NEUROSECRETION 



1055 



^'H-M'^ 



FIG. 23. Portal vessels iVP) in the wall of the infundibulum in close relationship to neurosecre- 

 tory fibers {.VS) of the supraopticohypophyseal tract of the dog. The pars distalis iPD) is shown be- 

 low. [From Scharrer (284).] 



FIG. 24. Neurosecretory a-cells from the brain of Lumbrkus terreslris. Centrally the two cells appear 

 vacuolar while those at the lower right are full of neurosecretory material. Azan stain. [From Hubl 

 (176).] 



logically (193, 264), while neurosecretory-like mate- 

 rial has been found in the cells of the pars tuberalis 

 (193, 197, 224). A basic requirement for such hypo- 

 thalamic control of adenohypophyseal function is that 

 the direction of blood flow in the portal vessels be 

 from the hypothalamus to the pituitary. This has 

 been shown by direct observations of the portal 

 vessels of various amphibia (133), the rat (135, 342) 

 and the dog (178, 327). 



Several investigations (35, 264) have shown that 

 stressful conditions produced marked morphological 

 changes in the neurosecretory system. It has further 

 been shown that the release of ACTH is dependent 

 upon the integrity of the supraopticohypophyseal 

 tract as far as the median eminence, while the subse- 

 quent course of this pathway from the infundibulum 

 into the posterior lobe is not necessary for ACTH 

 secretion (209). Suomalainen (320) believes that the 

 seasonal variation in activity in the hypothalamic 

 pituitary system in the hedgehog is related partly to 

 varying ACTH need. Kovacs and co-workers (188), 

 however, feel that no relationship exists between 

 hypothalamic nuclei and ACTH control. ACTH 



release is evoked only by high do.ses of posterior lobe 

 extracts (298). Posterior lobe hormones can release 

 ACTH from pituitary glands transplanted to the 

 anterior chamber of the eye (213). Pituitary portal 

 blood collected from the dog is capable of stimulating 

 increased ACTH secretion in the rat (256). Attempts 

 to isolate the active hypothalamic principle collected 

 in such portal blood suggest that it is a high molecular 

 weight protein similar but not identical to vasopressin 



(257)- 



Cultures of anterior lobe tissue which lose their 

 ACTH activity in several days can be stimulated to 

 renewed ACTH secretion by the addition of hypo- 

 thalamic extracts (140). The active hypothalamic 

 principle is not histamine, acetylcholine, epinephrine, 

 norepinephrine, 5-hydroxytryptamine, oxytocin or 

 vasopressor substance. An ACTH-stimulating factor 

 has been isolated from posterior lobe extracts and 

 shown by paper chromatographic inethods to be 

 distinctly different from vasopressin or oxytocin (269). 

 This ACTH-stimulating factor has peptide properdes 

 and occurs as a contaminent of vasopressin. These 

 observations explain the high doses of posterior lobe 



