Gastroduodenal bicarbonate secretion in mucosal protection. Possible role of vasoactive intestinal peptide and opiates.
HCO3- secretion by surface epithelium in duodenum devoid of Brunner's glands was titrated in situ in anesthetized rats. Intravenous injection of small amounts (20 ng/kg) of the endogenous opioid peptide beta-endorphin significantly increased secretion. Naloxone prevented this effect, suggesting that stimulation is mediated by mu-opiate receptors. Morphine 50 microgram/kg had a similar stimulatory action. Vasoactive intestinal peptide (VIP) 0.5-100 microgram/kg dose-dependently increased secretion and this response was independent of simultaneous cholinergic stimulation. The HCO3- secretion maintained pH in the mucus gel adherent to the luminal surface at neutrality for long periods of time (greater than or equal to 60 min); even when the pH in the terminal bulk solution was as low as 2.0. Mucosal HCO3- secretion is thus very probably important in mucosal protection and VIP and endogenous opioid peptides may have a role in its control.
Flemström
G
G
Kivilaakso
E
E
Briden
S
S
Nylander
O
O
Jedstedt
G
G
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D004386:Duodenum; D004723:Endorphins / Q000494:pharmacology / Q000502:physiology*; D005753:Gastric Mucosa / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014660:Vasoactive Intestinal Peptide / Q000502:physiology*; D001615:beta-Endorphin
D001639:Bicarbonates; D004723:Endorphins; D014660:Vasoactive Intestinal Peptide; D001615:beta-Endorphin; D009020:Morphine