Effect of nitrous oxide on the concentrations of opioid peptides, substance P, and LHRH in the brain and beta-endorphin in the pituitary.

Many studies have indicated that nitrous oxide (N2O) exposure results in specific effects on the reproductive system, some of which are antigonadotropic. The neurochemical events regulating the pituitary-gonadal axis are probably influenced by N2O, but precise documentation is lacking. The effects of exposure to 30% N2O in air on the brain tissue concentrations of luteinizing hormone releasing hormone (LHRH), substance P (SP), met-enkephalin, and beta-endorphin and on beta-endorphin concentrations of the pituitary gland are described in this study. Female rats were exposed to either N2O or air for 8 hr a day over one estrous cycle, and the brain and pituitary tissues were collected and processed. Neuropeptide concentrations were measured by specific radioimmunoassays. Exposure to N2O resulted in significant elevation of LHRH in the preoptic area, with a concomitant decrease in SP. The SP concentration of the medial basal hypothalamus was significantly elevated in N2O-exposed animals. Exposure to N2O resulted in significant increases in met-enkephalin in the brainstem area and beta-endorphin in the pituitary. These results suggest that exposure to N2O alters the interactive neural system activity regulating gonadotropin secretion from the pituitary. The significance of increased met-enkephalin in the brainstem of N2O-exposed animals is not known.