The mode of secretion in the anterior pituitary gland of the cow and the ewe.
In the present study of the bovine and ovine pars distalis adenohypophysis another secretion mechanism besides the well established exocytosis is described. Within cellular accumulations surrounded by a sparse connective tissue the process of secretion seems to be induced by fusion of the glandular cells. The direct passage of glandular cell material out of these syncytia into the adjacent sinusoidal capillaries is demonstrated in light and electron microscopic photographs. This secretion mechanism must be considered to be holocrine in nature, because the nuclei of the glandular cells are also found to pass directly into the blood vessels. The question concerning the replacement of the glandular cells, however, could not be finally clarified. The significance of the holocrine secretion in the adenohypophysis might be seen in the maintenance of a certain base-line secretion, while the fine hormonal regulation presumably is controlled by exocytosis, with the release of individual hormones being receptor mediated.
Schwarz
R
R
Anatomisches Institut, Tierärztlichen Hochschule Hannover, FRG.
Fath el-Bab
M R
MR
Peukert-Adam
I
I
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D005260:Female; D008854:Microscopy, Electron; D010903:Pituitary Gland, Anterior / Q000378:metabolism* / Q000648:ultrastructure; D012756:Sheep / Q000378:metabolism*