Ovulation in the Domestic Fowl 147 



Stimulation was estimated to vary from about 26 min to 2.5 hr. van Tienhoven 

 believed his results to indicate a concurrent stimulation and release of LH 

 from the hen's pituitary, 



Oviducal Suppression of 01 H Release 



Huston and Nalbandov (35) reported that interposition of various obstruc- 

 tions, or even of a surgical thread, in the lower magnum of the hen's oviduct 

 interrupted ovulation without signs of other hormonal disruption. The combs 

 of all hens remained throughout the period of observation like those of 

 normally laying hens, betokening the continued secretion of estrogen and 

 thus of some LH secretion. Upon sacrifice of hens carrying such irritants for 

 as long as 20 days the ovary was found to bear a practically normal comple- 

 ment of follicles, with little or no evidence either of follicular overgrowth or 

 of atresia. No recently ruptured follicles were seen, thus disposing of possible 

 failure of the oviduct to engulf yolks from otherwise undetected ovulations. 

 The oviduct itself was equal in size to that of normally laying hens, indicating 

 the continued secretion of estrogen. In other hens, the injection of LH or of 

 progesterone was followed by ovulation and lay of normal eggs. 



These observations were confirmed and extended by van Tienhoven (63), 

 who noted an increasing effectiveness of thread loops in the magnum with 

 increasing distance from the infundibulum, and more regular suppression 

 of ovulation by loops placed in the isthmus. Loops similarly placed in the 

 uterus, where the shell of the egg is deposited, were without eflFect on the 

 course of ovulation. 



Huston and Nalbandov (35) believed the oviducal irritant to operate over 

 neurogenic pathways to block the usual activation of the pituitary for release 

 of OIH (or LH). Since either LH or progesterone will induce ovulation of 

 the mature follicle or follicles, the induced condition is apparently comparable 

 with that existing during the period of lapse, and nervous blockade of the 

 usual stimulus for OIH release might reasonably be postulated. The mechan- 

 ism by which such a blockade might be accomplished in the experimental 

 birds and the possible role of the oviducal egg will be discussed later. 



Brain Lesions and Injections 



The effects of electrolytic lesions in the hypothalamus have recently been 

 investigated in the normally ovulating hen (48). Exploratory experiments 

 soon indicated that lesions in a medial region in the ventral preoptic hypo- 

 thalamus caused an immediate and prolonged interruption of ovulation. 

 Lesions elsewhere in the hypothalamus also, as a rule, interrupted ovulation, 

 but not regularly nor immediately, nor generally for more than about 15 days. 

 Subsequently, lesions in the median eminence were often found to be effective 

 in the immediate interruption of ovulation, but this region was not adequately 

 investigated. 



