CENTRAL CONTROL OF PITUITAR\- SECRETION 



'O33 



posterior pituitary extract (in doses of up to 200 to 

 500 mu of the oxytocic fraction). 



The clearest evidence that the neurohypophysis is 

 normally concerned in labor comes from the experi- 

 ments of Ferguson (99). In a study on rabbits 8 to 

 48 hr. after parturition, he found that dilatation of 

 the body or cervix of the uterus or vagina stimulates a 

 nervous reflex release of oxytocic horiTione and an 

 increase in the contractions of the body of the uterus. 

 This response was abolished by section of the spinal 

 cord or by hypophy.sectomy. On this and other evi- 

 dence Ferguson suggests that the mechanism of 

 parturition involves reflex stimulation of oxytocic 

 secretion, probably in amounts varying with the part 

 of the reproductive canal undergoing dilatation. 

 That oxytocin is secreted during parturition is indi- 

 cated by the observation (142) of a woman still 

 lactating from a previous pregnancy who came into 

 labor. The mammary expulsion of milk was observed 

 to coincide with the labor pains and was duplicated 

 by the injection of pituitrin at the end of the second 

 stage of labor. 



In summary, it is very probable that reflex excita- 

 tion of the neurohypophysis is involved in normal 

 parturition, but it is possible that other factors, such 

 as the motor innervation of the uterus and contrac- 

 tions of the abdominal wall, may compensate for loss 

 of the gland in some cases. 



Oxytocic hormune and sperm transport. There is good 

 e\'idence that in many animals, including the rat, 

 guinea pig, dog, rabbit, sheep and cow, sperm 

 (whether alive or dead) reach the upper end of the 

 uterus within a few minutes from insemination, that 

 is with a speed that cannot be accounted for in terms 

 of sperm motility. Ever since the observations of 

 Heape (172) in 1898, it has been suspected that 

 increased uterine contractions after coitus might 

 facilitate the transport of seminal fluid and the fact 

 that mechanical stimulation of the vulva was found to 

 result in such increased motility of the uterus (172, 

 204) supported this view. Following the observation 

 that electrical stimulation of the supraopticohypoph- 

 ysial tract resulted in a marked uterine response in 

 the estrous rabbit it was suggested (149) that coitus 

 may excite a nervous reflex release of oxytocin with a 

 resultant increase in motility of the uterus. Millar 

 (243) measured the intrauterine pressure in the mare 

 during mating and found that a considerable negative 

 pressure developed and that up to 80 ml of fluid 

 might thereby be sucked into the uterus. Van Demark 

 and his colleagues have studied the problem in cows 

 and found an increa.sed uterine motility following 



mechanical stimulation of the vulva and cervix (334), 

 an increase in uterine tone and contractions when the 

 bull is brought into sight of the cow and a further 

 increase during mating (335), and an increase in 

 intramammary pressure (perhaps a more certain 

 indication of oxytocin release than increased uterine 

 motility) after manipulation of the vulva and cervix 

 uteri (171). In this latter connection it is of interest 

 that coitus excites milk ejection in lactating women 

 (49, 163, 264). 



At the moment the data are suggestive that nervous 

 reflex release of oxytocic hormone plays a role in 

 sperm transport. However, from the fact that concep- 

 tion may occur in the presence of diabetes insipidus it 

 would appear that the neurohypophysis plays only a 

 supporting, rather than an essential, role in this 

 respect, a conclusion similar to that regarding its 

 function during parturition. 



Adrenal Medullary Hormones and Nervous 

 Reflex Activation of Neurohypophysis 



It is well known that the hxpothalamus is inti- 

 mately concerned not only with the release of posterior 

 pituitary hormone or hormones but with the release 

 of the hormones of the adrenal medulla. In recent 

 years it was found by O'Connor & Verney (252) that 

 an increased blood concentration of epinephrine may 

 block the nervous reflex release of antidiuretic hor- 

 mone. Somewhat similar results were obtained by 

 Cross (60, 61) who studied the reflex discharge of 

 oxytocic hormone from the neurohypophysis. Cross 

 found that administration of exogenous epinephrine, 

 or an increase in the blood concentration of adrenal 

 medullary hormones produced by stimulation of the 

 more lateral region of the hypothalamus, might block 

 a refle.xlv e.xcited release of oxytocic hormone and 

 might also block the effect of injected oxytocic hor- 

 mone in producing milk ejection. The fact that emo- 

 tional stress (forcible restraint) frequently resulted in 

 inhibition of the inilk-ejection reflex to suckling but 

 did not affect the response to injection of oxytocic 

 hormone led to the conclusion (61 ), ". . . the main 

 factor in emotional disturbance of the milk-ejection 

 reflex is a partial or complete inhibition of oxytocic 

 release from the posterior pituitary gland." 



These studies demonstrate again the close relation- 

 ship that appears to exist between different emotional 

 states and endocrine activity, and indicate a further in- 

 tegrative function of the hvpothalamus in this respect. 



Further advances in knowledge of the central 



