Submitted to: Reproductive Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2002
Publication Date: 7/1/2002
Citation: Estienne, M.J., Harper, A.F., Knight, J.W., Rampacek, G.B., Barb, C.R. Circulating concentrations of luteinizing hormone, testosterone and growth hormone after naloxone in sexually mature boars. Reproductive Biology. 2002. v. 2. p. 133-142. Interpretive Summary: Luteinizing hormone (LH) secreted from the pituitary gland stimulate testosterone secretion from the testis which is necessary for sexual maturation and maintenance of semen production in the boar. Brain opioid peptides, hormones with morphine like activity, inhibit gonadotropin releasing hormone (GnRH) release, necessary for the release of LH from the pituitary, subsequent reproductive activity in the female pig. It was determined that brain opioid peptides inhibit LH secretion in the sexually mature boar. These results indicate that brain opioid peptides suppress LH secretion in the sexually mature boar.
Technical Abstract: Treatment of gilts and sows with naloxone, an endogenous opioid receptor antagonist, increased LH secretion. The objective of the current study was to determine the effects of naloxone on circulating concentrations of LH and testosterone in sexually mature boars. Five boars averaging 187kg BW and 289 d of age were fitted with indwelling jugular vein catheters. Beginning 24 h after catheterization, blood samples were collected at 15-min intervals for three hours. Two h after initiation of blood sampling, boars received an i.v. challenge of naloxone 1 mg/kg BW (n = 2) or .9% saline (n = 3). Twenty-four h later the experiment was repeated, but boars that previously received naloxone received .9% saline and vice versa. Samples were analyzed for concentrations of LH and testosterone using specific RIA. Prior to i.v. injections, LH serum concentrations were similar between groups. Naloxone increased LH concentrations, with peak values occurring 45 min after treatment. Injection of .9% saline had no effect on LH secretion. Serum testosterone concentrations increased by 1 h after naloxone treatment. Testosterone levels decreased by 1 h after saline injection. These results indicate that endogenous opioid peptides suppress LH secretion in sexually mature boars.