Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 50, Issue 6 B342-B350, Copyright © 1995 by The Gerontological Society of America
GnRH receptor site increase on the surface of cultured gonadotropes of senescent C57BL/6NNia mice
TA Parkening and D Pal
Department of Anatomy and Neurosciences, University of Texas Medical Branch, Galveston, USA.
Anterior pituitary cells were cultured for 2 days from 6-, 14-, and 23-
25-month-old C57BL/6NNia mice. The cells were then stimulated with one of
three biotinylated GnRHs [biotinyl-Lys6]-[D-Lys6]GnRH, [biotinyl-
Ser4]-[D-Lys6]GnRH, [biotinyl-Ser4]-[D-Trp6, des-Gly10]GnRH) at 4 degrees C
for 1 h. Some of these cells were processed unfixed, attaching
avidin-fluorescein and examined with fluorescent microscopy. Other cells
were fixed and the biotinylated GnRH coupled to avidin-gold (20 nm
particles), which was subsequently silver-enhanced (70 nm particles) and
examined with light and scanning electron microscopy (SEM). To enhance the
location of receptor sites for quantitation, a back-scattering electron
detector was employed with the SEM. Gonadotropes from all three age groups
ranged in size from 3 to 13 microns in diameter. The largest gonadotropes
in each age group displayed the highest number of GnRH receptors, but the
concentration/surface area (microns2) was less than for smaller cells.
Smaller gonadotropes (3-6 microns diameter) from 14- and 23-25-month- old
mice contained more GnRH receptor sites/microns2 (p < .001) than those
from 6-month-old mice; the percentage of these gonadotropes was markedly
higher for 14-(65%) and 25-(52%) versus 6-month-old (5%) mice. The number
of receptor sites in larger gonadotropes (6.1-13 microns diameter) did not
decline with the increasing age of the mouse. Decreased secretory activity
in gonadotropes of 25-month-old mice may result from age-related changes in
pituitary peptide processing or release, but it is not due to a lack of
GnRH receptors or the inability of GnRH to bind to its receptor site.
