Effects of luteinizing hormone releasing hormone on the gonadotrophs of hypogonadal (hpg) mice.

Hypogonadal (hpg) mice lack hypothalamic luteinizing hormone releasing hormone (LH-RH); consequently the pituitary gonadotrophs, though differentiated, remain inactive. The acute and chronic responses of gonadotrophs in hpg mice to LH-RH to male hpg mice produced an eightfold increase in plasma LH after 5 min, but granule depletion was not detectable ultrastructurally. Vacuoles (300-600 nm) were present more frequently in gonadotrophs from hpg mice given LH-RH compared with control mice. Daily s.c. administration of 2 micrograms LH-RH to male hpg mice for 20 days stimulated a 63-fold increase in the pituitary content of FSH but only a twofold increase in the pituitary content of LH. Testicular weight increased fivefold but the weight of the seminal vesicles did not change. The frequency of cells immunoreactive for LH increased (x 1.6), the gonadotrophs hypertrophied (x 1.9) and the cell content of granules increased (x 2.3) to values close to the normal range. The rough endoplasmic reticulum and Golgi apparatus became more prominent. A striking result of long-term daily administration of LH-RH was the accumulation of large (1-2 micrometers) lipid droplets in about 40% of gonadotrophs. All these changes induced by LH-RH regressed towards the untreated hpg state when LH-RH administration wad discontinued for 5 and 10 days. These results show that the gonadotrophs of hpg mice can be stimulated trophically by LH-RH, and that long-term administration stimulates the synthesis and release of the gonadotrophins but the effect on FSH is much greater than on LH.