Byrnes E M, Bridges R S
Department of Biomedical Sciences, Tufts University, Cummings School of Veterinary Medicine, North Grafton, MA 01536, USA.
J Neuroendocrinol. 2007 Oct;19(10):773-8. doi: 10.1111/j.1365-2826.2007.01586.x.
Reproductive experience (i.e. pregnancy and lactation) leads to reduced levels of circulating prolactin in both women and rats. Stimulation of prolactin secretion by dopamine antagonists is also blunted following reproductive experience in both species. Whereas a parity-induced reduction in haloperidol-stimulated prolactin secretion is evident in ovariectomised rats, it is unknown whether a similar attenuation of prolactin secretion is present in reproductively experienced, cycling pro-oestrous rats. The present study examined this possibility. Moreover, to determine possible mechanisms involved in parity-mediated changes in prolactin secretion, both dopamine utilisation within the arcuate nucleus/median eminence and expression of dopamine D(2) receptor mRNA (short and long forms) in the anterior pituitary were measured across the afternoon of pro-oestrous in reproductively experience and inexperienced females. Prolactin secretion was lower on the afternoon of pro-oestrous in primiparous females compared to age-matched, nulliparous controls. In addition, haloperidol-stimulated prolactin secretion was reduced in ovariectomised, reproductively experienced females. Although no differences in dopamine utilisation were observed as a function of reproductive experience, parity did affect the expression of both forms of D(2) receptor mRNA in the anterior pituitary. Compared with nulliparous controls, primiparous females had increased D(2 long) mRNA expression at 12.00 h on pro-oestrous as well as increased D(2 short) mRNA expression at 14.00 h. Because the ratio of D(2 long)/D(2 short) can significantly effect lactotroph proliferation and prolactin secretion, a shift in relative expression of the two D(2) receptor isoforms within the anterior pituitary of parous females may help account for the reduction in prolactin secretion that occurs following reproductive experience.
生殖经历（即怀孕和哺乳）会导致女性和大鼠体内循环催乳素水平降低。在这两个物种中，生殖经历后多巴胺拮抗剂对催乳素分泌的刺激作用也会减弱。虽然在去卵巢大鼠中，经产导致的氟哌啶醇刺激催乳素分泌减少是明显的，但尚不清楚在有生殖经历的发情前期周期性大鼠中是否存在类似的催乳素分泌减弱情况。本研究探讨了这种可能性。此外，为了确定经产介导的催乳素分泌变化所涉及的可能机制，在发情前期的下午，对有生殖经历和无生殖经历的雌性大鼠，测量了弓状核/正中隆起内的多巴胺利用情况以及垂体前叶中多巴胺D(2)受体mRNA（短型和长型）的表达。与年龄匹配的未生育对照相比，初产雌性大鼠在发情前期下午的催乳素分泌较低。此外，在去卵巢、有生殖经历的雌性大鼠中，氟哌啶醇刺激的催乳素分泌减少。虽然未观察到多巴胺利用随生殖经历的差异，但经产确实影响了垂体前叶中两种形式的D(2)受体mRNA的表达。与未生育对照相比，初产雌性大鼠在发情前期12.00 h时D(2长型)mRNA表达增加，在14.00 h时D(2短型)mRNA表达增加。由于D(2长型)/D(2短型)的比例可显著影响催乳素细胞增殖和催乳素分泌，经产雌性大鼠垂体前叶中两种D(2)受体亚型相对表达的变化可能有助于解释生殖经历后催乳素分泌减少的原因。
