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The hypothesis that multiaxonal neurons of the myenteric plexus of the small intestine are sensory neurons, was tested. The rising principle of the issue to sensory information in the metasympathetic ganglions of the small intestine was discovered by microapplication of the salt acid solution. Serotonin (5-hydroxytriptamine) and acetylcholine can participate in forming primary sensory signals in the multiaxonal neurons. Pulsed activity in primary sensory neurons by mucous perfusion of the small intestine by physiological solution with pH 3.5-3.8 was revealed. The enterochromaffin cells of the mucosa and multiaxonal neurons of the submucous and myenteric plexuses take part in reception of the salt acid.

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Experiments were carried out in lactating white mice. Removal of Ca(2+)-ions from the perfusion solution reduced the amplitude and duration of the membrane potential changes in the secretory cells in the mammary gland alveolus. The extra- and intracellular Ca(2+)-ions participate in development of contraction responses of myoepithelial cells. Removal of K(+)-ions from perfusion solution and increase of K(+)-ions concentration in the medium to 20 mmol/l inhibit the development of response of secretory cells to oxytocin action. These changes in K(+)-ions concentration do not affect the contractile response of the myoepithelial cells. The findings suggest that there are essential differences in the participation of Ca(2+)- and K(+)-ions in mechanisms of the mammary secretory and myoepithelial cells responses to oxytocin action.

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In studies on lactating laboratory mice an influence of prostaglandin F2 alpha on the value of transepithelial potential difference and resistance of the alveolar secretory epithelium in the mammary gland, was studied. Prostaglandin F2 alpha did not affect initial level of transepithelial potential difference and resistance in alveoles. In all experiments with the preliminary application of prostaglandin F2 alpha in different concentrations (1 x 10(-5)-1 x 10(-11) M) was registered a reliable increase in an amplitude (before 31 +/- 2%) and duration (before 43 +/- 3%) to return reactions on oxytocin. Prostaglandin F2 alpha caused a reduction of transepithelial resistance in the alveolar secretory epithelium of first phase to return reaction on oxytocin on 28 +/- 22%. The data obtained indicate a possibility of participation of prostaglandin F2 alpha in development of certain stages of shaping a composition of milk.

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Secretory cells' membrane potential and transepithelial potential difference in the mouse mammary gland diminish within 2.5 hours following breast-feeding of the litter. The transepithelial resistance for up to 20 hours after the feeding did not drop below 40-70 k omega. The secret pressure in the mammary gland does not grow during this period. Therefore an increase of interval between litter feeding up to 20 hours does not entail any mechanical lesion of the secretory epithelium. The latter's cells seem to secrete organic and inorganic substances in concentrations which do not change significantly during their transfer along the outgoing ducts.

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Histological studies revealed that the mammary gland nipple have smooth muscle fibres along the nipple channel. These fibres infiltrate the connective tissue parallel to the skin. The ring muscles are not obvious. Delays in the milk excretion in mice may be due to specifics of allocation and functioning of the nipple smooth muscles. To obtain milk, a mechanical action upon the nipple and a synchronised release of oxitocin into the blood are necessary.

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The data obtained suggests that the period following the cessation of suckling their young in mice induces no inhibition of the contractile response of myoepithelial cells or of the milk ejection. For the first time, the inhibitor (Gd3+ ions) of the mechanosensitive ion channels was shown to inhibit the secretory and myoepithelial cells responses in the mammary gland alveoli.

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The effect of acetylcholine inducing the exocytosis of secretory vesicles, upon the development of changes in electrical resistance in mammal gland's alveoli, was studied in mice. A decrease in the ACh concentration and in potassium ions concentration gradient was followed by a deceleration of the reduction of transepithelial electrical resistance. The data obtained suggest that the exocytosis of secretory vesicles is not reflected in changes of transepithelial electrical resistance in mammal gland's alveoli.

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The MP levels of the mammary gland's secretory cells and transepithelial differences of potential were found to depend on extracellular ions of sodium and chloride in lactating white mice. Substitution of the sodium ions with the choline ions increased a little the difference of potentials, whereas substitution of the chloride ions with sulfuric acid ions decreased it. Transepithelial electrical resistance increased in both cases. Substitution of the sodium ions with ions of choline and of the chloride ions with sulfuric acid ions suppressed hyperpolarization changes of the MP and increased the transepithelial difference of potentials. Contractile responses of myoepithelial cells to the action of acetylcholine and oxytocin were also depressed. The sodium and chloride ions seem to affect simultaneously the processes of the potassium ions release from secretory cells and contractile responses of the alveoli's myoepithelial cells.

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The development of depolarization mesaton-induced and hyperpolarization isadrine-induced changes of the membrane potential of the mice mammary gland secretory cells was followed by a decrease in transepithelial electrical resistance and in potassium ions activity in the alveoli. The isadrine-induced hyperpolarization could be reversibly depressed by a substitution of chloride ions with sulphuric acid ions. Neither mesaton nor isadrine altered the MP after blocking of the Na+/K+ pump. Catecholamines seem to exert a direct alpha-adrenomimetic and an indirect beta-adrenomimetic reversible blocking effect upon the activity of the Na+/K+-ionic pump.

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In lactating albino mice, an augmentation of the membrane potential of secretory cells and of transepithelial potential difference caused by oxytocin and acetylcholine, was shown to be accompanied by the fall of transepithelial electrical impedance. The calcium-dependent increase of the permeability of plasmatic membrane for K+ seems to be the main cause of the above responses.

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The hyperpolarization of the secretory cells MP and the alveolar myoepithelium contraction in response to oxytocin depend to a greater extent on the accompanying effects of catecholamines as compared with acetylcholine. The hyperpolarization of the secretory cells MP induced with oxytocin and acetylcholine diminishes in its amplitude and duration in presence of colchicine (25 microM). Rhythmic hyperpolarization changes of the MP induced with 1-minute action of oxytocin and acetylcholine coincide in time with the exocytosis period of secretory vesicles and the beginning of new biosynthesis.

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Participation of Na, K-pump of the surface basal-lateral membrane in the process was shown to determine the MP-level. Restriction of Ca-++ entrance into the cell depressed MP-changes in the secretory cells curing the action of acetylcholine and oxytocine.

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The effect of oxytocine and its combinations with the acetylcholine, adrenaline, atropin, and prozerin on the level of membrane potential of mammary secretory cells was studied. Short oxytocine application (5-10(-4) ME/ml) evoked hyperpolarization of the contraluminal membrane (12+/-1 mV for 54+/-5 sec). Their response was increased by joint application of acetylcholine or proserine and decreased by preliminary application of atropin. Adrenaline increased or decreased the amplitude of the membrane potential's changes and considerably reduced the duration of the oxytocine reaction. Existence of oxytocine receptors was supposed on the membrane of secretory cells, as well as the possibility of acetylcholine and adrenaline effects on the structure of oxytocine receptors or the interaction of adreno--and cholinergic receptors with the oxytocine those.

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