Demarest K T, Moore K E, Riegle G D
Endocrinology. 1985 Apr;116(4):1316-23. doi: 10.1210/endo-116-4-1316.
In male rats the concentrations of dopamine (DA) in the adenohypophysis and of PRL in serum increase progressively with age. The increase in the DA content is not a consequence of reduced metabolism of DA, since the activities of the enzymes that deaminate (monoamine oxidase) and O-methylate (catechol-O-methyltransferase) this amine are not reduced in the anterior pituitary of aged male rats; indeed, both type A and B monoamine oxidase activities are increased in the pituitaries of aged rats. The increased DA present in the aged adenohypophysis is not in a static pool but, as in young rats, is rapidly decreased by pharmacological treatments that reduce the activity of tuberoinfundibular DA neurons (gamma-butyrolactone), reduce the synthesis of DA in these neurons (alpha-methyltyrosine), or block DA receptors (haloperidol) in the adenohypophysis. All of these treatments increased serum PRL levels and reduced DA concentrations in the adenohypophysis of both young and aged rats. Similarly, in female rats, where age-related differences in BW and body composition are minimized, serum PRL concentrations and DA concentrations in the adenohypophysis of both young and aged rats changed in the same way after the administration of a DA agonist (apomorphine) or a DA antagonist (haloperidol). Apomorphine reversed the alpha-methyltyrosine-induced increase in serum PRL concentrations and the decrease in anterior pituitary DA content in both young and aged rats, although the latter animals appear to be more responsive to this drug. Similarly, aged rats were more sensitive to the increase in serum PRL concentrations and the decrease in anterior pituitary DA content caused by haloperidol. The actions of acute and chronically administered haloperidol are reversible, with the reduced DA content of the adenohypophysis and the elevated serum concentrations of PRL returning to respective pretreatment levels in both young and aged rats once treatment stops. The time course for recovery of serum PRL levels and anterior pituitary DA contents after both the acute and chronic haloperidol treatment is of longer duration in the aged rat, which is consistent with a decreased rate of clearance of haloperidol in these animals. Twelve daily injections of bromocriptine, a DA agonist, reduced serum PRL and anterior pituitary DA concentrations in both young and aged rats, and these effects persisted for up to 7 days after the injections were stopped.(ABSTRACT TRUNCATED AT 400 WORDS)
在雄性大鼠中，腺垂体中多巴胺（DA）的浓度以及血清中催乳素（PRL）的浓度会随着年龄的增长而逐渐升高。DA含量的增加并非DA代谢减少的结果，因为在老年雄性大鼠的垂体前叶中，使该胺脱氨基（单胺氧化酶）和O - 甲基化（儿茶酚 - O - 甲基转移酶）的酶活性并未降低；实际上，老年大鼠垂体中A 型和B型单胺氧化酶的活性均有所增加。老年腺垂体中增加的DA并非处于静态池，而是与年轻大鼠一样，通过降低结节漏斗部DA神经元活性（γ - 丁内酯）、减少这些神经元中DA合成（α - 甲基酪氨酸）或阻断腺垂体中的DA受体（氟哌啶醇）的药理处理，DA会迅速减少。所有这些处理均会提高年轻和老年大鼠血清PRL水平，并降低腺垂体中的DA浓度。同样，在雌性大鼠中，体重和身体组成的年龄相关差异被最小化，在给予DA激动剂（阿扑吗啡）或DA拮抗剂（氟哌啶醇）后，年轻和老年大鼠腺垂体中的血清PRL浓度和DA浓度变化方式相同。阿扑吗啡可逆转α - 甲基酪氨酸诱导的年轻和老年大鼠血清PRL浓度升高以及垂体前叶DA含量降低的情况，尽管老年动物似乎对这种药物更敏感。同样，老年大鼠对氟哌啶醇引起的血清PRL浓度升高和垂体前叶DA含量降低更为敏感。急性和长期给予氟哌啶醇的作用是可逆的，一旦停止治疗，年轻和老年大鼠腺垂体中降低的DA含量以及升高的血清PRL浓度都会恢复到各自的预处理水平。在老年大鼠中，急性和慢性氟哌啶醇治疗后血清PRL水平和垂体前叶DA含量恢复的时间进程更长，这与这些动物中氟哌啶醇清除率降低一致。连续12天注射DA激动剂溴隐亭可降低年轻和老年大鼠的血清PRL和垂体前叶DA浓度，并且这些作用在注射停止后可持续长达7天。（摘要截断于400字）
