Suppression of luteinizing hormone secretion by atrial and brain natriuretic peptides in ovariectomized rats

Brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) are present in brain regions regulating LH secretion. Similarities in the molecular structure of these peptides suggest similar physiological function within the brain. This study examined the effects of centrally administered BNP and ANP on LH secretion in mature ovariectomized (OVX) rats. Intracerebroventricular (icv) administration of 2 nmol ANP or BNP decreased mean plasma LH concentration and LH pulse amplitude (P less than 0.05 for ANP; P less than 0.01 for BNP; n = 8/group) and frequency (P less than 0.01 for ANP and BNP). LH secretion was not affected by ANP or BNP at a lower concentration (0.2 nmol, icv; P greater than 0.05; n = 8/group). It was concluded that ANP and BNP may be involved in central regulation of LH secretion. Mechanisms possibly involved in suppression of LH secretion by ANP and BNP were also examined. OVX rats were treated with an opioid antagonist, naloxone (0.5 mg, iv), 45, 75, and 105 min after ANP or BNP (2 nmol, icv). Naloxone eliminated suppression of mean plasma LH concentration and LH pulse amplitude by 2 nmol ANP and BNP (P less than 0.05; n = 7/group). OVX rats were treated with a dopamine antagonist, pimozide (0.6 mg/kg, sc), 90 min before treatment with ANP or BNP (2 nmol, icv). Pimozide pretreatment blocked suppression of LH secretion by ANP or BNP (P less than 0.05; n = 9/group). Naloxone alone did not affect LH secretion (P greater than 0.05; n = 5). It was concluded that components of ANP and BNP suppression of LH secretion may depend upon opioid and dopamine activity.