NEUROENDOCRINE REGULATION OF POSTPARTUM ANESTROUS IN EWES

Abstract

In order to analyze and discuss the neuroendocrine events implied in postpartum anestrous in the ewe, the present review was made. In mammals, during the phase subsequent to the birth, an anovulatory period known as postpartum anestrous exist, evolutionary strategy that assures the survival of the lamb through an increased attention from the mother. In the ewe the presence of the lamb delays the resumption of the ovulatory activity and its partial or total separation advances first estrus and postpartum ovulation. The endogenous opioids peptides (POEs) are neurotransmitters released at central level in acute or chronic form during periods of alert, stress and during the lactation in females; they are implicated in neuroendocrine mechanism that prevents the postpartum ovulation during this period, act as intermediaries between estradiol (E2) and the producing neurons of gonadotropin releasing hormone (GnRH), diminishing its frequency of the pulses and those of luteinizing hormone (LH). The POEs are synthesized in frontal and intermediate lobes of hypofisis and in the A12 hypothalamic nucleus. In ewes it is not clear if the suckling encourages the inhibitory effect of POEs. The sites of action of this neurotransmitter, in relation to reproduction are the preoptical area (APO), median eminence (EM) and ventromedial nucleus (NVM). It has not been yet determined if the gamma aminobutyric acid (GABA) or the dopamine participates in this physiological event.