Goodman R L
Department of Physiology, West Virginia University, Morgantown.
Neuroendocrinology. 1989 Oct;50(4):406-12. doi: 10.1159/000125256.
Both dopaminergic (DA) and noradrenergic (NA) neural systems contribute to the suppression of luteinizing hormone (LH) pulse frequency in intact anestrous ewes. In this study, we explored the functional relationship between these two inhibitory neural systems by determining if DA or NA antagonists could block the inhibitory actions of DA and NA agonists in ovariectomized anestrous ewes. If these systems are linked 'in series' with one (e.g. NA) exerting its effects by stimulating the other (e.g. DA), then one antagonist (e.g. DA) should block the inhibitory actions of both agonists. If they are organized 'in parallel', then each antagonist should only block the actions of the homologous agonist. In the first experiment, the DA agonist, apomorphine, suppressed LH pulse frequency and this action was blocked by the DA antagonist, pimozide, but not by the NA antagonist, phenoxybenzamine. Similarly, in experiment 2, the ability of the NA agonist, clonidine, to suppress LH pulse frequency was blocked by the NA antagonist. However, the DA antagonist also partially blocked the inhibitory effects of this NA agonist. We next repeated experiment 2 using a lower dose of the NA agonist. The lower dose of clonidine again inhibited LH pulse frequency and this effect was completely blocked by the DA antagonist. These results suggest that the NA agonist suppressed LH pulse frequency by stimulating a set of inhibitory DA neurons and are thus compatible with the hypothesis that the catecholaminergic neurons controlling LH secretion in anestrous ewes are organized 'in series' with the NA neurons stimulating a DA neural system that directly suppresses GnRH release.
多巴胺能（DA）和去甲肾上腺素能（NA）神经系统均有助于抑制完整的处于乏情期母羊的促黄体生成素（LH）脉冲频率。在本研究中，我们通过确定DA或NA拮抗剂是否能阻断DA和NA激动剂对去卵巢乏情期母羊的抑制作用，来探究这两种抑制性神经系统之间的功能关系。如果这些系统“串联”连接，即其中一个（如NA）通过刺激另一个（如DA）发挥作用，那么一种拮抗剂（如DA）应能阻断两种激动剂的抑制作用。如果它们“并联”组织，那么每种拮抗剂应仅能阻断同源激动剂的作用。在第一个实验中，DA激动剂阿扑吗啡抑制了LH脉冲频率，且这种作用被DA拮抗剂匹莫齐特阻断，但未被NA拮抗剂酚苄明阻断。同样，在实验2中，NA激动剂可乐定抑制LH脉冲频率的能力被NA拮抗剂阻断。然而，DA拮抗剂也部分阻断了这种NA激动剂的抑制作用。接下来我们使用较低剂量的NA激动剂重复实验2。较低剂量的可乐定再次抑制了LH脉冲频率，且这种作用被DA拮抗剂完全阻断。这些结果表明，NA激动剂通过刺激一组抑制性DA神经元来抑制LH脉冲频率，因此与以下假设相符：在乏情期母羊中，控制LH分泌的儿茶酚胺能神经元与刺激直接抑制促性腺激素释放激素（GnRH）释放的DA神经系统的NA神经元“串联”组织。
