70 G. W. Harris 



Four days later half-hourly blood samples (0.5 ml each) were taken from 

 the marginal vein of the ear for 6-8 hr, during which time the infusion of the 

 various extracts or solutions was made either into the pituitary (at the above 

 rate) or intravenously (at a rate of 2.1 ml/hr) for 2 hr. Two days later the 

 animals were killed and the ovaries inspected under a binocular microscope. 

 If any sign of follicular activation was observed, serial sections were made of 

 the ovaries and histological studies carried out. 



Since ovulation is said to occur "spontaneously" in the occasional female 

 rabbit, it is necessary to know the frequency with which this happens in any 

 particular colony. In thirty-one normal, isolated Chinchilla rabbits from the 

 present stock, killed for various reasons, corpora lutea of various ages were 

 found in the ovaries of three. In a previous study, in which various adrenalin 

 and noradrenalin solutions were infused under ether anesthesia into the 

 anterior pituitary gland, Donovan and Harris (19) found three out of thirty- 

 eight isolated Chinchilla rabbits had ovulated. For control purposes then, 

 one out of about eleven rabbits could be expected to show corpora lutea in 

 the ovaries. But since freshly ruptured follicles are distinguishable from 

 mature corpora lutea the experimental error would be less than indicated 

 by these figures. 



Infusion of median eminence extract in various doses into the pituitary 

 gland resulted in ovulation in nine out of sixteen rabbits. In three cases, 

 fresh cystic and hemorrhagic follicles were found in the ovaries, though no 

 ruptured follicles were present. 



Following infusion of extracts of the cerebral cortex, hypothalamus or 

 solvent only, into the pituitary gland only one animal out of thirteen rabbits 

 was found to have ovulated. 



Infusion of median eminence extract intravenously, in doses greater than 

 those given (ranging up to x 20) in the pituitary resulted, in ovulation in 

 three out of seventeen rabbits. 



The following conclusions may be tentatively put forward: 



(1) Infusion of extracts of median eminence tissue directly into the anterior 

 pituitary gland results in an increased blood level of LH, and so 

 ovulation. 



(2) It is unlikely that this result can be explained in terms of damage to 

 anterior pituitary tissue, since control infusions of hypothalamic 

 extract, cerebral cortical extract or solvent only did not produce a 

 similar result. 



(3) It is unlikely that the effect is due to gonadotropic material in the 

 median eminence extract, since intravenous infusion did not evoke 

 comparable results. 



(4) It is probable that there is some substance in extracts of the median 

 eminence which is active in causing discharge of LH from anterior 

 pituitary cells. 



