Immunohistochemical Evidence for the Presence of Glucokinase in the Gonadotropes and Thyrotropes of the Anterior Pituitary Gland of Rat and Monkey

Robert L. Sorenson ¹, Laurence E. Stout ¹, T. Clark Brelje ¹, Thomas L. Jetton ¹ and Franz M. Matschinsky ^1*

¹ Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota (RLS,LES,TCB); Department of Medicine, University of Vermont College of Medicine, Burlington, Vermont (TLJ); and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania (FMM)

^* To whom correspondence should be addressed. E-mail: matsch{at}mail.med.upenn.edu.

Submitted on October 13, 2006
Accepted on 17 January 2007

	Abstract

A recent report provides new evidence for the presence of glucokinase in the anterior pituitary. In the present study immunohistochemistry was used to identity the cells containing glucokinase in the pituitary of rats and monkeys. In rats glucokinase was detected as a generalized cytoplasmic staining in a discrete population of cells in the anterior pituitary. In co-localization experiments the majority of the cells expressing FSH or LH also contained glucokinase. In addition to the gonadotropes, glucokinase was observed in a sub-population of corticotropes and thyrotropes. Glucokinase was not detected in cells expressing growth hormone or prolactin. In monkeys glucokinase was also observed in a discrete population of cells. The intracellular distribution differed from the rat in that glucokinase in most cells was concentrated in a perinuclear location that appeared to be associated with the Golgi apparatus. However, similar to rats the co-localization experiments showed that the majority of the cells expressing FSH or LH also contained glucokinase. In addition to the gonadotropes, glucokinase was observed in a sub-population of corticotropes and thyrotropes. In the monkey only a few cells had generalized cytoplasmic staining for glucokinase. These experiments provide further evidence for the presence of glucokinase in the anterior pituitary. Although some corticotropes and thyrotropes contained glucokinase, the predominant cell type expressing glucokinase were gonadotropes. In view of the generally accepted role of glucokinase as a glucose sensor in a variety of cells including the insulin producing pancreatic beta-cells as the prototypical example, it is hypothesized that hormone synthesis and/or release in pituitary cells containing glucokinase may be directly influenced by blood glucose.

Key Words: glucokinase, gonadotropes, thyrotropes

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