Desmosomes between mammotrophs suggest the existence of a functional syncytium.

Lactotrophs in the adenohypophysis have the apparent inherent capability to produce simultaneous secretion of prolactin from individual cells. There are two possibilities to account for this synchronized, discrete pulsatile secretion: (1) humoral communication, or (2) cell-to-cell syncytial communication. As a first step in examining the second possibility, we searched for ultrastructural evidence of intercellular contacts. The presence of desmosomes, the conventional junctions that serve to anchor adjacent cells, would be the first step in proving contact between homologous cells. In order to increase the observation of desmosomes, the population of lactotrophs in the adenohypophysis was increased by implantation of capsules containing estradiol in male Sprague-Dawley rats. The adenohypophyses were then examined by electron microscopy for indications of these intercellular bridges. Desmosomes were discovered between lactotrophs, indicating that cell-to-cell contact does exist, and suggesting that the desmosome may help the formation of a syncytium among lactotrophs, either directly or indirectly. Since an ectopic pituitary without direct help from the hypothalamus can secrete prolactin in a pulsatile fashion and since there are desmosomes between lactotrophs, it is possible that the synchronized prolactin release occurs through a direct cell-to-cell communication system which is linked by the desmosomes.