Interactions between the Central Nervous System and Hormones 



93 



The progestational effects of 17a-hydroxyprogesterone caproate (Delalutin) 

 are particularly long lasting (48). Interestingly enough (Fig. 13) this esterified 

 steroid exerts a diphasic effect on both EEG afterreaction and arousal 

 thresholds and both phases are very much prolonged. By way of contrast 

 the effect on the EEG afterreaction threshold of a single injection of 25 mg 



1.5 



'0.5- 



k EEG AFTERREACTION 



FOLLOWING 25 MG PROGESTERONE 



>6.5V >65V 



D.-.0 



EEG AROUSAL D AND 

 EEG AFTERREACTION ■ 

 FOLLOWING 25 MG OF 

 DELALUTIN 



8 16 24 32 40 48 



TIME IN HOURS AFTER STEROID 



56 



Fig. 13. Prolonged diphasic effect on EEG thresholds of treating an estrogen-primed 

 ovariectomized rabbit with a single injection of 1 7a-hydroxyprogesterone caproate 

 (Delalutin). The figures (5.25 V, >6.5 V) at the upper right refer to oif-limits values of EEG 

 afterreaction thresholds. The time course of changes in EEG afterreaction threshold 

 following a similar dosage of progesterone is included for comparison. 



progesterone is included in Fig. 13. Its phase of elevated threshold is termi- 

 nated long before the completion of the first phase (lowered threshold) 

 following Delalutin. In keeping with the functional concepts relative to these 

 phases expressed above, during the Delalutin-prolonged first phase the rabbit 

 will mate and ovulate; whereas she remains in an anestrous anovulatory 

 condition during the phase of elevated thresholds. 



Of the 19-nor steroid gestagens which have proven such potent inhibitors 

 of ovulation as to receive extended clinical trial as contraceptives, the 

 following have been tested for their effects on the two EEG thresholds: 

 1 7a - ethynyl - 1 9 - nortestosterone (Norlutin), 1 la - ethyl - 1 9 - nortestosterone 

 (Nilevar) and Ha-ethynyl, A^'^°'-estrenolone (norethynodrel, which with 

 added estrogen is known as Enovid). All of these agents affected the two 

 thresholds in the differential manner illustrated in Fig. 14, prepared from 

 norethynodrel data: they left the EEG arousal threshold essentially un- 

 changed but rapidly raised the EEG afterreaction threshold. In confirmation 

 of Pincus et ah (49) we found that the rabbits would readily mate 24 hr after 



