Hypothalamic KiSS1/GPR54 Gene Expressions and Luteinizing Hormone Plasma Secretion in Morphine Treated Male Rats

The inhibitory effects of morphine and the stimulatory influence of kisspeptin signaling have been demonstrated on gonadotropin releasing hormone (GnRH)/luteinizing hormone (LH) release. Hypothalamic kisspeptin is involved in relaying the environmental and metabolic information to reproductive axis. In the present study, the role of kisspeptin/ GPR54 signaling system was investigated on relaying the inhibitory influences of morphine on LH hormone secretion.
In this experimental study, 55 wistar male rats weighing 230-250 g were sub-grouped in 11 groups (in each group n=5) receiving saline, kisspeptin (1 nmol), peptide234 (P234, 1 nmol), morphine (5 mg/kg), naloxone (2 mg/kg), kisspeptin/P234, morphine/naloxone, kisspeptin/morphine, kisspeptin/naloxone, P234/morphine or P234/naloxone respectively. Blood samples were collected via tail vein. Mean plasma (LH) concentrations and mean relative KiSS1 or GPR54 mRNA levels were determined by radioimmunoassay (RIA) and real time reverse transcriptase-polymerase chain reaction (RT-PCR), respectivwely.
Morphine significantly decreased mean plasma LH concentration and mean relative KiSS1 gene expression compared to saline; while it did not significantly decrease mean relative GPR54 gene expression compared to saline. Naloxone significant increased mean LH level and mean relative KiSS1 gene expression compared to saline; while it did not significantly increase mean relative GPR54 gene expression compared to saline. Injections of kisspeptin plus morphine significantly increased mean LH concentration compared to saline or morphine, while simultaneous infusions of them significantly declined mean plasma LH level compared to kisspeptin. In kisspeptin/naloxone group mean plasma LH level was significantly increased compared to saline or naloxone. Co-administration of P234/morphine significantly decreased mean LH concentration compared to saline.
Down regulation of KiSS1 gene expression may be partly involved in the mediating the inhibitory effects of morphine on reproductive axis.