Vizcarra J A, Wettemann R P, Braden T D, Turzillo A M, Nett T M
Animal Science Department, Oklahoma Agricultural Experiment Station, Stillwater 74078-0425, USA.
Endocrinology. 1997 Feb;138(2):594-601. doi: 10.1210/endo.138.2.4938.
Thirty-two nutritionally anestrous cows were used to determine the effect of the frequency of exogenous GnRH pulses on ovarian follicular growth, serum concentrations of LH and FSH, and concentrations of LH, FSH, GnRH receptors (GnRH-R), messenger RNA (mRNA) for GnRH-R, and mRNA for gonadotropin subunits in the pituitary. Cows were randomly assigned to one of four treatments: 2 micrograms GnRH infused (i.v.) continuously during 1 h, 2 micrograms GnRH infused during 5 min once every hour, 2 micrograms GnRH infused during 5 min once every fourth hour, or saline (control) for 13 days. Infusion of GnRH every hour increased LH concentrations in serum (P < 0.05), but FSH concentrations were not affected by GnRH infusion. Luteal activity (LA) was assessed by the presence of corpora lutea and/or serum progesterone greater than 1 ng/ml. Six of eight cows infused with GnRH every hour had LA by day 13, whereas only 25% of cows infused either continuously or with a pulse every fourth hour had LA by day 13. None of the control cows had LA during the experiment (P < 0.01). Concentrations of LH and FSH in the pituitary were significantly reduced when GnRH was infused hourly or continuously. Concentrations of common alpha and FSH beta mRNA were not influenced by treatment. However, continuous infusion of GnRH decreased (P < 0.05) LH beta mRNA subunit. Concentrations of GnRH-R (P < 0.1) and GnRH-R mRNA (P < 0.05) were reduced when GnRH was infused continuously. We concluded that pulsatile secretion of LH is necessary for follicular growth and LA in beef cattle, and GnRH treatment differentially regulates LH and FSH gene transcription and serum concentrations of LH and FSH in cattle.
选用32头营养性乏情奶牛，以确定外源性促性腺激素释放激素（GnRH）脉冲频率对卵巢卵泡生长、血清促黄体生成素（LH）和促卵泡生成素（FSH）浓度以及垂体中LH、FSH、GnRH受体（GnRH-R）、GnRH-R信使核糖核酸（mRNA）和促性腺激素亚基mRNA浓度的影响。奶牛被随机分为四种处理之一：在1小时内持续静脉输注2微克GnRH；每小时一次，每次5分钟输注2微克GnRH；每四小时一次，每次5分钟输注2微克GnRH；或输注生理盐水（对照），持续13天。每小时输注GnRH可提高血清中LH浓度（P<0.05），但FSH浓度不受GnRH输注影响。通过黄体的存在和/或血清孕酮大于1纳克/毫升来评估黄体活性（LA）。每小时输注GnRH的8头奶牛中有6头在第13天出现LA，而持续输注或每四小时脉冲输注GnRH的奶牛在第13天只有25%出现LA。实验期间，对照奶牛均未出现LA（P<0.01）。每小时或持续输注GnRH时，垂体中LH和FSH浓度显著降低。共同的α亚基和FSHβ亚基mRNA浓度不受处理影响。然而，持续输注GnRH可降低（P<0.05）LHβ亚基mRNA。持续输注GnRH时，GnRH-R浓度（P<0.1）和GnRH-R mRNA浓度（P<0.05）降低。我们得出结论，LH的脉冲式分泌对肉牛的卵泡生长和LA是必需的，GnRH处理可不同程度地调节牛体内LH和FSH基因转录以及LH和FSH的血清浓度。
