AJP - Gastrointestinal and Liver Physiology

Jensen, SL; Fahrenkrug, J; Holst, JJ; Kuhl, C; Nielsen, OV; Schaffalitzky de Muckadell, OB

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The effect of pure natural porcine secretin on endocrine and exocrine pancreatic secretion was studied in the totally isolated perfused porcine pancreas. The exocrine pancreatic responses to secretin correspond well with those obtained in the anesthetized pig. The lowest concentration of secretin observed to increase pancreatic secretion was 2.8 pmol/liter, whereas the maximum pancreatic responses were obtained at a secretin concentration of 92 pmol/liter. The infusion of secretin in concentrations ranging from 2.8 to 278 pmol/liter in the presence of a constant concentration of glucose (7.5, 5.0, or 3.5 mmol/liter) was without effect on the insulin and glucagon release. Infusion of secretin at a concentration of 834 pmol/liter in the presence of glucose at 7.5 mmol/liter provoked a significant (P less than 0.01) short-lived increase in insulin secretion. However, there was no effect on the glucagon secretion. The results of this study indicate that neither the augmented insulin response nor the suppression of glucagon elicited by oral glucose depend on secretin.

Lichtenberger, LM; Shorey, JM; Trier, JS

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The regulation of gastrin release in rodent antral mucosal organ cultures was investigated. The tissue was well preserved morphologically and medium gastrin concentration increased steadily throughout a 24-h culture period. The effects of peptone and a bovine serum albumin digest on gastrin release were independently investigated. During the periods these agents were in contact with the tissue, medium gastrin concentration did not differ from those of control cultures. However, treatment cultures released a significantly greater amount of gastrin into the medium than did control cultures during the two posttreatment periods. Prolongation of the period of exposure to peptone did not alter this secretory pattern. The rise in medium gastrin concentration that followed the removal of peptone was directly related to the medium peptone concentration and was partially inhibited by readdition of peptone to cultured antral explants. These results suggest that substances which stimulate gastrin release in vivo may cause the accumulation of an antral inhibitor of gastrin release when exposed to rat antral mucosa in culture.

Tapper, EJ; Powell, DW; Morris, SM

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The autonomic control of intestinal electrolyte transport has been investigated in the in vitro, short-circuited rabbit ileum with varying doses of carbachol and with neuroeffector blocking agents. Low-dose carbachol (less than 10(-6) M) and high-dose carbachol (greater than 10(-4) M) had different effects on Na and Cl transport. Low-dose carbachol caused a transient increase in the potential difference and short-circult current, stimulated Cl secretion, and inhibited the residual flux (probably HCO3 secretion). This is a muscarinic response since it is inhibited by atropine (10(-6) M). After an initial increase of the potential difference and short-circuit current, high-dose carbachol reduced these electrical parameters, stimulated Na and Cl absorption, and abolished the residual flux. This is a nicotinic response since it is inhibited by hexamethonium (10(-5) M). This nicotinic response is identical to that reported by others with alpha-adrenergic agents and it was inhibited also by phentolamine (10(-7) M). We propose that high-dose carbachol stimulates nicotinic receptors on postganglionic sympathetic fibers present in our preparations causing a release of catecholamines and a resulting alpha-adrenergic response by the intestinal epithelial cell. The physiological significance of this response in the gut remains to be determined.

Taylor, IL; Impicciatore, M; Carter, DC; Walsh, JH

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In four conscious dogs the pancreatic polypeptide (PP) response to a standard beef-liver meal was measured by specific radioimmunoassay and compared with the response seen after the intravenous injection of 25 or 100 microgram/kg atropine. All three tests were performed twice in each animal and then repeated after truncal vagotomy. The mean prevagotomy postprandial PP increment was 85 +/- 16 pmol/liter in the first 2-h period and 54.5 +/- 13 pmol/liter in the second. After the injection of 25 microgram/kg atropine there was significant reduction in the early response (mean delta PP = 39 +/- 17 pmol/liter, P less than 0.05), but not the late (mean delta PP = 62 +/- 18 pmol/liter). After 100 microgram/kg atropine sulfate, the response was significantly reduced during both periods (mean delta PP = 5.5 +/- 5.2 and 20 +/- 8.8 pmol/liter, respectively, P less than 0.01). Truncal vagotomy significantly (P less than 0.01) reduced the PP response over both time periods (mean delta PP = 6.4 +/- 2.2 and 5.8 +/- 3.8 pmol/liter), and the small residual response was completely abolished by atropine. In five additional dogs an infusion of bethanechol (100 microgram . kg-1.h-1) caused a significant increase (P less than 0.05) in the plasma concentration (mean delta PP = 40.9 +/- 11.8 pmol/liter), which was abolished by pretreatment with atropine (mean delta PP = -2.9 +/- 2.1 pmol/liter). These studies suggest that PP release in response to a meal in the dog is largely under vagal-cholinergic control.

Yokoyama, S; Ozaki, T

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The effects of repetitive electrical stimulation of nodes in Auerbach's plexus on the longitudinal muscle of rabbit intestine were investigated. Peeled longitudinal muscle strips, with adherent Auerbach's plexus, were obtained and placed under a stereodissecting microscope. Neural elements within nodes of Auerbach's plexus were stimulated repetitively using a metal microelectrode with tip diameter of 5 micrometer. Stimuli applied to a node generally caused excitation of the longitudinal muscle on the oral side and inhibition on the anal side of the point of stimulation. Excitation of the muscle was mainly cholinergic, and inhibition of the muscle was nonadrenergic. From the results of the present study the concept of the law of the intestine, excitation above and inhibition below the stimulated spot, was supported.

Prior, R. L.; Christenson, R. K.

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Page E462 : R. L. Prior and R. K. Christenson. "Gluconeogenesis from alanine in vivo by the ovine fetus and lamb." Page E466: substitute corrected Table 5. (See PDF)

Bruce, LA; Behsudi, FM; Danhof, IE

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Male Sprague-Dawley rats were pretreated subcutaneously with either progesterone (3 mg/kg per day) in a vehicle or a vehicle only for 3 days. Antral and gastroduodenal junctional tissues (GJT) were excised from both groups of animals and prepared for in vitro mechanical measurements. Responses from the circular muscle axis of these tissues were recorded with strain gauge transducers over a 30-min period. Chemical stimulation of the tissue was achieved with a muscarinic agonist, bethanechol chloride. Log-dose response curves suggested that untreated antral tissue generated stronger contractile activity than untreated GJT on an equal weight basis at bethanechol dose levels of 6.4 X 10(-6) M to 1 X 10(-4) M (P less than 0.005). Antral tissue and GJT contractile activity from the progesterone pretreated animals was significantly reduced (P less than 0.01) compared to the corresponding tissues from untreated animals at bethanechol dose levels of 6.4 X 10(-6) M and 1.28 X 10(-5) M. Progesterone pretreatment appeared to have little effect on the contractile frequency of either tissue. These results suggest possible progesteronic influences on contractile force in gastrointestinal smooth muscle.

Beam, HE; Henning, SJ

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In the adult rat, fed ad libitum, the activity of jejunal sucrase shows a diurnal rhythm with a peak during the dark period. Ontogenically, sucrase activity appears around the 16th postnatal day, then rises rapidly, and reaches adult levels by the 25th day. Our aim was to determine the developmental stage at which the diurnal rhythm appears and to elucidate its physiological basis. When sampled every 3 h on the 19th day, jejunal sucrase showed no discernible pattern with time. In contrast, at 22 days (1 day after completion of weaning) a circadian rhythm very similar to that of adults had appeared. Weights of stomach contents showed that the adult pattern of nocturnal feeding also matured between days 19 and 22. When weaning was prevented, no sucrase rhythm was detected on day 22, despite an imposed rhythm of suckling. Thus the sucrase rhythm is normally cued by some aspect of weaning other than rhythmic ingestion per se. Although corticosterone seemed a likely mediator of the sucrase rhythm, studies in adult rats showed that the rhythm persists in adrenalectomized animals.

Villegas, L

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The effects of hydrostatic pressure differences up to 0.4 atm/413 cmH2O were studied on frog gastric mucosa in vitro. Net water flux, transmucosal electrical potential difference, and acid secretion were measured. A significant correlation between hydrostatistic pressure difference and net water flow (r=0.77) was obtained. The intercept of the regression line, at zero hydrostatic pressure difference, is 9.3 +/- 0.5 microliter/cm2.h, and the slope 42.9 +/- 3.2 microliter/cm2.atm.h. No significant correlation was obtained between the hydrostatic pressure difference and the transmucosal potential difference (P greater than 0.20), the acid secretion (P greater than 0.20), or the nonacidic chloride transport, measured as short-circuit current (P greater than 0.20). Hydrostatic water flux is compared to osmotically induced flux previously reported. It is proposed that the difference between hydrostatic and osmotic induced water fluxes is due to the area of cells exposed to the pressures. Only part of surface cells are directly exposed to the osmotic pressure due to the presence of restricted extracellular compartments.

Voigt, J; Sekeris, CE

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The modulation of tryptophan-oxygenase (TO) and tyrosine amino-transferase (TAT) in the rat liver after a single dose of hydrocortisone has been studied under various physiological conditions. Differences in the induction behavior of the two enzymes have been observed dependent on sex, age, amount of administered hormone, and presence or absence of the adrenals. Some of the results observed are the following: 1) TO reached its maximum induction level 3 h prior to TAT in normal male rats. This difference disappeared when adrenalectomized male rats or when female animals were tested. 2) The maximal induction values of both enzymes were 50--80% higher in adrenalectomized rats than in normal rats. This effect was independent of sex. 3) Higher doses of hydrocortisone were necessary for optimal induction of TO and TAT in normal than in adrenalectomized rats. 4) The minimum dose of hydrocortisone necessary for enzyme induction was significantly lower for TO than for TAT. 5) Actinomycin D caused a complete inhibition of the induction of TO and TAT when given simultaneously with the glucocorticoid. The inhibition was less complete the longer the interval between hormone and actinomycin D administration. The activity of TAT was suppressed to a larger extent than TO.