Thorn S R, Meyer M J, Van Amburgh M E, Boisclair Y R
Department of Animal Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2007 Aug;90(8):3742-50. doi: 10.3168/jds.2007-0009.
Plasma leptin concentrations increase as growing dairy heifers approach puberty and have greater plasma estrogen. In intact and ovariectomized rodents, estrogen has been shown to modulate expression of leptin and its receptor (Ob-R). To determine if estrogen regulates the bovine leptin system, prepubertal dairy heifers were ovariectomized at 140 d of age or left intact. A month later, both groups received a subcutaneous injection of excipient or 17beta-estradiol for 3 consecutive days. Neither ovarian status nor 17beta-estradiol injection altered plasma leptin or leptin mRNA abundance in adipose tissue depots. To assess whether these factors affected Ob-R expression, we tested 20 bovine tissues for leptin receptor (Ob-R) by using quantitative real-time PCR assays for the short receptor isoform (Ob-Ra), the long receptor isoform (Ob-Rb), and all receptor isoforms (Ob-R(TOTAL)). Ob-R(TOTAL) was detected in all tissues, with copy numbers covering 3 orders of magnitude between the lowest and highest expressing tissues (kidney cortex vs. liver). The Ob-Rb isoform accounted for 40% of Ob-R(TOTAL) in the hypothalamus, but averaged less than 3% of Ob-R(TOTAL) in peripheral tissues. Reciprocally, Ob-Ra accounted for only 19% of Ob-R(TOTAL) in the hypothalamus and for nearly all of Ob-R(TOTAL) in most peripheral tissues. Finally, we evaluated the effects of ovarian status and 17beta-estradiol on Ob-R expression in selected tissues. Treatment with 17beta-estradiol reduced Ob-R(TOTAL), Ob-Rb, and Ob-Ra expression by 70% in the uterine endometrium and tended to do the same in mammary adipose tissue. There was no effect of 17beta-estradiol on Ob-R in the hypothalamus, liver, soleus muscle, or subcutaneous adipose tissue. We conclude that greater estrogen secretion does not cause increased plasma leptin in prepubertal dairy heifers but estradiol can modulate Ob-R expression in some estrogen-responsive tissues.
随着生长中的奶牛小母牛接近青春期且血浆雌激素水平升高，血浆瘦素浓度也会增加。在完整和去卵巢的啮齿动物中，雌激素已被证明可调节瘦素及其受体（Ob-R）的表达。为了确定雌激素是否调节牛的瘦素系统，在140日龄时对青春期前的奶牛小母牛进行去卵巢手术或保持完整。一个月后，两组连续3天皮下注射赋形剂或17β-雌二醇。卵巢状态和17β-雌二醇注射均未改变脂肪组织库中的血浆瘦素或瘦素mRNA丰度。为了评估这些因素是否影响Ob-R表达，我们通过使用针对短受体异构体（Ob-Ra）、长受体异构体（Ob-Rb）和所有受体异构体（Ob-R(TOTAL)）的定量实时PCR测定法，对20种牛组织进行了瘦素受体（Ob-R）检测。在所有组织中均检测到Ob-R(TOTAL)，最低表达组织（肾皮质）和最高表达组织（肝脏）之间的拷贝数相差3个数量级。Ob-Rb异构体在下丘脑中占Ob-R(TOTAL)的40%，但在周围组织中平均占Ob-R(TOTAL)的比例不到3%。相反，Ob-Ra在下丘脑中仅占Ob-R(TOTAL)的19%，而在大多数周围组织中几乎占Ob-R(TOTAL)的全部。最后，我们评估了卵巢状态和17β-雌二醇对选定组织中Ob-R表达的影响。17β-雌二醇处理使子宫内膜中Ob-R(TOTAL)、Ob-Rb和Ob-Ra的表达降低了70%，在乳腺脂肪组织中也有类似趋势。17β-雌二醇对下丘脑、肝脏、比目鱼肌或皮下脂肪组织中的Ob-R没有影响。我们得出结论，青春期前奶牛小母牛中较高的雌激素分泌不会导致血浆瘦素增加，但雌二醇可调节某些雌激素反应性组织中的Ob-R表达。
