A whole range of fine structural criteria for immunohistochemically identified LH cells in rats.

Pituitaries from normal, young and adult male rats were fixed either in sublimate-formalin or in glutaraldehyde-osmium. In adjacent Paraplast sections, almost all the gonadotrophs were immunostained with both LH and FSH antisera. The rat LH beta and FSH antisera used were shown to be highly specific by the absorption test and by double antibody radioimmunoassay. Thin and thick adjacent Epon sections were prepared for EM and immunohistochemical examination. Cells stained with the rat LH beta antiserum were identified by LM, and the observed in detail by EM. On the basis of these observations we suggest that the LH cells are arranged in a sequence of basophils, i.e., Types II/III, III, III/IV and IV: Type II/III basophils are elongate with a cytoplasmic process and less vesiculated. They have morphological features of Type II (classical thyrotrophs) and also of Type III basophils. Type III basophils are oval in shape and moderately vesiculated. Both Types II/III and III basophils can be divided into two classes of cell characterized mainly by the existence of only small secretory granules (150-220 nm in diameter) (Type A) or by the coexistence of small and large (350-500 nm) (Type B). Type III/IV basophils are cells intermediate between types III and IV basophils, and moderately vesiculated with an abundance of secretory granules (150-300 nm in diameter). Type IV basophils are large, spherical or oval cells whose RER cisternae are conspicuously dilated; they contain less numerous secretory granules (150-300 nm in diameter). It is concluded that LH cells are not a single cell type, but include a wide range of subtypes.