Effect of ACTH 4-10 on copulatory bahavior and on the response for socio-sexual motivation in the female rat.

Female copulatory behavior and the urge of a female rat to seek contact with a sexually active male was studied after treatment with the peptide ACTH 4-10. No effects of this peptide were seen on the copulatory response of ovariectomized females treated with estradiol benzoate (EB) alone or EB and progesterone combined. An increasing barrier technique was used to measure how much of an average stimulus (cresssing an electrified grid) a female was willing to endure to gain contact with sexually active male. It has been shown in previous investigations (15) with ovariectomized rats that after a certain time of adaptation and training in this apparatus the response attained remains at a certain basal level from which it is increased by treatment with EB. Animals treated with ACTH 4-10 during the phase of adaptation and training attained a significantly higher basal response level than controls. This effect was only observed when the peptide treatment covered the period of adaptation and was not seen when the treatment was started after this critical period. The EB-induced response was not influenced by ACTH 4-10 given during the period of adaptation or given in connection with the EB treatment. It is concluded that ACTH 4-10 influenced the acquired response level but had no effect on steroid induced responses, which are probably controlled by more innate mechanisms.