Rz. Sokol et al., EFFECTS OF LEAD-EXPOSURE ON GNRH AND LH-SECRETION IN MALE RATS - RESPONSE TO CASTRATION AND ALPHA-METHYL-P-TYROSINE (AMPT) CHALLENGE, Reproductive toxicology, 12(3), 1998, pp. 347-355
Animal and clinical studies suggest that lead exposure disrupts the hy
pothalamic-pituitary axis. To define more precisely the toxic action o
f lead on the hypothalamic-pituitary unit, a series of in vivo and in
vitro experiments were performed. The first experiment was designed to
determine whether lead exposure exerts an inhibitory effect on GnRH s
ecretion as reflected by an enhanced inhibitiion of luteinizing hormon
e (LH) secretion in response to the tyrosine hydroxylase inhibitor met
hyl-p-tyrosine (AMPT). In the control animals, the AMPT dose had no si
gnificant effect on LH secretion, whereas LH fell significantly in the
lead-treated animals, In experiments designed to evaluate the effects
of lead exposure on the pattern of pulsatile release of gonadotropins
castrated control and lead-dosed animals were cannulated, and serial
blood sampling was performed. Baseline LH and follicle-stimulating hor
mone values were not statistically different between the control and l
ead-treated group. There were no significant differences noted in puls
atile patterns when the data were analyzed as groups. Pituitary cells
harvested from lead-treated animals released significantly more LH tha
t did the control animals. These data are consistent with the hypothes
is that the signals between the hypothalamus and pituitary gland are d
isrupted by lead exposure in the intact animal. However, the lead-expo
sed castrated rat's hypothalamic-pituitary unit is able to adapt to th
e toxic effects of lead. (C) 1998 Elsevier Science Inc.