Quarterly journal of experimental physiology (Cambridge, England)最新文献

We have examined the influence of preventing the passage of swallowed fluid on the development of the small intestine during late gestation in fetal sheep. In four fetuses at 90 d of gestation, the oesophagus was ligated and fistulated, causing swallowed fluid to enter the amniotic sac. Tissue was removed from proximal and distal parts of the small intestine for histological analysis at 136 d (term is 147 d). The body weights of the four experimental fetuses were not significantly different from those of fourteen age- and breed-matched fetuses which were used as controls. However, the width of the mucosal layers at both sites in the small intestine was reduced by approximately 25% in the fistulated fetuses. This was largely attributable to a reduction in villus height of approximately 30%. The densities of villi and crypts increased significantly at the proximal and distal sites respectively. These findings indicate that the ingestion of fluid during late gestation plays a role in promoting growth of the mucosal elements of the small intestine. The way in which this occurs is not clear although it may be mediated either by trophic factors present in either amniotic or pulmonary fluid, or by the release of gastrointestinal hormones, such as gastrin, as a result of gut distension.

Human eccrine sweat glands were isolated by shearing and the potential differences across the basolateral membranes determined using bevelled micro-electrodes filled with 4 M potassium acetate. Stable resting potentials of up to -81 mV were recorded. Alterations in external potassium concentration from 1.2 to 100 mM caused the membrane potential to change over a 70 mV range in cells of high resting potential, indicating that the basolateral membrane is largely potassium permeable. Input impedance was determined by constant current injection and found to be in the range 4-80 M omega. On giving a bolus injection of acetylcholine to produce a final concentration of 10(-6)-10(-7) M, four types of response were observed: depolarization, in a proportion of cells with resting potentials of -66 to -80 mV (n = 19), hyperpolarization, in a group of cells with resting potentials of -47 to -70 mV (n = 22), no change, in some cells of -40 to -81 mV resting potential (n = 22) and micro-electrode dislodgement (n = 8). In cells depolarizing to acetylcholine, the depolarization was short-lived and in thirteen cases was followed by a 'rebound' hyperpolarization. Input impedance decreased during depolarization in one-third (n = 5) of the cells in which satisfactory measurement could be made and increased during the final phase of depolarization or during rebound hyperpolarization. In cells hyperpolarizing to acetylcholine, the hyperpolarization was usually accompanied by an increase in input impedance. In ten of the twenty-two cells which showed no change to a first dose of acetylcholine, the agonist was administered at least two more times. In two cells (resting potentials -62 mV, -64 mV) a hyperpolarization was observed whereas in three others (resting potentials -66 mV, -70 mV, -81 mV) depolarization occurred. The effects of acetylcholine, whether depolarizing or hyperpolarizing, were reversibly inhibited by atropine and irreversibly reduced by ouabain. Experiments performed on glands maintained for up to 30 h in supplemented RPMI 1640 tissue culture medium yielded essentially similar results to those performed on freshly isolated glands.

To determine the normal maternal heart rate and stroke volume response to exercise and the role of the autonomic nervous system in this response, pregnant and non-pregnant pygmy goats were studied at rest, during and following treadmill exercise, and after autonomic blockade. Resting heart rates, stroke volumes and cardiac outputs were 10%, 60%, and 76% higher in pregnant compared to non-pregnant animals (P less than 0.05, 0.001, and 0.001 respectively). During exercise, heart rate and stroke volume rose in both pregnant and non-pregnant animals by similar amounts. Immediately post-exercise, stroke volume in pregnant animals dropped precipitously below resting levels by 15% (P less than 0.005) but cardiac output was preserved by heart rate. This fall in stroke volume was not seen in control animals. Autonomic blockade lowered resting and exercise heart rates in both groups without changing stroke volume. The elevations in heart rate and stroke volume in pregnancy are not primarily mediated via the autonomic nervous system. Although the maternal cardiac output response to exercise appears normal, the post-exercise fall in stroke volume, presumed secondary to a reduction in preload, could potentially be harmful to both mother and fetus.

beta-Cells in microdissected islets of Langerhans produce rhythmical bursts of electrical activity. This was monitored with two micro-electrodes simultaneously and the frequency and phase (collectively referred to as synchrony) of the two signals was investigated. At any instant two impaled cells produced bursts of the same frequency even when separated by up to 400 micron. When the electrode tips were separated by less than about 20 micron and current injection showed the cells to be ionically coupled the two signals were in phase and had almost identical shape. The phase relations between cells further apart were variable, the leading cell usually being located deeper within the islet than the other impaled cell. Increasing the glucose concentration increased electrical activity, reduced any phase lags and made the shape of the bursts more similar. There was less lag between the responses from two cells when the glucose concentration was suddenly reduced, than when it was suddenly increased. Qualitatively similar observations were made in glibenclamide-treated mice, a treatment previously shown to increase dye coupling between islet cells. However, the response to increasing glucose concentrations showed less phase lag; likewise the phase lag between bursts was reduced. Furthermore the response to current injected into one cell could be detected at much larger distances (up to 80 micron) than in control islets. This suggests that electrical coupling of beta-cells was improved in sulphonylurea-treated mice. Electron microscopy of both control and glibenclamide-treated mouse islets fixed at the end of each electrophysiological experiment showed the region impaled by the electrodes to be well preserved and, whenever the electrodes penetrated at least 20 micron into the islet, to contain a large proportion of beta-cells. The data support the view that, within an islet, most but not necessarily all cells are electrically synchronized, and that the coupling can be modulated by natural and pharmacological secretagogues.

During eating the parotid and submandibular salivary glands of sheep are stimulated via parasympathetic and sympathetic pathways. The response of the glands depends on the nature of the diet and the duration of a meal. In anaesthetized animals a continual activity in the parasympathetic nerve supply to the parotid gland reflects the excitatory effects of rumino-reticular (gastric) distension and contraction. This activity is reduced by high levels of rumino-reticular distension and increased osmolality of venous blood. It is argued that in conscious sheep these factors are important in determining the volume of saliva that is normally produced. Mechanoreceptors in the parotid glands of sheep are also a source of considerable afferent activity. Some of these receptors are active during naturally stimulated secretion and it is suggested they may also have a role in regulating salivary gland function.

Adrenal medullary cells can be obtained in high yield by protease digestion of slices of bovine adrenal medulla. The properties of catecholamine release from these isolated cells have been determined and compared with the intact perfused gland. Exposure to carbamylcholine, veratridine or high K evokes a transient increase in the rate of catecholamine release in association with dopamine beta hydroxylase but not lactate dehydrogenase. Exposure to A23187 releases catecholamine together with lactate dehydrogenase. In all cases release requires extracellular Ca. A comparison is made of the sensitivities of catecholamine release evoked by various agonists and the effects of nicotinic antagonists, D 600, Na-free media, TTX, Mg and trifluoperazine. Resting and carbamylcholine-evoked catecholamine release is relatively insensitive to the nature of the major extracellular anion and to the external pH over the range 6.4 to 7.8. Measurements with the dye 3 3'-Diethylthiadicarbocyanine iodide (di S-C2-(5)) show that release evoked by carbamylcholine or low concentrations of veratridine is associated--on average--with a small steady depolarization of the cells. Catecholamine release in response to nicotinic agonists, but not the other secretagogues, is greater at 20 degrees C than at 37 degrees C, possibly because of a slower rate of receptor desensitization at this temperature. Transmission electron microscopy of stimulated cells reveals a marked increase in the proportion of large membrane bounded vesicles that lack electron-dense cores. After stimulating secretion in the presence of horseradish peroxidase, the vesicles contain reaction product suggesting that they are generated by endocytosis.

The effect of vagal stimulation induced by 2-deoxy-D-glucose (2DG) on gastric acid and pancreatic bicarbonate output, and portal gastrin and secretin concentrations, was assessed in conscious miniature pigs. Electrical vagal stimulation has previously been shown to induce profuse pancreatic water and bicarbonate secretion in anaesthetized pigs. Pigs in this study were surgically prepared with gastric and pancreatic fistulas and indwelling jugular and portal catheters. An intravenous bolus of 2DG (100 mg/kg body weight) caused a significant increase in both gastric acid and pancreatic bicarbonate output although the latter was about 50% of the reported response to electrical vagal stimulation. Portal gastrin concentration rose significantly after 2DG, but the portal secretin concentration did not change. The presence of secretin in the small intestine was confirmed by intrajejunal HCl infusion. Failure of portal secretin concentration to rise after 2DG infusion rules against a role for this hormone in the pancreatic response.

The effects of hypophysectomy on the cell population of the adrenal cortex has been examined with light and electron microscopy. The sensitivity of the adrenal cortical cells to exogenous ACTH in both normal and hypophysectomized fetuses has been investigated by comparing plasma cortisol concentrations with structural changes in the adrenal cortex. Hypophysectomy was carried out at about 100 d and the subsequent analysis was made at about 135 d on fetuses catheterized at least 6 d earlier. The zona fasciculata of intact fetuses contained about 25% mature and 75% immature cells at 130-136 d. After hypophysectomy this zone contained a uniform population of immature cells and no mature cells; there was a significant reduction in both adrenal weight and cortical thickness. The zona glomerulosa was unaffected by hypophysectomy. The infusion of Synacthen 0 . 25 mg/d I.V. for 48 h did not affect the zona glomerulosa but resulted in a 2-fold increase in the thickness of the zona fasciculata in hypophysectomized and intact fetuses. This cortical growth was due to both hypertrophy and hyperplasia. All the cells in the zona fasciculata were mature following Synacthen treatment in both groups. The most striking difference between the secretory response of the adrenal cortex to Synacthen in the two groups was found within 3-6 h of the onset of infusion. Within this period there was a significant increment in the plasma cortisol concentration in the intact fetuses while no response was observed in the hypophysectomized animals. After 12 h infusion by contrast, a steadily rising response was observed in both groups. There was a significant correlation between the final plasma cortisol concentration and both the adrenal weight and cortical thickness after 48 h treatment. The increased sensitivity of the adrenal cortex to exogenous ACTH as term approaches in the sheep is considered to be dependent upon the increasing proportion of mature zona fasciculata cells within the adrenal cortex.

A procedure is described for maintaining segments of rat jejunum in vitro in a steady state of fluid and solute absorption for periods of up to 2 h so that the secretion of endogenous and exogenous nucleic acid derivatives across the serosa may be followed. Methods of high performance liquid chromatography for the separation and measurement of some nucleic acid derivatives are also described. These procedures are applied to investigate three endogenous components found in the washout into the serosal secretions. The kinetics of the washout are, in each case, mono-exponential and the effects of pre-feeding, of pre-feeding a glucose solution and of the diabetic state on the washouts have been investigated. One of the components of the washout is uric acid, the initial pool size of which varies from 13-22 mumol/g dry wt. of jejunum. Negligible amounts of derivatives of endogenous origin appear in the lumen.