Robert Sorenson, PhD

Research Techniques:

Islet cytochemistry; Insulin secretion; Confocal microscopy

Research Instersts:

Sorenson's research focuses on the long term modulating effects of pregnancy on pancreatic islets of Langerhans. Although rapid regulation of insulin secretion by nutrients and hormones has been the focus of considerable research, the examination of long-term modulation of islets has received much less attention. Pregnancy is a normally occurring physiological condition where there is a long term need for increased insulin secretion at normal serum glucose levels. This demand is met by many major alterations in islet structure and function. Among these changes the most important are: (a) an increase in glucose-stimulated insulin secretion (4-10 fold at normal serum glucose concentrations); (b) a lowering of the glucose-stimulation threshold; and (c) increased ß-cell proliferation. Using species specific lactogenic hormones (placental lactogen and prolactin which share a common receptor) Sorenson and his lab have demonstrated that these hormones induce all of the known changes in islets that occur during pregnancy.

Using islets from pregnancy and islets treated with lactogenic hormones in vitro the lab is investigating: (1) The signal transduction pathways used by prolactin receptors in islets. (2) How the lactogen induced changes in gene expression lead to enhanced insulin secretion. (3) How the lactogen induced changes in metabolism lead to enhanced insulin secretion. (4) How lactogens stimulate ß-cell proliferation. (5) The role of lactogens in the development and growth of islets. (6) The glucose dependence of the lactogen induced changes in vivo and how these changes compare with those induced by in vivo glucose infusion. Although mechanisms of lactogen regulation of islets will likely share some features with other prolactin sensitive cells, they will also be very unique as they must include features for affecting the islet specific metabolic sensing system. The Sorenson lab's long term goal is to delineate the mechanisms responsible for the increased islet function observed during pregnancy.

These studies will provide important information on the long term regulation of islet function and ß-cell mass. Understanding the regulation of ß-cell glucose sensitivity has important implications for understanding the progression of events that lead to gestational and type II diabetes. In addition, the studies on regulation of islet ß-cell growth will provide essential information on development of ß-cells and the growth potential of differentiated islet ß-cells.

Development of Histology Teaching Materials:

One of my strategies for teaching is to identify areas where students have problems and develop methods and tools to overcome these issues.  For the Human Histology Course I developed a complete set of previews for the Histology Laboratories and a corresponding Atlas of Human Histology.  The previews and atlas are unique to our collection of tissue specimens.  That is, the atlas is based on the exact same slides that the students study and the images in the atlas show the specimens at several levels of magnification – exactly the way one examines specimens through a microscope.  In this way the atlas guides the students as if they are working one on one with an instructor.

We are fortunate to have an unusually excellent collection of teaching slides that was developed by Dr. Anna Mary Carpenter.  I selected the best individual specimens for high resolution digitization.  These specimens can now be viewed on-line and in much the same way that one would examine a slide through the microscope.  That is, the specimen can be examined at various levels of magnification on a computer screen in the same way that one would examine these slides with a microscope.  With the atlas that corresponds to these slides, one can study histology on the computer monitor just as if one were using a microscope.

1) Sample chapter (Gastro-intestinal System) from the "Atlas of Human Histology: A Guide to Microscopic Structure of Cells, Tissues and Organs" by Robert L. Sorenson. The printed atlas is available from the University of Minnesota Book Store and is the atlas for use with the Virtual Histology Collection of Slides.

2) The Virtual Histology Collection of Human Tissue specimens.  To view samples (Gastro-intestinal System) from the collection, log on to the Virtual Microscope ( http://aperio.ahc.umn.edu )  Username: Virtual, Password: sample.  Username and password are case sensitive.

Selected Publications:

R.L. Sorenson and T.C. Brelje, (2009) Prolactin Receptors are Critical to the Adaptation of Isets to Pregnancy. Endocrinology 150:1566-1569

T.C. Brelje, NV Bhagroo. L.E. Sout and R.L. Sorenson, (2008) Beneficial Effects of Lipids and Prolactin on Insulin Secretion and Beta Cell Proliferation: A Role of Lipids in the Adaptation of Islets in Pregnancy. Journal of Endocrinoloyg 197: 265-276

A.J. Weinhaus, L.E. Stout, N.V. Bhagroo, T. Clark Brelje, R.L. Sorenson, (2007) Regulation of Islet Glucokinase in Pancreatic Islets by Prolactin: A Mechanism for Increasing Glucose-Stimulated Insulin Secretion during Pregnancy. Journal of Endocrinology 193:367-381.

R.L. Sorenson, L.E. Stout, T.C. Brelje, T.L. Jetton and F.M. Matschinsky 2007 Immunohistochemical Evidence for the Presence of Glucokinase in the Gonadotropes and Thyrotropes of the Anterior Pituitary Gland of Rat and Monkey. Journal Histochemistry and Cytochemistry 55:555-566.

R.L. Sorenson, D.G. Garry and T.C. Brelje,  (2006) Structural and Functional Considerations of GABA in Islets of Langerhans:  Beta-cells and Nerves  A Retrospective. In Perspectives in Diabetes, Vol I, ed. R. Paul Robertson.

Sorenson RL, Weinhaus AJ, and Brelje TC (2004) Regulation of Glucokinase as Islets Adapt to Pregnancy in Glucose and Glycemic Diseases: from Basics to Novel Therapeutics (F Matschinsky and M Magnuson eds.) S Karger AG Basel

Brelje TC, Stout LE, Bhagroo NV, and Sorenson RL (2004) Distinctive Roles for Prolactin and Growth hormone in the Acivation of STAT5 in Pancreatic Islets of Langerhans. Endocrinology 145:4162-4175.

Brelje, TC, Svensson AM, Stout LE, Bhagroo NV and Sorenson RL 2002 An Immunohistochemical approach to monitor the prolactin-induced activation of the JAK/Stat5 pathway in pancreatic islets of Langerhans. Journal Histochemistry and Cytochemistry 50:365-383.

Sorenson, R.L., and Brelje, T.C. 2001 Differences in the regulation of pancreatic islets by prolactin, growth hormone and placental lactogen. In Prolactin (ed. Nelson Horseman) Kluwer, Boston. 297-316. Full Text

Brelje, TC, Svensson AM, Stout LE, Bhagroo NV and Sorenson RL 2001 An Immunohistochemical approach to monitor the prolactin-induced activation of the JAK/Stat5 pathway in pancreatic islets of Langerhans. Journal Histochemistry and Cytochemistry

Weinhaus, A.J., Bhagroo, N.V., Brelje, T.C. and Sorenson, R.L. 2000 Dexamethasone counteracts the effect of prolactin on islet function: Implications for islet regulation in late pregnancy. Endocrinology 141:4:1384-1393

Weinhaus, A.J, Bhagroo, N.V., Brelje, T.C. and Sorenson, R.L. 1998 Role of cAMP in Up-Regulation of Insulin Secretion during the Adaptation of Islets of Langerhans to Pregnancy. Diabetes 47:9:1426-1435

Stout, L.E., A.M. Svensson, and R.L. Sorenson 1997 Prolactin regulation of islet-derived INS-1 Cells: Characteristics and immunocytochemical analysis of STAT5 translocation. Endocrinology 138:1592-1603.

Sorenson RL, and Brelje T.C. 1997 Adaptation of islets of Langerhans to pregnancy: B-cell growth, enhanced insulin secretion and the role of lactogenic hormones. Horm. and Metab. Res. 29:5:1-7. Full Text

Brelje, TC, and Sorenson RL 1997 The physiological roles of prolactin, growth hormone, and placental lactogen in the regulation of islet b-cell proliferation. In Pancreas Regeneration (ed. Nora Sarvetnick) Landes Company Biomedical Publishers. pg. 1-23

Weinhaus, A.J., L.E. Stout and R.L. Sorenson 1996 Glucokinase, hexokinase, glucose transporter 2 and glucose metabolism in islets during pregnancy and prolactin treated islets in vitro: Mechanisms for long term up-regulation of islets. Endocrinology 137:1640-1649

 

To view these and other publications visit http://www.ncbi.nlm.nih.gov/PubMed
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