Acta physiol. scand. 1977. 99. 126-128 From the Department of Pharmacology, Karolinska institutet, and the Department of Endocrinology, Karo!inska sjukhuset, Stockholm, Sweden
Vagal Release of Somatostatin into the Antral Lumen of Cats BY
KERSTIN UVNAS-WALLENSTEN, SUADEFENDIC and ROLFLUFT
Large amounts of gastrin-17 have been demonstrated in the gastric juice of cats (UvnasWallensten 1976, Uvnas-Wallensten and Rehfeld 1976). Anderson and Nilsson (1974) rcported that gastrin is present in antral perfusates of dogs. In the cat gastrin is released directly into the antral lumen in parallel with the release of gastrin into the gastric venous outflow. Thus electrical vagal stimulation causes a release of gastrin both into the antral lumen and into the gastric venous blood ( Uvnas-Wallensten, to be published). The occurrence of gastrin in the gastric lumen, as well as in the circulation, might be explained as due to gastrin being released diffusely into the interstitial fluid from the G-cell (Fig. I ) . Gastrin might then exert local or paracrine effects on neighbouring cells, as well as blood borne remote endocrine effects. Somatostatin containing cells are located close to the G-cells in the antral mucosa and both types of cells have similar morphological characteristics. Therefore somatostatin might also be expected to be released into the antral lumen. The only well established mechanism, by which the release of gastrin can be inhibited is by low intra-antral pH. It has been assumed that the effect of low pH is exerted directly on the G-cells. The presence of somatostatin cells close to the G-cells in the antrum, and its ability to antagonize the release of gastrin (Bloom ef a / . 1974, Le Roith et al. 1975, Raptis et a/. 1975, Uvnas-Wallensten ef a/. in press), suggested to us that the inhibitory effect of low pH might be mediated via a release of somatostatin. To test this hypothesis, the antrum of 5 cats was perfused with slightly alkaline or/and acid solutions and vagal stimulations ( 5 Hz) were performed during the perfusions. Perfusates were assayed for both somatostatin and gastrin immunoreactivity. Immediately upon collection, the pH of the samples was adjusted to 7, they were boiled for 15 min and then frozen until the hormone content was determined by radioimmunoassay. Since the antrum was perfused at a constant rate ( I ml/min) the output of hormone per minute could be calculated. In all expts. vagal stimulation caused an increased release (10090) of somatostatin into the antral lumen during perfusion with 0.1 M HCI, when the output of gastrin was reduced to about 30%. During perfusion with a slightly alkaline medium, vagal stimulations almost failed to cause a release of somatostatin (7O/,), but large amounts of gastrin were released instead (100%) (Table I). A typical experiment is illustrated in Fig. 2. On the average 351 ng of gastrin were released by vagal stimulation during perfusion with phosphate buffer (pH 7-8), while the maximal 126
127
ANTRAL RELEASE OF SOMATOSTATIN
ANTRAL
G
- CELL
LUMEN
D-CELL
_ _ _ _D P
t *
RELEASE
‘ P
OF
SOMATOSTATIN
SUBMUCOSA
t
CAPILLCRY
Fig, 1. Schematic pictura of a gastrin containing cell (G-cell) and somatostatin containing cell (D-cell). The arrows illustrat2 how the two hormones might be released diffusely from the cells. This model would explain how the hormones from one typz of hormone producing cells can, at the same time, exert paracrine and endocrine actions and also appear in the gastrointsstinal lumen.
release of somatostatin, obtained during perfusion with 0.1 M HCI, was only about 72 ng (Table I). Both gastrin and somatostatin can be released by vagal stimulation. The results with a reciprocal occurrence of gastrin and somatostatin in the antral lumen suggest that the inhibitory effect exerted by HCl on the release of gastrin, might at least partially be due to a local cffect of somatostatin on the G-cells. The antral gastrin and somatostatin producing cells probably release their hormones into the surrounding interstitial tissue, from which the hormones diffuse in all directions. Gastrin has been demonstrated to reach the antral lumen as well as the blood. Until now, in respmse to vagal stimulation, somatostatin has only been demonstrated to OCCUI in the antral lumen. However, a simultaneous release of the hormone might be expected to occur into the circulation. The gastrointestinal mucosa contains a large number of different hormone producing cells. It might therefore be expected, that the hormones produced by these cells also will pass
GASTRIN SOMATOSTATIN P G I M I N PG/MIN
100000 10000
Fig. 2. Experiment in which the antrum was perfused with phosphate buffer p H 8 and 0.1 M HCI. Vagal stimulation (5 Hz for 5 min) was performed during perfusion with both solutions.
50000 5000
10 000 1007, -10
0
10
20
30
40
50
60
70
80 MIN
I28
KERSTIN UVNAS-WALLENSTEN, SUAD EFENDICAND ROLF LUFT
TABLF 1. Release of gastrin (G) and somatostatin (S) into the antral lumen during perfusion with 0.1 M HCI and/or phosphate bufFer pH 7-8. The output of hormone was determined quantitatively and expressed in ng. In experiments i n which stimulations were performed at both pHs, the lowest output was expressed i n *
Vagal Release of Somatostatin into the Antral Lumen of Cats BY
KERSTIN UVNAS-WALLENSTEN, SUADEFENDIC and ROLFLUFT
Large amounts of gastrin-17 have been demonstrated in the gastric juice of cats (UvnasWallensten 1976, Uvnas-Wallensten and Rehfeld 1976). Anderson and Nilsson (1974) rcported that gastrin is present in antral perfusates of dogs. In the cat gastrin is released directly into the antral lumen in parallel with the release of gastrin into the gastric venous outflow. Thus electrical vagal stimulation causes a release of gastrin both into the antral lumen and into the gastric venous blood ( Uvnas-Wallensten, to be published). The occurrence of gastrin in the gastric lumen, as well as in the circulation, might be explained as due to gastrin being released diffusely into the interstitial fluid from the G-cell (Fig. I ) . Gastrin might then exert local or paracrine effects on neighbouring cells, as well as blood borne remote endocrine effects. Somatostatin containing cells are located close to the G-cells in the antral mucosa and both types of cells have similar morphological characteristics. Therefore somatostatin might also be expected to be released into the antral lumen. The only well established mechanism, by which the release of gastrin can be inhibited is by low intra-antral pH. It has been assumed that the effect of low pH is exerted directly on the G-cells. The presence of somatostatin cells close to the G-cells in the antrum, and its ability to antagonize the release of gastrin (Bloom ef a / . 1974, Le Roith et al. 1975, Raptis et a/. 1975, Uvnas-Wallensten ef a/. in press), suggested to us that the inhibitory effect of low pH might be mediated via a release of somatostatin. To test this hypothesis, the antrum of 5 cats was perfused with slightly alkaline or/and acid solutions and vagal stimulations ( 5 Hz) were performed during the perfusions. Perfusates were assayed for both somatostatin and gastrin immunoreactivity. Immediately upon collection, the pH of the samples was adjusted to 7, they were boiled for 15 min and then frozen until the hormone content was determined by radioimmunoassay. Since the antrum was perfused at a constant rate ( I ml/min) the output of hormone per minute could be calculated. In all expts. vagal stimulation caused an increased release (10090) of somatostatin into the antral lumen during perfusion with 0.1 M HCI, when the output of gastrin was reduced to about 30%. During perfusion with a slightly alkaline medium, vagal stimulations almost failed to cause a release of somatostatin (7O/,), but large amounts of gastrin were released instead (100%) (Table I). A typical experiment is illustrated in Fig. 2. On the average 351 ng of gastrin were released by vagal stimulation during perfusion with phosphate buffer (pH 7-8), while the maximal 126
127
ANTRAL RELEASE OF SOMATOSTATIN
ANTRAL
G
- CELL
LUMEN
D-CELL
_ _ _ _D P
t *
RELEASE
‘ P
OF
SOMATOSTATIN
SUBMUCOSA
t
CAPILLCRY
Fig, 1. Schematic pictura of a gastrin containing cell (G-cell) and somatostatin containing cell (D-cell). The arrows illustrat2 how the two hormones might be released diffusely from the cells. This model would explain how the hormones from one typz of hormone producing cells can, at the same time, exert paracrine and endocrine actions and also appear in the gastrointsstinal lumen.
release of somatostatin, obtained during perfusion with 0.1 M HCI, was only about 72 ng (Table I). Both gastrin and somatostatin can be released by vagal stimulation. The results with a reciprocal occurrence of gastrin and somatostatin in the antral lumen suggest that the inhibitory effect exerted by HCl on the release of gastrin, might at least partially be due to a local cffect of somatostatin on the G-cells. The antral gastrin and somatostatin producing cells probably release their hormones into the surrounding interstitial tissue, from which the hormones diffuse in all directions. Gastrin has been demonstrated to reach the antral lumen as well as the blood. Until now, in respmse to vagal stimulation, somatostatin has only been demonstrated to OCCUI in the antral lumen. However, a simultaneous release of the hormone might be expected to occur into the circulation. The gastrointestinal mucosa contains a large number of different hormone producing cells. It might therefore be expected, that the hormones produced by these cells also will pass
GASTRIN SOMATOSTATIN P G I M I N PG/MIN
100000 10000
Fig. 2. Experiment in which the antrum was perfused with phosphate buffer p H 8 and 0.1 M HCI. Vagal stimulation (5 Hz for 5 min) was performed during perfusion with both solutions.
50000 5000
10 000 1007, -10
0
10
20
30
40
50
60
70
80 MIN
I28
KERSTIN UVNAS-WALLENSTEN, SUAD EFENDICAND ROLF LUFT
TABLF 1. Release of gastrin (G) and somatostatin (S) into the antral lumen during perfusion with 0.1 M HCI and/or phosphate bufFer pH 7-8. The output of hormone was determined quantitatively and expressed in ng. In experiments i n which stimulations were performed at both pHs, the lowest output was expressed i n *
