These studies were done in Gwen V. Childs, Ph.D's lab, The University of Texas Medical Branch, Galveston, TX.

Do gonadotropes express growth hormone mRNA (GH mRNA)?

If GH cells retain their phenotype as they express gonadotropin mRNAs, then they may also retain the ability to express GH mRNA.  Thus, we should see expression of GH mRNA by gonadotropes.  This characteristic can be tested by dual labeling for GH mRNA and gonadotropin antigens with in situ hybridization histochemistry followed by immunochemistry.

Ongoing studies show that expression of GH mRNA changes with the stage of the cycle.  It is lowest in GH cells early in the cycle and then begins to rise.  Nearly all of the GH cells express GH mRNA by proestrus.  Also, there is a significant increase in expression of GH mRNA by cells with LH and FSH antigens during this rise.  Counts are continuing to validate the pattern seen in the early experiments.  Thus far, the hypothesis that GH cells retain their phenotype is supported by these data.

The following figures show dual labeling for GH mRNA and GH antigens.  The labeling for GH mRNA is in linear patches or spots distributed in the cytoplasm.  The GH antigen label is pale amber or dense orange.

Labeling for GH mRNA and LH-beta subunits is seen in proestrous rats.  At peak expression in proestrous, as many as 60% of LH cells contain GH mRNA. The arrows show the linear or vacuolar distribution of label for GH mRNA in the gonadotropes. U= unstained cell.

Labeling for GH mRNA and FSH is shown in the next photographs.  Sometimes the labeling appears to circle the nucleus, as if it is focused on mRNA over the nuclear envelope (the outer membrane of the envelope is rough endoplasmic reticulum).  Sometimes the labeling in gonadotropes is polarized and shown in only one pole of the cell.  These photos show examples of these labeling patterns.  The arrows point to the dense gray-black labeling for GH mRNA and the FSH label os orange-amber.

Do gonadotropes from proestrous rats secrete GH?  Do GH cells from proestrous rats secrete gonadotropins?

Stay tuned, this study is just beginning.  We are still completing the study that addresses the previous question.  However, our early evidence shows that a population of nearly pure somatotropes (90% GH cells by immunolabeling) taken from diestrus or proestrous rats will secrete LH or FSH and secretion is stimulated by GnRH.  They store little LH or FSH unless they are stimulated by GnRH.  After stimulation, labeling for LH or FSH appears in cellular processes in the GH cells.  This is depicted in the photograph below: The black label is for FSH antigens and the orange label is for LH antigens.  Most of the label is in cellular processes.

Protocols and related web pages on gonadotropes:

| Affinity Cytochemistry | In situ hybridization histochemistry | Go to Childs Home Page |

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