Effects of epinephrine, norepinephrine, and dopamine on gonadotropin-releasing hormone-induced secretion of luteinizing hormone in vitro

Recent evidence indicates that catecholamines may directly alter anterior pituitary function. In the present study, an in vitro perifusion system was used to investigate whether catecholamines affect the gonadotrope. Pituitary tissue from castrated ram lambs was incubated in the presence of epinephrine (EPI), norepinephrine (NE), or dopamine (DA). During a 2-h treatment period, neither DA (10(-8) M), NE (10(-7) M), nor EPI (10(-7) - 10(-9) M) significantly affected basal LH secretion. In contrast, the LH response to a subsequent 10(-10) M GnRH challenge was significantly potentiated by NE and EPI. NE increased the amount of LH secreted in response to GnRH 14 +/- 1.1% (P less than 0.01). Likewise, 10(-7), 10(-8), and 10(-9) M EPI resulted in 22 +/- 1.4% (P less than 0.001), 13 +/- 1.2% (P less than 0.001), and 6 +/- 1.3% (P less than 0.03) increases, respectively. The stimulatory effect of 10(-7) M EPI was blocked by pretreatment with propranolol (a beta-adrenergic blocker), but not with phentolamine (an alpha-adrenergic blocker). The beta-adrenergic agonist isoproterenol enhanced GnRH-induced LH secretion 46 +/- 1.5% (P less than 0.001), but had no effect on basal LH release. DA had no effect on LH secretion; however, it inhibited PRL release 24 +/- 0.9% (P less than 0.001). Neither NE, EPI, nor isoproterenol had any effect on PRL secretion. These results suggest that EPI, acting by a beta 2-adrenergic receptor, modulates the pituitary gonadotrope's response to GnRH.