role of arginine-phenylalanine-amide-related peptides in mammalian reproduction

Until 2000 it was believed that gonadotropin-releasing hormone [GnRH] was the sole regulator of hypophyseal gonadotropes. In 2000, the discovery of a gonado-tropin inhibitory hormone [GnlH] initiated a revolution in the field of reproductive physiology. Identification of GnlH homologues in mammals, the arginine-pheny-lalanine-amide [RFamide]-related peptides [RFRPs], indicated a similar function. Subsequently, further works conducted in various laboratories worldwide have shown that these neuropeptides inhibit the hypothalamic-hypophyseal axis. This review discusses the role of RFRPs in mammalian reproductive processes

Increased litter size and suckling intensity stimulate mrna of rfamide-related peptide in rats

RFamide-related peptide-3 [RFRP-3] inhibits gonadotropin releasing hormone [GnRH] and luteinizing hormone [LH] secretion in rats. This study evaluates the effects of litter size and suckling intensity on RFRP mRNA expression in the dorsomedial hypothalamic nucleus [DMH] of rats. A total of 32 pregnant and 4 non-lactating ovariectomized [control group] Sprague-Dawley rats were used in this experimental study. Lactating rats were allotted to 8 equal groups. In 3 groups, the Utter size was adjusted to 5, 10, or 15 pups upon parturition. Dams were allowed to suckle their pups continuously until 8 days postpartum. In the other 3 groups, the litter size was adjusted to 5 pups following birth. These pups were separated from the dams for 6 hours on day 8 postpartum, after which the pups were allowed to suckle for 2.5, 5, or 7.5 minutes prior to killing the dams. In 2 groups, lactating rats with 10 and 15 pups were separated from their pups for 6 hours on day 8 postpartum. In these groups, the pups were allowed to suckle their dams for 5 minutes before the dams were killed. All rats were killed on day 8 postpartum and the DMH was removed from each rat. We evaluated RFRP mRNA expression using real-time polymerase chain reaction [PCR. The expression of RFRP mRNA in the DMH increased with increased litter size and suckling intensity compared to the controls. The effect of suckling intensity on the expression of RFRP mRNA was more pronounced compared to the litter size. Increased litter size and suckling intensity stimulated RFRP mRNA expression in the DMH which might contribute to lactation anestrus in rats

Expression of RFamide-related peptide-3 [RFRP-3] mRNA in dorsomedial hypothalamic nucleus and KiSS-1 mRNA in arcuate nucleus of rat during pregnancy

RFamide-related peptide-3 [RFRP-3] and kisspeptin [KiSS-1] are known to respectively inhibit and stimulate gonadotropin releasing hormone [GnRH] and luteinizing hormone [LH] secretion in rat. The aim of the present study was to evaluate the relative mRNA expression of RFRP-3 and KiSS-1 in the hypothalamus of pregnant rats. In a randomized controlled experimental study, the exact pregnancy day of 18 Sprague-Dawley rats were confirmed using the vaginal smear method and were equally assigned to three groups of days 7, 14 and 21 of pregnancy. Four non-pregnant female rats were ovariectomized and assigned as the control group. All rats were decapitated, and the dorsomedial hypothalamic nucleus [DMH] and the arcuate nucleus [ARC] for detection of KiSS-1 mRNA were separated from their hypothalamus to detect RFRP-3 and KiSS-1 mRNA respectively. Then, their relative expressions were compared between control and pregnant groups using real-time polymerase chain reaction [PCR]. The relative expression of RFRP-3 mRNA in DMH did not change significantly during pregnancy [p>0.01]. However, the relative expression of KiSS-1 mRNA in ARC was at its highest in day 7 of pregnancy and decreased until day 21 of pregnancy [p<0.01]. Decrease in GnRH and LH secretion during the pregnancy of rat may be controlled by constant expression of RFRP-3 mRNA and reduced expression of KiSS-1 mRNA in hypothalamus

Hypothalamic expression of KiSS1 and RFamide-related peptide-3 mRNAs during the estrous cycle of rats

Kisspeptin and RFamide-related peptide-3 [RFRP-3] are known to affect GnRH/luteinizing hormone [LH] in several species, including the rat. It has been hypothesized that GnRH/LH changes during the rat estrous cycle may result from changes in the expression of KiSS1 and RFRP-3 genes. Therefore, the present study investigates KiSS1 and RFRP-3 gene expression at the transcriptional level in the rat hypothalamus during the estrous cycle. In the present experimental study, 36 adult female Sprague-Dawley rats [3-4 months old] were used to study the expression of KiSS1 and RFRP-3 mRNA in the hypothalamus during the estrous cycle. Four rats were ovariectomized, whereas the remainder were allotted to four different phases of the estrous cycle [n=8 per estrus phase]. Rats were decapitated, and the hypothalami were immediately dissected and frozen in liquid nitrogen. Expressions of KiSS1 and RFRP-3 mRNAs were analyzed by real-time PCR. The expression of KiSS1 mRNA during estrus was lower than other phases of the cycle [p<0.01]. Expression of KiSS1 mRNA during the metestrus phase was lower than the proestrus phase [p<0.01]. The expression of RFRP-3 mRNA during proestrus was lower than the diestrus phase [p<0.01]. Results of the present study showed the role of coordinated expression of KiSS1 and RFRP-3 mRNA in the hypothalamus in the control of the rat estrous cycle