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The regional blood supply to consecutive segments of the small intestine in the anaesthetized rat was investigated with a radioactive microsphere technique. A blood flow gradient with the lowest flow in the distal segments (0.85--0.89 ml/min.g) and the highest in the proximal segments (1.13--1.15 ml/min.g) was observed. Very few microspheres were found in the portal vein blood, indicating negligible arteriovenous shunting in the splanchnic area. The mean cardiac outputs in two consecutive measurements were 27.9 and 28.7 ml/min . 100 g, respectively. The cardiac output and regional blood flow values were in accordance with those obtained with other techniques.

Two groups of rats were subjected to segmental ischaemia of the small intestine for 2 h. According to our previous findings such ischaemia causes impairment of the central circulation as well as of the splanchnic blood flow. Dopamine treatment was initiated 30 or 90 min after the establishment of ischaemia. In the 30-min group cardiac output increased and the blood flow was normalized in those parts of the small intestine where the arteries were not ligated (the non-occluded parts). This result corresponds well to our previous observations when dopamine treatment was started immediately after the establishment of ischaemia. In the 90-min group cardiac output was not affected. Again the intestinal blood flow was normalized in the non-occluded parts. In both groups the pancreatic circulation was impaired.

The influence of segmental small intestinal ischemia on the central circulation and on the regional blood flow to consecutive segments of the small intestine in the rat was investigated with the microscphere method. Ischemia was established by ligating 11 arterial mesenteric end arcades, corresponding to one quarter of the total length of the small intestine. The blood supply to different organs and central circulatory variables were determined before, and 10 min, 30 min, 2 h and 14 days after the establishment of the ischemia. After 10 min of ischemia, there was an increase of the blood flow to the segments distal to the ischemic region but after 30 min, this blood flow was the same as the control flow. The central circulatory variables weere not affected. After 2 h of ischemia, the blood supply to both the ischemic and the non-ischemic part of the small intestine had deteriorated considerably. Thus, the vascular resistance in the ischemic segments and the segments surrounding it was increased. Cardiac output was reduced by about 50%. In the experimental group investigated 14 days after establishment of the ischemia, the mortality rate was about 50%. In the survivors, the intestinal blood supply had returned to normal.

The early diagnosis of acute mesenteric occlusion presents a difficult problem in abdominal surgery. In a study on rats the relation between graded small bowel ischemia and the concentration of heme compounds in the plasma was investigated. The ischemia was produced by ligation of terminal vessels at the mesenteric margin of the intestine (mesenteric end arcades) or the superior mesenteric artery. Heme compounds were assayed by a benzidine method developed by Crossby et al. The concentration of heme compounds in the plasma was higher in animals with various grades of intestinal ischemia than in animals subjected to laparotomy alone. This increase was noted as early as 4 hours after induction of moderate and severe grade of ischemia. The results indicate that an increase in plasma concentration of heme compounds takes place at an early stage of moderate and severe small bowel ischemia following mesenteric vascular occlusion but not until after 48 hours in mild ischemia. The clinical value of this method has to be tested in a clinical study.

Massive doses of methylprednisolone were given to rats subjected to segmental intestinal ischemis. The central and regional blood flows were studied with the microsphere technique. Ischemia was induced by ligating the arteries to 1/4 of the length of the small intestine. In rats subjected to 2 h of segmental intestinal ischemia methylprednisolone seemed to prevent the decrease in blood flow, previously noted in untreated rats, in the regions where the arteries were not occluded. When adequate volume replacement was given in combination with methylprednisolone, the blood flow in the ischemic region showed a slight improvement. The edema in the ischemic segments tended to be less marked in rats treated with methylprednisolone.

Segmental ischemia of the small intestine in the rat was established by ligating the mesenteric arterial end arcades of 1/4 of the length of the small intestine. Regional and central blood flow was measured with the microsphere technique before and 2 h after induction of the ischemia. In one series of rats an i.v. infusion of 16 ml plasma per kg body weight (b.w.) was given during the experimental period, which maintained the central circulation. However, the impairment of blood supply to the whole small intestine caused by the segmental ischemia was not normalized. Two other series of rats were treated with either phenoxybenzamine alone, 3 mg.kg-1 b.w., or the same dosage of phenoxybenzamine plus plasma infusion (16 ml.kg-1 b.w.). The central circulation was deteriorated and the blood flow to the small intestine reduced in the rats receiving phenoxybenzamine alone. Both the central circulation and the blood supply to the non-ischemic parts of the intestine were maintained in rats treated with both phenoxybenzamine and plasma. Combined treatment with phenoxybenzamine and volume replacement thus seems to be valuable for limiting the secondary hemodynamic changes caused by segmental intestinal ischemia.

Factors of decisive importance for the fate of the intestine following circulatory occlusion incluse the bacterial flora of the intestine, intravascular thrombosis peripheral to the level of occlusion, and the capacity of the collateral circulation. Standardized ischaemia of the small intestine was produced in the rat by ligation of a given number of mesentric end arcades. The passive absorption of radioiodide from a defined, central loop within the ischaemic intestinal segment-as an expression of the exchange circulation of the intestinal mucosa-was determined 14 days after induction of the ischaemia. Different forms of treatment were studied. In Sprague-Dawley rats the effect of heparin, oxitetracycline (OCD) and a combination of these two drugs was examined both concerning the survival of the animals and with regard to the available exchange circulation in the mucosa of the ischaemic intestinal segment. The survival frequency was increased in all treatment groups. The exchange circulation in the ischaemic segment was improved significantly by ODC-treatment and by treatment with heparin and ODC combined. Treatment with heparin alone gave no improvement of the mucosal circulation.

Corticosteroid therapy in pharmacological doses has a well documented positive effect in shock caused by severe intestinal ischaemia. In this study the effect of high doses of corticosteroids on the exchange circulation of the mucosa was analysed in varied, regional small bowel ischaemia. Thirty minutes after establishment of moderate ischaemia the exchange circulation in the mucosa of the ischaemic intestinal segment in animals treated with 100 mg/kg hydrocortisone showed no improvement compared with untreated animals. Higher corticosteroid doses impaired the exchange circulation. On analysis 7 days after establishment of the ischaemia, treatment with 100 mg/kg hydrocortisone during the first 3 days was found to have impaired the exchange circulation. The same treatment in rats with more severe intestinal ischaemia gave a greatly increased mortality. Possible reasons for the impaired mucosal circulation following corticosteroid therapy in pharmacological doses in regional small bowel ischaemia are discussed. One possibility is that corticosteroids induce a "steal syndrome" due to the better vasodilative effect on healthy than on ischaemic intestinal tissue.

Radioactive test substances were infused slowly into the duodenum of conscious rats via a permanent catheter starting 2, 12 and 24 h after a standardized laparotomy. Two differently labelled but otherwise identical test substances were used. The first test substance (125I-PVP) was infused for 4 h, the second (131I-PVP) for the remaining 1 h of the 5-hour infusion period. Immediately after the infusion the animals were killed, and the radioactivity emanating from each isotope was recorded from the excised bowel specimen. The bowel length passed by the border zone and the degree of overlap between the labels in this zone were taken as measures of propulsion and mixing, respectively. Propulsion and mixing were uninfluenced by laparotomy as measured 2--17, 12--17 and 24--29 h after laparotomy. The present findings indicate that laparotomy is not followed by a disturbance in the capability of the small bowel to transport and mix chyme, at least when no high demands with respect to chyme volume are required.

Two groups of rats were subjected to a segmental intestinal ischaemia of a degree which, according to earlier investigations with this experimental model, causes secondary impairment of the splanchnic blood flow. Both groups were given plasma and an alpha-adrenergic blocking agent (phenoxybenzamine). They were also given dopamine but in different doses, 12 and 50 micrograms X min-1 X kg-1 b.w., respectively. It was found previously that a normal blood flow in the non-occluded parts of the small intestine could be maintained by phenoxybenzamine or the lower dose of dopamine alone in combination with plasma, but the higher dopamine dose caused vasoconstriction, probably because of an alpha-stimulating effect. The combined treatment with penoxybenzamine and dopamine in the present experiments normalized the intestinal blood flow in the non-occluded parts in both groups, i.e. also in the group treated with the higher dose of dopamine. Moreover, the pancreatic circulation was normalized in both groups. Hence alpha-adrenergic blockade combined with dopamine and plasma administration seems to have a positive effect on the splanchnic circulation during segmental intestinal ischaemia in the rat.

Research in recent years has shown that under certain conditions digitalis has a strong vasoconstrictive effect in the splanchnic region. This may imply that in cases of mesenteric ischaemia, digitalization may inhibit a collateral circulation necessary for restoration of the intestinal function. In this investigation the effect of digitoxin on the exchange circulation of the small bowel mucosa was studied in rats with induced regional ischaemia of the intestine. On analysis 30 min after establishment of the ischaemia a statistically significant negative effect of digitoxin was observed.