The Ebner glands: a pancreatic-like gland secreting an acid lipase. Secretory regulation in vitro.

The lingual serous glands of rat tongue, the Ebner glands, secrete a potent acid lipase that acts in the stomach where it initiates the digestion of dietary fat. The factors affecting its secretion were studied 'in vitro' on Ebner slices. The lipolytic activity was measured in the incubation medium using tributyrine as substrate and by titration at pH: 5.4. Cholecystokinin (10(-9) M) and carbachol (10(-5) M) efficiently stimulated lipase secretion (3 fold over basal rate). The parasympathetic agent triggered secretion involving a calcium dependent system. Atropin (10(-4) M) blocked this cholinergic effect by about 40%. Lipase secretion was stimulated by epinephrine and isoproterenol. Propranolol (beta-antagonist) inhibited the adrenergic stimulation, while phentolamine was ineffective. The inhibitory effect of the selective beta 1-antagonist (Betaxolol) and the lack of effect of the selective beta 2-antagonist (ICI 118551) suggest the participation of beta 1-adrenoceptors in the secretion mechanism.

Studies on human pancreatic acini: action of secretagogues on amylase release and cellular cyclic AMP accumulation.

A technique for preparing a suspension of dispersed functional acini from human pancreas has been developed. The changes in pancreatic enzyme secretion and accumulation of cellular cyclic AMP caused by various secretagogues have been studied. Ca2+-mobilizing agents stimulated amylase release from human pancreatic acini. The relative potencies with which secretagogues increased amylase release were as follows: gastrin-releasing peptide's potency (Ec50, 0.1 +/- 0.01 nM) was greater than bombesin 14's (Ec50, 0.2 +/- 0.01 nM), which was greater than litorin's (Ec50, 0.6 +/- 0.18 nM), which was greater than bombesin 9's (Ec50, 6 +/- 0.1 nM). For CCK-peptides, the relative potencies were as follows: CCK-39's potency (Ec50, 0.28 +/- 0.15 microM) was equal to cerulein's (Ec50, 0.3 +/- 0.07 microM). Both of these potencies were greater than CCK-8's (Ec50, 1.6 +/- 0.1 microM), which was greater than that of CCK-4. Carbamyl choline was poorly potent (Ec50 greater than 1 mM). The 12-O-tetradecanoylphorbol-13-acetate (TPA) was active from 0.1 nM to 0.1 microM. Neither secretin nor VIP increased amylase release from human pancreatic acini but they did cause an accumulation of cellular cyclic AMP, secretin (Ec50, 0.5 +/- 0.2 nM) being more potent than VIP.

VIP regulation of a human pancreatic cancer cell line: Capan-1.

VIP and secretin control the secretory function of the normal pancreas. We analysed their regulatory functions in a human pancreatic cancer cell line: Capan-1. Saturation binding experiments with 125I-VIP showed the existence of one class of binding sites of very high affinity: KD 6.4 +/- 3.0 X 10(-11) M and a low Bmax: 12 fmoles/10(6) cells, in both intact cells and membrane preparations. This site has not yet been described in normal or tumorous digestive cells. Competition binding experiments let us characterize two more binding sites, KD: 2.1 +/- 0.7 X 10(-9) M and 5.0 +/- 0.6 X 10(-8) M and the corresponding Bmax: 120 and 500 fmoles/10(6) cells. These sites are similar to those found on cells of the digestive tract. Competition binding experiments gave the following IC50: 3.0 +/- 0.9 X 10(-9) M for VIP; 2 +/- 0.6 X 10(-6) M for PHI; and 1 +/- 0.7 X 10(-5) M for secretin. VIP elicited a cAMP rise, the half maximal response being obtained at 1.2 X 10(-10) M. Secretin induced a cAMP response but only for concentrations higher than 10(-8) M. VIP receptors were found to be modulated by two factors: cell ageing and cell density. Cells chronically treated with VIP showed a slight decrease of their proliferation; insulin exerted an opposite effect. It is concluded that at the difference of normal pancreatic cells, the present cell line lacks secretin-preferring receptors and acquires some of the properties of intestinal cells.

Dopamine receptors in a human colonic cancer cell line (HT29). Some receptor-related biological effects of dopamine.

The presence of dopamine receptors in normal colonic cells has been postulated from physiological studies. The existence of such receptors in human colonic tumor cells and their role in tumor progression are still unknown. The aim of the present work was to characterize the dopaminergic receptors in a human colonic adenocarcinoma cell line (HT29) and to evaluate the effect of dopamine on cAMP, protein and DNA synthesis. The binding characteristics of 3H-dopamine on the tumor cells were rapid, reversible, specific, saturable and stereospecific. The first site characterized corresponds to a D3 subtype:KD 3.09 nM, insensitive to sulpiride, unrelated to adenylate cyclase. Competitive inhibitions of 3H-dopamine binding by different drugs showed the existence of a second binding site, D1, with an apparent affinity for dopamine of 6,700 nM. The rank order of potency of inhibitors of 3H-dopamine binding was: haloperidol greater than dopamine greater than cis flupenthixol greater than (+) butaclamol greater than (-) butaclamol greater than trans flupenthixol greater than isoproterenol greater than clonidine greater than prazosin. D3 binding sites are modulated with age, Bmax was 116 fmol/10(6) cells on the 5th day and decreased to 8.2 fmol/10(6) cells on the 15th day of culture. Cell culture in serum-deprived medium allowed an increase in the number of high-affinity receptor sites. D1 sites are coupled to adenylate cyclase as shown by a dose-dependent cAMP accumulation from 10(-8) M to 10(-5) M dopamine concentrations. Interacting with D1 sites, dopamine evokes an increase in protein synthesis with no modification of 3H thymidine incorporation. The present results indicate that the human colonic cancer cell line HT29 exhibits dopamine receptors and that stimulation may induce metabolic modifications in the tumor cells.