Acute and subacute effects of a synthetic kisspeptin analog, C6, on serum concentrations of luteinizing hormone, follicle stimulating hormone, and testosterone in prepubertal bull calves.
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Kisspeptin (KP) is a neuropeptide integral in regulating puberty and gonadotropin releasing hormone. Compound 6 (C6), a KP analog, is more potent invitro, has a longer half-life, and may have greater therapeutic applications than KP. To determine the acute and subacute effects of KP and C6 on serum concentrations of luteinizing hormone (LH), follicle stimulating hormones (FSH), and testosterone (T), prepubertal bull calves [12.11.1 (SD) weeks of age; 91.210.8kg BW] were assigned to one of three treatment groups [Saline (n=4), KP (n=4; 20 nmoles), or C6 (n=4; 20 nmoles). Treatments were administered intramuscularly once daily for four consecutive days. Blood samples were collected every 15min for 6h immediately following treatment administration on Day 1 (acute) and Day 4 (subacute). Serum concentrations of LH, FSH, and T were determined by radioimmunoassay. For each day, effects of treatment, time, and interactions on LH and FSH concentrations and pulse parameters were analyzed using procedures for repeated measures with JMP Software (SAS Inst. Inc., Cary, NC). There was a treatmenttime interaction during Day 1 (P<0.0001) and Day 4 (P=0.02) such that LH concentrations were greatest following administration of C6 (albeit diminished during Day 4). Number of LH pulses were least (P=0.02) and LH nadirs were highest (P=0.04) following administration of C6 (P=0.02). There was no effect of treatment (P=0.95) or treatmenttime interaction (P=0.10) on serum FSH concentrations during Day 1. During Day 4 FSH concentrations (P=0.02) and number of FSH pulses (P=0.02) were least following administration of C6. There was no effect of treatment (P=0.33), time (P=0.19) or treatmenttime interaction (P=0.44) on T concentrations. In conclusion, acute and subacute C6 increased LH concentrations and subacute C6 decreased FSH concentrations and pulse parameters. Despite suppression of FSH with subacute daily administration of C6, altered frequency and timing of treatment with KP analogs may have application to affect the onset of puberty in livestock.
