Ultrastructural, Immunocytochemical Study of the LH Secreting Cell of the Rat Anterior Pituitary Gland: Changes Occurring After Ovariectomy12

Abstract

We have correlated changes in rat anterior pituitary gland LH secretion with morphological changes in LH gonadotrophs as a function of time after ovariectomy. We decapitated rats on the early afternoon of proestrus or at 7, 19, 35, or 92 days after ovariectomy. Anterior pituitary gland LH concentration was determined in one-half of each anterior pituitary gland, and LH cells in the other half were stained immunocytochemically with rabbit anti-rat LHβ sera and examined at the ultrastructural level. In the proestrous rat, the shape of the basic LH cell was usually polygonal. The cells contained a single population of granules, usually scattered throughout a homogenous cytoplasm, and a nucleus which was generally ovoid. Golgi complexes were not commonly observed. Anterior pituitary gland LH secretion (synthesis and release) increased progressively as time after ovariectomy increased. Mean anterior pituitary gland LH concentration increased fivefold while serum LH concentration increased 22-fold by 92 days postovariectomy. At 7 and 19 days postovariectomy, the same basic LH cell was present except that the Golgi complexes became enlarged and prominent. In addition, another cell type, not commonly observed in proestrous rats, became more abundant. The cytoplasm of these cells was usually filled with small ovoid vesicles. The vesicles in these cells became larger and more irregular in outline by 35 days postovariectomy and a few signet ring cells were observed at this time. At 92 days postovariectomy, LH cells were nearly equally divided by cytoplasmic type into homogeneous, vesiculated, and signet ring. The cytoplasm surrounding the signet ring was homogeneous or vesiculated. As time after ovariectomy increased, the size of LH cells increased, secretion granules per LH cell profile increased, nuclei became more irregular in shape, and light-dense bodies became more obvious. In all LH cells we observed, the stain was only on the secretion granules and sometimes on the light-dense bodies. We did observe some vesiculated and signet ring cells which did not stain for LH. The results suggest that after ovariectomy in rats 1) an increase in LH concentration in individual cells and an increase in the release rate of LH from these cells is likely; 2) three cytoplasmic types of LH cells become prominent: homogeneous, vesiculated, and signet ring; 3) vesiculated cells arise from homogeneous cells and signet ring cells arise from either homogeneous or vesiculated cells; and 4) caution is warranted in the identification of LH gonadotrophs on the basis of morphological criteria alone.