Animal definition: a necessity for the validity of animal experiments?

In most scientific journals, experimental animals are described poorly. Whether this is scientifically justified is discussed in this article. It was concluded that when laboratory animals are used in scientific experiments, which almost always are of a quantitative nature, a detailed animal definition is imperative.

Histamine and gastric acid secretion. A review.

Histamine was found to be a potent stimulus for acid secretion in 1920. It was then for about 20 years considered to be identical to the antral factor gastrin. It stimulates the parietal cells--the site of acid production--via an H2-receptor in a dynamic manner--that is, there is a continuous turnover of histamine at the receptor site. Cyclic AMP is formed by the receptor stimulation, but how this is coupled to the proton transport is unknown. It could even be possible that the main function of the histamine action is to initiate the drastic morphologic transformation of the parietal cells which occurs in connection with acid secretion. Possible sites for some acid inhibitors are elucidated.

Prostaglandin interaction with histamine release and parietal cell activity in isolated gastric glands.

The effects of different prostanoids on parietal cell activity and glandular histamine (Hi) release were examined in isolated rabbit gastric glands. [14C]aminopyrine accumulation and glandular oxygen consumption were used as indices of parietal cell activity, and Hi was determined fluorophotometrically in the supernatant of the glandular suspensions. Both prostaglandins (PG) E2 and E1 dose dependently (10(-8) and 10(-6) M) increased the release of endogenous Hi. Carbacyclin was less effective and PGF2 alpha was almost without effect. Hi release induced by acetylcholine (Ach) and pentagastrin (Pg) was markedly potentiated in the presence of PGE2 (10(-8) to 10(-5) M). The Ach-induced sti ulation of Hi release was also potentiated by arachidonic acid (10(-5) M), an effect that was inhibitable by the cyclooxygenase inhibitor meclofenamate (3 X 10(-5) M). Somatostatin partially inhibited the response to Pg (3 X 10(-9) M) in combination with PGE2 (10(-5) M). Atropine (10(-5) M) strongly reduced the response elicited by Ach (3 X 10(-6) M) combined with PGE2 (10(-6) M). All prostanoids inhibited Hi (10(-4) M)-induced parietal cell activity in a dose-dependent manner (60-70%) but displayed different potency. The stimulatory response to Ach (3 X 10(-6) M) or Pg (3 X 10(-9) M) in combination with isobutylmethylxanthine (IBMX, 10(-5) M) was inhibited by PGE2 in a dose-dependent fashion. PGE2 (10(-6) M) was considerably more effective than cimetidine (10(-5) M) in inhibiting IBMX (10(-4) M)-stimulated oxygen consumption, and the remaining IBMX-PGE2 response (approximately 40%) was dose dependently (10(-8) to 10(-5) M) inhibited by cimetidine. Addition of Hi (10(-7) to 4 X 10(-7) M) or Pg (3 X 10(-10) to 3 X 10(-9) M) counteracted the PGE2 inhibition of the IBMX response. In addition, IBMX (10(-4) M) combined with PGE2 (10(-6) M) gave rise to a threefold increase in Hi release. These results suggest that prostaglandins have two opposing effects, i.e., liberation of endogenous Hi and inhibition of the action of Hi on the parietal cell.

Dual inhibitory actions of somatostatin on isolated gastric glands.

The growth hormone release-inhibiting hormone or somatostatin is a potent inhibitor of gastric acid secretion. In the present paper these inhibiting properties were tested on isolated gastric glands from rabbit fundic mucosae, prepared as according to Berglindh & Obrink (1976). Parietal cell activity was measured as [14C]aminopyrine (AP) accumulation and O2-consumption. Glandular histamine release was determined after condensation with o-phthalaldehyde and measured fluorometrically. In the gastric glands there are two possible main processes that can be inhibited, namely (1) the release of histamine from some endocrine cells and (2) the activity of the parietal cell itself. It was found that somatostatin acted on both mechanisms. Basal histamine release was, however, not affected by somatostatin while the release induced by pentagastrin (Pg) at a concentration of 3 X 10(-9) M, or acetylcholine (10(-5) M) was dose-dependently (10(-12) to 10(-6) M) inhibited by this peptide. Maximal inhibition, which was about 70%, occurred at a dose of 10(-8) M somatostatin. Somatostatin also depressed parietal cell activity induced by histamine (10(-6) to 10(-4) M), isobutyl-methyl-xanthine (IMX, 10(-5) to 10(-4) M) or the combination of IMX (10(-5) M) and Pg (3 X 10(-9) M) Basal parietal cell activity was, however, unaffected. The IMX (10(-4) M) induced parietal cell activity in cimetidine-treated (10(-4) M) glands was also depressed by somatostatin, which indicates an action directly on the parietal cell not mediated via H2-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat gastric mucosal microcirculation in vivo.

The superficial gastric mucosal microcirculation was observed microscopically by transillumination in the anesthetized rat. The vessels surrounding the gastric crypts were monitored on a television screen through a microscope and the pictures stored on a videotape for off-line analysis of red cell velocity (VRBC) and vessel diameter. From these measurements microvascular volume flows were calculated. VRBC reached steady values after 1-4 h (mean 2 h) and showed a regular pulsatile flow (4-7 cycles/min) in most experiments. Acid output was measured at regular intervals; 50% of the rats showed no spontaneous acid output, but the others secreted up to 100 mu eq/h. The microvessels in the superficial mucosa were classified into three orders according to their branching hierarchy and relative dimensions, and their distribution per unit mass was estimated. VRBC and volume flow were shown to decrease in the successive orders of the microvessels. Calculation of organ blood flow from microvascular flow data and vessel distribution gave values (21 ml.min-1.100 g tissue-1) that agree with earlier reported values. A higher flow velocity was detected in rats with spontaneous acid output than in those without, but there was a poor correlation between the magnitude of the acid output and VRBC. Pentagastrin (96 micrograms.kg-1.h-1) induced a significant increase in both blood flow and acid secretion. Results from this study indicate that this experimental model is potentially useful for studies of the correlation between acid secretion and mucosal blood flow.

Gastrin-histamine as a normal sequence in gastric acid stimulation in the rabbit.

In a suspension of isolated gastric glands the effect of secretagogues on the oxyntic cells can only be detected by direct stimulation. An indirect stimulus like gastrin inducing one type of cell to liberate histamine which then acts on the oxyntic cells will not be detectable because of the very high dilution of the liberated substance. Thus the isolated gland preparation presents a means by which two steps in a sequential stimulation can be separated. There is no evidence that gastrin acts directly on the oxyntic cells but it does liberate histamine in a dose-effect relationship, which would in an intact stomach give histamine concentrations sufficient to effectively stimulate the acid secretion. Thus in the rabbit histamine seems to be a normal physiological mediator for gastrin stimulation.

Effects of secretagogues on oxygen consumption, aminopyrine accumulation and morphology in isolated gastric glands.

A recently developed method to isolate gastric glands from the rabbit gastric mucosa (Berglindh and Obrink 1976) was used to study the effects of some common gastric secretagogues. Three parameters were investigated: 1) Respiratory activity; 2) Intraglandular accumulation of the weak base aminopyrine; 3) Quantitative morphology of the parietal cells. The following substances were tested: Histamine, cAMP, db-cAMP, aminophylline, carbachol and pentagastrin. The strongest effect was obtained with db-cAMP which dose-dependently stimulated the respiration up to 200%, increased the aminopyrine accumulation 80% and altered the parietal cell morphology from a typically resting to a typically stimulated state. cAMP also stimulated the respiration but was about 10 times less effective on a molar basis than the dibutyryl form. Histamine, like db-cAMP, stimulated the respiration in a dose-dependent manner and strongly increased the aminopyrine accumulation. The morphological changes were, however, not of the same magnitude as after db-cAMP. Aminophylline, tested only for respiratory activity, stimulated the oxygen consumpation moderately. Carbachol induced a transient increase in both the oxygen consumption and in the aminopyrine accumulation with a peak value after approximately 15 minutes for both, but gave no significant morphological alterations. Pentagastrin, finally, was incapable of inducing changes in any of the three parameters. Aminopyrine was also found to accumulate approx. 50 times in unstimulated, morphologically resting glands. This seems to indicate that there might be acid sites already in resting glands.

A method for preparing isolated glands from the rabbit gastric mucosa.

A method for isolating gastric glands from the corpus of the rabbit gastric mucosa is presented. The stomach of an anesthetized rabbit was perfused with saline under high pressure through the aorta, taken out and emptied. The mucosa was stripped off, minced into small pieces and transferred to a 1 mg/ml collagenase solution. After 90 min at 37 degrees C, a large number of isolated gastric glands and cells were separated free. By a simple washing procedure the glands were freed from cell contamination and collagenase. The gastric glands were viable, as demonstrated by dye exclusion technique, oxygen consumption and electrolyte content. For identification of the glandular cells both common staining techniques and electron microscopy were used. Four types of cells were identified, viz. parietal cells, zymogen cells, mucous neck cells and some endocrine cells. The intracellular morphology of the glandular cells did not differ significantly from that seen in intact gastric mucosa. The glands could be stimulated with histamine, in a dose-response manner, as revealed by the increase in oxygen consumption (ED-50 equal 3 X 10(-6) M). This isolated gastric gland preparation may serve as a useful tool for new approaches in gastric physiology.

Sodium secretion as part of the formation of gastric juice.

Experiments with Heidenhain pouch dogs showed the well known high sodium concentrations at low secretion rates and low sodium concentrations at high ones after stimulation with a continuous intravenous injection of histamine. It was previously thought that the primary secretion did not contain any sodium, but that all the sodium present in the gastric juice appeared as a result of diffusion. A more detailed analysis of the experimental data showed, however, that there is in fact sodium present also in the primary juice in the small concentration of 3-5 mEq/l. The origin of the secreting volume containing this concentration of sodium is unknown.