The actions of natural secretin on the small intestinal vasculature of the anaesthetized cat

Regulation of postprandial mesenteric blood flow in humans: evidence for a cholinergic nervous reflex

Duplex ultrasound was used to investigate superior mesenteric artery haemodynamics in humans in order to determine the physiological importance of postprandial blood concentrations of cholecystokinin octapeptide (CCK8), gastrin 17, secretin, and glucagon and to study whether a nervous cholinergic reflex mechanism has a role in the postprandial mesenteric blood flow response. Duplex parameters of vessel diameter, mean velocity, and flow volume were determined serially in the basal state and after stimulation. Changes were compared with baseline values. Superior mesenteric artery parameters were significantly increased over baseline values after a liquid test meal, but ingestion of saline did not cause any changes. Hormones infused simultaneously at postprandial concentrations did not change mesenteric blood flow. When they were infused at pharmacological doses, however, a significant increase in flow parameters was observed. Pretreatment with atropine significantly (p less than 0.05) reduced the mesenteric blood flow response to meal stimulation (57%). These data suggest that the four hormones tested are not of quantitative importance in regulating postprandial superior mesenteric artery blood flow. A cholinergic nervous reflex, however, participates in the control of food induced mesenteric artery flow changes.

The effects of isoprenaline and bradykinin on capillary filtration in the cat small intestine

1 Lymph flow, and both lymph and plasma protein concentrations were measured in isolated, blood-perfused loops of cat ileum. 2 Permeability-surface ares (PS) products and the osmotic reflection coefficient (sigma) of the intestinal capillaries were calculated. 3 Isoprenaline (one dose) or bradykinin (two different doses) was infused into the superior mesenteric artery. 4 Isoprenaline (blood concentration about 50 ng/ml) did not affect PS or sigma. 5 Bradykinin (about 36 ng/ml) increased PS but as a sigma was unaltered, this was primarily due to an increased capillary surface area. 6 Bradykinin (about 680 ng/ml) increased PS and as sigma was reduced, there was an increased capillary permeability. 7 Reasons for the lack of effect of isoprenaline at concentrations which increase capillary filtration coefficient are discussed. 8 These data show that this technique separates drug effects on capillary surface area from effects on capillary permeability.

Effects of gastrointestinal hormones on transport by peritoneal dialysis

Because the gastrointestinal hormones are known to dilate the splanchnic vasculature, their effects on transport of water and solutes during peritoneal dialysis were studied in an experimental model, the rabbit. In unanesthetized rabbits, dialysate volume was calculated by isotope dilution, and clearances were estimated by dialysate/plasma concentration ratio factored by minute volume. With isotonic dialysis solution, the mean increment in dialysate volume per minute of intraperitoneal dwell was 0.19 ml/kg/min, and mean clearances of creatinine and urea were 0.71 and 0.90 ml/kg/min, respectively. When administered intravenously, secretin significantly augmented osmotically induced water flux, but not when given intraperitoneally. Neither glucagon nor cholecystokinin affected dialysate volume. Intravenously, but not intraperitoneally, glucagon increased peritoneal clearances of creatinine and urea to more than 150% of control values. Neither cholecystokinin nor secretin augmented significantly peritoneal mass transport when given by either route. The data suggest that the site of acton is the endothelial surface of the membrane, that the mechanisms of augmenting transport involve increased permeability and/or surface area, and that agents which combine an increase in mass transport and capillary filtration coefficient may be clinically useful.

Volumetric assessment of the capillary filtration coefficient in the cat small intestine

The capillary filtration coefficient of the cat small intestine was measured in four ways; the conventional measurement was compared with the "zero time extrapolation" technique, and with two methods designed to assess the end of the blood volume shift due to venous pressure elevation. If the capillary filtration coefficient (CFC) was determined using small elevations of venous pressure (10 mm Hg or less), there was good agreement between the techniques. Larger elevations of venous pressure resulted in apparent over-estimates of CFC measured by the conventional technique, probably because of increased "smearing" of the blood volume shift into the component of the response measured as the CFC. In general, larger elevations of venous pressure gave smaller CFC's, and using venous pressure elevations of 10 mm Hg or less, the CFC was greater if the final elevated venous pressure was 10 mm Hg than if it was 20 or 30 mm Hg. Changes in CFC due to noradrenaline and isoprenaline (about 15 ng/ml arterial blood concentration) were in agreement when small venous pressure elevations were used and CFC measured in three different ways.

The effects of glucagon, secretin, pancreozymin and pentagastrin on the hepatic arterial vascular bed of the dog

1 The sympathetically-innervated arterial vascular bed of the dog's liver was perfused from a femoral artery. Arterial blood flow and perfusion pressure were monitored continuously and the hepatic arterial vascular resistance (HAVR) calculated from these measurements. 2 Commercial preparations of secretin, pancroezymin, glucagon and pentagastrin were administered by intra-arterial (i.a.) injection and infusion. 3 Secretin and pancreozymin by injection caused dose-dependent hepatic arterial vasodilatation, and on a molar basis were both more potent than glucagon or pentagastrin. 4 Intra-arterial infusions of secretin and pancreozymin caused hepatic arterial vasodilatation at calculated blood concentrations close to those measured under physiological conditions by other investigators. The vasodilatation was of the same duration as that of the hormone infusions. 5 Pentagastrin by i.a. injection caused dose-dependent hepatic arterial vasodilatation; by i.a. infusion, vasodilatation occurred but there was marked 'escape' from the effects during the continued infusion. 6 As reported previously, glucagon by injection caused dose-dependent hepatic arterial vasodilatation of long duration; by infusion, glucagon caused vasodilatation that persisted after the cessation of the infusion. 7 Glucagon infused i.a. inhibited the vasoconstricter effects of i.a. noradrenaline, over the same range of infusions that caused hepatic arterial vasodilatation. 8 Secretin or pancreozymin did not antagonize the effects of noradrenaline on the hepatic arterial vascular bed at any doses used. 9 Pentagastrin did not antagonize the vasoconstrictor effect of noradrenaline whether hepatic arterial vasodilatation resulted from the pentagastrin infusion, or not. 10 These results are discussed with respect to the possible control of the hepatic arterial vascular bed by gastrointestinal hormones.