Tomohiro Ichikawa

Differences in the Response of Three Embryologically Distinct Segments of the Isolated Canine Posterior Vena cava to Vasoactive Substances

The canine posterior vena cava was excised and divided into three embryologically distinct segments: segment A (supradiaphragm), segment B-C (intrahepatic and that between liver and renal veins), and segment D (infrarenal). Circular and longitudinal strips were cut from each segment, suspended in Krebs bicarbonate solution and isometric tensions were recorded. The responses to six vasoactive agents, as well as transmural neural stimulation were studied. Maximum tension and ED50 were obtained for norepinephrine, epinephrine, acetylcholine, bradykinin, histamine and 5-hydroxytryptamine (5-HT). The responses were not only quantitatively, but qualitatively different among the three segments. Bradykinin constricted the strips in A and B-C but not in D. 5-HT (less than 10(-5) M) caused a dose-dependent contraction in A and D through its direct stimulating action, while in C, a contractile response appeared only after administration of a higher dose of 5-HT. This was due to an indirect sympathomimetic action of the agent. Segment B-C, which histologically contained massive longitudinal muscle bundles in the outer layer of the wall, exhibited spontaneous, rhythmic contractions. The existence of a cholinergic excitatory innervation, in addition to adrenergic, was demonstrated in C by transmural neural stimulation.

Effect of histamine on the gastric smooth muscles of guinea pig.

The responses to histamine were studied in circular smooth muscles of three different regions of the guinea pig stomach: the fundus, the antrum and the pylorus. Histamine elicited contractions in all three regions. The contractile responses to histamine were completely abolished by mepyramine (10(-3) g/l). These results showed the presence of H1 receptors, which mediate contractile response, in all regions of the stomach. In the presence of mepyramine, histamine caused marked relaxation in the preparations from the fundus contracted by acetylcholine. This relaxation was noticeably suppressed by cimetidine, indicating the existence of H2 receptors in the fundus.

The effect of motilin on the gastrointestinal propulsion in rats.

SummaryWe studied the gastrointestinal propulsion in unanaesthetized rats by51Cr method that permits the simultaneous determination of two functions of the gastric emptying and the intestinal propulsion. The results obtained are as follows:1)The semi-logarithmic presentation of the gastric emptying showed a linear relationship with the time.2)When synthetic motilin was subcutaneously injected at the dose of 1µg/kg, the gastric emptying was promoted to a statistically significant extent.

The further investigation on the gastric acid secretion in the primary hyperparathyroidism

SummaryThe gastric acid output was studied in the 11 patients of hyperparathyroidism before and after parathyroidectomy. The gastric acid output before operation was almost equal to the normal control in our hospital. After the correction of serum calcium by parathyroidectomy, the gastric acid output and serum gastrin were decreased. The decreased gastric acid output was recovered as the days passed since operation and approached to the preoperative level. The acid output in hyperparathyroidism was less in the case whose activity of alkaline phosphatase was more, which suggested that the calcium deposition on gastric mucosa might damage the parietal cell as the result of long lasting hypercalcemia.

Innervation of the Canine Inferior Vena Cava

The innervation of three embryologically distinct segments of the canine inferior vena cava was investigated. These segments were termed A (supradiaphragm), B-C (intrahepatic and that between liver and renal veins), and D (infrarenal). Strips were cut from these segments, and their isometric tensions were recorded. Transmural electrical stimulation induced contractile responses in circular strips from segment B-C (66.5% of the maximum norepinephrine-induced response) and in those from D (14.4%), but not in A. These responses almost completely disappeared in the presence of phenoxybenzamine. In segment B-C, however, the remaining small contraction was markedly enhanced by neostigmine and abolished by atropine. The same phenomenon was also observed in the contraction remaining after reserpinization. Longitudinal strips from segment C responded similarly. Concentration-response curves of circular strips for acetylcholine were shifted by neostigmine markedly to the left only in segment B-C, while no significant shift occurred in A and D. It was concluded that the adrenergic innervation is remarkably dense in B-C, sparse in D, and probably lacking in A. In addition, a cholinergic excitatory innervation is present in segment B-C.

The regional difference in the responses of the guinea pig gastric muscles to gastrin

SummaryThe responses to gastrin were studied in the circular muscles of guinea pig stomach. The muscle strips were prepared from the three different regions of the stomach; the pylorus, the antrum and the upper body. The responses to gastrin, which were concentration dependent contractions, appeared only in the preparations from the upper body. The contractile response of the upper body was observed not by the cumulative application of gastrin, but by the one shot applications between which interval was 30 minutes. In contrast, any response to gastrin was not obtained in the other two regions. The contractile response to gastrin in the upper body was not affected by any antagonist, mepyramine 10-6g/ml, atropine 10-6g/ml, cimetidine 3 × 10-5g/ml or tetrodotoxin 10-7g/ml. In conclusion, it is reasonable that gastrin may act on the circular muscle of the upper body and cause the concentration dependent contraction by its direct effect.

An experimental study on histamine H2-receptor antagonist on calcium, gastrin and histamine induced gastric acid secretion in rat.

SummaryThe suppressive effect of histamine H2-receptor antagonist, cimetidine, on gastric secretion was investigated in Ghosh-Schild rat. The study above was done in basal state under infusing normal saline (l ml/h) and stimulated state by histamine-di-chloride (3.5mg/kg-h), tetragastrin (50mcg/kg-h) or calcium chloride (4 mg/kg-h). Dose related increase of cimetidine (1.7, 3.5, 7.0 and 14.0mg/kg-h) were observed and correlated with the degree of inhibition of acid secretion. Cimetidine had a potent inhibitory activity on either basal and stimulated acid output by the agents above. Basal acid secretion was completely abolished by 3.5 mg/kg-h of cimetidine to the level of anacidity. The degree of inhibition by the same dose of cimetidine was different among the agents used as stimulant on acid secretion and it followed in the order of calcium, gastrin and histamine subsequently. This study indicated that histamine H2-receptor participated the gastric secretion induced by either gastrin or calcium other than histamine itself. This fact indicated the important role of endogenous histamine in gastric secretion induced by calcium and gastrin.