transient increases in short circuit current (Isc), which were accompanied by increased tissue production of 6-keto-PGF1a, the stable metabolite of PGI2; however, no increased PGE2 production was detectable. A stable analog of PGI2, carbacyclin, mimicked the transient Isc response to H2O2; however, several antioxidants failed to alter the abnormal Isc of infected tissue. These results suggest that there is evidence of increased ROM production in cryptosporidial infection and that intestinal PG synthesis and inhibited NaCl absorption may be mediated partially by ROM in this model. Additional, cooperative factors, such as PGE2 production, however, are likely needed to induce the alterations in ion transport seen in this infection.

Topics: Animals; Animals, Newborn; Biological Transport; Catalase; Cryptosporidiosis; Diarrhea; Electrolytes; Ileum; Indomethacin; Lipid Peroxidation; Malondialdehyde; Prostaglandins; Reactive Oxygen Species; Swine; Tetrodotoxin

Peptide YY (PYY) is a powerful inhibitor of intestinal secretion mediated by cAMP agonists such as vasoactive intestinal peptide and prostaglandin E2. We hypothesized that PYY would attenuate the secretory diarrhea in piglet cryptosporidiosis, which is mediated by prostaglandins E2 and I2. Control and infected ileal tissues from piglets were studied in Ussing chambers. The addition of PYY to the serosal bathing solution abolished net Cl- secretion in infected tissue. The inhibitory effect of PYY was eliminated with the prostaglandin synthesis inhibitor indomethacin and with the nerve conduction blocker tetrodotoxin. PYY completely blocked the antiabsorptive and secretory effects of the prostaglandin I2 analog carbacyclin, which has previously been shown to operate through enteric nerve pathways in this tissue. In contrast, PYY had no inhibitory effect on the secretory responses induced by prostaglandin E2 or vasoactive intestinal peptide. Results suggest that the antisecretory effects of PYY are mediated by inhibition of prostaglandin I2 induction of enteric nerves. Thus, PYY may play an important role in moderating the secretory diarrhea in cryptosporidiosis.

Topics: Animals; Chlorides; Cryptosporidiosis; Cyclic AMP; Indomethacin; Intestinal Mucosa; Peptide YY; Prostaglandins; Sodium; Swine; Tetrodotoxin

Piglet cryptosporidiosis is characterized by intestinal villous damage and malabsorption and by reduced NaCl absorption in response to prostaglandin (PG) release from inflamed tissue. We hypothesized that the PG effect is mediated by the enteric nervous system. Piglets were infected with cryptosporidium and ileal mucosa was studied in Ussing chambers. Studies with tetrodotoxin and indomethacin showed that 75% of the PG-induced alteration in NaCl transport was mediated by the enteric nervous system. Prostacyclin was elevated in infected tissue, and its analog, carbacyclin, mimicked the altered transport response in indomethacin-treated tissue. This carbacyclin response was abolished by tetrodotoxin. The vasoactive intestinal peptide (VIP) receptor antagonist, VIP-10-28, and the muscarinic antagonist, atropine, individually reduced and together abolished the response to carbacyclin, whereas the nicotinic blocker, hexamethonium, reduced the carbacyclin response by 75%. The somatostatin analog, octreotide, and the a-2 adrenergic agonist, clonidine, each abolished the carbacyclin response and partially or completely rectified the altered NaCl transport of the infection. These results indicate that PGs alter NaCl transport in this infection primarily by stimulating cholinergic interneurons that innervate VIPergic and cholinergic motor nerves. The enteric nervous system may be a potential target for pharmacological control of the acute diarrhea in this infection.

Topics: Animals; Animals, Newborn; Clonidine; Cryptosporidiosis; Dinoprostone; Enteric Nervous System; Epoprostenol; Intestinal Absorption; Intestines; Ion Transport; Octreotide; Swine; Tetrodotoxin