[Sensory stimuli in the reproductive function].

Abstract

There is very ancient evidence that sensory systems and specific stimuli affect reproductive functions. Studies of the reproductive cycles and behavior led to the concept that simuli acting through the nervous system could affect the endocrine system. The event which normally induces the milk ejection reflex is stimulation of the teat; however under certain conditions the reflex can be provoked by other sensory stimuli as the sound of other rats nursing their litters. The endocrine mechanisms involved in the termination of pregnancy in rats seem to be essential for the occurrence of parturition, the expression of maternal behavior and lactation. Ovariectomy performed on day 20 of pregnancy impaired parturition, maternal behavior and lactation. Treatment with estrogen permitted normal delivery, maternal response and lactation only when the hormone was injected immediately after ovariectomy. Estrogen administered the day after was not effective. The administration of progesterone to ovariectomized pregnant rats prevented parturition. Maternal behavior did not occur in ovariectomized-progesterone treated rats when delivery was induced by Caesarean section on day 22 of pregnancy. The association of a progesterone decrease and a simultaneous estrogen secretion is an important step for normal parturition, maternal behavior appearance and normal lactation. After parturition a progressive increase in circulating progesterone seems to "adapt" the C.N.S. to the steroid which may modulate the release of prolactin induced by suckling. An acute increase of the progesterone level by s.c. silastic implant or injection during the first 3 or 6 days following parturition impairs the normal growth of the litter probably by impairing milk secretion and milk ejection. Prolactin release was significantly diminished by the progesterone treatment. Pretreatment with an antiestrogen potentiates the inhibitory effect of progesterone on litter growth.(ABSTRACT TRUNCATED AT 250 WORDS)