Detection of Relaxin mRNA in the Corpus Luteum, Uterus, and Uterine Cervix in the Bitch

Abstract

ABSTRACT. In the pregnant bitch, the placenta is a major source of circulating relaxin, but its local expression in the reproductive organs is not clear. This study demonstrated expression of relaxin mRNA in the corpus luteum, uterus, uterine cervix as well as placenta in the pregnant and nonpregnant bitch by reverse transcriptase-polymerase chain reaction (RT-PCR).KEY WORDS: canine, corpus luteum, relaxin, uterine cervix, uterus.J. Vet. Med. Sci. 72(10): 1383-1386, 2010 Relaxin is a peptide hormone of about 6 kDa that has been traditionally associated with pregnancy in mammals. The major biological actions of relaxin include inhibition of uterine myometrial contractility [6] and promotion of connective tissue remodeling in the uterine cervix [8]. However, since the physiology of relaxin are richly diverse among species [22], accumulation of knowledge concerning this hormone for a given species is needed. As a fundamental step toward understanding how relaxin initiates its effects, it is important to identify the site of its production.The major source of circulating relaxin is different among species. It is the ovarian corpus luteum in the mouse [2], rat [11,14] [26,31], and mare [28], and the endometrial gland cells of the uterus in the guinea pig [20]. In addition to its hormonal roles during pregnancy, it has been suggested that relaxin has autocrine and paracrine roles in the ovary and uterus. In the ovary, locally produced relaxin may have stimulatory effects on the follicular growth and corpus luteum function [3,19], and it could be possible that relaxin expressed in the uterus acts directly on the inhibition of uterine contractility and the control of collagen remodeling in fetal membranes [5].In the dog, both the placenta and ovary are reported to secrete relaxin, with the placenta being the major contributor to the serum relaxin levels during pregnancy [26,31]. Klonisch et al. [16] showed the nucleic acid sequence of canine preprorelaxin cDNA and the localization of the mRNA and its protein in the syncytiotrophoblasts of the placenta. However, local expression of relaxin in the reproductive organs of the bitch remains to be elucidated. This study examined expression of relaxin mRNA in the corpus luteum, uterus and uterine cervix in the bitch.Ovaries, uteri, uterine cervices or placentae were taken from 12 bitches. There were 2 pregnant bitches in the late stage of gestation (2.5-year-old mongrel and 3-year-old dachshund) and 10 nonpregnant bitches (6 beagles, a shibainu, a golden retriever, a basset hound, and a shih tzu, 2-10 years of age). The tissue samples excised by ovariohysterectomy were kindly provided by the dog owners at our Veterinary Teaching Hospital and the other animal hospitals close to our laboratory, and no animal was operated upon or killed specifically for this study. The corpora lutea excised from the ovary, uteri, uterine cervices and placentae were frozen in liquid nitrogen and stored at -80C for RNA extraction. For the uteri the middle portion of the uterine horn was used. In ...

Luteal and hypophyseal expression of the canine relaxin (RLN) system during pregnancy: Implications for luteotropic function

“…In the same study [ 15 ], RLN synthesis was confirmed in the uterus, i.e., endometrium and myometrium. Additionally, luteal expression of RLN mRNA and protein was previously reported [ 14 , 16 ] in the dog. However, the CL seems to be a rather secondary source of RLN in this species, since ovariectomy performed during pregnancy does not affect circulating RLN [ 14 ].…”

Correlation of Oxytocin (OTR) and Estrogen Receptor (ER) mRNA in the Canine Placenta with the Detected Circulating Levels of Oxytocin and Estrogen during Pregnancy and Parturition

“…Hence, circulating estrogen in pregnant dogs is apparently derived from the ovaries and is less dependent on the placenta. On the other hand, the canine placenta is not totally deprived of hormone synthesis, for it is the major source of relaxin, which has an autocrine and paracrine role, evidenced by the presence of relaxin receptors (Klonisch et al, 1999;Tamada et al, 2010). Thus, the canine placenta can also serve as a target organ for sex steroids and pituitary hormones, i.e., its responsiveness depends on the availability of hormone receptors.…”