Morphometric study of immunoreactive GH-cells of the adenohypophysis of rats treated with Met-enkephalin.

Morphological and morphometric changes were found in adenohypophyseal GH immunoreactive cells after intraventricular administration of Met-enkephalin to adult rats of both sexes. Morphologically, following Met-enkephalin treatment, the males showed cells stained intensely and homogeneously in their cytoplasm, while the females showed cells with a weaker degree of staining and a cytoplasm with a granular aspect; previous administration of naloxone prevented the changes observed in the males and intensified the reaction in the females. Morphometrically, in all the groups of animals studied, the males showed a greater cellular area than the females, accompanied by a decrease in the cytoplasmic area but without significant differences in the nuclear area. Met-enkephalin in both sexes produced an increase in cellular area, accompanied by a significant increase in the cytoplasmic area and, although less manifest, in the nuclear area. Neither kind of change appeared when naloxone was administered prior to Met-enkephalin treatment.