Retardation of protein synthesis in rat foetal liver on inhibiting rate of histamine formation

Decarboxylases of histidine and ornithine in chick embryo

1. The activities of histidine and ornithine decarboxylases as well as the histamine content of the developing chick embryo were studied.2. Histidine decarboxylase (L-histidine carboxy-lyase; E.C. 4.1.1.22) activity was fairly low with a tendency to increase at later stages of development. This enzyme was preferentially present in the supernatant fraction of the tissue homogenate. alpha-Methyl-histidine, but not alpha-methyl-DOPA, inhibited its activity.3. The histamine content per gramme of embryo was low with a tendency to increase with the age of the embryo.4. Ornithine decarboxylase (L-ornithine carboxy-lyase; E.C. 4.1.1.17) activity was high at the beginning of the stages of development investigated, but later there was a steep fall in activity. A noticeable feature was that while the activity in the residual fraction of the homogenate remained almost constant during development, the activity in the supernatant fraction was high in the early stages, then fell rapidly to nearly zero at later stages.

Secretory behaviour and histamine formation in the rat Heidenhain pouch following antrectomy

1. In conscious rats provided with a Heidenhain pouch, the changes in the secretion of acid and pepsin following antrectomy were investigated in the interdigestive state and in response to graded doses of intravenous hog gastrin II and methacholine. The change in mucosal histamine formation (histamine-forming capacity, HFC, i.e. histidine decarboxylase activity) was determined in the fasting state in the Heidenhain pouch following antrectomy.2. Antrectomy was followed by a substantial reduction in the interdigestive secretion of acid.3. Methacholine infusion when the antrum was intact evoked a maximal acid secretory response that exceeded twice the response obtained with gastrin.4. After resection of the antrum the acid response to graded doses of methacholine and to gastrin at maximal but not at submaximal dose levels was significantly reduced.5. After antrectomy, threshold or submaximal infusion of gastrin accentuated the acid secretory responses to methacholine, but did not restore the maximal secretory response to methacholine obtained before antrectomy.6. The changes in pepsin secretion following antrectomy were similar to those in acid secretion but smaller.7. Mucosal HFC of the pouch was significantly lowered following antrectomy.8. After antrectomy gastrin failed to accelerate histamine formation in the mucosa in the usual way.

The role of the antrum and the vagus nerve in the formation of gastric mucosal histamine

1. The effects of the vagus nerve and of antral gastrin on the rate of histamine formation (histamine forming capacity, HFC, i.e. histidine decarboxylase activity) in the parietal cell region of the gastric mucosa has been investigated in the following stomach preparations: gastric fistula, denervated Heidenhain pouch, antral resection with gastrojejunostomy, gastrojejunostomy with exclusion of the duodenum and in the intact stomach. The determinations of mucosal HFC were made on fasting rats and on re-fed animals when the effect of feeding was studied.2. In fasting rats with a gastrojejunostomy and the antrum intact the mucosal HFC of the innervated stomach was about 4 times higher than in the corresponding preparation with the antrum resected. In the innervated main stomach the mucosal HFC was about twice as high as in the denervated pouch, indicating that the vagus and endogenous antral gastrin each contribute to maintaining mucosal HFC in the fasting state.3. Acidifying the stomach caused a substantial lowering of the mucosal HFC presumably by inhibiting antral gastrin release, whereas acid in the stomach did not interfere with the elevation of mucosal HFC evoked by injection of gastrin.4. Injection of gastrin elevated mucosal HFC in the innervated main stomach and in the denervated pouch to approximately equal levels. With the dose of gastrin employed there was about a fourfold increase in the HFC of the pouch mucosa.5. In antrectomized rats enhanced vagal influence, evoked by insulin injection or by feeding, raised the mucosal HFC. In rats with the antrum intact and the stomach acidified, insulin injection produced an increased HFC. Thus, a vagal effect on mucosal HFC exists independent of participation of antral gastrin.6. The stable choline esters carbachol and methacholine act directly on the parietal cell without involving mucosal HFC. The vagus nerve and gastrin, however, are assumed to provide secretory stimulation by means of accelerated histamine formation.7. The interrelation between increased histamine formation and hydrochloric acid secretion is discussed.