Islet cell growth and function. A reappraisal of the role of progesterone and prednisolone

Glucocorticoid administration and brief occlusion of the main pancreatic duct are likely to increase islet mass by a similar mechanism

OBJECTIVES

Both glucocorticoid (GC) administration and brief occlusion of the main pancreatic duct result in an increase in total islet mass. Consequently, it was questioned whether these 2 stimuli would produce similar islet growth, indicating commonality in the mechanism of expansion. To test this, we assessed the effects on morphology after single and dual stimulation of the pancreas.

METHODS

Rat pancreata were harvested 56 days after (1) brief occlusion of the main pancreatic duct, (2) daily GC administration, (3) GC administration and brief occlusion, or (4) sham operation without GC administration or occlusion. The pancreata were weighed, fixed, wax embedded, and sectioned for morphologic analysis. The endocrine to exocrine ratio, endocrine mass, and the contribution that small, medium, and large islets made to increased pancreatic endocrine mass were assessed. Blood was taken immediately before termination, after overnight fasting, for analysis of serum glucose, amylase, and insulin.

RESULTS

GC treatment resulted in increased total pancreatic mass and exocrine mass, which were dissimilar to increases elicited by brief occlusion. However, there was no significant difference in the increase in the total endocrine mass or the increased mass of small, medium, or large islets between the GC, occluded, and dually stimulated pancreata. There were also no significant differences in the mean number of cells per islet between these groups. GC administration increased both circulating glucose and insulin in both occluded and nonoccluded groups, whereas occlusion alone had no effect on these parameters.

CONCLUSIONS

Glucocorticoid administration and brief occlusion of the main pancreatic duct result in a similar expansion of islet mass. This is reflected in nonsignificant increases in endocrine mass/body weight and the percentage contribution of small, medium, and large islets to this increase. The majority of additional islet mass is from the expansion of the large islet population, although extra large islets are not found after either pancreatic treatment. The effects of GC treatment and occlusion are not additive, indicating that there is commonality in the mechanism of expansion. Because occlusion does not result in elevated glucose or insulin levels and gives rise to increased islet mass equivalent to GC administration and dual stimulation, it is unlikely that the increased islet mass after GC treatment is caused by the accompanying hyperinsulinemia as previously hypothesized.

Stimulated endocrine cell proliferation and differentiation in transplanted human pancreatic islets: effects of the ob gene and compensatory growth of the implantation organ

Neogenesis is crucial for the maintenance of beta-cell mass in the human pancreas and possibly for the outcome of clinical islet transplantation. To date, no studies have reported a stimulation of human beta-cell neogenesis in vivo. Therefore, we investigated whether human alpha-, beta-, and duct cell growth can be stimulated when human islets are xenotransplanted to obese hyperglycemic-hyperinsulinemic ob/ob mice immunosuppressed with anti-lymphocyte serum. Moreover, we wanted to study whether beta-cell growth and duct-to-beta-cell differentiation were induced in the hepatocyte growth factor (HGF)-dependent compensatory kidney growth model. For that purpose, we evaluated human islets grafted to nude (nu/nu) mice before uninephrectomy of the contralateral kidney for DNA-synthesis and duct cell expression of the beta-cell-specific transcription factor Nkx 6.1 as an estimate of differentiation. Human islet grafts were well preserved after 2 weeks when transplanted to ob/ob mice during anti-lymphocyte immunosuppression. Both human beta-cells (P < 0.01) and duct cells (P < 0.001) were growth stimulated when islets were transplanted to ob/ob mice. We also observed a correlation between increased duct cell proliferation and increased organ donor age (P = 0.02). Moreover, duct (P < 0.05) and beta-cell (P < 0.05) proliferation, as well as duct cell Nkx 6.1 expression (P < 0.05), were enhanced by the compensatory kidney growth after uninephrectomy. We conclude that it is possible to stimulate human beta-cell neogenesis in vivo, provided that the recipient carries certain growth-stimulatory traits. Furthermore, it seems that duct cell proliferation increases with increasing organ donor age. Altogether, these data and previous results from our laboratory suggest that human beta-cell neogenesis becomes more dependent on differentiation and less dependent on proliferation with increasing age.