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A Haymovits

Publications and source records attributed to A Haymovits.

13 recordsLinked to original sources
PubMed1980

Potassium- and ionophore A23187-induced discharge of secretory protein in guinea pig pancreatic lobules. Role of extracellular calcium.

Elevated concentrations of potassium chloride (50 to 120 mM) in the incubation medium stimulated in vitro discharge of secretory protein from guinea pig pancreatic lobules. The effect of potassium was not inhibited by 10(-4) M atropine, sodium substitutes, or 10(-5) M tetrodotoxin. Exposure of lobules to elevated concentrations of potassium chloride did not increase the release of tissue lactic dehydrogenase and resulted in the appearance of exocytotic images detected by electron microscopy. The time course and extent of discharge due to 75 mM KCl were similar to those caused by the ionophore A23187 and the secretory effect of both agents depended on extracellular calcium and intracellular energy reserves. Potassium chloride stimulation of 75 mM increased the influx of extracellular calcium by 49%, as measured by net 45Ca uptake. Optimal carbamylcholine chloride or pancreozymin stimulation consistently showed a greater effect on discharge than optimal KCl or A23187 stimulation and the additional effect depended on the ability of these physiological secretagogues to recruit calcium from intracellular sources. Potassium chloride stimulation did not result in cyclic GMP elevations in the presence of atropine and those elevations due to A23187 stimulation were small (21 to 30%) and dissimilar both in character (calcium dependence) and time course compared to those resulting from the physiological secretagogues. These findings allow us to define two interrelated pathways which couple hormonal stimulation and discharge of secretory protein in the exocrine pancreas.

Anti-Bacterial Agents↗
PubMed1979

Amino acid transport in the exocrine pancreas. IV. Do glucagon or insulin mediate the in vivo effect of caerulein on amino acid transport and incorporation?

The direct in vitro effect of caerulein on pancreatic protein synthesis and amino acid transport has been investigated. In contrast to in vivo conditions we were unable to demonstrate any effect on alpha-aminoisobutyric acid and leucine uptake and on leucine incorporation usin rat pancreatic lobules. Insulin and glucagon were therefore examined as possible mediators for the in vivo effect of caerulein. Insulin (1--5 microM) slightly enhanced AIB uptake (16% but did not change uptake and incorporation of leucine. Glucagon (0.01--1 microM) was ineffective. Both islet hormones had no influence on the formation of cyclic GMP induced by secretagogue either in rat (40% increase) or in guinea pig lobules (500% increase). It seems unlikely that the two islet hormones exert any direct effect on the exocrine pancreas and thus could serve as mediators for the in vivo synthetic effect of caerulein.

Aminoisobutyric Acids↗
PubMed1976

Cellular cyclic nucleotides and enzyme secretion in the pancreatic acinar cell.

Cellular levels of cAMP and cGMP were measured in guinea pig pancreatic lobules incubated in vitro, during basal or stimulated secretion. Stimulation with optimal concentrations of carbamylcholine (carbachol) (10(-5) M), pancreozymin (0.1 unit/ml), and caerulein (10(-9) M) resulted within seconds in a sharp rise in cGMP levels, from five to more than 20 times that of basal levels. cAMP levels did not change significantly. cGMP increases were maximal at 2 min then subsided by 4-7 min to a plateau about two to three times that of basal level. This plateau was maintained for the duration of the secretagogue stimulus. Removal of the carbachol stimulus resulted in a rapid decrease in cGMP levels to that of the basal state. The cellular cGMP levels observed within the first 2 min of stimulation correlated closely with the dose of carbachol and the secretory response. Atropine at 10(-4) M blocked the cGMP elevation due to carbachol but not that due to pancreozymin, while carbonyl cyanide m-chlorophenyl hydrazone, an uncoupler of oxidative phosphorylation, blocked the response to both secretagogues. Similar though less extensive findings were observed using rabbit pancreatic lobules incubated in vitro. High concentrations (10(-2)-10(-3) M) of the dibutyryl and 8-bromo analogues of both nucleotides were effective, though suboptimal, secretagogues. In the case of the cAMP analogues, the secretory response was associated with a rise in endogenous cGMP levels, similar to that observed during suboptimal carbachol stimulation. These findings suggest that cGMP may be an intracellular mediator in the process of stimulus secretion coupling in the acinar cell of the exocrine pancreas.

Animals↗
PubMed1976

Calcitonin: antagonism at intestinal muscarinic receptors.

The action of calcitonin was studied on the motility of isolated innervated segments of rabbit and guinea-pig intestines as well as longitudinal muscle with adherent myenteric plexus dissected from the guinea-pig ileum. Calcitonin (0.25 muM) antagonized contractile responses to acetylcholine and the cholinergic response to electrical field stimulation. This hormonal effect was relatively specific since it was not observed at nicotinic receptors or adrenoceptors, nor did calcitonin act as a local anaesthetic or directly on the contractile machinery of smooth muscle. Perivascular adrenergic and intrinsic non-adrenergic inhibitory responses also were unaffected by calcitonin. However, calcitonin did have antihistaminic properties directed against H1-receptors. The concentration of calcitonin required to achieve muscarinic antagonism in our experiments is not reached at the resting level of circulating hormone.

Acetylcholine↗