Modification of salivary duct electrolyte transport in rat and rabbit by physalaemin, VIP, GIP and other enterohormones

Abstract

The effects of various polypeptide enterohormones and the tachykinin secretogogue, physalaemin, on electrolyte transport by the main excretory duct of the mandibular gland of the rabbit were studied in vitro. Vasoactive intestinal peptide (VIP, 2×10⁻¹¹ mol l⁻¹) and gastric inhibitory polypeptide (GIP, 10⁻¹¹ mol l⁻¹) reduced nett Na⁺ movement from lumen to interstitium and VIP also reduced the transepithelial potential difference; the effective concentrations of the two hormones lay within the range of normal plasma concentrations. Gastrin (5×10⁻⁷ mol l⁻¹) and synthetic secretin (2×10⁻⁷ mol l⁻¹) had similar effects but only at concentrations well above the normal plasma levels. Caerulein, an analogue of the octapeptide of cholecystokinin, had no effect on duct function even at a concentration of 10⁻⁶ mol l⁻¹. The potent salivary secretogogue, physalaemin (4×10⁻⁸ mol l⁻¹), which is an analogue of SubstanceP, a putative mammalian enterohormone and neurotransmitter substance, caused a marked increase in ductal Na transport (in rat as well as rabbit). It is concluded that VIP and GIP would normally play a role in determining salivary electrolyte composition and it is postulated that their action may be antagonized by a tachykinin such as SubstanceP.