Regulation of ornithine decarboxylase activity in LoVo cells.

The role of Na+ and Na(+)-H+ exchange in the stimulation of ornithine decarboxylase (ODC) activity has been investigated in a human colon adenocarcinoma cell line, LoVo. Asparagine (Asn; 10 mM) or 10% fetal bovine serum (FBS) increased ODC activity from undetectable levels to greater than 500 pmol CO2.mg protein-1.h-1 in 4 h. This increase could be reduced 50% by concentrations of Na(+)-H+ exchange inhibitors that did not reduce protein synthesis. (approximately 0.2 mM for amiloride and 0.05 mM for hexamethyleneamiloride). Asn was able to double the uptake of 22Na+, whether an ionic (choline chloride) or nonionic (D-mannitol) substance was substituted for Na+, and the substitution of these compounds as well as N-methyl-glucamine for Na+ largely prevented the stimulation of ODC by Asn. Another factor influencing ODC activity was extracellular pH (pHo). When pHo was lowered, intracellular pH (pHi) also fell, and ODC activity was reduced. When pHo was raised, pHi also rose, and ODC activity increased. The well-known correlation between increased pHi and Na+ uptake with the stimulation of growth may be due to their influence on ODC activity.

Secretion of H+ and K+ by bullfrog gastric mucosa: characterization of K+ transport pathway.

The transport of K+ and H+ (both expressed as mueq/h) by in vitro chambered bullfrog (Rana catesbeiana) gastric mucosa have been studied under a variety of conditions such as anoxia, addition of p-chloromercuribenzene sulfonic acid (PCMBS) into the secretory solution, inclusion of ouabain in the nutrient solution, addition of thiocyanate (SCN-) into the mucosal solution, and replacement of nutrient chloride (Cl-) with sulfate (SO4(2-)), or gluconate (Gl). Anoxia reversibly reduced the H+ transport close to zero within 15 min and gradually reduces the K+ transport throughout the 2-h period of anoxia. The presence of 2.5 X 10(-4) M mucosal PCMBS in the histamine-stimulated mucosa increases the K+ transport, which is promptly reduced by changing the gas phase to 95% N2-5% CO2. Addition of ouabain to the nutrient solution of the histamine-stimulated mucosa with PCMBS on the mucosal side significantly (P < 0.05) reduces the K+ transport within 60 min. Addition of SCN- to the mucosal solution of a histamine-stimulated mucosa with regular nutrient or O, K+ nutrient and 10, K+ mucosal solution reduces the H+ transport to near zero within 60 min. This SCN- inhibition can be reversed by elevating secretory K+. Substitution of nutrient Cl- with SO4(2-) or Gl in the histamine-stimulated mucosa reversibly inhibits H+ transport and reduces K+ transport to a low level (0.7 +/- 0.05). Our data suggest that the K+ transport across the apical membranes of gastric cells is to a large extent a passive carrier-mediated process, and the transport of both K+ and Cl- are coupled at the apical membrane.

Inhibition of canine gastric acid secretion by an H-1 receptor antagonist to histamine.

Histamine H-2 receptors are thought to mediate gastric acid secretory responses, whereas H-1 receptors supposedly regulate mucosal vascular responses to histamine. In an in vivo chambered canine stomach flap preparation, the H-1 receptor antagonist, tripelennamine, injected intraarterially (22.1 mumol/kg) into the stomach flap reduced histamine-stimulated (1.25 micron/kg/min intravenously) acid secretion by approximately two thirds with a secondary reduction in gastric mucosal blood flow. This antisecretory action does not appear to be due to nonspecific mucosal damage. The H-2 receptor antagonist, metiamide, injected intraarterially (2.5 mumol/kg) also inhibited gastric acid secretion by about two thirds as did intravenously injected metiamide (4.5 mumol/kg), whereas intravenously administered tripelennamine (40.8 mumol/kg) was ineffective as an acid secretory inhibitor. Intraarterial tripelennamine reduced the secretory actions of the H-2 agonist, 4-methylhistamine (2.2 micron/kg/min intravenously), while intravenous metiamide depressed the gastric mucosal dilator responses to the H-1 agonist, 2-methylhistamine (5 micron/kg/min intravenously). Both histamine-receptor antagonists also reversed the systemic circulatory depressor effects of histamine and its analogs. These results suggest the need for reevaluation of inferences based upon the assumed specificity of H-2 and H-1 agonists and antagonists.

Histamine H1- and H2-receptor vasodilation of canine intestinal circulation.

Studies were conducted in anesthetized dogs to determine whether the mesenteric vasodilator response to histamine is mediated by H1 receptors alone or whether H2 receptors are also involved in the response. Evidence favoring a role for both receptors included: 1) the vasodilator response to histamine was inhibited by either the H1-receptor antagonist, tripelennamine, or the H2-receptor antagonist, metiamide; 2) both the H1 agonist, 2-methylhistamine, and the H2 agonist, 4-methylhistamine, induced dilator responses in the mesenteric circulation; and 3) two temporal patterns of vasodilation could be distinguished, namely a transient spike and subsequent fade of blood flow (seen with either the H1 agonist or with histamine after H2-receptor blockade) and a sustained and stable increase in flow (seen with either the H2 agonist or with histamine after H1 blockade). Metiamide appeared to be a potent inhibitor of the mesenteric vasodilator response to histamine at least equal to tripelennamine.

Cyclic nucleotide metabolism and vasodilation in canine mesenteric artery.

The uptake and extracellular and intracellular metabolism of radioisotopically labeled cyclic 3',5'-adenosine monophosphate (cAMP) and dibutyryl cAMP (DBcAMP) was determined in canine mesenteric arteries incubated in vitro. Intracellular tissue uptake was measured by radioisotope counting and labeled metabolites separated by thin-layer chromatography. Extracellularly, cAMP was extensively metabolized to AMP, adenosine, and Pi. DBcAMP was metabolized to monobutyryl cAMP (MBcAMP) intracellularly. Vasodilation of the mesenteric circulation in vivo was produced by cAMP, its metabolites and DBcAMP. DBcAMP caused greater vasodilation than cAMP but had a response time to its peak effect of 12 min versus 90 s for cAMP. The vasodilator properties of cAMP and DBcAMP were related to their metabolism. It was concluded that the vasodilation caused by cAMP was due to cAMP metabolites produced by extracellular metabolism.

Histamine, cyclic AMP, and gastric secretion in the dog.

Canine gastric mucosal cyclic AMP content was determined at 1, 5, 30, 60, and 120 min after commencing a 2-hr continuous intravenous infusion of histamine of sufficient dose to elicit a brisk acid secretory response from the dog stomach. The increase in acid output was significant at 30 min and stabilized at the stimulated level for the duration of histamine infusion. By contrast, there was no significant increase in mucosal cyclic AMP content at any time of measurement. Our findings indicate that the acid secretory response of the canine stomach to histamine does not require prior accumulation of cyclic AMP in the mucosal tissue.

Evaluation of (14C)aminopyrine clearance for determination of gastric mucosal blood flow.

This study has demonstrated high correlation between the radiometric and spectrophotometric determinations of gastric mucosal aminopyrine clearance. The radiometric method is technically easier, allows a larger number of samples to be determined and is safer to the subject. The clearance of small amounts of [14C]aminopyrine was unaffected by large doses of unlabeled aminopyrine showing that mucosal extraction is not concentration limited. Small amounts of [14C]aminopyrine may provide an excellent tool for examining the role of mucosal blood flow in the pathogenesis of gastric disease in man.