Hyperenteroglucagonaemia and small intestinal mucosal growth after colonic perfusion of glucose in rats.

Beside intraluminal factors, humoral agents play an important role in intestinal adaptation. Enteroglucagon, the mucosal concentration of which is maximal in the terminal ileum and colon, is the strongest candidate for the role of small intestinal mucosal growth factor. The present experiment was designed to study the role of colonic enteroglucagon in stimulating mucosal growth in rats with a normal small intestine. After eight days of glucose large bowel perfusion, enteroglucagon plasma concentrations were 120.7 +/- SEM 9.2 pmol/l, versus 60.1 +/- 6.8 in mannitol perfused control rats (p less than 0.001). Gastrin, cholecystokinin, neurotensin, pancreatic glucagon, and insulin plasma concentrations were unchanged. Crypt cell proliferation, measured by the vincristine metaphase arrest technique, increased significantly in the small intestine of glucose perfused animals (p less than 0.005-0.001) in comparison with the controls. This resulted in a greater mucosal mass in both proximal and distal small bowel: mucosal wet weight, DNA, protein and alpha D-glucosidase per unit length intestine were all significantly higher (p less than 0.05-0.001) than in mannitol perfused rats. Our data, therefore, support the hypothesis that enteroglucagon is an enterotrophic factor and stress the possible role of the colon in the regulation of small bowel trophicity.

Influence of somatostatin and bombesin on plasma enteroglucagon and cell proliferation after intestinal resection in the rat.

The possible relationship between enteroglucagon and cellular proliferation in a rat model of intestinal adaptation after suppression and stimulation of enteroglucagon by somatostatin and bombesin has been investigated. Forty eight rats were divided into three groups of 16 animals, each group being further sub-divided into eight animals having intestinal resection and eight having intestinal transection. Group 1 was given somatostatin to suppress enteroglucagon, group 2 was given bombesin to stimulate enteroglucagon and group 3 (control group) had neither peptide. All animals were killed 12 days after operation. Circulating enteroglucagon and crypt cell production rate (CCPR) in the terminal ileum were measured. After administration of somatostatin (group 1) both CCPR and plasma enteroglucagon were lower after resection than controls (group 3) (p less than 0.001). Transected rats receiving somatostatin showed a reduction in both plasma enteroglucagon and CCPR, but only the fall in enteroglucagon was statistically significant (p less than 0.001). Transected rats receiving bombesin (group 2) had raised plasma enteroglucagon and CCPR compared with the control group (group 3) (P less than 0.005) but there was no significant further rise in these already raised parameters in resected animals. This study indicates that cell proliferation in the rat small bowel after surgery can be influenced by regulatory peptides. The changes in enteroglucagon corresponded closely with changes in CCPR, and this peptide remains a favoured candidate for the humorally mediated trophic influence on the small bowel.

Plasma enteroglucagon and CCK levels and cell proliferation in defunctioned small bowel in the rat.

Luminal nutrients exert a powerful trophic effect on small bowel mucosa. Recent evidence suggests that a circulating factor, possibly enteroglucagon, is also growth-promoting. In order to study the isolated effect of nonluminal influences on bowel mucosa, Thiry-Vella fistulae (TVF) were constructed in rats. Circulating enteric hormone concentrations were manipulated by resecting different lengths of remaining gut. Thirty-two male Wistar rats had either 25%, 50%, 75%, or 90% proximal small bowel resection. In each animal the first 25% of resected bowel was exteriorized as a Thiry-Vella fistula. Seven control rats underwent jejunal transection. Twelve days postoperatively the fasted animals were killed, and circulating and tissue concentrations of enteroglucagon and CCK were estimated by radioimmunoassay. Crypt-cell production rate was used as an index of cellular proliferation in the Thiry-Vella fistulae. Proximal small bowel defunctioned in the Thirty-Vella fistulae had a significantly lower crypt-cell production rate and enteroglucagon and CCK content than the equivalent segment in transected rats. Further small bowel resection produced a subsequent increase in circulating enteroglucagon and CCK concentrations, an increase in the Thiry-Vella fistula content of these hormones, and a doubling of the crypt-cell production rate in the Thiry-Vella fistulae. These results show that circulating enteroglucagon and CCK concentrations match closely with enterocyte production even when luminal influences are excluded. It is suggested that circulating factors may play a major role in postresectional ileal hyperplasia. This hyperplasia apparently affects endocrine cells as well as enterocytes.

Pattern of cell proliferation and enteroglucagon response following small bowel resection in the rat.

Gut resection triggers off a complex series of adaptive changes in the remaining bowel. There is evidence that these are partly mediated by hormonal factors and enteroglucagons have been proposed as candidates for this role. It is uncertain, however, whether plasma enteroglucagon concentrations rise quickly enough to be involved in the rapid initial response or are persistent enough for chronic maintenance. Plasma concentrations of enteroglucagon were therefore estimated at varying times following gut resection and related to crypt cell production rate (CCPR), which was used as an index of cellular proliferation. 96 male Wistar rats had either 75% proximal small bowel resection or jejunal transection (controls). Groups of animals were killed at 1.5, 3, 6, 12, 24 and 48 days following operation and the plasma enteroglucagon and CCPR in the terminal ileum were estimated. Both values were markedly elevated at 1.5 days and continued to rise in a very similar manner in the resected group of rats. Gel permeation chromatography on Sephadex G-50 of plasma samples showed that the increase in plasma enteroglucagon was mainly due to an increase in a component of Kav 0.25, of similar molecular size to that of porcine glicentin. Thus the principal form of enteroglucagon, as a possible trophic hormone, does respond sufficiently quickly, and the response is maintained for long enough, to be involved throughout the adaptive process.

The role of pancreatico-biliary secretions in intestinal adaptation after resection, and its relationship to plasma enteroglucagon.

Two groups, each containing 16 male Wistar rats, had either 75 per cent small bowel resection or jejunal transection; 8 animals from each group; had previously been subjected to pancreatico-biliary diversion. All animals were killed 12 days after the operation, plasma enteroglucagon levels were measured and crypt cell production rate (CCPR) at different sites of the remaining small intestine was measured using a metaphase arrest technique with vincristine. In each of the resected groups there was a significant increase in the CCPR and enteroglucagon levels compared with the transected groups. Furthermore it was found that the CCPR and enteroglucagon levels were higher in the resected group without the pancreatico-biliary diversion compared with the resected group with the diversion. This study, although it confirms the importance of pancreatico-biliary secretions in intestinal adaptation, could also indicate that a humoral factor may be important in the control of intestinal cell proliferation. Our findings do not exclude the possibility that enteroglucagon could be a candidate for such a role.

Evidence for a humoral mechanism after small intestinal resection. Exclusion of gastrin but not enteroglucagon.

It is generally agreed that the adaptive response in the residual bowel after major intestinal resection is dependent on luminal nutrition and pancreaticobiliary secretions. Recent evidence, however, suggests that humoral mechanisms, e.g., gastrin or enteroglucagon, may also play a part in this process. A 75% proximal small bowel exclusion was performed in 16 male Wistar rats and the excluded bowel was fashioned into a Thiry-Vella fistula. Half of the animals were allowed food ad libitum, while the rest were fed intravenously. The animals were killed at 12 days, and plasma, gastrin, and enteroglucagon were measured, while cell proliferation was determined by measuring the crypt cell production rate employing a stathmokinetic method using vincristine and crypt microdissection. In addition to these animals, 16 rats had a jejunal transection only, with half of these animals nourished intravenously, while the remainder were allowed food ad libitum. In the Thiry-Vella rats, plasma enteroglucagon was greater with oral feeding (566 +/- 59 pmol/L) than with intravenous feeding (120 +/- 452 pmol/L) (p less than 0.01), but gastrin levels did not differ in the two groups. In the ileum in continuity, crypt cell production rate per hour was greater in the orally fed animals (52 +/- 8) compared with the intravenously fed group (18 +/- 5) (p less than 0.001). In the excluded fistula, crypt cell production rate per hour was reduced by 23.8 +/- 2 in orally fed rats, but this was greater than in the intravenously fed group (16 +/- 1.5) (p less than 0.01). Both orally and intravenously fed transected rats had significantly lower plasma hormone levels, and reduced crypt cell production rate compared with the respective Thiry-Vella groups. This study suggests a distinct role for a humoral agent responsible for the proliferative changes seen after small bowel resection, and in this respect enteroglucagon appears more relevant than gastrin.

Cell proliferation, plasma enteroglucagon and plasma gastrin levels in starved and refed rats.

The effects of starvation and refeeding on intestinal cell proliferation at several sites of the rat gastrointestinal tract were studied and used as a model of altered cell proliferation in order to investigate the relationship between the rate of cell production and plasma gastrin and enteroglucagon. There was a marked fall in crypt cell production rate after four days starvation, with the proximal sites of the gut being most affected. The response to refeeding varied with site, suggesting that there was more than one mechanism for the control of intestinal cell proliferation. Plasma gastrin and enteroglucagon both fell to one fifth of their control level after starvation. Plasma gastrin increased slowly after refeeding, whilst plasma enteroglucagon increased rapidly to values significantly above control. Plasma gastrin was only correlated with crypt cell production in the duodenum, while plasma enteroglucagon was correlated with crypt cell production rate at several sites, indicating that enteroglucagon may be involved in the control of intestinal cell production.

The effect of altered luminal nutrition on cellular proliferation and plasma concentrations of enteroglucagon and gastrin after small bowel resection in the rat.

Luminal nutrition is known to have a trophic effect on small bowel mucosa after intestinal resection. Humoral agents, however, may also contribute to this process. Two of the proposed humoral agents, enteroglucagon and gastrin, were therefore investigated after intestinal resection and transection in the rat, and changes in their concentration in the plasma were related to cellular proliferation. Forty-eight male Wistar rats had either 75 per cent proximal small bowel resection or jejunal transection. The animals were further divided into three groups, each with a different nutritional intake. The first group were allowed food ad libitum. The second group were kept under hypothermic conditions which resulted in hyperphagia, while the last group were nourished intravenously. A further 8 animals had a laparotomy only (sham operation). All animals were killed 12 days after operation, plasma enteroglucagon and gastrin were measured, while determination of the crypt cell production rate (CCPR) was used to denote cellular proliferation. In each group resected rats had significantly higher crypt cell production rates and greater enteroglucagon levels compared with transected animals. However, only in the normally fed group was plasma gastrin increased in resected animals, there being no significant difference in the plasma concentration of this peptide in transected compared with resected rats, in both the intravenously fed and hyperphagic groups. In the models studied enteroglucagon appears to be a more likely candidate for a humoral trophic agent than gastrin in intestinal adaptation.