[Cytological and immunocytochemical studies of the anterior pituitary gland of the beagle bitch during various reproduction phases].

The changes in anterior pituitary (AP) of pregnant and lactating dogs as compared with pituitary of animals in metestrus-anestrus phase are described with special reference to the relative proportion, topography and morphology of prolactin cells, somatotrophs, corticotrophs, thyrotrophs and gonadotrophs. For demonstration of these cells, suitable histological, histochemical and immunoenzyme cytochemical methods are used. The prolactin cells show progressive hyperplasia during pregnancy, so that at the end of this phase and during lactation, they comprise the most predominant glandular cells in AP. At the same time, they reveal massive hypertrophy with marked morphological features of high secretory activity, After transient or continous interruption of the suckling stimulus they show signs of functional inhibition on involution. The corticotrophs appear at 20. and 30. days of pregnancy to be relatively increased in number. While in the last third of pregnancy and during lactation, they only seem to be more active than those in pituitary of metestrus-anestrus dogs. The somatotrophs appear to be progressively reduced in relative number during pregnancy and lactation. However, they show some morphological signs of active secretion. The thyrotrophs did not show any morphological alterations during the different reproductive phases. The gonadotrophs reveal during pregnancy, especially at 30. day morphological signs of stimulation. On the contrary they appear atrophied during lactation. This may be a result of suckling stimulus and morphological expression of the inverse relationship in the secretion pattern of gonadotrophins and prolactin in dogs during suckling. The estrogen and progesterone levels in plasma as well as the changes in their relative concentrations may largely account for the structural changes on AP of pregnant dogs. However, neuroendocrine reflexes (e.g. suckling stimulus) seem to be of a great importance for the maintainance of stimulation of prolactin cells during lactation.